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Keywords:

  • microanalysis;
  • glass reference materials;
  • NIST;
  • characterisation;
  • sample inhomogeneity
  • microanalyse;
  • verre de référence;
  • NIST;
  • caractérisation;
  • inhomogénéité de l’échantillon

Abstract

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

We present new reference values for the NIST SRM 610–617 glasses following ISO guidelines and the International Association of Geoanalysts’ protocol. Uncertainties at the 95% confidence level (CL) have been determined for bulk- and micro-analytical purposes. In contrast to former compilation procedures, this approach delivers data that consider present-day requirements of data quality. New analytical data and the nearly complete data set of the GeoReM database were used for this study. Data quality was checked by the application of the Horwitz function and by a careful investigation of analytical procedures. We have determined quantitatively possible element inhomogeneities using different test portion masses of 1, 0.1 and 0.02 μg. Although avoiding the rim region of the glass wafers, we found moderate inhomogeneities of several chalcophile/siderophile elements and gross inhomogeneities of Ni, Se, Pd and Pt at small test portion masses. The extent of inhomogeneity was included in the determination of uncertainties. While the new reference values agree with the NIST certified values with the one exception of Mn in SRM 610, they typically differ by as much as 10% from the Pearce et al. (1997) values in current use. In a few cases (P, S, Cl, Ta, Re) the discrepancies are even higher.

Nous présentons des nouvelles valeurs de référence pour les verres NIST SRM 610–617 en suivant les recommandations de l’ISO et le protocole de l’IAG. Les incertitudes au niveau de confiance de 95% ont été déterminées à des fins d’analyse totale et de micro-analyse. Contrairement aux procédures de compilation précédentes, cette approche fournit des données qui tiennent compte des exigences actuelles dans la qualité des données. De nouvelles données analytiques et le jeu de données presque complet de la base de données GeoReM ont été utilisés pour cette étude. La qualité des données a été vérifiée par l’application de la fonction de Horwitz et par un examen minutieux des procédures analytiques. Nous avons déterminé quantitativement les possibles inhomogénéités d’élément en utilisant des prises d’essai de masses différentes correspondant à 1, 0.1 et 0.02 μg. Bien que nous ayons évité les zones de bordure des disques de verre, nous avons trouvé des inhomogénéités modérées pour plusieurs éléments chalcophiles/sidérophiles et des inhomogénéités flagrantes de Ni, Se, Pd et Pt pour les prises d’essai de petites masses. La mesure d’inhomogénéité a été incluse dans la détermination des incertitudes. Alors que les nouvelles valeurs de référence sont en accord avec les valeurs NIST certifiées à la seule exception du Mn dans SRM 610, elles sont généralement différentes, avec des écarts de près de 10%, des valeurs de Pearce et al. (1997) qui sont d’un usage courant. Dans quelques cas (P, S, Cl, Ta, Re), les écarts sont encore plus élevés.

Reference material glasses play an important role in micro-analytical techniques such as laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ionisation mass spectrometry (SIMS) and synchrotron radiation induced X-ray fluorescence (XRF) (Jochum and Stoll 2008). They are used as samples in geo- and cosmochemistry, environmental research, biogeochemistry and forensics for calibration, development of methods, quality control and for inter-laboratory comparisons. For the purposes of calibration of LA-ICP-MS and other micro-analytical techniques, the National Institute of Standards and Technology (NIST) reference materials of the SRM 61x series (SRM 610–617) are used most frequently. NIST SRM 610–611 and 612–613 have the advantage that they contain many trace elements, whose concentrations are uniform and sufficiently high for a precise primary calibration (ca. 400 μg g−1 for NIST SRM 610–611, ca. 40 μg g−1 for NIST SRM 612–613). The disadvantages are that the NIST glasses – with the exception of a few elements – have not been certified and were not designed for micro-analytical purposes. Because of this, several authors (e.g., Pearce et al. 1997, Rocholl et al. 1997) compiled published data to derive consensus values. The possibility of micro-inhomogeneity in the NIST glasses has been investigated in many publications (e.g., Carpenter 1972, Sylvester and Eggins 1997, Hinton 1999, Eggins and Shelley 2002, Kurosawa et al. 2002). The most widely used compilation of NIST SRM 610–611 and SRM 612–613 concentration data is that of Pearce et al. (1997), who used literature data published up to 1996 to derive reference values and their uncertainties by simply calculating standard deviations (s). This procedure was regarded as best practice at that time, but does not comply with ISO Guide 34 (2009) and ISO Guide 35 (2006) of the International Organization for Standardization (ISO). However, because of the great need for the best possible reference values for the NIST glasses, in this paper we act in a similar way as the International Association of Geoanalysts (IAG) would proceed in recertifying a reference material. Improving micro-analytical data can only be achieved by improving the quality of reference materials.

Since 1997, analytical techniques such as multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) and LA-ICP-MS have been applied for bulk and in situ analysis and have provided many new high-precision data for the NIST SRM glasses. However, since that time, the requirements for data quality have changed. In particular, the determination of the uncertainty budget (Kane et al. 2003, Jochum et al. 2006, Luo et al. 2007) has received wide attention within the analytical community. Therefore, a revision of the reference values of Pearce et al. (1997) is necessary.

The aims of this paper are:

  • 1
     To provide new data and quantify possible element inhomogeneities in the NIST glasses for different test portion masses using electron probe microanalysis (EPMA) (0.01 μg) and LA-ICP-MS (1, 0.1, 0.02 μg).
  • 2
     To present the currently best possible reference (‘true’) values, which may be useful for inter-laboratory comparisons from now on, by following ISO guidelines and the IAG protocol for certifying reference materials similar to the certification programmes recently performed for rock powders (Kane 2004, 2010, Cotta and Enzweiler 2008, Kane et al. 2009) and geological reference glasses (Jochum et al. 2006).
  • 3
     To determine uncertainties at the 95% CL for bulk- and micro-analytical purposes by considering the main sources of error.

Samples

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

A detailed history of the development of the NIST glasses SRM 610–617 has been given by Kane (1998). The base glass, consisting of high purity quartz sand, alumina, soda ash and calcium carbonate, was fused in a Pt/Rh-lined electrically heated furnace. About 100 kg of NIST SRM 610–611, 612–613, 614–615 and 616–617 were prepared by doping with sixty-one trace elements to nominal concentrations of 500, 50, 1 and 0.02 μg g−1. Each glass is available as either 3 mm (NIST SRM 610, 612, 614, 616) or 1 mm (NIST SRM 611, 613, 615, 617) wafers, hence the eight reference glasses have only four glass compositions. Loss of volatile species during high temperature fusion and sequestration of highly siderophile elements into the noble metal furnace components led to possible inhomogeneities in the final NIST glasses. Eggins and Shelley (2002) demonstrated, by compositional profiling and mapping using LA-ICP-MS, that extensive compositional inhomogeneity affects at least twenty-five of the doped trace elements in the NIST SRM 610–617 glasses.

New data and inhomogeneity

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

To obtain new data for the NIST SRM glasses and to quantify possible inhomogeneity of major and trace elements in these samples, we analysed different wafers using LA-ICP-MS, ID-TIMS, (ID)-ICP-MS and EPMA. The following sections provide short descriptions of each of the techniques employed by the different participating laboratories.

LA-ICP-MS at the MPI Mainz

A detailed documentation of the LA-ICP-MS procedure at the MPI Mainz has been given by Jochum et al. (2007). For the investigations of possible inhomogeneities of the NIST glasses, we used a New Wave UP-213 laser ablation system, where ablation in the New Wave Large Format Cell was carried out in a He atmosphere. Spot analyses were performed at different times using crater diameters of 80, 40 and 25 μm at energy densities of about 7–11 J cm−2 (determined at the sample surface), whereas laser energy was uniform within one experiment. Ablation times were 95 s (80 μm spot), 50 s (40 μm) and 35 s (25 μm), washout time between spots was 30 s and blank count rates were measured for 15 s prior to ablation. Ion intensities were measured in the low mass resolution mode of a Thermo Scientific Element2 sector field mass spectrometer. Important instrumental parameters were: RF power = 1200 W, plasma gas flow rate = 15 l min−1, auxiliary gas flow rate = 1 l min−1, sample gas flow rate (Ar) = 0.5 l min−1, carrier gas flow rate (He) = 0.8 l min−1. The mass spectrometer was tuned to give maximum, stable signals at low oxide formation (ThO/Th < 1%). Molecular interferences on the investigated isotopes from oxides were low, as shown by measurements of different isotopes of one element. In the case of the low abundance 103Rh, 105Pd and 195Pt (element concentrations: about 1–3 μg g−1) in NIST SRM 610, possible interferences of argides and oxides from high abundance Cu, Gd and Hf (about 450 μg g−1) isotopes were less than 1–2% (CuAr, GdAr) and 7% (HfO), respectively, of the element peaks of the noble metals as determined at a high mass resolution of 10000. About 60–80 single spot analyses (80, 40, 25 μm; crater depths similar to the spot sizes) were performed at 200 μm spacing across the diameters of the NIST wafers. To correct for possible signal drift, the ion intensities were measured at one fixed position of the sample after every ten spot analyses to minimise potential calibration bias caused by compositionally different spots, similar to the procedure of Eggins and Shelley (2002). Data reduction was done by calculating the blank corrected count rates of the isotopes relative to the internal standard 43Ca. The low abundance 43Ca peak (isotopic abundance = 0.135%) may be subject to interference by the 27Al16O peak. However, in the case of NIST glasses, where Al2O3/CaO < 0.2, the interference of 27Al16O on 43Ca is less than 1% (Regnery et al. 2010).

For the determination of NIST SRM 616 data (Table 3), we used the UP-213 system and NIST SRM 612 (Table 9) for calibration. The spot size used was 100 μm. The crater depth was less than 100 μm to avoid elemental fractionation associated with ablating at a single spot (Mank and Mason 1999, Gaboardi and Humayun 2009). USGS and MPI-DING reference glasses were included in the measurements as quality control samples. We also determined concentrations of some rarely determined trace elements (e.g., Cl, S, Cd) in NIST SRM 610, 612 and 614 using UP-193SS (spot size = 75 μm) and UP-213 (spot size = 80 μm) laser ablation systems, respectively, and the certified BAM-S005-B glass (final certification report BAM-S005-A and BAM-S-005-B; http://www.rm-certificates.bam.de) of the Federal Institute for Materials Research and Testing (BAM), Germany, for calibration. The BAM glass is homogeneous, has a similar matrix to the NIST glasses and is therefore suitable as a calibration material in microanalysis (Yang et al. 2011). Analytical data for refractory (e.g., Ti, Zr) and volatile elements (e.g., Se, Sn, Cd) of the NIST glasses obtained by the 193 and 213 nm Nd:YAG lasers (Table 4), respectively, agree well.

Table 3.    Element concentrations (in μg g−1) in NIST SRM 616 obtained by LA-ICP-MS at the MPI Mainz using NIST SRM 612 data (Table 9) for calibration
ElementIsotope usedNIST SRM 616
Conc.SEU (95% CL)
  1. SE, standard error; U, Uncertainty at the 95% confidence level (CL) (containing the main sources of error, such as inhomogeneity of the calibration material NIST SRM 612).

Ag1070.0470.0010.002
As750.1250.0040.066
Au1970.210.010.03
B111.200.030.32
Ba1372.530.010.15
Bi2090.0200.0010.008
Cd1110.0470.0060.014
Ce1400.0300.0010.001
Co590.0300.0020.004
Cr530.480.030.09
Cs1330.0280.0010.002
Cu650.730.010.11
Dy1630.0190.0010.002
Er1670.0170.0030.007
Ga710.4410.0030.027
Ge740.300.010.05
Hf1780.0190.0010.002
Ho1650.0150.0010.001
In1150.0330.0010.004
La1390.0310.0010.002
Li70.9490.0080.094
Lu1750.0140.0010.001
Mo950.1010.0040.014
Nb930.0220.0010.003
Nd1460.0240.0010.002
Ni620.520.050.11
Pb2081.850.010.07
Pd1051.730.030.45
Pr1410.0160.0010.001
Rb850.1050.0020.005
Rh1030.950.010.05
Sb1210.0770.0020.012
Se770.220.030.06
Sn1181.250.010.11
Sr8844.20.10.7
Ta1810.0280.0010.003
Tb1590.0150.0010.001
Th2320.0260.0010.001
Tl2030.00980.00040.0015
Tm1690.0160.0010.001
U2380.0760.0010.003
V510.2420.0040.021
W1820.0450.0010.004
Y890.0320.0010.003
Yb1730.0200.0010.002
Zn661.280.020.15
Zr900.0940.0020.008
Table 9.    Summary of compositional data for NIST SRM 612–613. Data are grouped into five categories of analytical techniques (see text)
AnalyteOv. meanType of dataUncertainty (U) at 95% CLCategoryNNo. techn.tLiterature
Test portion mass12345NISTPearce et al. (1997)Other comp. (see GeoReM)
mg range1 μg0.1 μg0.02 μgIDICP-MSBulk techn.LA-ICP-MSMicroanal.
mean ± s (N)
  1. Ov. (overall) mean, unweighted mean of all results; N, number of laboratory means; No techn., number of techniques used.

  2. NIST certified (CV), reference (RV) and information (IV) values are indicated.

  3. Uncertainties (U) at the 95% confidence level (CL) determined for different test portion masses; t: coverage factor. Trace elements in μg g−1; oxides in % m/m.

