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Hyphenated Methods for Speciation Analysis

Environment: Water and Waste

  1. Rajmund Michalski,
  2. Magdalena Jabłońska-Czapla,
  3. Aleksandra Łyko,
  4. Sebastian Szopa

Published Online: 20 SEP 2013

DOI: 10.1002/9780470027318.a9291

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Michalski, R., Jabłońska-Czapla, M., Łyko, A. and Szopa, S. 2013. Hyphenated Methods for Speciation Analysis. Encyclopedia of Analytical Chemistry. 1–17.

Author Information

  1. Institute of Environmental Engineering of Polish Academy of Sciences, Zabrze, Poland

Publication History

  1. Published Online: 20 SEP 2013

1 Introduction

  1. Top of page
  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References

The term speciation originates from the Latin word species, which means species or species evolution 1 and is used in biology. The notion of speciation analysis was first used in the literature in 1993. At the beginning, it was defined as the movement and transformation of the element forms in the environment.2

Toxicological test results show that in many cases specific forms of a given element, rather than its total content, have a decisive impact on living organisms. For this reason, the information on the total element content in a given sample is less important than understanding the occurrence of various element forms.

Physical speciation considers the occurrence of free and bound analytes. For example, while analyzing surface water samples, the fraction bound with the suspension is separated from the solved fraction after it is filtered with a 0.45-µm filter. Consequently, it is possible to demonstrate that approximately 80% of the determined analyte is adsorbed on the suspension. The remaining 20% is solved and passed into water, a natural solvent according to which the leaching of contaminations from samples is determined. The obtained filtrate and insoluble suspension constitute materials for speciation analysis (filtrate) and fractionation (suspension).

The notion of fractionation was separated from speciation analysis and it mainly concerns solid samples. Substances such as suspensions, dust, wastewater sludge, municipal and bottom sediments, or compost and industrial samples can be fractionated thoroughly, first in the granulometric and then in the chemical way. Fractionation is the classification process of an analyte or analyte group in a sample according to the physical properties (e.g. different particle size or solubility) or chemical characteristics (e.g. reactivity).

Fractionation distinguishes diverse metal forms. The chemical sequential extraction separates trace metals into chemical forms that can be released into the solution under different environmental conditions. The most common practice is using Tessier's3 procedure of metal fractionation from bottom sediments, which differentiates five fractions. Fraction 1 is bound to exchangeable metals. It is related to the metal adsorption process on the surface of solids. It is the most easily available fraction. Metal can pass from its solid phase into water as a consequence of water ionic content change that results from sorption–desorption balance shift. Fraction 2 embraces carbonate-bound metals. They can be released in the wake of pH level reduction. Fraction 3, i.e. metals bound with hydrated iron and manganese oxides, is sensitive to redox potential changes. It is thermodynamically unstable under anaerobic conditions. Metals bound with the organic matter constitute Fraction 4. They are temporarily unavailable. After some time, metals pass into pelagic zone or other fractions under the influence of anaerobic and aerobic digestions of the organic matter. Fraction 5 includes metals bound with the remaining fraction. It is mainly made by primary and secondary minerals containing metal atoms built into their crystal lattice. These metals are practically unavailable for living organisms under natural conditions. They are said to be permanently immobilized.

The definition provided by the IUPAC (International Union of Pure and Applied Chemistry) describes speciation as the occurrence of an element in different chemical forms defined by the isotopic composition, electron configuration, oxidation state, and complex or molecule structure.4 Speciation of a single element concerns its occurrence or prevalence in different forms. Therefore, speciation analysis is the analytical procedure that identifies and determines the amount of one or more element forms present in the sample.

Chemical speciation is divided into four main categories,5 i.e. screening, group, distribution, and individual speciation. The first type determines only the most dangerous analyte present in the examined matrix. A good example is determining tribulytin in seawater or methylmercury in tissues. In group speciation, concentration levels of a given compound group or analyzed element at different oxidation states are determined. It deals with problems such as simultaneous determinations of Cr(III) and Cr(VI); Fe(II) and Fe(III); Mn(II), Mn(IV), and Mn(VII); BOD (biochemical oxygen demand) and COD (chemical oxygen demand); and elemental or organic and inorganic mercury. Distribution speciation is used for biological samples, e.g. body fluids and blood serum. The remaining type, i.e. individual speciation, identifies and determines all individual chemicals that contain a given element in their composition in the sample.

At first, speciation analysis predominantly coped with precisely determined analytes (mainly anthropogenic organometallic compounds, such as alkyl lead, buthyltin, and phenyltin compounds), as well as simple organoarsenic and organoselenium forms and their degradation products. The research range has been extended to other organic and inorganic forms of many elements since then.

Substances studied with speciation analyses can be divided into two categories. The first one is constituted by substances produced and introduced into the environment by humans and is interesting for the environmental analysis. The other one comprises natural chemical compounds formed as a result of biochemical transformations in living organisms or the environment. Thus, they are chiefly researched by biochemists and ecotoxicologists.

