Previous studies in our laboratory (1,2) have shown that the phenylt,hiohydantoin (PTH) derivative of all the amino acids except arginine could be analyzed in submicrogram amounts by gas chromatography. The analysis was performed by direct injection of all derivatives except the aspartyl, glutanlyl, and cysteic acid ~o~npounds, which required prior conversion to the volatile trimethylsilyl derivative (1). Complete separation of all the amino acid PTH's could not be achieved with a single stationa~ phase. Two phases, however, DC-560 and XE-60, were complementary, and allowed unequivocal identification of all the derivatives. A single column system composed of a blend of three phases (DC-560, XE-60, and OV-22), designated DXO, was developed, and came close to providing the desired resolution of all the phenylthiohydantoins. Only the resolution of the isoleucyl and leucyl derivatives and the silylated aspartyl and asparaginyl PTH's were not. entirely satisfactory.
This communication describes a superior blend of silicone phases as well as new r~rocedures that provide higher resolution, better peak symmet,ry and less baseline rise during temperature programming than hitherto obtained. The new procedure includes high temperature conditioning of the packing, the use of helium as carrier gas, and a sodium carbonate prewash of the support. Sequence analyses employing columns composed of the new blend are included. In addition, procedures are presented for the gas ~hromatographi~ analysis of the amino acid methylthiohydantoins fMTH's), which may also be employed in sequence nnitlysis.