Quantitative determination of oxalate in Bayer liquor by capillary zone electrophoresis. A validative study

The applicability of capillary zone electrophoresis (CZE) for the routine determination of oxalate in Bayer liquors was investigated. The effects of electrolyte composition, capillary conditioning, temperature and applied voltage were studied, with the use of temperature control, isomigration mode and an appropriate capillary conditioning regime proving critical in minimising variations in peak migration time. The CZE method, which utilised a chromate-based electrolyte (containing an osmotic flow modifier) and indirect photometry, demonstrated excellent within-batch precision, giving a migration time precision of less than 0.30% R.S.D. and an analysis precision of less than 1.2% R.S.D. The method also demonstrated excellent between-batch precision, with the overall analysis precision, obtained for five alumina refinery samples run over five days, being 2.3, 1.1, 1.7, 1.5 and 1.3% R.S.D., respectively. The between-batch migration time precision for the oxalate peak was 0.89% R.S.D., while the absolute oxalate peak area precision was 2.5% R.S.D. The method within- and between-batch precision values were comparable to those expected from other instrumental separation techniques, demonstrating that CZE can be an appropriate technique for routine analysis, even for complicated sample matrices, such as Bayer liquors.