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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
Author(s) -
Lian HongZhen,
Wang WeiHan,
Li DanNi
Publication year - 2005
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.200400092
Subject(s) - chemistry , perchloric acid , phthalic acid , partition coefficient , acetic acid , chromatography , analytical chemistry (journal) , ion , aqueous solution , alkylbenzenes , inorganic chemistry , benzene , organic chemistry
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 K ow . The k and K ow of an ionizable analyte are greatly influenced by the mobile phase pH. In this paper, log k w 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 K ow values of the three analytes are calibrated according to the apparent octanol‐water partition coefficient, K ´´ ow , under different pH conditions, and the log K ´´ ow values show a much better correlation with log k w than do log K ow . 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. pH w 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.