Ag22.0CV0.30.32.63.0 21 ± 2 (3) 23 ± 3 (5) 822.3722.0 ± 0.321.9222
Al2O32.03IV0.040.040.040.04   2.07 ± 0.02 (2)2.01 ± 0.04 (4)622.5722.111.95–2.11
As35.7IV5.55.55.58.9 48.1 (1)31 (1)34 ± 2 (5) 732.45 37.3337
Au4.77IV0.310.550.651.72 4.3 ± 0.4 (2)5.1 ± 0.1 (2)4.9 ± 0.3 (4) 832.3755.094.58–5.1
B34.3IV1.71.71.712.2  34 ± 2 (2)35 ± 3 (4)35 ± 2 (2)852.373234.7335
Ba39.3RV0.90.90.90.940 ± 1 (4)40 ± 1 (5)37.6 ± 0.6 (2)39 ± 2 (10) 2162.094137.7438.5–39.7
Be37.5RV1.51.51.51.5 38 ± 2 (3)34.3 (1)38 ± 2 (8) 1232.20 37.7338
Bi30.2IV2.32.32.32.3 31.5 ± 0.1 (2) 29 ± 2 (3) 522.78 29.8429.8–30
CaO11.9IV0.10.10.10.1    11.9 ± 0.1 (5)512.781211.9311.85–12
Cd28.1IV1.11.11.16.0 27.9 ± 0.7 (3) 28 ± 2 (6) 922.31 28.3228.3
Ce38.4RV0.70.70.70.738.8 ± 0.2 (3)38 ± 2 (10)38.1 (1)38 ± 2 (17) 3142.043938.3538–38.7
Cl142IV58585858  88 (1)179 (1)150 ± 50 (3)542.78 200 
Co35.5RV1.01.01.01.0 36 ± 3 (6)36 ± 1 (3)35 ± 2 (13) 2242.0935.5 ± 1.235.2635–35.5
Cr36.4RV1.51.710.626.336.3 (1)36 ± 4 (3)30.1 (1)37 ± 2 (12) 1742.12 39.8836–40
Cs42.7RV1.81.81.81.8 42 ± 2 (6)42.8 (1)43 ± 4 (7) 1432.16 41.6438.5–42
Cu37.8RV1.51.58.216.337.7 (1)33.5 (1)38 ± 1 (2)38 ± 3 (11) 1552.1537.7 ± 0.936.7136.8–37
Dy35.5RV0.70.70.70.735.9 ± 0.5 (5)35.3 ± 0.9 (7)31.1 (1)36 ± 2 (13) 2662.063535.9736–37.1
Er38.0RV0.90.90.90.938.6 ± 0.6 (5)37.8 ± 0.7 (6) 38 ± 2 (13) 2452.073937.4338–40.1
Eu35.6RV0.80.80.80.835.7 ± 0.4 (2)35 ± 1 (8)35.6 (1)36 ± 2 (13) 2452.073634.4435–36.2
F80IV89898989  57 (1) 90 ± 40 (2)324.30   
Fe51CV2222  115 (1)54 ± 5 (4)120 ± 40 (3)632.5751 ± 256.3351–56.3
Ga36.9RV1.51.51.78.4 36 ± 2 (5)33.5 (1)38 ± 2 (5) 1132.23 36.2436
Gd37.3RV0.90.90.90.938.4 ± 0.9 (5)37 ± 1 (8) 37 ± 3 (12) 2552.063936.9536.7–39.1
Ge36.1IV3.83.83.812.1 32.8 (1) 37 ± 1 (3) 423.18 34.6435
Hf36.7RV1.21.21.21.237.5 ± 0.5 (2)38 ± 2 (6)35 (1)36 ± 3 (11) 2052.09 34.7734.77–37.3
Ho38.3RV0.80.80.80.8 38 ± 1 (10) 39 ± 2 (12) 2222.08 37.8738–40.2
H2O0.021IV        0.021 (1)11    
In38.9RV2.12.12.12.1 40 ± 3 {4} 38 ± 2 (4) 822.37 42.9343
Ir0.0045IV       0.0045 (1) 11    
K62.3IV2.42.42.42.460.6 (1) 64 (1)62 ± 1 (2) 433.186466.2666.3
La36.0RV0.70.70.70.735.9 ± 0.1 (3)35 ± 2 (12)36 ± 2 (2)37 ± 2 (15) 3262.043635.7735.8–36.5
Li40.2RV1.31.31.36.2 39 ± 3 (4) 40 ± 2 (8)41.5 (1)1332.18 41.5442
Lu37.0RV0.90.90.90.936.9 ± 0.3 (3)36 ± 2 (9)40 (1)37 ± 3 (12) 2552.06 37.7136.9–39.6
Mg68.0IV5.15.15.15.1 68 ± 10 (2) 68 ± 7 (8) 1022.26 77.4477
Mn38.7RV0.90.90.90.9 39 ± 2 (3)40 ± 2 (4)38 ± 2 (12) 1952.1039.6 ± 0.838.4338
Mo37.4RV1.51.75.811.435.8 (1)37 ± 2 (5) 38 ± 3 (8) 1432.16 38.338
Na2O13.7IV0.30.30.30.3   13.7 ± 0.4 (4)13.6 ± 0.5 (4)822.371413.9814–14.02
Nb38.9RV2.12.12.12.1 40 ± 3 (3) 39 ± 3 (10) 1322.18 38.0640–42
Nd35.5RV0.70.70.70.735.6 ± 0.4 (5)35 ± 1 (9) 36 ± 2 (11) 2552.063635.2435–36.2
Ni38.8CV0.23.728.245.337.7 (1)43 ± 1 (2) 39 ± 2 (9) 1232.2038.8 ± 0.238.4436.8–38.8
P46.6IV6.96.96.96.9 50 (1)39.1 (1)50 ± 7 (4)38.3 (1)742.45 55.1645–55
Pb38.57CV0.200.200.200.2038.6 (1)39 ± 2 (6) 39 ± 3 (16) 2332.0738.57 ± 0.238.9636.9–38.6
Pd1.05IV0.100.290.971.74 1.09 (1) 1.0 ± 0.1 (3) 423.18   
Pr37.9RV1.01.01.01.0 38 ± 1 (10) 38 ± 3 (11) 2122.09 37.1637.2–38
Pt2.51IV0.100.411.843.11 2.59 (1) 2.48 ± 0.03 (3) 423.18  2.59
Rb31.4CV0.40.40.40.431.8 (1)32 ± 1 (8)33 (1)33 ± 2 (8) 1842.1131.4 ± 0.431.6326.7–32
Re6.63IV0.610.610.612.96 6.2 ± 0.5 (2) 6.9 ± 0.5 (4) 622.57 8.126.57
Rh0.91IV0.020.060.200.49 0.896 (1) 0.91 ± 0.01 (3) 423.18   
S377IV7085197461   411 ± 40 (4)310 ± 60 (2)632.57 16 
Sb34.7IV1.81.81.81.8 36 ± 5 (2) 34 ± 2 (7) 922.31 38.4438
Sc39.9RV2.52.52.52.5 40 ± 5 (5)40.8 (1)40 ± 3 (6) 1232.20 41.0539–41
Se16.3IV1.92.77.819.0 15.6 (1)14.8 (1)17 ± 2 (4)15.1 (1)742.45   
SiO272.1IV0.60.60.60.6   72 ± 1 (3)72.1 ± 0.4 (6)922.317271.971.9
Sm37.7RV0.80.80.80.837.7 ± 0.7 (5)36.8 ± 0.8 (7)38.5 (1)38 ± 2 (12) 2562.063936.7238–38.1
Sn38.6IV1.31.34.68.0 38 ± 2 (2) 39 ± 2 (8) 1022.26 37.9638
Sr78.4CV0.20.20.20.278.4 ± 0.1 (3)78 ± 4 (6)73.9 (1)77 ± 4 (15) 2552.0678.4 ± 0.276.1577.8–78.4
Ta37.6RV1.91.91.91.935.93 (1)39 ± 1 (3) 37 ± 3 (9) 1332.18 39.7739.8–41.4
Tb37.6RV1.11.11.11.1 37 ± 2 (9)38.3 (1)38 ± 3 (11) 2132.09 35.9236
Th37.79CV0.080.080.080.08 37 ± 1 (5)38.1 (1)38 ± 2 (13) 1932.1037.79 ± 0.0837.2337.8–39.7
Ti44.0RV2.32.32.32.3 45 ± 6 (3)45 ± 6 (3)43 ± 4(10) 1652.1350.1 ± 0.848.1140–48
Tl14.9RV0.52.23.24.615.7 (1)14.7 ± 0.7 (4) 14.8 ± 0.4 (3) 832.3715.7 ± 0.315.0715.1
Tm36.8RV0.60.60.60.6 37 ± 1 (9) 37 ± 2 (10) 1922.10 37.5538
U37.38CV0.080.080.080.0837.7 (1)37 ± 1 (4)35 (1)38 ± 3 (14) 2042.0937.38 ± 0.0837.1533.2–37.4
V38.8RV1.21.21.21.2 39 ± 3 (5)36.6 (1)39 ± 2 (10) 1632.13 39.2233.2–39
W38.0IV1.11.11.11.138.08 (1)  38 ± 1 (4) 522.78 39.5540
Y38.3RV1.41.41.41.4 38 ± 3 (9)40.4 (1)38 ± 3 (10) 2032.09 38.2538–42
Yb39.2RV0.90.90.90.940 ± 1 (5)38 ± 1 (7)42.4 (1)39 ± 2 (12) 2562.064239.9539–40.2
Zn39.1RV1.71.71.716.9 40 ± 4 (5)35.2 ± 0.4 (2)40 ± 2 (8) 1542.15 37.9234.9–38
Zr37.9RV1.21.21.21.239 ± 2 (2)38 ± 3 (8)37.4 (1)38 ± 3 (11) 2252.08 35.9938–41.9
Table 4.    Element concentrations (in μg g−1) for NIST SRM 610, 612 and 614 obtained by LA-ICP-MS at the MPI Mainz using UP-193SS and UP-213 ablation systems
ElementIsotope usedNIST SRM 610NIST SRM 612NIST SRM 614
UP-193SSUP-213UP-193SSUP-213UP-193SSUP-213
Conc.sConc.sConc.sConc.sConc.sConc.s
  1. Data were calibrated with the certified values of the BAM-S005-B reference glass.

As7534853501336.80.236.21.90.740.02  
Ba1374498  39.80.7  2.970.023.060.04
Cd11128382961128.00.529.91.30.510.030.490.06
Cl35229142624  1794.0  1778
Co5938073961133.90.334.30.90.640.010.680.01
Cr533786417635.60.136.01.31.40.21.20.1
Cu634116455538.70.240.21.4    
Fe574607496451.20.452.30.712.00.616.41.3
Mn554417456439.40.339.00.61.270.031.300.27
Mo954257455838.70.739.21.40.740.020.820.03
Ni6141154381037.91.337.81.0  1.650.40
Pb20838594131137.50.742.01.92.050.052.450.16
S34614961763891436610305332227
Sb1214218426736.40.436.11.40.730.040.750.05
Se771502153319.50.119.11.10.400.120.430.12
Sn1174436473740.90.640.61.41.870.051.780.08
Ti474466448539.70.539.60.33.10.13.60.3
V5145374841039.90.440.11.30.930.021.00.04
Zn67486115031041.20.943.41.13.770.053.710.17
Zr9047312435638.30.437.70.80.840.020.840.01

LA-ICP-MS at the University of Mainz

LA-ICP-MS measurements were carried out in the New Wave Large Format Cell of a New Wave UP-213 laser ablation system coupled with an Agilent 7500ce quadrupole ICP-MS. Helium was used as the carrier gas at a flow rate of ca. 0.7 l min−1 mixed with Ar sample gas at 0.7 l min−1. The NIST SRM 616 glass was ablated in nine single spot analyses, irregularly spaced in the centre of the wafer, at 10 Hz and 1.9 J cm−2 with crater sizes of 100 μm. Analyses were undertaken with the ICP-MS in standard mode (RF power = 1200 W) at ThO/Th ratios of less than 0.5%. General information on the system and detection limits is given in Jacob (2006). Each measurement consisted of 30 s background followed by 60 s of signal collection.

43Ca was the internal standard (Regnery et al. 2010) and NIST SRM 612 was used as the external calibration material using the new reference data (Table 9). The USGS reference glass BCR-2G (six single spot analyses) was measured as an unknown. A second data set of five single spot analyses, also spaced randomly across the centre of the wafer, was produced with 29Si as the internal standard and NIST SRM 612 as the external reference material under otherwise identical conditions. In this session, the MPI-DING glass BM90/21-G (eight single spot analyses) was measured as an unknown, using the same isotope as internal standard. Data reduction was carried out with the software GLITTER 4.0 (Macquarie University, Sydney, Australia). Table 5 lists the new data for NIST SRM 616.

