The use of the mass spectrometer for the quantitative analyses of mixtures of amino acids

Abstract

The quantitative analysis of a low vapor pressure unstable solid mixture of amino acids is possible by putting the solid mixture in a crucible which is then placed directly into the ionization chamber of a mass spectrometer. Relative sensitivities for the various acids in a mixture can be established by the proper use of a particular amino acid as an internal-calibrating standard. The success of the method depends upon: (1) the reproducibility of the mass spectra of the pure components, (2) the ideal vapor pressure behavior of the solid mixture, (3) the preparation of an intimate solid mixture by rapid freezing of the water solution of the acids with subsequent vacuum sublimation of the ice and ball-milling the dried mixture.