Although speciation analysis is relatively expensive, it is gaining more and more importance. It helps to deal with situations that require both determination of total element contents and consideration for various forms in which these elements occur.6 Speciation analysis is used in studying biochemical cycles of selected chemical compounds,7 determining toxicity and ecotoxicity of elements, determining quality of food8 and pharmaceuticals,9 and in technological process control and clinical analysis.10

Lowering the detection limits of analytes to extremely low concentration levels resulted in the fact that methods used so far did not always meet the necessary requirements. For this reason, there has been a tendency for several years to combine various methods and techniques. These combinations are known as the hyphenated methods.

2 Sampling and Sample Preparation in Speciation Analysis

  1. Top of page
  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References

Analyte determination makes the final stage of the analytical procedure. It includes sampling, sample preservation, transport, storage, preparation for analyses, determination, and processing of results. No analyst and no analytical method will be able to provide credible results if the sample has been collected, stored, or prepared for the analysis in an inappropriate way. For this reason, sample preparation process is usually the most laborious task. Consequently, it frequently constitutes the major source of errors.11

Processes routinely applied in speciation analysis (e.g. dilution, shifting pH with sample fixation, or alterations in pressure and temperature) may cause irreversible changes in the primary analyte form. The most serious difficulties arise when both sampling and analyzing take place under significantly different conditions. It happens when samples are collected from lower strata of water reservoirs, in which the pressure drop provokes gas emissions. In the case of CO2, the sample pH rises, acid dissociation constants shift, the stability of complexes increases, and low-soluble sediments precipitate. Both sample instability and its changeability are vital when the biological material is analyzed. Such samples can undergo microbiological, enzymatic, photochemical, and other unexpected or unclear processes after the sampling is completed.12

Proper sampling, sample preservation, and preparation methods are used for different analytes and sample matrices in speciation analysis. If the rules are not strictly followed, samples can be secondarily contaminated. It happens with mercury. It penetrates low-density plastic materials and so they should not be used for mercury storage. In addition, some organic tin compounds are used as plasticizers and hence should not be collected into plastic containers. Glass vessels seem to be the best solution.

Similar requirements apply to sampling of solids and gases. Suspended matter (dust and aerosols) and gas phase are distinguished in gas samples. When sampling takes place, both dust and aerosols are separated from the gas phase on appropriate filters, on which they are later stored in this form. It is recommended to store solid samples in polyethylene or PTFE (polytetrafluoroethylene) containers at lowered temperature and without light access.13

The most frequent reasons for initial processing of samples include:

  • analyte isolation and preconcentration;
  • removal of interferences;
  • conversion of analytes into forms possible to detect with a proper detector;
  • the analyte concentration is either too low or too high for the limits of detection and quantification. Thus, sample needs enrichment or dilution, respectively;
  • research methods require transforming solid or gas samples into their liquid forms.

Speciation analysis makes use of classical methods, such as digestion, extraction,14 purification, or analyte enrichment. It also employs analyte derivatization techniques,15 capillary cryogenic trapping and preliminary analyte enrichment,16 or SPME (solid-phase microextraction).17

3 Hyphenated Methods in Speciation Analysis

  1. Top of page
  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References

The toxicological data analyses involve constant lowering of analyte detection limits to extremely low concentration levels. Unfortunately, many methods used so far cannot provide analysts with appropriate tools to perform such procedures. For this reason, various separation and detection techniques are combined and known as the hyphenated methods.

A proper hyphenated method should be selective toward determined analytes and sensitive in a broad concentration range. It should also allow possibly the best identification of determined substances. The selection of a hyphenated method should be conditioned by the analyte nature, possible combination of various methods, demanded determination sensitivity and apparatus availability. Chromatographic methods are mainly used for separation,18 whereas spectroscopic techniques enable detection.19 Hyphenated methods also include couplings of several chromatographic methods.20 Although speciation analysis is dominated by chromatographic techniques, other ones are also applied.21

Chromatography had been known as a separation method since the beginning of the twentieth century,22 but its rapid development occurred 50 years later. Its most developed types are GC (gas chromatography), TLC (thin layer chromatography), and varieties of LC (liquid chromatography). As chromatographic methods allow quick separation and determination of substances in complex matrix samples, they are nowadays among the most popular instrumental methods in the analytical chemistry.

Another group of separation methods is made by techniques based on electrophoresis. CE (capillary electrophoresis) describes electromigration techniques, such as CZE (capillary zone electrophoresis), CIEF (capillary isoelectric focusing), CGE (capillary gel electrophoresis), or CITP (capillary isotachophoresis). It can also include MECC (micellar electrokinetic capillary chromatography).

CZE is the most common CE method and the notion of CE is often used to denominate all electromigration techniques in the literature. In CIEF, mixture components are separated on the basis of different values of the isoelectric points. CGE enables separation of macromolecular substances on the basis of differences in their sizes. MECC is mainly used for separation of mixtures whose molecules do not have electric charges. In CITP, the sample is placed between the leading and terminal buffers. After DC (direct current) is applied, ions present in the sample move between the buffers. Their mobility differs and they become separated in consequence. CEC (capillary electrochromatography) is rapidly developing now. It combines CE performance with high selectivity of typical stationary phases employed in LC.

