Table 2

Mass isotopomer distribution of labeled and unlabeled lactate and acetate determined by GC/MSa

AnalyteMass isotopomer fractionSourceMass isotopomer distribution
Unlabeled standardLabeled standardUnlabeled sample
Lactatebm+0Exp.0.754 ± 0.0010.003 ± 0.0010.752 ± 0.005
Calc.0.7570.0000.757
m+1Exp.0.165 ± 0.0000.004 ± 0.0000.165 ± 0.002
Calc.0.1710.0000.171
m+2Exp.0.071 ± 0.0000.039 ± 0.0000.068 ± 0.001
Calc.0.0720.0290.072
m+3Exp.0.011 ± 0.0000.955 ± 0.0010.014 ± 0.002
Calc.0.0110.9700.011
Acetatecm+0Exp.0.960 ± 0.0050.067 ± 0.0090.958 ± 0.001
Calc.0.9760.0000.976
m+1Exp.0.029 ± 0.0010.044 ± 0.0060.031 ± 0.001
Calc.0.0220.0120.022
m+2Exp.0.012 ± 0.0000.889 ± 0.0150.011 ± 0.000
Calc.0.0020.9800.002
  • a The data comprise experimental values (exp.) and theoretical mass isotopomer distributions (calc.) derived from natural isotopic enrichment in unlabeled substances (38) and a 99% 13C enrichment in the labeled compounds.

  • b [M-57] fragment of TBDMS2-lactate.

  • c [M-87] fragment of acetic acid (pentyl ester).