Determination of sodium acetate in antisense oligonucleotides by capillary zone electrophoresis

The determination of sodium acetate in antisense oligonucleotides purified by reverse phase chromatography in acetate buffer is important in both impurity profiling and drug concentration assay. A method has been developed for the quantitation of sodium acetate in a 20-mer phosphorothioate oligonucleotide drug substance employing capillary zone electrophoresis. Chloride was included as an internal standard to increase accuracy and precision of the measurement. Interference due to oligonucleotide matrix was eliminated by filtering the olignucleotide solution through a Centricon SR-3 column. The linear dynamic range for the method is 0.06-240 mu g/mL. The electrophoretic separation requires only 6 min. The method has been demonstrated to be simple and reliable for the quantitation of acetate salts in oligonucleotide drug substances.