GC dominates research into gaseous analytes. It possesses high separation performance and provides extremely low detection limits. On the other hand, many element forms interesting for speciation analysis do not occur in the gas form and cannot be transformed into it with derivatization reactions. This group includes nearly all trace metal coordination complexes and numerous organometallic compounds (containing metal or metalloid in a covalent bond). Column separation methods in the liquid phase, such as varieties of HPLC (high-performance liquid chromatography) or CE, are frequently applied for those forms. These techniques are easily connected on-line and provide diverse separation mechanisms and stationary phase availability. Consequently, they allow preserving the determined form in an unchanged condition.

The most often used detection methods in speciation analysis are MS (mass spectrometry), ICP-MS (inductively coupled plasma-mass spectrometry), FAAS (flame atomic absorption spectrometry), ET AAS (electrothermal atomic absorption spectrometry), AFS (atomic fluorescence spectrometry), ICP-OES (inductively coupled plasma-optical emission spectroscopy), MIP AES (microwave-induced plasma atomic emission spectroscopy), FTIR (Fourier transform infrared spectroscopy), and NMR (nuclear magnetic resonance).

Hyphenated methods were first introduced through coupling GC with different detectors in the following systems: GC-AAS (gas chromatography-atomic absorption spectroscopy), GC-AES (gas chromatography-atomic emission spectroscopy), GC-MS (gas chromatography-mass spectroscopy), or GC-ICP-MS-TOF (gas chromatography-inductively coupled plasma-mass spectrometry-time of flight). Owing to technological reasons, couplings using LC methods for separation of analyzed substances such as HPLC-ICP-MS (high-performance liquid chromatography-inductively coupled plasma-mass spectrometry) and HPLC-MS (high-performance liquid chromatography-mass spectrometry) appeared later.23

MS is the most popular detection method in speciation analysis. It offers information on the quantitative and qualitative sample compositions and helps to determine analyte structure and molar masses. The access to the structural data (necessary for the identification of the already known or newly found compounds) poses a challenge for speciation analysis as higher sensitivity of detection methods contributes to the increased number of detected element forms. The main difficulties in the coupling of MS detector with chromatographic methods arise from the necessity for maintaining very low pressure in the spectrometer. However, separated analyte ions leave the chromatographic column under relatively high pressure. Analyte ions are separated in the spectrometer on the basis of the mass-to-charge ratio, and the collected data is obtained in the spectrum form.

The ionization chamber is the fundamental spectrometer part. It can be coupled with any available mass analyzer, such as Q (quadrupole), IT (ion trap), TOF (time of flight), SF (sector field), and FT-ICR (Fourier transform-ion cyclotron resonance). Other options include Q-Q (double quadrupole) or hybrid couplings, such as Q-TOF (quadrupole with time of flight).

Mass spectrometers can use different ionization sources, such as ESI (electrospray ionization), APCI (atmospheric pressure chemical ionization), or APPI (atmospheric pressure photochemical ionization). ESI24 and APCI are the most popular ones as they solve most analytical problems related to both big and small molecules. ESI-MS (electrospray ionization-mass spectrometry) is used to determine compounds in biological materials, i.e. nucleic acids, amino acids, peptides, proteins, and their complexes with metals and metalloids.25 APPI is a more modern solution and is chiefly employed to analyze small particles, including the nonpolar ones. All the discussed techniques belong to the so-called soft ionization methods.

Detection with MS can be performed in two ion monitoring modes, i.e. SIM (selected ion monitoring) or SM (scan mode). The former delivers information on the analyte mass, whereas the latter provides data on mass spectra and mass distribution. The identification problems concerning big molecules are mainly related to the possibility of obtaining a bigger number of spectra in which mass-to-charge ratios are the same.

The coupling of a chromatograph with an ICP-MS detector is performed directly, either with a nebulizer in column separation methods or with an LA (laser ablation) in planar techniques. The introduction of ICP-TOF-MS (inductively coupled plasma-time of flight-mass spectrometry) apparatus increases the speed of data obtaining. It allows isotope measurement of chromatographic peaks whose width is measured in milliseconds. It also improves the precision of isotope ratios determination. The TOF-MS (time of flight-mass spectrometry) coupling is more sensitive than a quadrupole mass spectrometer. When it is coupled with MALDI (matrix-assisted laser desorption/ionization), it becomes useful in biochemical examinations of molecules with large masses. The hyphenated method of HPLC-ICP-TOF-MS (high-performance liquid chromatography-inductively coupled plasma-time of flight-mass spectrometry) for environmental biomarkers research was first used in 2006.26

Even though an ICP-MS detector does not offer information on the chemical or structural analyte forms, it makes a perfect elemental analyzer, particularly when coupled with a gas or liquid chromatograph.27 Its main advantages include broad concentration ranges, high sensitivity of determinations, high selectivity, fast multielement analysis, and isotope measurements. Nevertheless, its disadvantages embrace spectrum and matrix interferences, lower precision than in ICP-OES method, and relatively high price of the apparatus. Moreover, the total content of soluble salts should be <1000 ppm.

