Liquid Chromatographic Determination of the Composition of Thiacetarsamide Solutions

Abstract

Abstract Sodium thiacetarsamide in solution is a mixture of p-arsenosobenzamide and thiacetarsamide as determined by two reverse phase liquid chromatographic (LC) procedures with the following mobile phases: Procedure I: methanol:0.25 mM sodium phosphate and 0.0125 mM sodium ethylenediaminetetraacetic acid aqueous buffer, pH 7 (15:85); and procedure II: tetrahydrofuran:2.5 mM sodium metabisulfite and 0.5 mM phosphoric acid aqueous buffer, pH 3 (5:95). Procedure I separated p-arsenosobenzamide from unretained thiacetarsamide and degradation products. Procedure II retained and separated thiacetarsamide, p-arsenosobenzamide, and degradation products. Both procedures inhibited on-column hydrolysis of thiacetarsamide to p-arsenosobenzamide and allowed two independent estimations of the p-arsenosobenzamide content of thiacetarsamide solutions. Only p-arsenosobenzamide and unidentified degradation products were detected when sodium thiacetarsamide-p-arsenosobenzamide solutions were stored for 6 months at room temperature. However, the refrigerated solutions were composed of thiacetarsamide and p-arsenosobenzamide plus trace amounts of unidentified substances. Under strongly basic conditions, thiacetarsamide hydrolyzed to p-arsenosobenzamide, which later degraded to unknown compounds. To stabilize and maintain a relatively constant composition, sodium thiacetarsamide-p-arsenosobenzamide solutions must be refrigerated and protected from light and oxygen.