Table 5.    Element concentrations (in μg g−1) for NIST SRM 616, BCR-2G and BM90/21-G obtained by LA-ICP-MS at the University of Mainz using NIST SRM 612 (Table 9) for calibration
ElementIsotope usedNIST SRM 616BCR-2GBM90/21-G
Conc.sConc.sConc.sConc.s
Ag1070.0420.006  0.660.05  
Ba1372.470.212.280.0966970.500.1
Co590.0520.0040.0510.00734.90.794.31.3
Cr53/520.3070.060.420.1513.90.6218643
Ga69  0.500.02  1.940.15
K3932.04.2  14200300  
Li70.9270.06  8.060.10  
Mg2632.10.629.81.523800200  
Mn550.6660.0640.570.0514812588512
Ni600.510.100.390.0510.860.19176232
P3113.72.4  145911  
Pb2081.910.15  9.720.35  
Rb850.1070.016  42.40.7  
Sn1181.210.08  1.910.05  
Sr8841.40.8  3242  
Tl2050.0080.002  0.210.01  
U2380.0790.008  1.530.05  
V51  0.210.02  56.51.3
Zn661.440.211.440.271667428

ID-TIMS data at the MPI Mainz

Highly precise and accurate isotope dilution (ID) determinations of K, Rb, Sr, Ba and the multi-isotopic rare earth elements (REEs) in NIST SRM 612 by TIMS were performed at the MPI Mainz. Two different glass splits (ca. 60–70 mg) were used. The NIST glasses were dissolved together with spikes using HF and HClO4. The separation procedure used for the alkalis, Sr, REE and Ba was the same as that of Raczek et al. (2001). Up to four measurements were performed on a Finnigan MAT 261 mass spectrometer equipped with a multi-collector consisting of seven Faraday cups. Preliminary data (I. Raczek, unpublished data) of these investigations were already given in Jochum et al. (2005). Table 6 lists the ID-TIMS data. Relative standard deviations (RSDs) ranged between about 0.1% and 0.5%.

Table 6.    Element concentrations (in μg g−1) for NIST SRM 612 obtained by ID-TIMS at the MPI Mainz
ElementSplit 1Split 2Mean ± s
K60.65 60.63 ± 0.03
60.61 
Rb 31.7931.79 ± 0.01
 31.80
 31.79
Sr78.2878.4478.36 ± 0.09
78.2878.43
Ba39.69 39.69 ± 0.01
39.69 
La35.8335.9235.85 ± 0.06
35.81 
Ce38.7838.7138.73 ± 0.04
38.7538.68
Nd35.9735.9335.95 ± 0.03
Sm38.0838.0538.07 ± 0.02
Gd36.5436.8336.67 ± 0.19
36.4736.83
Dy36.1936.2736.28 ± 0.09
36.37 
Er38.7838.7738.70 ± 0.10
38.5638.68
Yb39.0839.3339.16 ± 0.15
39.06 
Lu36.9636.8936.93 ± 0.05

(ID)-ICP-MS at the ETH Zürich

The ICP-MS analyses followed the multi-element (ID)-ICP-MS method described by Willbold and Jochum (2005), but with some modifications. A total of thirty-two elements were determined, fifteen by ID (Cr, Ni, Sr, Zr, Mo, Ba, Nd, Sm, Gd, Dy, Er, Yb, Hf, Pb and U) and seventeen (Sc, V, Co, Rb, Y, Nb, Cs, La, Ce, Pr, Eu, Tb, Ho, Tm, Lu, Ta and Th) by calculating unknown concentrations using relative sensitivity factors (RSF) with the ID elements as internal standard elements. The RSF is the ratio of a non-ID element (e.g., Rb) and an ID element (e.g., Sr) measured in a 1 ng ml−1 solution prepared from a 1000 μg ml−1 standard solution (Specpure® Alfa Aesar, Ward Hill, MA, USA, stated uncertainty = 0.3%). With the ID concentration (e.g., Sr concentration), the measured RSF (Rb/Sr ratio in the standard solution) and the known concentrations in the 1 ng ml−1 standard solution (Rb and Sr), the concentration of the non-ID element (Rb) in the sample could be calculated. The RSF accounts for differences in the response between the element of interest (Rb) and the internal standard element (Sr) owing to the differences in ionisation potential, transmission, mass-dependent sensitivity of the detector system etc. See Willbold and Jochum (2005) for a more detailed discussion.

An aliquot of about 20–30 mg glass chips of NIST SRM 610 and SRM 612 was dissolved in HF-HNO3 at 160 °C for about 3 days. After evaporation the samples were redissolved in aqua regia (3:1 HCl:HNO3, about 2 days), HCl (about three times), and finally converted to 2 ml of 7 mol l−1 HNO3 with trace amounts of HF. Aliquots of the solution were spiked with different spike-sample ratios and the trace element measurements were performed on an Element2 ICP-MS at the Laboratory of Inorganic Chemistry, ETH Zürich, using a CETAC, Omaha, NE, USA Aridus I sample introduction system. NIST SRM 614 was spiked prior to dissolution and subjected to the same digestion and dissolution procedure as NIST SRM 610 and 612. An appropriate aliquot of the spiked sample solution was diluted to 4 ml 1 mol l−1 HNO3 to achieve a concentration of about 1 ng ml−1 in the analyte solution. The sample was introduced into the Aridus desolvation system with a micro-concentric polypropylene nebuliser with a nominal uptake rate of 50 μl min−1 and typical sample and auxiliary gas flows of 0.72 and 0.84 l min−1. Using Ar sweep gas and N2 gas flow rates in the Aridus system of about 3 l min−1 and 25 ml min−1, respectively, oxide formation rates UO+/U+ of less than 0.03% were achieved. Except for the transition metals (Sc, V, Cr, Co, Ni), which were measured in medium resolution mode (M/ΔM ca. 4000), measurements could therefore be performed in low resolution mode (M/ΔM ca. 300), even for the heavy REEs (Sm–Lu). In low resolution mode, flat-top peak shape allowed precise measurements of the isotope ratios.

USGS reference materials BCR-2, BHVO-2 and BIR-1 were analysed routinely with every batch of samples as quality control samples to assess accuracy, i.e., trueness, and precision. Multiple measurements of the reference materials (n of about 50) yielded an average RSD of better than 1–2% for the REE, Hf, Zr, Sr, Ba and U, and of about 3–6% for the transition metals Sc, V, Cr, Co and Ni and Y, Nb, Ta, Th and Rb. Most element concentrations were within 2–3% of the USGS reference values given in the GeoReM database.

For determination of the concentrations (Table 7), at least four different splits of NIST SRM 610 and SRM 612 were measured with different spike-sample ratios to be able to measure all elements with error magnification factors (Albarède 1995) of less than 2–3. Whenever error magnification factors were greater than 3–5, the ID and corresponding non-ID element concentrations were not taken into account (e.g., Zr (ID) and Nb (non-ID) in NIST SRM 614). During measurement of NIST SRM 612 and 614, the RSF factors for Th (Th/U), Eu (Eu/Sm), Tm (Tm/Er) and Lu (Lu/Yb) changed significantly compared with previous measurement sessions, leading to a constant offset of the Th, Eu, Tm and Lu concentrations in the NIST, but not in the USGS reference materials used as analytical control samples (BCR-2, BHVO-2 and BIR-1). The reason for this effect is unknown and hence, no Th, Eu, Tm and Lu concentrations for NIST SRM 612 and 614 are reported.

Table 7.    Element concentrations (in μg g−1) for NIST SRM 610, 612 and 614 obtained by ID-ICP-MS (bold type) and ICP-MS at the ETH Zürich
ElementNIST SRM 610NIST SRM 612NIST SRM 614 (= 1)
Conc.% RSDNConc.% RSDNConc.
  1. N, number of analyses.

Ba458.21.9839.371.233.281
Ce449.41.01237.252.460.790
Cr411.21.8436.261.630.999
Cs361.50.5442.142.210.655
Co414.90.8434.833.130.780
Dy444.31.7936.151.840.780
Er466.51.2738.861.140.781
Eu454.81.73    
Hf437.52.0937.131.440.739
Gd461.11.6938.561.740.801
Ho462.41.7738.691.040.779
La432.21.31234.652.360.686
Lu450.31.62    
Mo400.11.9735.791.740.792
Nb485.90.3641.542.63 
Nd432.31.11234.961.860.737
Ni469.32.2437.663.031.082
Pb434.31.2938.63.732.510
Pr448.01.11237.311.960.772
Rb417.11.2531.071.010.824
Sc451.83.7536.711.43 
Sm452.50.6937.151.540.761
Sr525.32.71078.511.2346.59
Ta446.32.7638.170.33 
Tb475.82.6939.961.240.805
Th464.11.64    
Tm463.90.12    
U474.52.21137.680.750.893
V447.92.5439.921.631.084
Y479.72.5940.141.730.799
Yb473.11.5739.840.940.788
Zr473.71.5940.361.73 

EPMA at the MPI Mainz

Electron probe microanalysis at MPI Mainz was used to determine the major element composition of the NIST glasses (Table 1) and to test homogeneity. Analyses were performed in the wavelength-dispersive detection mode of the Jeol JXA-8200 electron microprobe using an accelerating voltage of 15 kV and a beam current of 12 nA. The electron beam was defocused to 20 μm. Distances between spots were 30 and 50 μm respectively. Data were corrected using the routine ZAF procedure. Peak counting times were 30 s for Na and 60 s for the other major elements. Sets of reference materials, i.e., natural and synthetic oxides, minerals and glasses (P&H Developments Ltd., Calibration Standards for Electron Probe Microanalysis, Standard Block GEO; Smithsonian Institution standard set for electron microprobe analysis, Jarosewich 2002) were used for calibration and instrument stability monitoring. We used the USNM 111240/52 VG2 basaltic and 72854 VG-568 alkaline rhyolite glasses (Jarosewich 2002) as quality control samples.

Table 1.    Major element concentrations (% m/m) in core and rim regions of NIST SRM glasses determined by EPMA at the MPI Mainz
 NIST SRM 610NIST SRM 612NIST SRM 614
CoreRimCoreRimCoreRim
  1. Uncertainties are 1s.

Number of analyses194801357115490
 SiO269.4 ± 0.269.3 ± 0.271.7 ± 0.272.0 ± 0.372.0 ± 0.272.0 ± 0.2
 Al2O31.98 ± 0.032.01 ± 0.042.06 ± 0.022.07 ± 0.042.056 ± 0.0262.07 ± 0.03
 MnO0.051 ± 0.017     
 MgO0.057 ± 0.014     
 CaO11.59 ± 0.0611.54 ± 0.0711.93 ± 0.0511.98 ± 0.0611.98 ± 0.0612.04 ± 0.06
 Na2O13.6 ± 0.113.5 ± 0.114.0 ± 0.113.8 ± 0.213.9 ± 0.113.9 ± 0.2
 K2O0.048 ± 0.015     
 P2O50.10 ± 0.02     
 S0.050 ± 0.011 0.027 ± 0.010 0.023 ± 0.010 
 Cl0.033 ± 0.004 0.011 ± 0.004 0.008 ± 0.004 
 Ti0.046 ± 0.002     
 Zr0.045 ± 0.003     

Element inhomogeneity and test portion

The determination of the element inhomogeneity in the NIST glasses at the large-scale (mg sample range) and at the small-scale (ng–μg range) is important for micro-analytical purposes. Because the NIST glasses were originally designed for bulk-analytical work, the NIST certified values and their uncertainties are only valid if the entire wafer is used for analysis. Highly precise ID measurements on different glass wafers also demonstrate element homogeneity for smaller samples of about 2–50 mg, based on better than 1% precision (e.g., Rocholl et al. 2000, Nebel et al. 2009). Nuclear track and ID data by Carpenter (1972) show an excellent axial homogeneity for B and U over the entire length of the 600 feet of glass canes. These results have particular significance with regard to using the glasses as reference materials for microanalysis (Kane 1998). The main application of the glasses is currently their use as calibration material in microanalysis. Eggins and Shelley (2002) demonstrated that at least twenty-five elements (e.g., Ag, As, Au, B, Bi, Cd, Cr, Cs, Cu, Mo, Pb, Pt, Re, Rh, Sb, Se, Te, Tl, W) are inhomogeneously distributed at the 30–65 μm scale. These authors found that Tl is an excellent marker for compositionally inhomogeneous domains within the NIST glasses. This inhomogeneity appears to affect all NIST glasses, where severe depletions of some elements (Tl, Au, Re, Bi) are found in the rim region of the wafers. However, the majority of elements, including Be, Mg, Ca, Sc, Ti, V, Co, Ni, Zn, Ga, Rb, Sr, Y, Zr, Nb, In, Sn, Ba, REE, Hf, Ta, Th and U shows no evidence of significant compositional inhomogeneity. Kurosawa et al. (2002) investigated NIST SRM 614 and 616 by LA-ICP-MS at a larger sampling scale (80 μm spot size) and found no evidence for trace element inhomogeneities within the observed precision of 5% and 15% respectively.

In this paper we quantify possible inhomogeneities of four major and fifty-four trace elements in all NIST SRM 61x glasses using EPMA and LA-ICP-MS, undertaken at MPI Mainz. This was done by measuring element distributions in 1–2 wafers with electron beams of 20 μm (EPMA) and spot sizes up to 25 μm (LA-ICP-MS). Because of the small number of investigated wafers and the possibility that all wafers manufactured are not identically homogeneous we also used the results of other publications (e.g., Hinton 1999, Eggins and Shelley 2002).

For the evaluation of element inhomogeneity, the ‘test portion’ is of particular importance. After the International Union of Pure and Applied Chemistry (IUPAC; McNaught and Wilkinson 1997) a test portion is defined as the amount or volume of the test sample taken for analysis.