GC-ICP-MS (gas chromatography-inductively coupled plasma-mass spectrometry) method has been used in the speciation analysis of organometallic compounds for a few decades. It provides high separation capacity of GC combined with proper sensitivity and specificity of the ICP-MS technique. Even though GC with packed columns was employed at the beginning, it was replaced with capillary GC.28 Such a situation was conditioned by different factors. Firstly, packed columns are adapted to work at a high carrier gas flow rate and with large sample volumes. Secondly, their performance and resolution are low because of large analyte dispersion beyond the column. Finally, large column volume has a negative impact on sensitivity and detection limits, whereas the stationary phase can chemically interact with many organometallic forms. GC-ICP-MS with capillary columns offers suitable resolution, which is particularly important when complex organometallic compound mixtures in complex matrix samples are separated. The main requirement for the coupling switch (i.e. interface) is the capacity for maintaining gas form of analytes during the transport from the chromatographic column and into the detector so that their condensation is prevented. It can be done in two ways. One possibility is using a heated transfer line to avoid cold spots. The other is to apply a carrier in the aerosol form.

Practically, speciation analysis of volatile organometallic forms is dominated by three methods, i.e. GC-MIP-AED (gas chromatography-microwave-induced plasma-atomic emission detector), GC-ICP-MS, and GC-EI-MS (gas chromatography-electrospray ionization-mass spectrometry). GC-AAS and GC-AFS (gas chromatography-atomic fluorescence spectroscopy) are still widespread in determining methylmercury in environmental samples. GC-MIP-AED is particularly popular in speciation analysis of anthropogenic environmental pollution and its degradation products because it is universal and offers extremely low detection limits.29

Many studies concerning Flash GC appeared in the late 1990s. This method employs columns composed of several thousand capillaries whose internal diameter is short (20–40 µm). They are called multicapillary columns.30 Applying such a capillary bunch eliminates disadvantages related to both capillary and packed columns. The advantages of both column types are retained. Multicapillary GC is characterized by high carrier gas flow rates, which decreases the dilution factor and facilitates transport of analytes into plasma.

A proper switch between a chromatograph and a detector is essential for the coupling of a liquid chromatograph with ICP-MS. The simplest solution is a chromatographic column outlet connected with a conventional nebulizer. The switch must be compatible with the applied flow rates and the eluent composition. Water-based eluents can be harmful to nebulizer parts as they have large salt content. On the other hand, eluents that are organic liquids or contain organic components can destabilize plasma as their vapors have high thermal expansion. The pneumatic system is the most common when it comes to introducing samples with nebulization.

Nonetheless, there are analytes whose determination with conventional nebulizers, specifically at low concentration levels, is hindered. These include some mercury, iodine, thallium, and silver compounds. Their mutual interactions with polymeric components of the nebulizer are unpredictable. Boron is another example. It interacts with glass surfaces of the nebulizer.

Quadrupole analyzers are most often used in ICP-MS. They are comparatively inexpensive and easy to operate. They provide quick data transfer and fast separation of ions on the basis of mass-to-signal ratios. The latest apparatus generation offers detection limits at the level of µg L−1 or ng L−1 for many elements. Mass analyzers with double focusing or DRC (dynamic reaction cell) can be used to reach better resolution and hence reduce isobaric interferences.31

The resolution increase leads to an inevitable drop in the method sensitivity. Importantly, the quadrupole spectrometers used now offer resolution that is only twice or three times lower than that provided by high-resolution spectrometers.

The application of enriched isotopes in ICP-MS detectors has significantly helped in the development of speciation methods. The isotopic specificity of the ICP-MS technique opens possibilities for the introduction of stable isotopes or forms enriched with stable isotopes into the research on transformations and artifact formation during extraction and derivatization processes. It also contributes to the employment of quantitative determination with isotope dilution technique on a larger scale. The sources of systematic errors are well known and can be easily eliminated, which makes ID-MS (isotope dilution-mass spectroscopy) a definitive analytical technique.32 The development of the method was summarized in the work by Prorock and Prang.33

Elements occurring in ionic forms are generally believed to be biologically and toxicologically interactive with living organisms. Ions of a given element can occur in the environment as free anions or cations or as ions bound to organic or inorganic ligands. Speciation analysis concerns elements that occur at different oxidation states and copes with the identification and determination of their individual concentrations. It is particularly valuable for elements that demonstrate highly diversified toxicological properties depending on the oxidation state (e.g. Cr(III)/Cr(VI), As(III)/As(V), and Sb(III)/Sb(V)).

Couplings of different LC varieties, such as HPLC, IC (ion chromatography), IEC (ion exclusion chromatography), or GPC (gel permeation chromatography), with ICP-MS or ESI-MS detectors belong to the most popular hyphenated methods used to determine different ion forms of metals and metalloids.34 IC is the most popular method for the separation and determination of organic and inorganic ion substances.35 It is predominantly employed in the determination of selected water disinfection by-products36 and metal and metalloid ions.37 The most widespread hyphenated methods using IC are IC-ICP-MS (ion chromatography-inductively coupled plasma-mass spectrometry), IC-ICP-OES (ion chromatography-inductively coupled plasma-optical emission spectroscopy), and IC-MS (ion chromatography-mass spectrometry).

