. Author manuscript; available in PMC: 2008 May 12.

Published in final edited form as: Anal Chem. 2002 Dec 15;74(24):6244–6251. doi: 10.1021/ac026061s

Table 2.

GC-C-IRMS Leucine Data for the Three Derivatives Tested^a

		Expected ¹³C enrichment		Measured ¹³C enrichment
Sample ID	Derivative Type	E (ape)	E_l(ape)	δ¹³C_PDB (per mil)	F (atom %)	E (ape)	E_l ape)
Natural	NAP	0.0000	0.0000	−31.95 ± 0.45	1.0761 ± 0.0005	0.0000	0.0000
Std 1	NAP	0.0350	0.1928	1.04 ± 0.21	1.1124 ± 0.0002	0.0363	0.1994
Std 2	NAP	0.0663	0.3647	27.95 ±0.48	1.1419 ± 0.0005	0.0658	0.3620
Natural	“mixed”	0.0000	0.0000	−28.12 ± 0.23	1.0803 ± 0.0003	0.0000	0.0000
Std 1	“mixed”	0.0257	0.1928	−2.48 ± 0.50	1.10851 ± 0.0006	0.0257	0.2115
Std 2	“mixed”	0.0486	0.3647	19.93 ± 0.29	1.1331 ± 0.0003	0.0486	0.3961
Natural	tBDMS	0.0000	0.0000	−27.77 ± 0.19	1.0809 ± 0.0002	0.0000	0.0000
Std 1	tBDMS	0.0214	0.1928	−5.81 ± 0.10	1.1049 ± 0.0001	0.0214	0.2172
Std 2	tBDMS	0.0405	0.3647	14.14 ± 0.31	1.1268 ± 0.0003	0.0405	0.4145

E = ¹³C enrichment in the entire derivatized molecule; E_l = ¹³C enrichment in the two labeled carbons (C-1 and C-2) in the leucine; F = the measured ¹³C in the derivatized molecule; NAP = N-acetyl n-propyl ester; TBDMS = t-butyldimethylsilyl ester; and mixed = N-acetyl t-butyldimethylsilyl ester.