Retention behavior of o-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids in ion-suppression reversed-phase high performance liquid chromatography using acids instead of buffers as ion-suppressors.
In reversed-phase high performance liquid chromatography, the logarithm of the retention factor, log k, is usually correlated with the logarithm of the octanol-water partition coefficient, log Kow. The k and Kow of an ionizable analyte are greatly influenced by the mobile phase pH. In this paper, log kw of diprotic o-phthalic, 3-nitrophthalic, and 4-nitrophthalic acids, are obtained by extrapolation to pure aqueous fraction of mobile phase in ion-suppression reversed-phase high performance liquid chromatography with acetic acid and perchloric acid as the ion-suppressors. The Kow values of the three analytes are calibrated according to the apparent octanol-water partition coefficient, Kow, under different pH conditions, and the log K"ow values show a much better correlation with log kw than do log Kow. The influences of two ion-suppressors, acetic and perchloric acids, on the retention behavior of these diprotic acids at different pH are contrasted. An abnormal trend is found in the k vs. pHw plot of the acetic acid system when the methanol content is low. A possible reason is that acetic acid is an even stronger organic modifier than methanol, besides being an ion-suppressor. The results make the selection of mobile phase for the separation of acidic compounds by ion-suppression reversed-phase high performance liquid chromatography direct, accurate, and practical.
Lian
Hong-Zhen
HZ
Key Laboratory of Analytical Chemistry for Life Science, The Ministry of Education, Center of Materials Analysis & Department of Chemistry, Nanjing University, Nanjing, P.R. China. hzlian@nju.edu.cn
Wang
Wei-Han
WH
Li
Dan-Ni
DN
D019342:Acetic Acid; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D000442:Octanols; D010472:Perchlorates; D010795:Phthalic Acids / Q000737:chemistry*; D014867:Water
D000442:Octanols; D010472:Perchlorates; D010795:Phthalic Acids; D014867:Water; D019342:Acetic Acid