Studies on separation selectivity in capillary zone electrophoresis of inorganic anions

摘要

Parameters influencing the separation selectivity of low molecular-mass anions usingudfree-solution reversed electroosmotic flow capillary zone electrophoresis (F'RECZE)udhave been studied. First, detailed preliminary investigations were performed to addressudtwo major limitations of FRECZE, namely, imprecision in migration times andudvariability of phosphate response. A capillary conditioning regime suitable for theudgeneration of stable migration times and optimal phosphate response was developed.udAlso, it was established that dried electroosmotic flow (EOF) modifiers generated moreudstable migration times and gave improved resolution. Second, a wide range of selectivity-influencing parameters was studied. Theseudparameters included electrolyte pH, EOF modifier chain length, nature of the EOFudmodifier counter-anion, EOF modifier concentration, binary EOF modifier mixtures,udtype of indirect detection probe, probe concentration, 1-butanol as an electrolyteudadditive, and instrumental variables (e.g. detection wavelength and separation voltage).udThe trends of migration order observed with the above parameters are discussed andudpossible mechanisms outlined. Major migration order changes were caused by pH andudEOF modifier effects. Electrolyte pH variation changed the migration order of weakudacid anions at pH values close to their pKa points by altering their charge to massudratios. Migration order changes due to either increased or reduced ion-pairing effectsudwere pronounced for lipophilic anions and could be induced particularly with EOFudmodifier changes, electrolyte concentration and 1-butanol as additive. Migration orderudchanges due to increased effective charge of anions were influenced particularly by 1-udbutanol as additive as well as electrolyte ionic strength. Third, information from the above studies was applied to the separation of inorganicudanions in samples having varying levels of matrix complexity, e.g. tap water, Bayerudliquor, acid-digested concrete, toothpaste, urine, a formulation for prevention of gallstoneudformation, corned beef, seawater and Antarctic saline lake water. Analyticaludperformance characteristics are discussed for the separation of anions in Bayer liquor,udconcrete and toothpaste.udThe highlights of this study were that the useful pH range of chromate-based electrolyteudcould be extended by 20% by incorporation of 1-butanol in the electrolyte; theudresolution between fluoride and phosphate could be improved by over 400% makingudpossible the separation of 1 gg.mL-1fluoride in the presence of over 800 p.g.mL-1udphosphate, and the use of binary EOF modifier mixtures was introduced and applied toudthe analysis of Bayer liquor. Two electrolyte compositions capable of simultaneouslyudseparating chloride, sulfate, oxalate, malonate, fluoride, formate, phosphate, succinate,udtartrate, carbonate and acetate in under 4 minutes were identified. Calibrations wereudlinear in the range 1 - 10 j.tg.tnL-1 , detection limits as low as 0.09 lig.mL-1 wereudobtained and near quantitative recoveries (except for phosphate) were recorded.