Plasma amino acid quantitation using gas chromatography chemical ionization mass spectrometry and 13C amino acids as internal standards.

A specific and sensitive method for the quantitation of 16 alpha amino acids has been developed. The technique employed uses methane chemical ionization gas chromatography mass spectrometry of the carboxy-n-butyl, N-trifluoroacetyl amino acid derivatives. A commercial 13C amino acid mixture provided individual internal standards for 14 alpha amino acids. A computer controlled quadrupole mass spectrometer was used for selected ion monitoring of those ions characteristic of each N-trifluoroacetyl amino acid/13C amino acid pair. A BASIC computer program located peak maxima and background intensities in each selected ion recording. Standard curves for each amino acid/13C amino acid pair were utilized by the program to calculate the plasma concentration of each detected amino acid. The total instrumental analysis occupied 30 min with sample preparation and derivatization accounting for an additional 2 h. Based on the detection of known amounts of standard amino acids the method will quantitate at the 1-5 nanogram level of detection.