Analysis of amino acid phenylthiohydantoins by gas chromatography.

A gas chromatographic procedure has been developed for the quantitative analysis of submicrogram amounts of the phenylthiohydantoins of all the amino acids except arginine. The compounds are divided into three groups according to their volatility and need for derivatization (trhnethylsilylation). The more volatile, relatively nonpolar thiohydantoins (Group I) are chromatographed with best results on columns coated with the stationary phase DC-560. For polar thiohydantoins of lower volatility (Group II), XE-60 is a much more suitable phase. The third group consists of thiohydantoins for which trimethylsilylation prior to analysis is either mandatory (aspartic, glutamic, and cysteic acids) or helpful (serine, S-carboxymethylcysteine, threonine, and lysme derivatives). A two column system employing the above stationary phases has been applied to the analysis of porcine thyrocalcitonin which was degraded by the threestage form of the Edman procedure. In addition, a single column system has been developed utilizing a blend of three silicone phases which allows identification of all three groups of thiohydantoins in two 50-min runs (before and after trimethylsilylation).