CE methods coupled with various detectors are successfully applied in speciation analysis of both environmental38 and biochemical39 samples. Unfortunately, there are no international standards available for CE as the method has lower repeatability in comparison with chromatographic methods.

Two important books discussing applications of hyphenated methods in speciation analysis appeared at the beginning of the twenty-first century.40, 41 They meticulously describe problems such as GC and LC methods with ICP-MS and ESI-MS detectors and quality control in speciation analysis. The books also relate numerous applications of those methods in the analysis of organic compounds of tin, lead, and mercury or metal speciation in petrochemical samples. Moreover, they refer to examinations of arsenic and selenium in biological samples as well as metal complexes in human tissues and body fluids.

The notions of speciation analysis and hyphenated methods are broad. Figure 1 schematically shows the most popular separation and detection methods used in hyphenated methods together with types of determined analytes and obtained data.

thumbnail image

Figure 1. Examples of hyphenated methods used in species analysis.

At the beginning of speciation analysis progress, i.e. in the 1980s and 1990s, speciation forms of arsenic, selenium, chromium, lead, mercury, and iron belonged to the most often determined speciation forms in water.42 Nowadays, the range is much wider and also embraces various others forms of inorganic and organic metals and metalloids species. Examples of selected element forms determined with hyphenated methods are given in Table 1.

Table 1. Examples of Metal and Metalloids Species Analyzed Using Hyphenated Methods
ElementInorganic speciesOrganic species
ArseniumAs(III), As(V)Arsenobetaine, monomethylarsinic acid (III), monomethylarsinic acid (amid), dimethylarsonic acid (III), dimethylarsonic acid (V), arsenosugars, arsenocholine, arsenolipids
SeleniumSe(IV), Se(VI)Selenocystine, selenomethionine, selenocystyne, methyloselenocysteine, and diphenylselenide
ChromiumCr(III), Cr(VI), hydroxy complexes
TinSn(II), Sn(IV)Mono-, di-, and tributyltin; mono-, di-, and triphenyltin; methylated tin; tetraphenyltin; tetracyclohexyltin; tripropyltin; trimethyphenyltin; monophenyltin; monooctyltin; monoethyltin; and methylbythyltin
MercuryHg(I), Hg(II)Methyl- and dimethylmercury, ethyl- and diethylmercury, higher alkyl mercury compounds, mixed alkyl mercury compounds, phenylmercury, and heptylmercury
AntimonySb(III), Sb(V), inorganic complexesTrimethylantimony dichloride, trimethylantimony dihydroxide
AluminumAl(III), fluoride and sulfate complexesHumic and fulvic aluminum complexes
ThalliumTl(I), Tl(III)
LeadPb(II), Pb(IV)Tetraethyllead, tetramethyllead, tripropyllead, and triphenyllead
OthersFe(II), Fe(III); Mn(II), Mn(III), Mn(V), Mn(VII); V(IV), V(V); Mo(V), Mo(VI); Au(I), Au(III); Pt(II), Pt(IV); Sc(I), Sc(II), Sc(III), Sc(IV), and Sc(V); Ga(III), Ga(IV), and Ga(V); and Np(IV), Np(V), and Np(VI) 
HalidesClO2 , ClO3 , ClO4 , Br, BrO3 , I, IO3 , and IO4 Haloacetic acids, organic derivatives

4 Examples of Applications of Hyphenated Methods in Speciation Analysis

  1. Top of page
  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References

The number of organic and inorganic metal and metalloid forms is vast. Their identification and quantitative analyses require sensitive and precise analytical techniques, such as hyphenated methods. Some of the organometallic compounds occurring in the environment are nontoxic (e.g. organoarsenic compounds such as arsenobetaine). Others are highly toxic (e.g. methylmercury). Generally, organic forms of certain elements (e.g. lead and mercury) are more toxic than the inorganic ones. However, speciation forms of arsenic or selenium have different properties. Inorganic arsenic is a well-known poison, whereas its organic forms, such as arsenobetaine or arsenocholine, are generally nontoxic. Their molecules are very stable and resistant to enzymes and oxidizing agents. Furthermore, some organometallic forms are more toxic because they are easily absorbed by internal tissues. They readily penetrate blood, which transports them all over the organism.43

Some plants have developed particularly effective mechanisms that sustain metal (metalloid) homeostasis. It helps them to function and propagate in the environment severely polluted with those elements. One of the well-known procedures entails the secretion of metal-binding proteins and peptides. It helps plants to accumulate and tolerate heavy metals. Metal complexation results in the formation of many relatively poorly characterized metal complexes.

