Application of indirect photometric chromatography to pharmaceutical analysis

Indirect photometric chromatography, which couples analyte separation by ion exchange with indirect photometric detection, is applied to the analysis of complex solutions encountered in the pharmaceutical industry. Applications of primary interest include simultaneous acetate, lactate, chloride, or phosphate determinations, a bisulfite/sulfate assay, and quantitation of trace levels of chloride in deionized water. Three commercially available ion chromatography columns are studied for their suitability in these applications. Due primarily to (A) the acid-base chemistry of the phosphate and bisulfite ions, (B) the need to stabilize the readily oxidized bisulfite, and (C) resin stability at high pH, the column packed with a polymer-based resin is capable of producing analytically superior separations of Cl-, HPO4-2, and matrix components and of SO3-2/SO4-2 in the samples of interest. Under rigid relative concentration conditions, the columns packed with a silica backbone resin are capable of separating acetate, lactate, Cl-, and H2PO4- with baseline resolution and are effective for determining Cl- levels at concentrations of less than one part-per-million.