Premium
Re‐evaluating the concentration dependence of isotope ratios measured via gas chromatography mass spectrometry (GCMS): Implications for protein turnover measurements
Author(s) -
Cendrowski Andrea,
Previs Stephen
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a335-c
Subject(s) - chemistry , isotope , urea , mass spectrometry , ion , chromatography , analytical chemistry (journal) , biochemistry , physics , quantum mechanics , organic chemistry
Accurate and precise measurements of isotope ratios made via GCMS are crucial in tracer studies. Investigators have demonstrated that the (M1)/(M0) natural abundance isotope ratios of certain analytes (e.g. methyl palmitate molecular ions) are concentration dependent. This has been attributed to ion‐molecule reactions in the source and detector nonlinearity. Since GCMS technology has improved over the past decade, we re‐evaluated the issue of concentration dependency. Using a 5987 Agilent GCMS and electron ionization, (M1)/(M0) ratios were determined for methyl palmitate (0.2 to 2 nmol) at 18.8 +/− 0.01 to 18.9 +/− 0.01 and for diTBDMS urea (0.2 to 2 nmol) 20.7 +/− 0.01 to 20.7 +/− 0.02, mean +/− sd. Although these studies considered a 10‐fold concentration range, the peak area only increased ~ 3‐fold for methyl palmitate, whereas for urea the peak area increased ~ 8‐fold. In summary, the data suggests that newer GCMS instruments have (i) excellent precision (ave. coefficient of variation 0.08%) and (ii) reduced concentration dependency (e.g. methyl palmitate). However, the variable responses of palmitate and urea suggest that ionization efficiency may play a role. Ongoing research is determining how intra‐ and inter‐daily variations affect these and other commonly analyzed molecules in studies of protein turnover (e.g. [2H]alanine). This work was supported by NIH (Roadmap 1R33DK070291‐01, GCRC M01 RR 00080).