The formed compounds are difficult to transform into gas form, which excludes the application of GC for their separation. There are no proper standards and reference materials for the majority of these substances because many naturally synthesized compounds have not been identified and characterized yet. During quantitative analyses of speciation forms, the quality control process makes use of standard recovery methods, internal standard addition, comparisons of results obtained with different methods, and interlaboratory comparisons.44 Even though the market offers more and more certified reference materials containing defined speciation forms of analytes (e.g. tribulytin or methylmercury standards), there is still a great demand for new materials.

Speciation analyses are most often used for inorganic ions of chromium, selenium, arsenic, and antimony, whose toxicological properties are diversified; products of mercury, selenium, arsenic, tin, or bismuth methylation; anthropogenic metalorganic pollution and its degradation products; organic and inorganic derivatives of chlorine, iodine, and bromine (e.g. ClO2 , ClO3 , ClO4 , BrO3 , and IO3 ); and speciation forms of platinum metal group, radionuclides, and rare earth metals.

Arsenic, selenium, chromium, tin, mercury, antimony, aluminum, thallium, lead, halides, platinum group metals, rare earth elements, and radionuclides fall into the scope of speciation analysis with hyphenated methods. They are particularly interesting because of their toxicological properties and types of organic and inorganic forms. The literature data concerning such applications is presented later.

Arsenic is a highly mobile element and it occurs in all elements of the environment. It easily passes between lithosphere and hydrosphere. Its content in natural water is highly diversified and determined by the substratum type and water pollution. Arsenic speciation is usually performed with HPLC-ICP-MS.45 Different matrices are analyzed, but determinations of arsenic speciation forms in various water types,46 including drinking water47 and seawater,48 dominate. The literature data concerning speciation analyses of arsenic and its compounds is vast. Among them, the most important are soil49 and soil extracts50 research; examinations of bottom sediments,51 including those of natural disaster origin52; and studies into industrial wastewater.53 They also embrace research into plant samples,54 including tobacco leaves55; clinical samples, such as urine,56 blood,57 and gastric fluids58; and examinations of hair59 and nails.60 The coupling of CE with a TOF-MS detector determines arsenic compounds in environmental samples61 and fish.62 Moreover, hyphenated methods are employed in arsenic speciation for the analyses of food samples, such as seafood,63 fish oil,64 or peanut butter.65 In many cases, analyses simultaneously determine speciation forms of arsenic and other elements, such as selenium66 or chromium.67

Selenium is one of the better-known elements in speciation analysis and the literature on it is vast. Works concern its numerous organic and inorganic forms. Hyphenated methods, such as HPLC-ICP-MS,68 are most often used for simultaneous separation and determination of selenium speciation forms in food samples,69 including rice,70 and soil71 or blood samples.72

Chromium is another classical example and its inorganic forms dominate. Physicochemical properties of chromium and its compounds and their occurrence and impact on the environment are thoroughly described in the literature.73 Cr(III) compounds have a positive influence on the functioning of living organisms. They are responsible for the correct glucose metabolism in mammals and easily undergo complexation processes with many substances. However, Cr(VI) compounds are highly toxic. IARC (International Agency for Research on Cancer) qualifies them within Group 2B, which includes substances that are carcinogenic and mutagenic for humans. Modern speciation methods are widely used for establishing hygienic standards and laws in many countries. However, regulations predominantly concern total chromium, rather than its particular forms. Examples of chromium speciation analyses in literature include research into water,74 including seawater75 and wastewater76; bottom sediments77; soil78; atmospheric dust79; and food products.80

The most often determined speciation forms of tin embrace its organic compounds.81 Hyphenated methods based on GC or LC are usually employed to determine them. These include GC-MIP-AED,82 GC-AFS,83 GC-MIP-AES (gas chromatography-microwave-inducted plasma atomic emission spectroscopy),84 HPLC-ETAAS (high-performance liquid chromatography-electrothermal atomic absorption spectrometry),85 and HPLC-MS.86 The research subjects include mussels,87 drinking water,88 seawater,89 and food samples.90 The comparison of advantages and disadvantages of GC-ICP-MS and HPLC-ICP-MS for the speciation analysis of tin was described in the work.91

Speciation analysis is also interested in mercury. Hyphenated methods, such as IC-ICP-MS,92 SEC-ICP-MS (size-exclusion chromatography-inductively coupled plasma-mass spectrometry),93 CE,94 FIA-CE-AFS (flow injection analysis-capillary electrophoresis-atomic fluorescence spectroscopy,95 HPLC-AFS (high-performance liquid chromatography-atomic fluorescence spectroscopy),96 SPE-GC-ICP-TOF-MS (solid-phase extraction-gas chromatography-inductively coupled plasma-time of flight-mass spectrometry),97 or GC-ICP-TOF-MS,98 are used in the speciation analysis of mercury. The comparison of three hyphenated methods based on GC with different detection methods (MS, ICP-MS, and AFS) was described in the work.99 The literature examples concern determining speciation forms of mercury in water,100 seawater,101 river sediments,102 animal tissues,103 and reference materials.104 The fast method of mercury determination in seawater with HPLC-ICP-MS was presented in the work.105 The research into organic and inorganic forms of mercury with HPLC-UV-CV-AFS (high-performance liquid chromatography with UV detector coupled to cold vapor atomic fluorescence spectroscopy) was described in the work.106 Another example is the application of multicapillary chromatography coupled with AFS detector and cold vapor technique for the determination of organic and inorganic mercury forms in environmental and biological samples.107 Monomethylmercury and ethylmercury can be determined with flow injection analysis coupled with AFS detection.108