The test portion mass for bulk-analytical work is typically in the mg range (e.g., aliquots of 5–50 mg were used for solution ICP-MS and TIMS analysis). In the non-destructive EPMA technique, interaction processes between electrons and target are important. Using our measurement conditions the penetration depth was about 2 μm and the test portion mass for our EPMA analysis was about 0.01 μg for the NIST glasses. For the LA-ICP-MS measurements three different spot sizes (80, 40, 25 μm) were used. The ablation rate of NIST glasses was about 0.1 μm pulse−1 using the 213 nm laser ablation system. From these data we obtained test portion masses (here: ablated material for one spot analysis) of about 1 μg (crater size = 80 μm), 0.1 μg (40 μm) and 0.02 μg (25 μm), when considering the different ablation times per crater diameter and the difference in fluence.

Major element profiles

Previous studies have shown that the major elements of the NIST glasses are homogeneously distributed (e.g., Rocholl et al. 1997, Hinton 1999). Our EPMA measurements confirmed these results. This is shown in Figure 1, where several profile measurements of SiO2 are plotted in different parts of NIST SRM 610, 612 and 614 wafers using 20 μm electron beams corresponding to a test portion mass of 0.01 μg. Within uncertainty limits all data agree. There is no indication for any inhomogeneity on the scale of precision of these measurements, in particular not in the rim regions when compared with the core. The same is true for other major elements, which is demonstrated in Table 1, where the mean values of SiO2, Al2O3, Na2O and CaO and some minor elements in the core and rim locations are listed. Uncertainties of the data were similar to the repeatability of EPMA (about 0.5–2%). Core and rim data were also identical within those repeatability limits.

image

Figure 1.  SiO2 variation across NIST SRM 610, 612 and 614 measured in the core and the rim regions of the glass wafers (EPMA profile, spot size = 20 μm; spacing = 30–50 μm). Also shown is the repeatability of EPMA (± 1s), which was determined by repeated analysis of homogeneous glasses (USGS, MPI-DING).

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Trace element profiles

The measurements were carried out using LA-ICP-MS with different spot sizes. As demonstrated by Kroslakova and Günther (2007), an increase of the mass load of the ICP by a factor of sixteen (crater diameter from 30 to 120 μm) leads to a decrease in Cu/Ca, Zn/Ca, Cd/Ca and Pb/Ca ratios. In addition, Gaboardi and Humayun (2009) documented that volatile elements were enhanced relative to Ca with their set-up. This may affect the inhomogeneity investigations. However, our measurements were normalised to the corresponding crater diameters to avoid different element response based on plasma effects. As a consequence, experiments with NIST SRM 610 showed that there was no significant decrease (less than about 5%) in the intensity ratios (crater diameter from 25 to 80 μm). In addition, fractionation indices calculated from the different element/Ca ratios agree within uncertainty limits of about 5% for the different crater sizes.

Figure 2 shows rim to rim profiles of typical elements for NIST SRM 610. As already noted by Eggins and Shelley (2002), some elements, such as Tl and Au, are strongly depleted in the rims. The reason for this is loss of volatile and siderophile elements during glass preparation (Kane 1998). Our LA-ICP-MS results confirm the data of Eggins and Shelley (2002). Consequently, the trace element depleted rims (about 1–1.5 mm) of the NIST glasses have to be avoided for microanalysis, especially for the elements Tl, Au and Se (Figure 2). Because the other NIST SRM 61x glasses show similar depletions, we do not recommend the rim region of NIST glass wafers for microanalysis and, hence, our discussion on inhomogeneity refers to the core region of the reference glasses.

image

Figure 2.  Rim to rim profiles of element concentrations across a single NIST SRM 610 glass wafer obtained by LA-ICP-MS using different spot sizes (spacing = 200 μm). Because of the lower amount of sample ablated and transported, the scatter of the data increases with smaller spot sizes. Se, Tl and Au were depleted in the rim regions.

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The ability to detect inhomogeneity is dependent on the test portion mass and the repeatability of the technique (LA-ICP-MS) used. The smaller the test portion mass (spot size), the more readily inhomogeneity can be detected. This effect is shown in Figure 3, showing a modified sampling diagram from Ingamells and Pitard (1986) for Pt in NIST SRM 610. The sampling error increases by a factor of 100 with decreasing test portion mass. To determine local trace element inhomogeneities in the core regions, we calculated the RSD values of about 60–80 independent spot analyses of fifty-four elements in NIST SRM 610, 612, 614 and 616. Significantly higher values for a given test portion mass and concentration can be interpreted as inhomogeneities.

image

Figure 3.  Modified sampling diagram from Ingamells and Pitard (1986). This diagram shows the variation of sampling error with test portion mass for Pt in NIST SRM 610. Both curves represent the expected maximum and minimum analytical results. The ‘true’ value determined by ID and the LA-ICP-MS data at large spot sizes (200 μm corresponding to a test portion mass of about 10 μg) are from Sylvester and Eggins (1997). Also shown is the repeatability field of LA-ICP-MS.

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In Figures 4a–d, we have plotted the element inhomogeneity for the different NIST glasses, defined as

  • image(1)

where RSDmeas is the RSD of the element concentration of interest (%) determined in the core region of the NIST glass and RSDrepeat is the repeatability (expressed as % RSD) of LA-ICP-MS. The repeatability varied between about 1.5% and 15% for 80–25 μm spot analyses (corresponding to test portion masses of 1–0.02 μg) and concentrations of about 0.02–400 μg g−1. Using this procedure, uncertainties of RSDinhom caused by counting statistics are excluded to a large extent.

image

Figure 4.  Element inhomogeneity, expressed as RSDinhom (%) for the NIST SRM 610 (a), NIST SRM 612 (b), NIST SRM 614 (c) and NIST SRM 616 (d) obtained by LA-ICP-MS analyses using different spot sizes (80, 40, 25 μm). Most trace elements (e.g., lithophile elements) were homogeneously distributed (RSDinhom < 2%). Some siderophile and chalcophile elements, especially Ni, Se, Pt, Pd were inhomogeneously distributed at low test portion masses.

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Figures 4a–d show that most elements are homogeneously distributed. Some siderophile and chalcophile trace elements, especially Ni, Se, Pt, Pd in NIST SRM 610, 612, 614 and Cu, Ga, Sn in NIST SRM 616 are inhomogeneously distributed at small test portion masses (0.1 μg) and Cr, Co, Ni, Se, Cd, Re in NIST SRM 616 at 1 μg. It is notable that Pb behaves differently to other chalcophile elements because it is homogeneously distributed in all NIST glasses at all spot sizes. The results of Sylvester and Eggins (1997), who found a homogeneous distribution for the noble metals of better than 3.5%, do not disagree with this study, because they used large spot sizes of 200 μm and crater depths of about 100 μm (corresponding to test portion masses of about 10 μg) for their LA-ICP-MS measurements. This is clearly demonstrated in the sampling diagram (Figure 3), where their data fit the expected relationship. As expected, the inhomogeneous distribution increases with smaller test portion masses and lower element abundances and RSDinhom can exceed up to 50%. Whereas RSDinhom of a grossly inhomogeneous trace element (e.g., Pt in NIST SRM 610; Figures 3, 4a) is about 3–4% for 1 μg test portion masses, it is 35–45% for 0.02 μg test portion masses but not detectable in bulk analyses.

Table 2 lists a summary of the investigations on inhomogeneity. We categorised the behaviour of the elements into three groups according to their RSDinhom values obtained from the LA-ICP-MS analyses using different spot sizes: homogeneous, moderately inhomogeneous and grossly inhomogeneous. Nearly all lithophile elements and the major elements were homogeneously distributed in all NIST SRM 61x glasses, even for test portion masses of 0.02 μg. Excluding Ni, Se, Pd and Pt the maximum inhomogeneity of moderately chalcophile/siderophile elements in NIST SRM 610 was less than 3% (1 μg test portion mass), 4% (0.1 μg) and 10% (0.02 μg), and 5% (1 μg), 15% (0.1 μg) and 30% (0.02 μg) for NIST SRM 612 respectively (Figures 4a, b). This means that these glasses are – in spite of some inhomogeneously distributed elements – suitable as calibration materials for most micro-analytical purposes. The results of Table 2 are in agreement with the observations reported by Eggins and Shelley (2002). In contrast to this study, Tl was found to be relatively homogeneously distributed; however, it must be noted that our data only refer to the core section of the NIST glasses (not considering the approximately 1 mm Tl depleted rim).

Table 2.    Summary of element inhomogeneity in NIST SRM 610, 612, 614 and 616
 HomogeneousModerately inhomogeneousGrossly inhomogeneous
  1. Elements are grouped according to their geochemical behaviour. The inhomogeneity of some elements may be different in some glasses (sample names in brackets). Elements not investigated in this paper are from Eggins and Shelley (2002). The table also contains approximate values for RSDinhom (1–0.02 μg) for test portion masses varying between 1 and 0.02 μg (corresponding to spot sizes between 80 and 25 μm in LA-ICP-MS).

Geochemical behaviourRSDinhom (1–0.02 μg) < 1%RSDinhom (1–0.02 μg) = 1–20%RSDinhom (1–0.02 μg) > 5% to > 20%
Major lithophileAl2O3, CaO, Na2O, SiO2  
LithophileLi, Be, B, Sc, Ti, V, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Th, ULi (614), B (614), W (616) 
Moderately chalcophile/siderophileCr (610), Ga (610), Ge (610), Cu (610), Ag (610), Tl (610, 614), Co (612), Sb (612), Cr, Cu, CoNi (610), Cr, Cu, Co, Zn, Ga, Ge, As, Mo, Se, Cd, Ag, Sn, Sb, Tl Se (616), Cd (616), Ni
Highly siderophileRh (616), Pd (616), Pt (616), Au (616)Pd (614), Rh (610, 612, 614), Re (610, 612), Au (610, 612, 614) Re (614, 616), Pd (610, 612),  Pt (610, 612, 614)
Others (Eggins and Shelley 2002) P?, Cl, K? Br, F Mn, Fe, S?, Te

Reference and information values following ISO guidelines

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

The ISO Reference Materials Committee (ISO/REMCO) develops guidelines regarding proper reference materials terminology, production, certification and use. According to the rules of these guides, especially of ISO Guide 34 (2009), the production of a reference material includes all necessary activities and tasks leading to a reference material supplied to customers. It can include characterisation, but necessarily assignment of and decision on property values and relevant uncertainties, authorisation and issue of certificates. In order to determine updated reference and information values of NIST glasses we adopt ISO Guide 35 (2006): Reference materials – general and statistical principles for certification. Furthermore, the IAG has prepared a protocol to promote best practice in the certification of new geological reference materials (Kane et al. 2003, 2007) following ISO guidelines as completely as possible.

Among other attributes, ISO Guide 35 (2006) defines a reference material (RM) as a sufficiently homogeneous material to be used in a measurement process, while a certified reference material (CRM) is a RM characterised by a metrologically valid procedure for one or more specified properties, accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability.

The importance of the NIST SRM 61x glasses arises from their use for calibration in many LA-ICP-MS and other micro-analytical laboratories. In general, uncertainties associated with values of calibration should be smaller than uncertainties with values for other applications, such as method validation (ISO Guide 35 2006). Analytical instruments in microanalysis are calibrated with reference materials. So, stated and preferably small uncertainties associated with the reference values are essential to avoid introducing error into analyses (Kane 2002). The situation is made more difficult by the added concern for homogeneity on a micro-scale.

Certifying body

We are aware that we are unable to act as a certifying body for the NIST SRM 61x glasses. The management of a collaborative recertification study is primarily the responsibility of the organisation that performed the original certification. However, in view of the increasing studies using LA-ICP-MS we have proceeded as the IAG would in recertifying an existing material (e.g., Kane et al. 2009). We therefore consider these values to be equal in status to certified values, because of the validity of the metrological procedure used in deriving both the reference values and their uncertainties.

Data

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

In contrast to a certification programme, where guidelines of the collaborative study have to be developed, which should account for establishing and demonstrating traceability, we used two different kinds of elemental data. These are:

  • 1
     New data: major element abundances using EPMA at the MPI Mainz (Table 1), trace element data obtained by LA-ICP-MS at MPI Mainz (Tables 3, 4) and University of Mainz (Table 5), high-precision ID-TIMS data from MPI-Mainz (Table 6), new (ID)-ICP-MS trace element data from the ETH Zürich (Table 7), and RSDinhom values obtained by LA-ICP-MS analyses using different spot sizes.
  • 2
     GeoReM data: The GeoReM database contains about 5000 concentration data for the NIST glasses mainly published between 1995 and 2010 in analytical, geoanalytical and geological journals. Therefore, we are confident that we have access to a nearly complete data set from the last 15 years. Tables S1–S6 list the literature values, which are available in Application Version 12 (March 2011) of GeoReM.

Identification of qualified laboratories and data quality

According to ISO Guide 35 (2006), a minimum number of laboratories is required for a certification programme. If well-established measurement methods exist, the number of laboratories involved can be as small as two or three. A typical example is the use of primary methods, such as ID. When the statistical and metrological control is less, but still adequate to accept every technically valid result, the minimum number of laboratories involved is typically six to eight. Finally, if there is a non-negligible chance of having statistically and technically invalid results, the minimum number should be at least ten and preferably fifteen. This minimum number allows data to be scrutinised with the aid of outlier treatment techniques.

The number of methods available has also to be taken into consideration. ISO Guide 35 (2006) proposes, in the case where no primary methods are available, that ideally about three methods should be used by six competent laboratories. The IAG (Kane et al. 2003) based certified values on no fewer than ten individual laboratory results using at least two methods of analysis that are in agreement.

