Compound-specific [delta]13C and [delta]15N analysis of amino acids: a rapid, chloroformate-based method for ecological studies

RATIONALE Compound-specific stable isotope analysis of amino acids has proven informative to many ecological systems, but only a handful of analytical methods are routinely employed. We evaluated a simple, rapid procedure in which biological samples undergo short-duration acid hydrolysis and the resulting amino acids are derivatized with methyl chloroformate for gas chromatography/combustion/isotope-ratio mass spectrometry (GC/C/IRMS). METHODS Amino acid derivatives were separated on a polar gas chromatography column, combusted, and [delta]13C and [delta]15N values were measured. Tests of reproducibility and accuracy were conducted for amino acid reference mixtures and biological samples. A brief case study of turtles was used to assess whether isotopic data were consistent with a priori ecological expectations. RESULTS The methyl chloroformate based reaction successfully converted 15 amino acids from acid hydrolysates of biological materials into separable derivatives. The [delta]13C and [delta]15N values had high average measurement precision (σ