CORRELATION BETWEEN HYDROPHOBICITY OF AMINO-ACIDS AND RETENTION DATA IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY WITH MICELLAR ELUENTS

Hydrophobic character is usually expressed in terms of the partition c oefficient in 1-octanol-water (log P-o/w). However, measurement of thi s coefficient is often problematic. Retention in micellar liquid chrom atography is mainly due to hydrophobic interactions and can also be us ed as an index of hydrophobicity. A hydrophobicity scale was establish ed with retention data for o-phthalaldehyde (OPA)-N-acetyl-L-cysteine (NAG) amino acid derivatives, using the glycine derivative as referenc e. Since the OPA-NAC derivatives only differ in the nature of R(1) in the amino acid (R(1)CH(COOH)NH2), in the absence of electrostatic inte ractions the hydrophobic character of the substituent was responsible for retention. Linear relationships were obtained between log of the r atio k' of amino acid derivatives: k' of the glycine derivative for a given mobile phase,and log P-o/w for the R(1) substituent. Good correl ations were also found for phenylthiohydantoin amino acid derivatives.