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Abstract
The hydrolytic reaction of thiacetarsamide with reversed-phase packing material produced p−arsenosobenzamide during high-performance liquid chromatography (HPLC). The on-column hydrolysis was inhibited by including compounds in the mobile phase that complex with trace metal contaminants. With ethylenediaminetetraacetic acid (EDTA) and sodium phosphate in the mobile phase at neutral pH, a unique chromatographic profile resulted, with thiacetarsamide not being retained, followed by a bridge to the p−arsenosobenzamide peak. EDTA, bound to the reversed-phase packing material, inhibited on-column hydrolysis of thiacetarsamide when EDTA was not present in the mobile phase. After the HPLC system was cleaned with water to remove the residual EDTA, the bridge disappeared and the p−arsenosobenzamide peak increased, illustrating increased hydrolysis. This occurred whether or not the silica had been treated to remove trace metals. EDTA probably interacted at secondary retention sites containing trace metal contaminants, thus inhibiting the hydrolytic reaction of thiacetarsamide at the silica surface.