Studies on separation selectivity in capillary zone electrophoresis of inorganic anions
Creators: name: Harakuwe, AHH
Publisher: name: University Of Tasmania
Year: 2023

description: Parameters influencing the separation selectivity of low molecular-mass anions using free-solution reversed electroosmotic flow capillary zone electrophoresis (F'RECZE) have been studied. First, detailed preliminary investigations were performed to address two major limitations of FRECZE, namely, imprecision in migration times and variability of phosphate response. A capillary conditioning regime suitable for the generation of stable migration times and optimal phosphate response was developed. Also, it was established that dried electroosmotic flow (EOF) modifiers generated more stable migration times and gave improved resolution. Second, a wide range of selectivity-influencing parameters was studied. These parameters included electrolyte pH, EOF modifier chain length, nature of the EOF modifier counter-anion, EOF modifier concentration, binary EOF modifier mixtures, type of indirect detection probe, probe concentration, 1-butanol as an electrolyte additive, and instrumental variables (e.g. detection wavelength and separation voltage). The trends of migration order observed with the above parameters are discussed and possible mechanisms outlined. Major migration order changes were caused by pH and EOF modifier effects. Electrolyte pH variation changed the migration order of weak acid anions at pH values close to their pKa points by altering their charge to mass ratios. Migration order changes due to either increased or reduced ion-pairing effects were pronounced for lipophilic anions and could be induced particularly with EOF modifier changes, electrolyte concentration and 1-butanol as additive. Migration order changes due to increased effective charge of anions were influenced particularly by 1- butanol as additive as well as electrolyte ionic strength. Third, information from the above studies was applied to the separation of inorganic anions in samples having varying levels of matrix complexity, e.g. tap water, Bayer liquor, acid-digested concrete, toothpaste, urine, a formulation for prevention of gallstone formation, corned beef, seawater and Antarctic saline lake water. Analytical performance characteristics are discussed for the separation of anions in Bayer liquor, concrete and toothpaste. The highlights of this study were that the useful pH range of chromate-based electrolyte could be extended by 20% by incorporation of 1-butanol in the electrolyte; the resolution between fluoride and phosphate could be improved by over 400% making possible the separation of 1 gg.mL-1fluoride in the presence of over 800 p.g.mL-1 phosphate, and the use of binary EOF modifier mixtures was introduced and applied to the analysis of Bayer liquor. Two electrolyte compositions capable of simultaneously separating chloride, sulfate, oxalate, malonate, fluoride, formate, phosphate, succinate, tartrate, carbonate and acetate in under 4 minutes were identified. Calibrations were linear in the range 1 - 10 j.tg.tnL-1 , detection limits as low as 0.09 lig.mL-1 were obtained and near quantitative recoveries (except for phosphate) were recorded.