Chromatography of substituted benzoic acids with methanol-water carbon dioxide mixtures

The impact of the proportion of CO2 concentration in methanol-water-CO2 mob ile phases on the separation of several substituted benzoic acids was explo red by studying the variation of retention with mobile phase pH in these mi xtures. As the amount of CO2 in methanol-aqueous buffer-CO2 mixtures increa sed, a more basic buffer was needed to control the dissociation of these ac ids. Differences in terms of retention, separation efficiency and peak asym metry were shown for substituted benzoic acids with methanol-water-CO2 and methanol-aqueous buffer-CO2 mixtures. Variations of these chromatographic p arameters with mobile phase pH were related to the dissociation of these ac ids and their interaction with methanol-aqueous buffer-CO2 mobile phases an d the stationary phase. The addition of a buffer into methanol-aqueous solu tion-CO2 was an effective means to optimize separations of acidic analytes with high fluidity liquid mobile phases. The substituted benzoic acids had baseline separation in the least amount of time using the high fluidity liq uid mobile phases. (C) 2001 Elsevier Science B.V. All rights reserved.