ANALYSIS OF ANTHRAQUINONE SULFONATES - COMPARISON OF CAPILLARY ELECTROPHORESIS WITH HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) are compared for the analytical separation of anthraquinone-1-sulphonate and its related impurities anthraquinone-2-sulphonate, anthraquinone-1,8-disulphonate and anthraquinone-1,5-disulphonate Optimum conditions for CE use a borate solution (50 mM NaH2BO3 and 8 mM H3BO3) as background electrolyte at pH 10.0, and for HPLC acetonitrile-water (60:40) containing 0.8% (w/v) cetyltrimethylammonium bromide as eluent. Analysis times are comparable by both techniques. Quantitative aspects including CE and HPLC efficiency, linearity, precision and limits of detection (LOD) arc compared. For anthraquinone-1-sulphonate the CE concentration LOD is 0.7 mug ml-1 and the HPLC LOD is 6 ng ml-1: mass LODs are 3 and 60 pg, respectively. Assay precision is 2% R.S.D. in peak area by CE using instruments from several manufacturers. This is improved to better than 0.5% R.S.D. in relative peak areas when a co-injected analyte is used as an internal standard, showing that injection is the factor limiting precision in CE. Integration errors give a significant contribution to the observed error in relative peak areas.