Determination of isotopic ratios of L-leucine and L-phenylalanine and their stable isotope labeled analogues in biological samples by gas chromatography/triple-stage quadrupole mass spectrometry.
A gas chromatographic/triple-stage quadrupole mass spectrometric (GC/MS/MS) method for measuring very low levels of enrichment of [5,5,5-2H3]-L-leucine and [ring-13C6]-L-phenylalanine 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-HF]- ions and fragment ions used for quantification were [P-2HF-C3H7]- (leucine) and [P-HF-OC4H9]- (phenylalanine), respectively. The limit of quantification was about 10 pg of the labeled compound co-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.
Schweer
H
H
Children's Hospital, Philipps University Marburg, Germany.
Watzer
B
B
Seyberth
H W
HW
Steinmetz
A
A
Schaefer
J R
JR
D016632:Apolipoprotein A-I / Q000097:blood / Q000737:chemistry; D001053:Apolipoproteins / Q000097:blood / Q000737:chemistry*; D002138:Calibration; D002247:Carbon Isotopes; D003903:Deuterium / Q000032:analysis; D004952:Esters; D008401:Gas Chromatography-Mass Spectrometry; D007930:Leucine / Q000031:analogs & derivatives / Q000032:analysis* / Q000097:blood; D008074:Lipoproteins / Q000097:blood / Q000737:chemistry*; D015394:Molecular Structure; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000032:analysis* / Q000097:blood
D016632:Apolipoprotein A-I; D001053:Apolipoproteins; D002247:Carbon Isotopes; D004952:Esters; D008074:Lipoproteins; D010649:Phenylalanine; D003903:Deuterium; D007930:Leucine