HPLC Post-Column Ion-Pair Extraction of Acidic Drugs Using a Substituted α-Phenylcinnamonitrile Quaternary Ammonium Salt as a New Fluorescent Ion-Pair Reagent

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Abstract
A reversed-phase HPLC post-column ion-pair extraction system was developed for the analysis of carboxylic acid drugs and their salts using α-(3,4-dimethoxyphenyl)-4′ -trimethylammonium-methylcinnamonitrile methosulfate (DTM) as a new fluorescent ion-pair reagent. The on-line post-column extraction system was optimized with respect to the reagent concentration, extraction coil length and internal diameter, ionic strength of mobile phase, extraction solvent, and the membrane phase separator. Sodium salicylate, ketoprofen, ibuprofen, probenecid, and valproic acid were used as model compounds to evaluate the ion-pair extraction system. The method was applied to pharmaceutical dosage forms containing ketoprofen and valproic acid. Other acidic compounds evaluated using the ion-pair reagent showed that lipophilic acids produced more extractable ion-pairs and higher sensitivities than hydrophilic acids.