Abstract
A measurement of the 15N abundance ratio in trace amounts of amino acids by GC-MS is possible. However, in the N-trifluoroacetyl ester derivatives of amides, the 15N abundance ratio of amido base nitrogen in the asparagine and glutamine is impossible to measure. The present report describes an analytical method for determination of the 15N abundance ratio of amido base nitrogens of amides. Normal and 15N amido base nitrogen-labeled asparagine and glutamine are converted to the trimethylsilyl derivative of methylthiazolinone (TMS-MT) . The 2TMS, and 3TMS MT derivatives of asparagine and glutamine formed are analyzed by a magnetic field scanning method using GC-MS. The mass fragment ions of asparagine of m/e 388 and 242 were monitored. For glutamine, the mass fragment ions of ml e 402 and 131 were monitored. By this method the 15N abundance ratio of amido base nitrogen in the amides is measurable with a coefficient of variation of less than 0.6%.
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