DL- (4

5-

2

H) -leucine was prepared by catalytic deuteration of its double-bond precursor. Its trifluoroacetyl butanolic ester derivative was prepared and the deuterium content was estimated by GC-MS. Analysis of the m/e=182 fragment by Biemann's method revealed that the

2

H content varied from 0 to 6. The percentage of molecules containing no deuterium atom was 16.4

indicating that the abundance of labelled molecules (regardless of the number of deuterium atoms in each molecule) was 83.6%. Calculated from the intensity of the fragments m/e=182

153

140 by Biemann's method the abundances of labelled atoms at different C positions of the leucine molecule was: C

1

—0%; C

2

—2.9%; C

3

—22.5%; C

4

C

5

C

6

—54.2% (average) .