Determination of Isotopic Ratios ofL-Leucine andL-Phenylalanine and their Stable Isotope Labeled Analogues in Biological Samples by Gas Chromatography/Triple-stage Quadrupole Mass Spectrometry
✍ Scribed by Schweer, Horst; Watzer, Bernhard; Seyberth, Hannsjörg W.; Steinmetz, Armin; Schaefer, Juergen R.
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 600 KB
- Volume
- 31
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
A gas chromatographic/triple-stage quadrupole mass spectrometric (GC/MS/MS) method for measuring very low levels of enrichment of [ 5,5,5-'H3 1 le leu cine and [ring-' 3C, 1 -~-phenylalanioe in plasma and lipoprotein hydrolysates is described. The amino acids were derivatized to their N-heptafluorobutyryl isobutyl ester derivatives and the isotope ratio was determined by GC/MS/MS in the negative-ion chemical ionization mode. Parent ions were the (M -HFjions and fragment ions used for quantification were (P -2HF -C,H,] -(leucine) and [P -HF -OC,H,] -(phenylalanine), respectively. The limit of quantification was about 10 pg of the labeled compound cs-eluting with 20 ng of the endogenous compound. The calibration curves were linear in the investigated range from 0.1% to 100% of the labeled compound. In biological samples, the higher selectivity of GC/MS/MS compared with GC/MS was demonstrated.