In contrast to certification procedures using the IAG protocol (Kane et al. 2003, Jochum et al. 2006, Cotta and Enzweiler 2008) competence of the laboratories could not be judged based on participation in a programme such as the GeoPT. However, the IAG protocol also allows qualification to be based on published geochemical research reports that focus on detailed method validation and/or the quantification of uncertainty (Kane et al. 2007).

Metrological traceability (King 1997, Potts 1997, ISO Guide 35 2006) is a key concept in the characterisation of reference samples. It links the validity of all analytical measurements to national and international standards through an unbroken chain of calibrations, each contributing to the measurement uncertainty. Traceability was established in the results by the use of international reference materials.

Data quality was checked in several different ways: the calibration procedures and analytical techniques used were verified, and the Horwitz function (Horwitz and Albert 1995) was employed to identify data ‘outliers’. As a first step, we excluded all concentration data of the NIST glasses that were obtained by using the same NIST sample for external calibration (e.g., NIST SRM 610 data using NIST SRM 610 for calibration), because a single reference material cannot be used for both calibration and validation of results in the same measurement procedure. These data are marked with ‘**’ in Tables S1–S4.

To test the quality of the remaining data we used the Horwitz function for the identification of ‘outliers’:

  • image(2)

where Ha is the target standard deviation, which is the precision value appropriate for the contributing laboratory, Xa is the assigned value (the best estimate of the ‘true’ value), the concentration of the element expressed as a fraction, and the factor k = 0.01 or 0.02 refers to pure and applied geochemistry or analytical laboratories respectively. Because of the high number of laboratories involved in quite different research fields, we used k = 0.02. After the IAG protocol for the operation of the GeoPT proficiency testing scheme (Thompson 2002) the assigned value is the mean of the results if the data are roughly symmetrically distributed, and the median of the results if the distribution is clearly skewed. In some instances it is not possible to estimate a satisfactory assigned value, e.g., for an unusually wide or multi-modal dispersion or when the number of results is low. Z-scores were calculated for each concentration value from

  • image(3)

where X is the contributed concentration value. Z-score results in the range −2 < z < 2 are considered to be ‘satisfactory’. This procedure is recommended by the IAG protocol (Kane et al. 2003). If the z-score falls outside this range, it would be advisable to examine the procedures of the laboratory and, if necessary, take action to ensure that determinations are not subject to unsuspected analytical bias. The number of ‘outliers’ rejected by this procedure in this work was low [5–7% (NIST 612–617), 12% (NIST 610–611)]. Figure 5 shows as an example the analytical data for Ba in NIST SRM 610 together with their calculated z-score results.

image

Figure 5.  Data distribution chart for Ba in NIST SRM 610. Horizontal lines show the limits of the z-score results for −2 < z < 2 (Horwitz and Albert 1995). Z-score results in this range are considered satisfactory.

Download figure to PowerPoint

We also tested data quality by the analytical technique applied, because the results obtained from different techniques may show systematic differences. We grouped the data into five categories according to the technique used:

  • 1
     ID by TIMS, MC-ICP-MS and ICP-MS.
  • 2
     Solution ICP-MS.
  • 3
     Other bulk-analytical techniques, such as XRF, INAA, SSMS, ICP-OES, AAS.
  • 4
     LA-ICP-MS.
  • 5
     Other micro-analytical techniques, such as SIMS, EPMA, PIXE.

Data of category 1 have the highest level of confidence. ID by TIMS and (MC)-ICP-MS is considered to be a primary method of measurement, whose operation can be completely described and understood, for which a complete uncertainty statement can be written down in terms of SI units (ISO Guide 35 2006). Isotope dilution data of 30, 25, 22 and 4 trace elements are available for NIST SRM 610–611, 612–613, 614–615 and 616–617 respectively (Tables 8–11, S1–S4). However, the ID results for some elements (e.g., Tl) may be questionable for the characterisation of the core when parts of the depleted rim were included.

Table 8.    Summary of compositional data for NIST SRM 610–611. Data are grouped into five categories of analytical techniques (see text)
AnalyteOv. meanType of dataUncertainty (U) at 95% CLCategoryNNo. techn.tLiterature
Test portion mass12345NISTPearce et al. (1997)Other comp. (see GeoReM)
mg range1 μg0.1 μg0.02 μgIDICP-MSBulk techn.LA-ICP-MSMicro-anal.
mean ± s (N)
  1. RV*: NIST certified value for Mn = 485 ± 10 μg g−1.

  2. NIST certified (CV), reference (RV) and information (IV) values are indicated.

  3. Uncertainties (U) at the 95% confidence level (CL) determined for different test portion masses; t: coverage factor. Trace elements in μg g−1; oxides in % m/m.

  4. Ov. (overall) mean, unweighted mean of all results; N, number of laboratory means; No techn., number of techniques used.

Ag251IV9999254 (1)   252 ± 11 (4) 245 (1)632.57254 ± 10239.4239
Al2O31.95IV0.040.040.040.04    1.98 ± 0.06 (3) 1.94 ± 0.04 (5)822.3722.0391.92–2.04
As325IV18182637   309 ± 8 (3) 330 ± 19 (4) 353 (1)832.37 317.4303–317
Au23.6IV1.71.72.27.1  22.1 (1) 25 ± 2 (4) 22.5 ± 0.6 (3) 742.452522.523
B350IV56565656351 (1)  357 (1) 348 ± 63 (3) 532.78351356.4356
Ba452RV9999456 ± 3 (2)451 ± 12 (6)  451 ± 22 (8) 1642.13 424.1412–435
Be476RV31313131 481 ± 42 (4) 421 ± 1 (2) 484 ± 21 (4) 1042.26 465.6421–466
Bi384RV26262626 390 ± 28 {4}  362 (1) 379 (1)632.57 357.7358–379
Br93IV       120 ± 150 (2) 33 (1) 32   123
CO20.0002IV         0.00022 (1)11    
CaO11.4IV0.20.20.20.2     11.4 ± 0.2 (6)612.571211.4511.39–11.5
Cd270RV16212863 265 ± 1 {2} 301 ± 1 (2) 261 ± 22 (6) 276 (1)1152.23 259.4259–288
Ce453RV8888458 ± 1 (2) 448 ± 15 (10) 451 ± 11 (3) 459 ± 26 (7) 442 (1)2372.07 447.8444–448
Cl274IV67676767   273 (1) 246 ± 23 (2) 330 (1)433.18 470 
Co410RV10101024 414 ± 23 (6) 412 ± 22 (7) 405 ± 26 (9) 2252.08390405403–405
Cr408RV10101010411 (1)412 ± 31 (5) 400 (1) 410 ± 20 (7) 401 ± 18 (4)1882.11 405.2405–409
Cs366RV9999 360 ± 17 (8) 383 ± 21 (5) 359 ± 7 (5) 1842.11 360.9357–376
Cu441RV15151515444 (1)439 ± 25 (4) 445 ± 34 (3) 433 ± 29 (6) 459 ± 44 (2)1672.13444 ± 4430.3430–443
Dy437RV11111111440 ± 4 (3) 430 ± 15 (10) 414 (1)446 ± 40 (9) 435 ± 35 (2)2572.06 426.5426–429.8
Er455RV14141414460 ± 6 (3)448 ± 14 (8) 442 (1) 457 ± 45 (8) 479 ± 59 (2)2282.08 426426–448
Eu447RV12121212447.7 (1) 445 ± 17 (12) 442 ± 21 (4) 440 ± 42 (8) 494 ± 16 (2)2762.06 461.1443.6–461
F304IV       205 (1)  354 ± 83 (2)32    
Fe458CV9999 461 (1) 517 (1) 479 ± 19 (7) 422 ± 78 (7)1662.13458 ± 9457.1458–464
Ga433RV13131313 435 ± 3 (2) 409 ± 20 (2)444 ± 15 (5) 427 (1)1052.26 438.1425–438
Gd449RV12121212 456 ± 5 (3) 440 ± 20 (11) 416 (1) 454 ± 39 (8) 483 ± 40 (2)2582.06 419.9441.6–456
Ge447IV78787878 391.3 (1)  424.4 (1) 486 ± 27 (2)443.18 426.3426–467
H15IV        15 (1)11    
Hf435RV12121212438 ± 1 (2) 437 ± 11 (6) 428 ± 2 (2) 439 ± 37 (7) 423 ± 31 (2)1972.10 417.7421.2–432
Ho449RV12121212  441 ± 17 (12) 466 ± 26 (2) 456 ± 43 (8) 457 (1)2342.07 449.4439.8–451
H2O0.013IV         0.0127 (1)11    
In434RV19191919  447 ± 19 {3} 396 (1) 435 ± 6 (2) 434 (1)742.45 441.4415–441
K464RV21212121463 ± 3 (2)  449 ± 10 (2) 429 ± 46 (2) 480 ± 40 (7)1372.18461486486–525
La440RV10101010440 ± 1 (2) 427 ± 14 (12) 445 ± 9 (4) 447 ± 35 (10) 497 (1)2972.05 457.4426–457
Li468IV24242424  455 ± 3 (2) 462 ± 48 (2) 477 ± 31 (4) 832.37 484.6428–485
Lu439RV8888439 ± 3 (3) 432 ± 17 (11) 441 ± 40 (2) 450 ± 20(7) 425 (1)2462.07 434.7420–435
Mg432RV29292929  488 (1) 429 ± 11 (2) 449 ± 45 (4) 420 ± 60 (7)1462.16 465.3440–464
Mn444RV*13131313  440.8 (1) 434 ± 36 (4) 450 ± 15 (9) 440 ± 40 (9)23102.07485 ± 10433.3443–485
Mo417RV21232756400 (1) 411 ± 15 (3) 319 (1) 429 ± 28 (8) 433 ± 33 (2)1562.15 376.8410
Na2O13.4IV0.30.30.30.3   13.4 ± 0.2 (3)13.4 ± 0.5 (5)822.371413.35213.4–13.82
Nb465RV34343434  473 ± 36 (3)  462 ± 51 (6) 922.31 419.4419–497
Nd430RV8888434 ± 5 (5) 425 ± 16 (11) 429 (1) 430 ± 22 (8) 480 (1)2682.06 430.8427–431
Ni458.7CV4425184469 (1) 457 ± 35 (3)436 ± 134 (2) 445 ± 24 (9) 477 ± 42 (4)1992.10458.7 ± 4443.9443–458.7
P413IV46464646  363 ± 82 (2) 380 (1) 420 ± 57 (2) 444 ± 55 (4)972.31 342.5343–427
Pb426CV1111434 (1) 421 ± 13 (9) 414 ± 29 (3) 417 ± 36 (9) 2262.08426 ± 1413.3417–428
Pd1.21IV0.440.480.652.71.05 (1)  1.30 ± 0.15 (2) 324.30   
Pr448RV7777  448 ± 17 (12) 451 (1) 447 ± 13 (5) 458 (1)1952.10 429.8430–454
Pt3.12IV0.080.460.975.53.15 (1)   3.10 ± 0.01 (2) 324.30   
Rb425.7CV1111415 ± 17 (2) 418 ± 19 (8) 401 ± 19 (3) 426 ± 28 (8) 450 ± 65 (2)2362.07425.7 ± 0.8431.1386–425.7
Re49.9IV3.73.73.71149.9 (1)  53 (1) 48.3 ± 1.3 (2) 433.18 103.737
Rh1.29IV0.070.070.230.87  1.31 (1) 1.28 ± 0.03 (2) 324.30   
S575IV323244307    597 ± 32 (5)548 ± 34 (4)932.31  456
Sb396RV19191922  340.4 (1)410 ± 5 (3)400 ± 25 (5)392 (1)1042.26 368.5369–405
Sc455RV10101010  450 ± 17 (7)454 ± 20 (5)468 ± 22 (3) 1542.15 441.1441–452
Se138IV42424391  95 (1)152 ± 2 (2)147 ± 36 (2)542.78 109110.5–183
SiO269.7IV0.50.50.50.5     69.7 ± 0.6 (6)712.457269.97569.06–70
Sm453RV11111111452 ± 5 (5) 442 ± 15 (11)457 ± 27 (4)458 ± 38 (8)532 (1)2982.05 450.5449.5–454
Sn430IV29293169   430 ± 30 (5)427 (1)622.57 396.3396–427
Sr515.5CV1111521 ± 6 (2) 505 ± 11 (7)473 ± 20 (2)507 ± 43 (10)599 ± 1 (2)2382.07515.5 ± 0.5497.4477–516
Ta446RV33333333429 (1) 392 ± 83 (4)475 ± 20 (3)471 ± 23 (6) 1442.16 376.6452–476
Tb437RV9999  443 ± 21 (12)439 ± 15 (3)424 ± 21 (6)443 (1)2242.08 442.8438–443
Te302IV        302 (1)11   302
Th457.2CV1111  451 ± 38 (10)450 ± 42 (5)453 ± 27 (8)478 ± 131 (2)2562.06457.2 ± 1.2450.6442–457.2
Ti452RV10101010  440 ± 3 (2)440 ± 4 (2)461 ± 16 (4)455 ± 18 (6)1462.16437434434–460
Tl59.6RV2.82.82.82.861.8 (1) 60 ± 4 {5} 59 ± 3 (3) 932.3161.8 ± 2.561.248–61
Tm435RV10101010  431 ± 20 (12)454 ± 32 (2)432 ± 22 (6)470 (1)2142.09 420.1420–447
U461.5CV1111475 (1) 461 ± 25 (8)484 ± 64 (2)464 ± 18 (7)428 (1)1952.1461.5 ± 1.1457.1447–461.5
V450RV9999  439 ± 10 (5) 435 (1)455 ± 18 (9)464 ± 2 (2)1752.12 441.7442–462
W444IV29292929446.6 (1)415 (1) 465 ± 61 (2)435 ± 16 (2)447 (1)752.45 445.3428–445
Y462RV11111111 453 ± 17 (9) 480 (1)467 ± 27 (6)484 ± 7 (2)1852.11 449.9450–478
Yb450RV9999459 ± 13 (3) 446 ± 15 (9)455 ± 35 (3)451 ± 26 (8) 2372.07 461.5440–445.7
Zn460RV18213379 457 ± 35 (5)415 ± 18 (3)469 ± 34 (9)497 ± 26 (2)1862.11433456.3456–505
Zr448RV9999460 ± 19 (2)447 ± 21 (8)435 (1)449 ± 29 (10)446 ± 8 (3)2472.07 439.9423–440
Table 10.    Summary of compositional data for NIST SRM 614–615. Data are grouped into five categories of analytical techniques (see text)
AnalyteOv. meanType of dataUncertainty (U) at 95% CLCategoryNNo. techn.tLiterature
Test portion mass12345NISTother comp. (see GeoReM)
mg range1 μg0.1 μgIDICP-MSBulk techn.LA-ICP-MS  Microanal.
mean ± s (N)
  1. Ov. (overall) mean, unweighted mean of all results; N, number of laboratory means; No techn., number of techniques used. NIST certified (CV), reference (RV) and information (IV) values are indicated. Uncertainties (U) at the 95% confidence level (CL) determined for different test portion masses; t: coverage factor. Trace elements in μg g−1; oxides in % m/m.

