Gas liquid chromatography and mass spectrometry of carbon-13 enriched and deuterated amino acids as trimethylsilyl derivatives

A study of the gas liquid chromatography (GLC) and mass spectrometry (MS) of normal, carbon-13 enriched, and specifically labeled deuterated amino acids as their trimethylsilyl derivatives has been carried out. No evidence for GLC fractionation of the normal and corresponding carbon-13 enriched amino acids was observed; however, in many cases the retention time of the deuterated compound was measurably shorter than that of its protium analog. The small differences to a first approximation were proportional to the number of deuterium atoms presents in the amino acid. Fractionation of the protium and deuterium forms within a single GLC peak has been demonstrated by combined GLC-multi scan MS. Characteristic relative intensities for the (S+l) isotope peak of fragment ions from the carbon-13 enriched amino acids facilitated the elucidation of the mass spectral fragmentation patterns observed for these compounds, and the MS of the deuterium containing amino acids has confirmed these proposals. The carbon-13 content of the carbon-13 enriched amino acids and their fragment ions was calculated from relative peak heights in the mass spectra; comparison of the values suggests a carbon-13 biosynthetic isotope effect.