The derivatisation of individual AA to their corresponding
N-pivaloyl-iso-propyl (NPIP) esters allowed the accurate determi-
nation of -
15N values of most AAs in muscle tissue and plant
material. Results proved that the pretreatment with Dowex cation-
exchange resin was a useful and reliable way to purify AA fraction.
The treatment with Dowex cation-exchange resin had no signifi-
cant effect upon the -
15N values of AA standards; the differences
prior to and following passage the resin were within 1‰. The
amount of sample used in GC-C-IRMS was also optimized;the sam-
ple amount required in our study is notless than 20 ngN on column.