SYSTEMATIC-APPROACH TO LINKS BETWEEN SEPARATIONS IN CAPILLARY ELECTROPHORESIS AND LIQUID-CHROMATOGRAPHY .4. APPLICATION OF BINDING CONSTANTRETENTION FACTOR RELATIONSHIP TO THE SEPARATION OF 2-METHYLBENZOATE, 3-METHYLBENZOATE AND 4-METHYLBENZOATE ANIONS USING BETA-CYCLODEXTRIN AS SELECTOR

Quantitative links between binding constants determined in CE and rete ntion factors in HPLC for 1:1 analyte-selector complexes, developed in a previous paper and applied to separations of cationic tioconazole e nantiomers with beta-cyclodextrin (beta-CD), have been extended to the separation of anionic positional isomers. In this paper we apply our unified theory to the separation of anionic methylbenzoate anions (MB- ), again using beta-CD as selector. There is only partial resolution f or all of the three isomeric methylbenzoates without beta-CD present, either in the CE background electrolyte or immobilised in the HPLC exp eriments. Using the same buffer as in CE (ammonium phosphate pH 7.0), and calculating the effective concentration of selector from the amoun t of beta-CD divided by the volume of the mobile phase in the column, HPLC is shown to give effective binding constants, K', which are in ex cellent agreement with binding constants, K, determined from the varia tion of CE mobility with beta-CD concentration. K'=11, 41, 87 M-1 and K=13.0, 45.5, 85.3 M-1 for 2-, 3-, 4-MB-, respectively. This demonstra tes the quality of our unified treatment of separations based on bindi ng equilibria, and suggests the potential of method development in CE and information transfer to HPLC or vice versa. Quantitative determina tion of K in CE also generates mobilities of free analyte and analyte- selector complexes, which after correction for non-ideality give radii and diffusion coefficients of the MB- and MB-:beta-CD ions. This in t urn allows a quantitative treatment of variance contributions from dif fusion to CE peak widths. Good agreement is found between calculated a nd observed peak widths when these are measured with the fastest possi ble data acquisition parameters. (C) 1997 Elsevier Science B.V.