Prediction of retention behaviour and evaluation of pK(a) values of peptides and quinolones in liquid chromatography

The present paper examines the effect of the solute ionisation on the reten tion behaviour in liquid chromatography of a series of peptide and quinolon e compounds of biological interest, using acetontrile-water media as mobile phases and a polymeric-based stationary phase. Polymeric columns with poly styrene-divinylbenzene (PS-DVB) polymer show advantages over silica-based r eversed-phase packings since the former are stable in a wide pH range. (S)( S)pK(a)values have been evaluated using chromatographic data in acetonitril e-water mixtures with acetonitrile percentages of 30, 35, 40 and 50% (v/v) for quinolones and 12.5 and 20% (v/v) for peptides. The quinolones show gre at retention on PS-DVB phase stationary. It was thus necessary to work with a higher acetonitrile content in the mobile phase than for the less retain ed peptides. The pH values were measured in the hydroorganic mixtures, used as mobile phases, instead of in water and account was taken of the effect of activity coefficients. The derived equations permit the chromatographic determination of (S)(S)pK(a). values of the peptides and quinolones in acet onitrile-water mixtures by fitting it to the experimental data in a nonline ar least-square procedure and also permit the prediction of the effect of ( S)(S)pH on their chromatographic behaviour. We have also compared the obtai ned (S)(S)pK(a)values with those previously obtained in acetonitrile-water mixtures from potentiometric measurements. (C) 2001 Elsevier Science B.V. A ll rights reserved.