Prediction of internal standards in reversed-phase liquid chromatography IV. Correlation and prediction of retention in reversed-phase ion-pair chromatography based on linear solvation energy relationships

This paper describes the results of the evaluation of a new solvation parameter model for reversed-phase ion-pair chromatography by linear gradient elution. This model is described as t = Int + r'R + s'pi(2)(H) + a' Sigma alpha(2)(H) + b' Sigma beta(2)(H) + m'V-X + U-1/(1 + V x 10(+/-(pKa-pH))) + gamma(IP)Z(s). The first six terms are the usual solvation parameter equation for neutral solutes, and the seventh term represents the contribution to retention from solute's ionization. The last term describes the retention increase due to ion-pair effect. Retention times obtained for 60 solutes (neutral, acidic and basic) in acetonitrile/aqueous mobile phases with different ion-pair reagents (phosphoric acid, trifluoroacetic acid, heptafluorobutyric acid, perchloric acid, and hexafluorophosphoric acid) are used to evaluate the capability of the function. It is concluded that the model describes the retention of ionizable/ionized compounds under ion-pair conditions very well. Accordingly, the function extends the application of linear solvation energy relationships (LSERs) to ionizable compounds in ion-pair chromatography, and allows us to easily predict their retention for chromatographic optimization, including selectivity optimization and internal standard selection. Finally, the conclusion can be extended to ioscratic elution. (C) 2004 Elsevier B.V. All rights reserved.