Assay of Abacavir Sulfate

Abstract

A modified volumetric method for assay of abacavir sulfate in substance is described; this is an intermediate salt [(C14H18N6O)2 ⋅ H2SO4)] containing trace quantities of the acid salt. Methods for abacavir sulfate assay in substance using volumetric methods are known, as are HPLC assays. We present here a modified method for the alkalimetric titration of abacavir sulfate with a correction for the initial pH of the substance solution being titrated. This excludes increases in results obtained by titration due to the presence of traces of the acid sulfate of abacavir in the test substance. The proposed method is shown to have advantages over known methods, including the standard alkalimetric titration without correction for the initial pH of the titration solution. The method is rapid, gives accurate results, is highly reproducible, and does not require the use of expensive reference samples. A relative metrological comparison of HPLC and alkalimetric titration methods is presented. The metrological characteristics of the HPLC method using reference samples indicate that it is unlikely to provide results to an accuracy of ± 2% with a confidence limit of 95% for assay in substance. The realistic accuracy range for normalization in this case is ± 3%.