Ag0.42RV0.040.040.38   0.41 ± 0.03 (4) 413.180.42 ± 0.040.42
Al2O32.04RV0.050.050.05   2.06 ± 0.05 (4)2.01 ± 0.06 (3)722.4521.99
As0.74RV0.230.250.42   0.74 ± 0.13 (4) 413.18 0.66
Au0.48RV0.070.100.23 0.519 (1)0.5 (1)0.46 ± 0.09 (6) 832.370.50.45
B1.49RV0.190.191.39  1.3 (1)1.6 ± 0.2 (6)1.13 (1)832.371.3 ± 0.021.4
Ba3.20RV0.090.090.093.28 (1)3.35 ± 0.08 (3) 3.2 ± 0.2 (16)3.02 (1)2142.09 3.2
Be0.753RV0.0510.0510.051   0.75 ± 0.08 (10)0.76 (1)1122.23 0.67
Bi0.581RV0.0430.0430.043 0.57 (1) 0.58 ± 0.05 (7) 822.37 0.58
CO20.0004RV       0.0004 (1)11   
CaO11.9RV0.20.20.2    11.9 ± 0.2 (5)522.781211.9
Cd0.56RV0.050.130.39 0.48 (1)0.55 (1)0.57 ± 0.06 (7) 932.310.550.58
Ce0.813RV0.0250.0250.0250.805 (1)0.80 ± 0.03 (4) 0.82 ± 0.06 (18)0.764 (1)2442.07 0.81
Cl102RV848484  57 (1)177 (1)87 ± 8 (2)443.18  
Co0.79RV0.090.090.27 1.0 ± 0.4 (2)0.73 (1)0.8 ± 0.1 (15) 1832.110.73 ± 0.020.85
Cr1.19RV0.120.811.110.999 (1)  1.2 ± 0.1 (7)0.99 (1)932.31 1.8
Cs0.664RV0.0340.4080.561 0.66 ± 0.05 (4) 0.66 ± 0.07 (13)0.76 (1)1832.11 0.66
Cu1.37RV0.070.271.57 1.86 (1) 1.5 ± 0.4 (9) 1032.261.37 ± 0.071.37
Dy0.746RV0.0220.0220.0220.77 ± 0.01 (2)0.75 ± 0.01 (2) 0.74 ± 0.05 (16)0.74 (1)2152.09 0.74
Er0.740RV0.0170.0170.0170.77 ± 0.01 (2)0.72 ± 0.04 (3) 0.74 ± 0.04 (16)0.73 (1)2252.07 0.74
Eu0.770RV0.0160.0160.0160.763 (1)0.78 ± 0.02 (3) 0.77 ± 0.04 (16)0.75 (1)2142.090.99 ± 0.040.76
F6.2RV     2.4 (1) 10 (1)2212.71  
Fe18.8RV6.06.06.0  13.3 (1)19 ± 7 (5)22.6 (1)732.4513.3 ± 119
Ga1.31RV0.090.0917.00  1.3 (1)1.3 ± 0.1 (10) 1122.231.31.5
Gd0.763RV0.0210.0210.0210.79 ± 0.01 (2)0.79 ± 0.04 (3) 0.76 ± 0.05 (16)0.74 (1)2252.08 0.75
Ge0.942RV0.0960.2080.585   0.94 ± 0.10 (7) 712.45 0.89
Hf0.711RV0.0220.0220.0220.739 (1)0.66 ± 0.07 (3) 0.72 ± 0.04 (15)0.66 (1)2042.09 0.7
Ho0.749RV0.0150.0150.015 0.74 ± 0.03 (4) 0.75 ± 0.03 (16)0.73 (1)2132.09 0.74
H2O0.019RV       0.0186 (1)11   
In0.79RV0.050.050.05 0.72 (1) 0.80 ± 0.06 (8) 922.31 0.88
Ir0.002RV      0.002 (1) 11   
K30RV111   29.9 ± 0.6 (3)33 (1)423.1830 ± 130
La0.720RV0.0130.0130.0130.722 (1)0.72 ± 0.04 (4) 0.72 ± 0.03 (17)0.68 (1)2342.070.83 ± 0.020.72
Li1.69RV0.090.090.65   1.7 ± 0.2 (9)1.73 ± 0.02 (2)1122.23 1.6
Lu0.732RV0.0180.0180.0180.748 (1)0.70 ± 0.03 (3) 0.74 ± 0.04 (16)0.7 (1)2142.09 0.73
Mg33.8RV1.91.91.9   33 ± 3 (10)36.9 (1)1122.23 35
Mn1.42RV0.070.070.07   1.4 ± 0.1 (12) 1212.20 1.4
Mo0.80RV0.030.060.280.792 (1)0.90 (1) 0.78 ± 0.05 (13)0.88 (1)1642.13 0.8
Na2O13.7RV0.30.30.3   13.9 ± 0.1 (3)13.6 ± 0.3 (4)722.451413.6
Nb0.824RV0.0300.0300.030 0.79 (1) 0.83 ± 0.06 (16)0.79 (1)1832.11 0.81
Nd0.752RV0.0140.0140.0140.75 ± 0.01 (2)0.75 ± 0.03 (3) 0.75 ± 0.03 (16)0.73 (1)2252.08 0.74
Ni1.1RV0.11.01.31.08 (1) 0.95 (1)1.1 ± 0.2 (7) 932.310.951
P11.4RV3.93.93.9 8 (1) 13 ± 4 (3)10 ± 2 (2)632.57 13
Pb2.32RV0.040.040.042.51 (1)2.2 ± 0.3 (3) 2.4 ± 0.2 (18)2.8 (1)2342.072.32 ± 0.042.32
Pd2.05RV0.100.661.241.98 (1)  2.1 ± 0.1 (3) 423.18  
Pr0.768RV0.0150.0150.015 0.78 ± 0.01 (4) 0.78 ± 0.03 (16)0.74 (1)2142.09 0.76
Pt2.36RV0.122.253.752.26 (1)  2.39 ± 0.04 (3) 423.18  
Rb0.855RV0.0050.0050.005 0.89 ± 0.08 (4) 0.89 ± 0.10 (14)0.88 (1)1932.100.855 ± 0.0050.855
Re0.170RV0.0080.0120.1420.179 (1)  0.167 ± 0.008 (4) 722.45  
Rh1.54RV0.180.180.18 1.67 (1) 1.5 ± 0.2 (5) 622.57  
S291RV66196    313 ± 12 (2)270 ± 60 (2)433.18  
Sb0.79RV0.0640.0640.11  1.06 (1)0.76 ± 0.06 (11) 1222.201.060.78
Sc0.74RV    0.89 (1)0.59 (1)  2212.710.59 ± 0.041.6
Se0.40RV0.080.240.56  0.3 (1)0.43 ± 0.04 (4) 522.78  
SiO272.1RV0.90.90.9   72 ± 2 (3)72.3 ± 0.5 (4)722.457272.3
Sm0.754RV0.0130.0130.0130.759 ± 0.002 (2)0.75 ± 0.04 (3) 0.75 ± 0.03 (15)0.79 (1)2152.09 0.75
Sn1.68RV0.150.150.18   1.7 ± 0.2 (10)1.5 (1)1122.23 1.6
Sr45.8RV0.10.10.146.6 (1)46.5 ± 0.9 (3) 45 ± 3 (20)44 (1)2542.0645.8 ± 0.145.8
Ta0.808RV0.0260.0260.026 0.76 (1) 0.81 ± 0.05 (14)0.79 (1)1632.13 0.79
Tb0.739RV0.0200.0200.020 0.77 ± 0.03 (4) 0.73 ± 0.04 (15)0.69 (1)2032.09 0.73
Th0.748RV0.0060.0060.006 0.74 ± 0.03 (3) 0.77 ± 0.04 (18)0.73 (1)2232.080.748 ± 0.0060.748
Ti3.61RV0.250.250.25 3.4 (1)3.1 (1)3.7 ± 0.4 (10)3.77 (1)1342.183.1 ± 0.33.4
Tl0.273RV0.0200.0200.0200.269 (1)0.23 (1) 0.28 ± 0.02 (6)0.3 (1)942.310.269 ± 0.0050.28
Tm0.732RV0.0200.0200.020 0.73 ± 0.02 (3) 0.73 ± 0.04 (15)0.72 (1)1932.10 0.73
U0.823RV0.0020.0020.0020.893 (1)0.87 ± 0.07 (3) 0.88 ± 0.08 (15)0.78 (1)2042.090.823 ± 0.0020.823
V1.01RV0.040.040.04 1.10 ± 0.03 (2) 1.0 ± 0.1 (15)0.9 (1)1832.11 1
W0.806RV0.0710.0710.071   0.81 ± 0.08 (7) 712.45 0.88
Y0.790RV0.0320.0320.032 0.87 ± 0.11 (3) 0.78 ± 0.05 (15)0.781 (1)1932.10 0.8
Yb0.777RV0.0210.0210.0210.76 ± 0.03 (2)0.73 ± 0.02 (3) 0.79 ± 0.05 (17)0.81 (1)2352.07 0.77
Zn2.79RV0.380.382.61 2.8 ± 0.8 (2) 2.8 ± 0.7 (13) 1522.15 2.5
Zr0.848RV0.0280.0280.028 0.88 ± 0.05 (3) 0.84 ± 0.06 (17)0.83 (1)2132.09 0.84
Table 11.    Summary of compositional data for NIST SRM 616–617. Data are grouped into five categories of analytical techniques (see text)
AnalyteOv. meanType of dataUncertainty (U) at 95% CLCategoryNNo. techn.tLiterature
Test portion mass12345NIST value
mg range1 μg0.1 μgIDICP-MSBulk techn.LA-ICP-MSMicro-anal.
mean ± s (N)
  1. Ov. (overall) mean, unweighted mean of all results; N, number of laboratory means, No techn., number of techniques used.

  2. NIST certified (CV) and information (IV) values are indicated.

  3. Uncertainties (U) at the 95% confidence level (CL) determined for different test portion masses; t: coverage factor. Trace elements in μg g−1; oxides in % m/m.

