Quantitative analysis of sodium dodecyl sulphate by capillary electrophoresis

The surfactant sodium dodecyl sulphate (SDS) is a widely used excipient in solid pharmaceutical formulations. Therefore, it is important to have appropriate analytical methods to measure the SDS content and to confirm its identity in manufactured batches of the preparation. Typically, the analysis is conducted by titrimetry or spectroscopy. However, it would be advantageous to have a more selective method with automation possibilities for the assay. The separation of alkylsulphates by capillary electrophoresis is simple and involves use of indirect detection as they have poor UV absorbance. In this work, a reliable quantitative determination of SDS in a cefuroxime axetil pharmaceutical preparation has been achieved. This is attained primarily by the incorporation of an internal standard. The adsorption of SDS onto filters was also quantified. The level of adsorption was found to vary between filter types and was minimised by filtration of large volumes. It was therefore recommended that large volumes of electrolyte used in micellular electrokinetic capillary chromatography (MEKC) are filtered to ensure repeatable separations. The modified conditions produced a fast, efficient, precise and highly automated means of assaying SDS levels and can provide a useful alternative to established methods of testing. (C) 1997 Elsevier Science B.V.