Antimony and its compounds are most frequently determined in various types of water, e.g. drinking water,109 surface water,110 and seawater.111 Literature describes many applications of hyphenated methods in its speciation analysis. These include environmental samples,112 such as soil,113 plants,114 sea flora, and fauna.115 They also embrace dust,116 suspended matter,117 volcanic ash,118 food samples,119 and reference materials in the form of bottom sediments.120 Antimony is frequently determined with arsenic,121 selenium, and tellurium122 at the same time. Many studies concern analyzing contents of antimony and its compounds in biomedical samples.123 They usually contain many proteins, macromolecular substances, and enzymes, which can bind antimony compounds and alter the forms of its occurrence.

The aluminum analysis is an essential problem. It is difficult because of the element characteristics. The most toxic aluminum forms are Al3+ ion, aluminum hydroxy complexes (Al(OH)2+, Al(OH)2 +, and Al(OH)4 ), and labile inorganic complexes with fluorides124 and sulfates.125 Aluminum speciation usually deals with soil, bottom sediment,126 and clinical samples.127 Computer programs, such as Mineql or Geochem and Solichem, support speciation analyses. Even though they do not guarantee complete success, they can be useful in identifying, determining, interpreting, and modeling aluminum forms present in the environment.128

Although there exist well-recognized analysis methods of chromium, selenium, antimony, and arsenic, there is a great need (both in toxicology and in chemical analysis) to develop reliable methodologies of thallium determination, particularly in complex matrix samples. Thallium compounds are highly toxic. They usually penetrate living organisms through skin as they are easily absorbed through it. The literature presents determinations of thallium and its compounds in plant samples,129 surface water,130 drinking water,131 river water,132 and lake133 water.

Lead has been interesting to analysts for centuries. The literature gives account of hyphenated methods used for lead speciation analyses in dust and soil samples,134 body fluids,135 river water,136 plants,137 and plant-derivative drugs.138 Among other elements, iron, magnesium, and manganese need mentioning. Hyphenated methods are also used for their speciation analyses. Iron speciation mainly concerns water139 and blood samples.140 The method of CE-ICP-MS (capillary electrophoresis-inductively coupled plasma-mass spectrometry) can be employed in the speciation of magnesium141 and manganese142 compounds.

Platinum, gold, and ruthenium compounds are used as chemotherapeutic drugs. Speciation analysis helps to select appropriate drugs and to understand processes occurring in organisms.143 The issues of radionuclide speciation are important from the viewpoint of the mobility, solubility, and behavior of radionuclides in the environment. They can occur in different physicochemical forms and at various oxidation states in the environment. May and colleagues144 presented the literature overview concerning hyphenated methods in speciation analysis of radionuclides.

Organic and inorganic anions and cations are usually determined with IC methods. At first, IC was used for speciation analyses of nitrogen, phosphorus, and sulfur ions. Nowadays, it is predominantly applied to determine metal and metalloid ions145 as well as chlorine, bromine, and iodine ions. The development of drinking water disinfection methods is believed to have been one of the greatest human achievements in the nineteenth century. Although modern disinfection methods, e.g. ozonation, have undeniable advantages, they also possess indisputable disadvantages and limitations. They mainly concern the formation of oxidized inorganic halide derivatives, such as bromates, chlorites, and chlorates. Bromates are the most important type. They can form in raw water that contains bromides and undergoes ozonation processes. IARC qualified them as potentially carcinogenic (Group 2B). The methods of bromate determination with IC techniques can be divided on the basis of the detection method into three groups,146 i.e. direct methods (conductivity detection), indirect methods (UV–vis detection), and hyphenated methods (MS).147

Perchlorates constitute a new threat. They occur in different elements of the environment as they are used in explosive and pyrotechnic materials as well as jet fuel additives. They are determined most frequently with hyphenated methods in drinking water148 and plants.149

5 Conclusions

  1. Top of page
  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References

Even though speciation analysis has made an enormous progress in recent 30 years, it is still a relatively new area of analytical chemistry. Its further development depends on many factors, such as developing new methods of separation, detection, and sample preparation as well as the availability of new certified reference materials. Hyphenated methods create unprecedented opportunities and their main advantages include extremely low limits of detection and quantification, high precision, and repeatability of determinations.

