Practical recommendations for the reduction of memory effects in compound-specific 15N/14N-ratio analysis of enriched amino acids by gas chromatography/combustion/isotope ratio mass spectrometry
Article first published online: 5 DEC 2011
Copyright © 2011 John Wiley & Sons, Ltd.
Rapid Communications in Mass Spectrometry
Volume 26, Issue 2, pages 195–204, 30 January 2012
How to Cite
Petzke, K. J. and Metges, C. C. (2012), Practical recommendations for the reduction of memory effects in compound-specific 15N/14N-ratio analysis of enriched amino acids by gas chromatography/combustion/isotope ratio mass spectrometry. Rapid Commun. Mass Spectrom., 26: 195–204. doi: 10.1002/rcm.5319
- Issue published online: 5 DEC 2011
- Article first published online: 5 DEC 2011
- Manuscript Accepted: 29 OCT 2011
- Manuscript Revised: 28 OCT 2011
- Manuscript Received: 28 AUG 2011
Gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) is a highly sensitive approach which allows the analysis of the 13C/12C and 15N/14N isotope composition of amino acids in the range of natural abundance or in slightly 13C- and 15N-enriched samples. However, the accuracy of measurements remains a permanent challenge. Here we show the effect of the presence of slightly 15N-enriched compounds in physiological samples on the accuracy and reproducibility of 15N-abundances of amino acids within or between analytical runs. We spiked several individual amino acids with the respective 15N-labelled isotopomer and measured the 15N/14N ratios of other amino acids in the same sample or in the following analytical runs. Intra- and inter-run memory effects can be observed in 15N/14N ratios of amino acids. Sample throughput is reduced when cleaning runs using standard mixtures are required to restore initial conditions after runs of samples with 15N-enriched analytes. Possible reasons for the observed phenomenon and its implications for work in the lower 15N-enrichment range (<0.5 APE) are discussed and include different aspects of gas chromatography, derivatisation, and hot catalytic metal surface effects. Results need to be interpreted with caution if complex physiological samples contain 15N-enriched amino acids beyond 500‰ δ15N (~0.18 APE). Copyright © 2011 John Wiley & Sons, Ltd.