Table 2.

Mass isotopomer distribution of labeled and unlabeled lactate and acetate determined by GC/MS^a

Analyte	Mass isotopomer fraction	Source	Mass isotopomer distribution
			Unlabeled standard	Labeled standard	Unlabeled sample
Lactateb	m+0	Exp.	0.754 ± 0.001	0.003 ± 0.001	0.752 ± 0.005
		Calc.	0.757	0.000	0.757
	m+1	Exp.	0.165 ± 0.000	0.004 ± 0.000	0.165 ± 0.002
		Calc.	0.171	0.000	0.171
	m+2	Exp.	0.071 ± 0.000	0.039 ± 0.000	0.068 ± 0.001
		Calc.	0.072	0.029	0.072
	m+3	Exp.	0.011 ± 0.000	0.955 ± 0.001	0.014 ± 0.002
		Calc.	0.011	0.970	0.011
Acetatec	m+0	Exp.	0.960 ± 0.005	0.067 ± 0.009	0.958 ± 0.001
		Calc.	0.976	0.000	0.976
	m+1	Exp.	0.029 ± 0.001	0.044 ± 0.006	0.031 ± 0.001
		Calc.	0.022	0.012	0.022
	m+2	Exp.	0.012 ± 0.000	0.889 ± 0.015	0.011 ± 0.000
		Calc.	0.002	0.980	0.002

^aThe 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).