Determination of quaternary alkylammonium compounds by capillary zone electrophoresis and indirect UV detection as a real alternative to ion chromatography with suppressed conductivity detection

A capillary electrophoretic (CE) method for the determination of residual m id-chain alkyltrimethylammonium compounds in the pharmaceutical product Wel chol (TM) tan alkylated, crosslinked polyallylamine) was developed, validat ed and compared with the existing ion chromatographic (IC) method with supp ressed conductivity detection. Excellent reproducibilities of migration tim es (RSD <0.5% within a series of 55 sample injections) and relative peak ar eas (RSD <2%) make the method suitable for quality central as a real altern ative to IC. Limits of quantification of 0.01% w/w of each impurity in the active substance were achieved. Buffer systems for indirect UV detection ba sed on creatinine as visualization reagent with different inorganic and org anic acids (phosphoric, sulfuric, formic, acetic, oxalic and citric acid) a nd their effect on selectivity to ten quaternary ammonium compounds were st udied. Selectivity changes were observed for the di- and trivalent analytes depending on the buffer applied. Also, the influence of acetonitrile, meth anol, I, ct-dioxane and tetrahydrofuran on selectivity was investigated. In addition, CE-MS experiments were carried out in order to identify several impurities in the product. (C) 2001 Elsevier Science B.V. All rights reserv ed.