A unique derivatization procedure is described for the simultaneous determination of protein and non-protein amino acids present in aqueous samples. This procedure involves N(O,S)-isobutyloxycarbonylation combined with solid-phase extraction with subsequent tert.-butyldimethylsilylation for gas chromatographic analysis. Using this combined procedure, linear responses were obtained in the range of 10-100 ppm, with correlation coefficients varying from 0.991 to 0.999, for the free amino acids studied except for homocysteine (0.922) and homoserine (0.982). The relative standard deviations ranged from 0.7 to 5% for most amino acids with a few exceptions. Temperature-programmed retention index (I) sets as measured on DB-5 and DB-17 dual-capillary columns were characteristic of each amino acid and thus useful for the screening of amino acids by computer I matching. The mass spectral patterns of amino acid derivatives, exhibiting characteristic [M-57]+, [M-113]+, [M-131]+, [M-159]+, [M-174]+ and other ions, permitted rapid structural confirmation. The present method allowed simultaneous screening of free protein and non-protein amino acids when applied to seed samples such as almond, walnut, and sunflower seeds.