Table 2.

Unlabeled Leucine and [1,2-¹³C₂]Leucine Isotopic Abundance Values Used to Calculate the Abundance of Isotopomers in [1,2-¹³C₂]Leucine

m/z	A matrix values					[1-13C]Leucine Isotopic Abundances (y)	Calculated Abundances (x,%)	Isotopomer
	i = 0	1	2	3	4
349	100	0.18	0.11	0	0	0.28 ±0.02	x0 = 0.16 ±0.13	Unlabeled Leucine
350	14.98	100	0.18	0.11	0	1.57 ±0.03	x1 = 1.28 ±0.02	[1-13C]leucine
351	1.71	13.88	100	0.18	0.11	100.00 ±0.04	x2 = 93.29 ±0.22	[1,2-13C2]leucine
352	0.14	1.57	12.79	100	0.18	12.99 ±0.01	x3 = 0.18 ±0.05	[1-13C,18O]leucine
353	0	0.14	1.44	13.88	100	6.91 ±0.03	x4 = 5.09 ±0.13	[1,2-13C2,18O]leucine

The measured unlabeled leucine intensities shown in Fig. 1 were used to construct the A matrix. The measured ion abundances (y vector) for the [1,2-¹³C₂]leucine material are shown with their respective standard deviations. The fractional abundances (x_i) of the different isotopomers (i = 0, 1, 2, 3, and 4 for unlabeled leucine, [1-¹³C]leucine, [1,2-¹³C₂]leucine, [1-¹³C,¹⁸O]leucine, and [1,2-¹³C₂,¹⁸O]leucine, respectively) were calculated. Standard errors are given for each abundance value.