Ag0.048IV0.0200.0200.020   0.048 ± 0.013 (4) 413.18 
Al2O31.99IV0.0890.0890.089    1.99 ± 0.04 (3)314.302
As0.20IV      0.2 ± 0.1 (2) 2112.71 
Au0.189IV0.0240.0240.024 0.194 (1)0.18 (1)0.19 ± 0.03 (4) 632.570.18 ± 0.01
B0.94IV0.470.470.47   1.1 ± 0.2 (3)0.54 (1)423.180.2 ± 0.02
Ba2.31IV0.120.120.12   2.3 ± 0.2 (8)2.19 (1)922.31 
Be0.028IV0.0250.0250.025   0.03 ± 0.01 (2)0.0221 (1)324.30 
Bi0.021IV0.0060.0060.006 0.020 (1) 0.022 ± 0.005 (4) 522.78 
CaO11.8IV0.10.10.1    11.79 ± 0.05 (4)413.1812
Cd0.036IV    0.024 (1) 0.045 (1) 2212.71 
Ce0.0292IV0.00110.00110.0011   0.030 ± 0.001 (6)0.0275 (1)722.45 
Co0.051IV0.0160.0530.089   0.051 ± 0.017 (6) 712.45 
Cr0.40IV0.130.540.79   0.44 ± 0.07 (4)0.24 (1)522.78 
Cs0.027IV0.0020.0020.002   0.027 ± 0.002 (6) 612.57 
Cu0.70IV0.300.300.30  0.8 (1)0.66 ± 0.10 (2) 334.300.80 ± 0.09
Dy0.0173IV0.00140.00140.0014   0.017 ± 0.002 (5)0.017 (1)622.57 
Er0.0157IV0.00130.00130.0013   0.016 ± 0.001 (5)0.014 (1)622.57 
Eu0.0146IV0.00070.00070.0007   0.015 ± 0.001 (4)0.014 (1)522.78 
Fe16IV888  11 (1)16 ± 4 (2)21.3 (1)433.1811 ± 2
Ga0.50IV0.130.130.15  0.23 (1)0.54 ± 0.13 (7) 822.370.23 ± 0.02
Gd0.0162IV0.00240.00240.0024   0.016 ± 0.002 (4)0.016 (1)522.78 
Ge0.283IV0.0390.1930.317   0.28 ± 0.03 (5) 512.78 
Hf0.0154IV0.00180.00180.0018   0.016 ± 0.02 (6)0.015 (1)722.45 
Ho0.0169IV0.00310.00310.0031 0.018 (1) 0.017 ± 0.004 (7)0.0158 (1)932.31 
In0.0302IV0.00350.00350.0035 0.024 (1) 0.031 ± 0.002 (5) 622.57 
K29CV111   31 ± 2 (2)31.6 (1)324.3029 ± 1
La0.0298IV0.00320.00320.0032  0.034 (1)0.029 ± 0.004 (6)0.029 (1)832.370.034 ± 0.007
Li0.895IV0.0590.0590.059   0.89 ± 0.07 (6)0.91 (1)722.45 
Lu0.0145IV0.00200.00200.0020 0.013 (1) 0.015 ± 0.003 (6)0.014 (1)832.37 
Mg34.7IV2.82.82.8   35 ± 3 (4)35.4 (1)522.78 
Mn0.609IV0.0270.0270.027   0.61 ± 0.02 (5) 512.78 
Mo0.0879IV0.0130.0470.066   0.084 ± 0.010 (6)0.113 (1)722.45 
Na2O13.7IV0.90.90.9    13.7 ± 0.4 (3)314.3014
Nb0.0194IV0.00150.00150.0015   0.020 ± 0.002 (5)0.019 (1)622.57 
Nd0.0227IV0.00310.00310.0031   0.023 ± 0.003 (5)0.023 (1)622.57 
Ni0.435IV0.100.811.11   0.44 ± 0.06 (4) 413.18 
P13IV101010   14 (1)12.2 (1)2212.71 
Pb1.85CV0.040.040.04   1.8 ± 0.1 (7)1.6 (1)822.371.85 ± 0.04
Pd1.77IV0.130.130.131.75 (1)  1.78 ± 0.07 (2) 324.30 
Pr0.0150IV0.00090.00090.0009   0.015 ± 0.001 (5)0.014 (1)622.57 
Pt1.77IV0.250.250.251.79 (1)  1.75 (1) 2212.71 
Rb0.104IV0.0040.0040.0040.1 (1)  0.105 ± 0.004 (7) 822.370.10 ± 0.007
Re0.0036IV0.00130.02520.0321 0.0035 (1) 0.0037 (1) 2212.71 
Rh0.98IV0.340.340.34   0.98 ± 0.04 (2) 2112.71 
Sb0.076IV0.0080.0190.040  0.078 (1)0.075 ± 0.008 (5) 622.570.078 ± 0.007
Sc0.026IV     0.026 (1)  11 0.026 ± 0.012
Se0.22IV      0.22 (1) 11  
SiO272.5IV0.70.70.7    72.5 ± 0.3 (3)314.3072
Sm0.0164IV0.00290.00290.0029   0.0165 ± 0.003 (4)0.016 (1)522.78 
Sn1.18IV0.080.730.81   1.2 ± 0.1 (6)1.07 (1)722.45 
Sr41.72CV0.050.050.05 41.95 (1) 41 ± 2 (10)39.9 (1)1232.2041.72 ± 0.05
Ta0.0299IV0.00550.00550.0055 0.028 (1) 0.031 ± 0.008 (7)0.022 (1)932.31 
Tb0.0145IV0.00210.00210.0021 0.019 (1) 0.014 ± 0.001 (5)0.012 (1)732.45 
Th0.0252CV0.0070.0070.007   0.026 ± 0.003 (7)0.026 (1)822.370.0252 ± 0.0007
Ti2.65IV0.290.290.29  2.5 (1)2.6 ± 0.2 (3)2.92 (1)532.782.5 ± 0.7
Tl0.0081IV0.00120.00420.00590.0082 (1)0.007 (1) 0.008 ± 0.002 (5)0.01 (1)842.370.0082 ± 0.0005
Tm0.0144IV0.00120.00120.0012 0.016 (1) 0.014 ± 0.001(5)0.013 (1)732.45 
U0.0721CV0.00130.00130.0013 0.084 (1) 0.074 ± 0.005 (8)0.063 (1)1032.260.0721 ± 0.0013
V0.228IV0.0150.0150.015   0.23 ± 0.02 (7) 712.45 
W0.043IV0.0040.0330.055   0.045 ± 0.002 (5)0.036 (1)622.57 
Y0.0288IV0.00240.00240.0024   0.029 ± 0.003 (5)0.029 (1)622.57 
Yb0.0171IV0.00230.00230.0023   0.017 ± 0.003 (6)0.016 (1)722.45 
Zn1.33IV0.270.270.27   1.3 ± 0.3 (6) 712.45 
Zr0.0951IV0.00800.00800.0080   0.094 ± 0.010 (7)0.101 (1)822.37 

Data of category 2 were obtained by solution ICP-MS, and certified standard solutions were generally used for calibration. Because of this, data of this category have a high level of confidence. For nearly all elements in NIST SRM 610–611, 612–613 and 614–615 solution ICP-MS data exist.

Data of category 3 were obtained by quite different analytical techniques. Whereas calibration of ICP-OES and AAS data was generally performed using standard solutions, this is not the case for INAA, XRF and SSMS, where solid reference materials were used.

Published LA-ICP-MS data of the NIST SRM 61x glasses were calibrated by using the same glasses (e.g., NIST SRM 610 data using NIST SRM 610 for calibration), which were excluded in this paper as explained above, other (than those measured) NIST SRM 61x glasses, geological reference glasses of the USGS, MPI-DING and other procedures. Because of some unsatisfactory calibration procedures, data of category 4 were carefully checked (e.g., type of laser, detection limit, uncertainty) and several outliers were rejected and not further considered in our calculation of reference values.

Data of category 5 were obtained by other micro-analytical techniques, mainly EPMA and SIMS. The accuracy of SIMS data may suffer from matrix effects; however, new technique developments and calibration procedures have improved the reliability of trace element data considerably (Hervig et al. 2006).

Whereas typical sample amounts needed for analytical techniques of categories 1–3 are 2–100 mg, they are much less for micro-analytical techniques of category 4 (several μg) and of category 5 (ng range).

Tables 8–11 list the concentration averages for each group with the corresponding standard deviation values. Nearly all mean values of the five groups agree within uncertainty limits indicating that possible systematic differences between the analytical techniques are absent or small, making a bias component of uncertainty unnecessary.

Reference and information values

To obtain the present best estimates of the ‘true’ values of the NIST SRM 61x glasses, we averaged the data of Tables 8–11 (= overall mean). As mentioned above, some data were not used for these calculations because they were inappropriately calibrated (marked by ‘**’ in Tables S1–S4) or they did not fulfil the Horwitz requirement and/or had low precision (marked by ‘*’). As recommended by the IAG (Kane et al. 2003) we used unweighted means because weighting procedures (Paule and Mandel 1982) cannot be applied successfully with many contributing laboratories. For some elements, two to five independently determined ID values exist and according to ISO Guide 35 (2006) this is a sufficient number of laboratories involved in a characterisation process. However, in these special cases we also determined the preferred values from all available data. As Tables 8–11 show, the overall mean values agreed very well with the ID values. The overall means were divided in two kinds of values: reference values and information values. The reference values are comparable with ‘certified’ values in a certification programme (Kane et al. 2003, 2007). We report reference values when they were derived from at least six laboratories, where at least three laboratories published data of category 1 (ID) or 2 (solution-ICP-MS). Where fewer data exist, data of at least three methods of categories 1–5 determined in at least ten laboratories were necessary to establish a reference value. Those elemental abundances that were determined by only one or two techniques, by fewer than three techniques or less than ten laboratories were assigned information values rather than reference values.

As already mentioned, some trace elements have been certified by NIST for bulk-analytical purposes. With the exception of Mn in NIST SRM 610 (Table 8), we did not find any systematic difference between the certified values and the new data. Therefore, there is no need to revise the certified values. However, it must be remembered that the uncertainty of the data given by NIST is only valid for bulk analysis and cannot be extended automatically to micro-analytical use.

Uncertainty of reference values and a discussion of the results

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

The reference values and most information values are accompanied with uncertainties at the 95% CL for the different test portion masses (Tables 8–11). These values were calculated using the IAG protocol (Kane et al. 2003), where the uncertainty, u, is based mainly on three components of variance which were combined in quadrature:

  • image(4)

The first component, the standard deviation of the mean of N contributing laboratories’ mean data, was used as the random component of variance. The second and the third components account for inhomogeneities in the NIST glasses and between-laboratory biases. VARinhom affects elements that are inhomogeneously distributed in the glasses. For such elements the RSDinhom values (Figure 4a–d) for test portion masses of 1, 0.1 and 0.02 μg were used. Because the laboratories were qualified, biases were already included in the standard deviation of the mean, so that VARbias = 0.

The uncertainty U of the reference value at the 95% CL is

  • image(5)

where t is the coverage factor. Student’s t-distribution was used to assign t, which is about 2 for > 30 and much larger at small values of N. As shown in Tables 8–11, the uncertainty U is constant regardless of test portion mass for elements that are homogeneously distributed. This allowed us to use the uncertainty determined by NIST for all homogeneously distributed elements, whose concentrations are certified, unchanged. However, inhomogeneities lead to higher values of U as test portion mass decreases. Because we found them to be large for Ni at test portion masses ≤ 0.1 μg, the uncertainty for Ni reference values must be higher at small test portion mass.

In the following, the reference and information values and their uncertainties for the different elements and element groups, respectively, will be discussed in detail. Of particular interest are possible differences between our data for NIST SRM 610–611 and SRM 612–613 with those of the frequently used compilation values of Pearce et al. (1997) (Figure 6).

image

Figure 6.  Deviation of the reference and information values from the compilation data of Pearce et al. (1997).

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Major elements

The NIST glasses were prepared from a single support matrix whose nominal concentration is 72% m/m SiO2, 12% m/m CaO, 14% m/m Na2O and 2% m/m Al2O3 (Kane 1998). However, the nominal composition of the matrix does not exactly represent the major oxide composition of the final glasses due to the spiking processes with trace elements and volatilisation losses. Given the measured concentrations of trace elements, the oxide total, based on major elements alone, should be different from about 100% m/m in NIST SRM 616–617 to about 96.7% in NIST SRM 610–611 (Hinton 1999). Our values for major elements (Tables 8–11) agreed very well with these considerations: total oxide = 99.99% m/m (NIST STM 616–617), 99.8% m/m (NIST SRM 614–615), 99.7% m/m (NIST SRM 612–613) and 96.5% m/m (NIST SRM 610–611). The measured H2O and CO2 contents were low (≤ 0.02% m/m; Tables 8–11).

As shown in this paper (Figure 1) and other publications (e.g., Hinton 1999) the major elements are homogeneously distributed at both the small- and the large-scale. Because results from fewer than ten laboratories and only two different analytical techniques (EPMA, LA-ICP-MS) were available, mean values are only for information. However, all published data agree well and therefore the information values have a high level of confidence.

Refractory lithophile trace elements

Such elements with high condensation temperatures include Ba, Sr, Y, Zr, Hf, Nb, Ta, REEs, Th, U, Sc and Ti. As shown by LA-ICP-MS analyses in this work (Figures 4a–d) and Eggins and Shelley (2002) as well as by ion microprobe measurements (Hinton 1999) these trace elements are homogeneously distributed at all scales. Even for small spot sizes there is no indication of inhomogeneities. This means that uncertainties are the same for all test portion masses. Strontium is over-abundant in the NIST glasses because of the Sr base glass composition of 50 μg g−1 (Kane 1998). Bulk- and micro-analytical techniques, including the highly precise and accurate ID technique, are able to determine precisely the concentrations of most refractory lithophile elements. Therefore, many published data for NIST SRM 610–611, SRM 612–613, SRM 614–615 exist. Our new reference values are of high quality with relative uncertainties of less than 3% (Figure 7) and agree well with existing ID measurements. Many values agree within the stated uncertainties [this work: about 2–3% (95% CL relative); Pearce et al. (1997): about 3–10% (RSD)] (Figure 6). Notable exceptions are Nb and Ta in SRM 610–611, where our reference values (Nb 465 μg g−1, Ta = 446 μg g−1), the ID value of Ta (429 μg g−1) and most other recently published data were significantly higher than the Pearce et al. (1997) value (Nb = 419.4 μg g−1, Ta = 376.6 μg  g−1). The NIST certified Sr, Th and U concentrations agree well with published bulk- and micro-analytical data. As Figure 4a–d demonstrate, these elements are homogeneously distributed in all NIST SRM 61x glasses, even for very low test portion masses. This means that the uncertainty at the 95% CL of the NIST certified Sr, Th and U values is valid to test portion masses as low as 0.02 μg.

image

Figure 7.  Diagram illustrating the relative uncertainties at the 95% confidence level for the reference and information values of NIST SRM 610–611 and 612–613 at different test portion masses.

