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Practical recommendations for the reduction of memory effects in compound‐specific 15 N/ 14 N‐ratio analysis of enriched amino acids by gas chromatography/combustion/isotope ratio mass spectrometry
Author(s) -
Petzke Klaus J.,
Metges Cornelia C.
Publication year - 2011
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.5319
Subject(s) - chemistry , isotope ratio mass spectrometry , isotopomers , amino acid , isotope , mass spectrometry , gas chromatography , chromatography , adduct , analyte , analytical chemistry (journal) , natural abundance , organic chemistry , molecule , biochemistry , physics , quantum mechanics
Gas chromatography/combustion/isotope ratio mass spectrometry (GC‐C‐IRMS) is a highly sensitive approach which allows the analysis of the 13 C/ 12 C and 15 N/ 14 N isotope composition of amino acids in the range of natural abundance or in slightly 13 C‐ and 15 N‐enriched samples. However, the accuracy of measurements remains a permanent challenge. Here we show the effect of the presence of slightly 15 N‐enriched compounds in physiological samples on the accuracy and reproducibility of 15 N‐abundances of amino acids within or between analytical runs. We spiked several individual amino acids with the respective 15 N‐labelled isotopomer and measured the 15 N/ 14 N 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 15 N/ 14 N 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 15 N‐enriched analytes. Possible reasons for the observed phenomenon and its implications for work in the lower 15 N‐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 15 N‐enriched amino acids beyond 500‰ δ 15 N (~0.18 APE). Copyright © 2011 John Wiley & Sons, Ltd.