On the other hand, hyphenated methods have their specific limitations, such as high price and complexity of the apparatus. Consequently, they are not in general laboratory usage. The application of hyphenated methods requires perfect understanding of analytical methodologies and apparatus. Those systems are expensive and used in scientific research, rather than for routine analyses. Nonetheless, the progress in the discussed methods is becoming more and more important and visible as the number of applications and works concerning them is constantly rising.150

Abbreviations and Acronyms

  1. Top of page
  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References
AFS

Atomic Fluorescence Spectrometry

APCI

Atmospheric Pressure Chemical Ionization

APPI

Atmospheric Pressure Photochemical Ionization

BOD

Biochemical Oxygen Demand

CE

Capillary Electrophoresis

CEC

Capillary Electrochromatography

CE-ICP-MS

Capillary Electrophoresis-Inductively Coupled Plasma-Mass Spectrometry

CGE

Capillary Gel Electrophoresis

CIEF

Capillary Isoelectric Focusing

CITP

capillary isotachophoresis

CZE

Capillary Zone Electrophoresis

COD

Chemical Oxygen Demand

DC

Direct Current

DRC

Dynamic Reaction Cell

ESI

Electrospray Ionization

ESI-MS

Electrospray Ionization-Mass Spectrometry

ET AAS

Electrothermal Atomic Absorption Spectrometry

FAAS

Flame Atomic Absorption Spectrometry

FIA-CE-AFS

Flow Injection Analysis-Capillary Electrophoresis-Atomic Fluorescence Spectroscopy

FTIR

Fourier Transform Infrared Spectroscopy

FT-ICR

Double Quadrupole

GC

Gas Chromatography

GC-AAS

Gas Chromatography-Atomic Absorption Spectroscopy

GC-AES

Gas Chromatography-Atomic Emission Spectroscopy

GC-EI-MS

Gas Chromatography-Electrospray Ionization-Mass Spectrometry

GC-ICP-MS-TOF

Gas Chromatography-Inductively Coupled Plasma-Mass Spectrometry-Time of Flight

GC-ICP-MS

Gas Chromatography-Inductively Coupled Plasma-Mass Spectrometry

GC-MIP-AED

Gas Chromatography-Microwave-Induced Plasma-Atomic Emission Detector

GC-MS

Gas Chromatography-Mass Spectroscopy

GC-AFS

Gas Chromatography-Atomic Fluorescence Spectroscopy

GC-MIP-AES

Gas Chromatography-Microwave-Inducted Plasma Atomic Emission Spectroscopy

GPC

Gel Permeation Chromatography

HPLC-ICP-TOF-MS

High-Performance Liquid Chromatography-Inductively Coupled Plasma-Time of Flight-Mass Spectrometry

HPLC-AFS

High-Performance Liquid Chromatography-Atomic Fluorescence Spectroscopy

HPLC

High-Performance Liquid Chromatography

HPLC-ICP-MS

High-Performance Liquid Chromatography-Inductively Coupled Plasma-Mass Spectrometry

HPLC-UV-CV-AFS

High-Performance Liquid Chromatography with UV Detector Coupled to Cold Vapor Atomic Fluorescence Spectroscopy

HPLC-MS

High-Performance Liquid Chromatography-Mass Spectrometry

HPLC-ETAAS

High-Performance Liquid Chromatography-Electrothermal Atomic Absorption Spectrometry

IC

Ion Chromatography

IC-ICP-MS

Gel Permeation Chromatography

IC-ICP-OES

Ion Chromatography-Inductively Coupled Plasma-Optical Emission Spectroscopy

IC-MS

International Agency for Research on Cancer

ICP-TOF-MS

Inductively Coupled Plasma-Time of Flight-Mass Spectrometry

ICP-MS

Inductively Coupled Plasma-Mass Spectrometry

ICP-OES

Inductively Coupled Plasma-Optical Emission Spectroscopy

ID-MS

Isotope Dilution-mass spectroscopy

IEC

Ion Exclusion Chromatography

IT

Ion Trap

IUPAC

International Union of Pure and Applied Chemistry

LA

Laser Ablation

LC

Liquid Chromatography

MALDI

Matrix-Assisted Laser Desorption/Ionization

MECC

Micellar Electrokinetic Capillary Chromatography

MS

Mass Spectrometry

MIP AES

Microwave-Induced Plasma Atomic Emission Spectroscopy

NMR

Nuclear Magnetic Resonance

PTFE

Polytetrafluoroethylene

Q

Quadrupole

Q-TOF

Quadrupole with Time of Flight

SEC-ICP-MS

Size-Exclusion Chromatography-Inductively Coupled Plasma-Mass Spectrometry

SIM

Selected Ion Monitoring

SM

Scan Mode

SF

Sector Field

SPE-GC-ICP-TOF-MS

Solid-Phase Extraction-Gas Chromatography-Inductively Coupled Plasma-Time of Flight-Mass Spectrometry

SPME

Solid-Phase Microextraction

TLC

Thin Layer Chromatography

TOF

Time of Flight

TOF-MS

Time of Flight-Mass Spectrometry

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  2. Introduction
  3. Sampling and Sample Preparation in Speciation Analysis
  4. Hyphenated Methods in Speciation Analysis
  5. Examples of Applications of Hyphenated Methods in Speciation Analysis
  6. Conclusions
  7. Abbreviations and Acronyms
  8. Related Articles
  9. References
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