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Other lithophile elements

The alkali elements Li, Rb, Cs were found to be homogeneously distributed in all NIST glasses. This is in contrast to the investigations of Eggins and Shelley (2002) who report slight to moderate inhomogeneities for these elements. Potassium appears to be grossly contaminated and over-abundant in the NIST SRM glass series by about 30 μg g−1, which is consistent with reported base glass compositions of 5–100 μg g−1 (Eggins and Shelley 2002). Caesium is a volatile element and may therefore be subject to loss during high temperature fusion. This, however, had no influence on the homogeneity of Cs in the NIST SRM 61x glasses; all measurements yielded a RSDinhom value of < 2% (Figure 4a–d). The NIST certified values of Rb are nearly identical to the mean values calculated from recently published data. Rubidium was homogeneously distributed in the glass wafers and therefore, the uncertainty given by NIST is also valid for micro-analytical applications.

The NIST certified value for Mn (485 ± 10 μg g−1) in NIST SRM 610 does not agree with our overall mean value (444 ± 13 μg g−1) determined from recent publications. Because the values determined by different techniques (Table 8) agree and are much lower than the certified value, this requires that the NIST Mn reference value for SRM 610 be revised. Manganese values lower than the certified value were also proposed by Pearce et al. (1997) (433 μg g−1) and Rocholl et al. (2000) (443 μg g−1).

Magnesium is homogeneously distributed in the NIST glasses (Eggins and Shelley 2002). The new reference values for NIST SRM 610 and 612 were found to be lower than the Pearce et al. (1997) data by about 10%. The discrepancies for P are even higher; the new reference values for NIST SRM 610 and SRM 612 were 21% higher and 16% lower than the Pearce et al. (1997) values respectively.

Because of the many published data for NIST SRM 610–615 the reference values for Be and V analyses are reliable. They agree within uncertainty limits with the Pearce et al. (1997) values. There are only a few, but somewhat consistent, data for the halogens F, Cl, Br, and none for I. The information values have, therefore, high uncertainties.

Chalcophile/siderophile trace elements

Members of this group include Ag, As, Bi, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, Mn, Mo, Ni, Pb, Re, S, Sb, Sn, Se, Te, Tl, W and Zn. Because of their volatility and their chalcophile/siderophile behaviour some of them are inhomogeneously distributed in the glass wafers. Such inhomogeneities have been explained by loss of volatile components from the molten glass surface (Eggins and Shelley 2002) and of siderophile elements to the platinum furnace (Rocholl et al. 1997) during preparation. Typical examples are Tl, Cr, Ni and Se (Figure 4a–d). Eggins and Shelley (2002) established the order of relative depletion: Tl ∼ Te > Re ∼ Au ∼ As ∼ Se > Cr ∼ Ag ∼ Cd ∼ B > Mo ∼ Sb ∼ Bi > Pb > W ∼ Cs, which is notable for closely matching the relative order of bulk composition in NIST glasses relative to the nominal concentration levels. Our investigations demonstrated that inhomogeneities for most of the chalcophile/siderophile elements exist, but they are low (< 4% and < 7% for NIST SRM 610 and 612, respectively, at a test portion mass of 0.1 μg) in the core parts of the glass wafers (Table 2, Figure 4a–d). Exceptions are Cr, Ni, Se and Tl with higher degrees of inhomogeneity.

Because of analytical difficulties the number of published data for some chalcophile/siderophile elements (e.g., Ge, Se, Te) is low. Therefore, uncertainties are significantly higher than for lithophile trace elements. Exceptions are the concentrations of Ag in SRM 612–613 and SRM 614–615, Fe and Ni in SRM 610–611 and SRM 612–613, Cu in SRM 614–615 as well as Pb in all NIST glasses, which have been certified by NIST. For Co, Cr, Cu sufficient literature data for SRM 610–611, 612–613 and 614–616 exist to establish reliable reference values. For some chalcophile/siderophile trace elements in the depleted SRM 616–617 glass we report first information values mainly obtained by LA-ICP-MS.

Our Cr reference value [36.4 ± 1.7 μg g−1 (95% CL for a test portion mass of 1 μg)] for NIST SRM 612–613 is similar to the Pearce et al. (1997) value [39.88 ± 15.17 μg g−1 (1s for bulk analysis)], but has a much lower uncertainty. There are large discrepancies in Ga data for NIST SRM 616–617. LA-ICP-MS (0.54 ± 0.13 μg g−1, Table 11) and SIMS values (1.25 μg g−1, Table S4) were significantly higher than the NAA value (0.23 μg g−1) proposed by NIST. Only a few reliable values for S were available. Our S reference value for NIST SRM 612–613 is much higher (377 μg g−1) than the value of S = 16 μg g−1 proposed by Pearce et al. (1997), which was based on a single semi-quantitative LIMS value (Bonham and Quattlebaum 1988). The present paper contains the first information value for Se. Because Se is inhomogeneously distributed at the small-scale in all NIST SRM glasses (Figure 4a–d), uncertainties are large. There is a need for Te determinations; only one LIMS value for NIST SRM 610–611 exists. New ID data for W improve considerably the reliability of W reference values. All recent Re determinations in NIST SRM 610–611 are about a factor of two lower than the Pearce et al. (1997) compilation value. Our Re reference value for SRM 612–613 was also lower, by 20% only.

Highly siderophile elements

There is a great need for micro-analytical reference materials containing well-known compositions of highly siderophile elements, including the noble metals Ru, Rh, Pd, Os, Ir, Pt and Au. One of the major problems is that in geological reference glasses (e.g., MPI-DING, USGS) these elements may be inhomogeneously distributed using small test portion masses (Jochum and Stoll 2008). As shown in Figure 4a–d this is also the case for Rh, Pd, Pt and Au in the NIST SRM 610–615 glasses. In particular, Pd and Pt showed relative inhomogeneities of up to 50% at very low test portion masses. Because of their very low abundances, Ru and Os concentrations have not been determined in the NIST glasses; only one Ir determination exists for NIST SRM 612. Because of the few published data the overall mean Rh, Pd, Pt and Au values in Tables 8–10 are only for information, although ID values for Pd and Pt are available (Sylvester and Eggins 1997). NIST SRM 616–617 seem to be homogeneous with respect to noble metals (Figure 4d). Even for test portion masses of 0.01 μg, RSDinhom was < 2%. This means that this sample may be useful as a calibration material for noble metals. Because of the high quality ID data of Sylvester and Eggins (1997), the overall means are confident.

Accuracy

Of particular importance is the accuracy of micro-analytical data, that is the closeness of agreement between the measured and the ‘true’ values. The reference and information values of the NIST glasses (Tables 8–11) have a high degree of confidence. Compared with former compilations (e.g., Pearce et al. 1997) the overall means were determined mainly from recent studies that used improved instrumentation and analytical procedures, such as ID-TIMS and ID-MC-ICP-MS (e.g., Rocholl et al. 2000, Nebel et al. 2009), and multi-element (ID)-ICP-MS measurements (this work) to obtain high-precision and accurate data, new laser ablation systems with low wavelengths and femtosecond pulses to minimise elemental fractionation (e.g., Horn and von Blanckenburg 2007), the use of dynamic reaction cells to minimise formation of metal-argide ions in the ICP-MS (e.g., Hattendorf et al. 2001), and high-resolution sector field ICP-MS to separate interferences from the mass peaks of interest (e.g., Guillong et al. 2008, Regnery et al. 2010). LA-ICP-MS data for lithophile refractory elements have been less influenced by the technological progress of lasers, because the fractionation factors of these elements are nearly identical as shown by Fryer et al. (1995). The chalcophile and siderophile elements are most prone to elemental fractionation relative to lithophile elements (e.g., Ca). As mentioned above, differences in elemental fractionation are significantly diminished using shorter wavelengths, which leads to more reliable LA-ICP-MS data. Although some of the bulk techniques (e.g., ID, solution ICP-MS) yield highly precise data, the results may be questionable for the characterisation of the core when parts of the depleted rim were used. However, as shown earlier, this affects only some elements (e.g., Tl, Se and Au; Figure 2). The ID and solution ICP-MS Tl data for NIST SRM 610 and 612 (Tables 8, 9) agree with the LA-ICP-MS data, indicating no systematic differences for this element. There is also no indication of a systematic difference for Se and Au data obtained using bulk- and micro-analytical techniques respectively.

The new reference and information values have been used to determine trace element concentrations in the synthetic certified reference glasses BAM-S005-A and BAM-S005-B (http://www.rm-certificates.bam.de). Data were obtained by LA-ICP-MS at MPI Mainz (Yang et al. 2011) and calibrated with NIST SRM 610 (Table 8), which has approximately the same major element composition as the BAM glasses. Figure 8 shows the results for BAM-S005-A. All data agreed within uncertainty limits with the BAM certified reference values. The figure also shows the LA-ICP-MS results using the Pearce et al. (1997) values for calibration. There were only small differences for Ti, Zr, V, Cr, Fe and Zn values. As mentioned earlier, the NIST certified Mn value for SRM 610 leads to a systematically higher concentration. Differences for As, Cd, Mo, Sn, Sb and especially Se and Cl are even higher; no value for sulfur in Pearce et al. (1997) exists.

image

Figure 8.  Normalised LA-ICP-MS trace element data of the reference glass BAM-S005-A using the new reference and information values for NIST SRM 610 (Table 8) for calibration. Within uncertainty limits all data agree with the BAM certified values. The NIST certified value for Mn leads to a systematically higher Mn value for BAM-S005-A. Also shown are the normalised LA-ICP-MS data using the Pearce et al. (1997) reference values for NIST SRM 610.

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The knowledge of the uncertainty of the reference values in reference materials is essential for assessment of the quality of the results of micro-analytical investigations. Unfortunately, some analysts only use the reference value and do not pay attention to its uncertainty. For example, when using NIST SRM 612–613 for calibration and the reference value has an uncertainty of 10%, the analytical result of an unknown sample cannot have measurement uncertainty better than 10%. As discussed earlier, the uncertainty of the reference and information values (Tables 8–11) is dependent on both the uncertainty of the overall mean data and the degree of inhomogeneity at a specific test portion mass (spot size in LA-ICP-MS). Figure 7 gives an overview of the expected uncertainty, which can be obtained by using NIST SRM 610–611 and 612–613 glasses for calibration of bulk- and micro-analytical methods. It illustrates the values for the relative uncertainty at the 95% CL in percent (= 100 × U/Overall mean) of different elements and element groups obtained for different test portion masses. Using this figure, the minimum test portion mass (or spot size in LA-ICP-MS) can be inferred, where the uncertainty for a trace element is less than 3%, 5%, 10% and 20% in NIST SRM 610–611 and 612–613.

Conclusions

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

Most reference values for the NIST SRM 610–617 glasses obtained by following ISO guidelines and the IAG protocol for certification of reference materials have a high degree of confidence. This is especially the case for most lithophile elements of NIST SRM 610–611 and SRM 612–613, where many published data using quite different analytical techniques including ID were available. In addition, these elements are homogeneously distributed at the small-scale and the large-scale. Altogether we have established forty-six reference and certified values for NIST SRM 610–611, forty-three for SRM 612–613, thirty-three for SRM 614–615, and five for NIST SRM 616–617. The data of many elements could not be classified as reference values because they did not satisfy the requirements of the ISO guidelines and the IAG protocol. This was particularly the case for the depleted NIST SRM 616–617 glasses. However, many of these elements (major elements, some lithophile and chalcophile/siderophile trace elements, where concentrations were partly determined by ID) are homogeneously distributed at the small- and the large-scale, and give reliable information values with uncertainties < 10% at test portion masses as low as 0.1 μg. The numbers of such information values are: 13 (SRM 610/611), 14 (SRM 612/613), 12 (SRM 614/615) and 24 (SRM 616/617). This means that the NIST glasses are suitable calibration materials for nearly all elements.

For some chalcophile and siderophile elements inhomogeneities occur, especially in the rim region (about 1–1.5 mm) of the wafers; but for most applications they are moderate in NIST SRM 610–611 and 612–613. Because of the extremely inhomogeneous distribution of Pd, Pt, Ni, Se some NIST glasses may be suitable for bulk-analytical but not for micro-analytical purposes at very low test portion masses. For F, Cl, Br and S few published data exist, which are partly inconsistent with one another; no data exist for Ru, Os, I and Hg.

In summary, we report the reference and information values of this work as a state of the art data set for inter-laboratory comparisons. Furthermore, we are confident that the data quality of micro-analytical investigations will improve by using these recommended values for calibration. However, further analyses are needed to improve the analytical data of some trace elements by reducing their uncertainties. This is especially true for elements where only information values can currently be determined.

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  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. Samples
  4. New data and inhomogeneity
  5. Reference and information values following ISO guidelines
  6. Data
  7. Uncertainty of reference values and a discussion of the results
  8. Conclusions
  9. Acknowledgements
  10. References
  11. Supporting Information

Table S1. Used data for NIST SRM 610 and 611.

Table S2. Used data for NIST SRM 612 and 613.

Table S3. Used data for NIST SRM 614 and 615.

Table S4. Used data for NIST SRM 616 and 617.

Table S5. GeoReM numbers and references.

Table S6. Abbreviations of analytical techniques.

FilenameFormatSizeDescription
GGR_120_sm_TableA1.xls137KSupporting info item
GGR_120_sm_TableA2.xls132KSupporting info item
GGR_120_sm_TableA3.xls100KSupporting info item
GGR_120_sm_TableA4.xls52KSupporting info item
GGR_120_sm_TableA5.docx23KSupporting info item
GGR_120_sm_TableA6.xls26KSupporting info item

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