Solvents orgànics en electroforesi capillar i cromatografia de líquids

Abstract

"Organic solvents in capillary electrophoresis and liquid chromatography" TEXT: The use of methanol- and acetonitrile- aqueous buffer mobile phases in RP-HPLC is a common election when performing chromatographic separations of ionisable analytes. The addition of organic solvent to the aqueous buffer to prepare such a mobile phase changes the buffer capacity and the pH of the solution. In this thesis work, the variation of these buffer properties is studied for acetic acidacetate, phosphoric aciddihydrogenphosphatehydrogenphosphate, citric aciddihydrogencitratehydrogencitratecitrate, and ammoniumammonia buffers. It is well established that the pH change of the buffers depends on the initial concentration and aqueous pH of the buffer, on the percentage of organic solvent added, and on the particular buffer used. The proposed equations allow the pH estimation of methanol- and acetonitrile-water buffered mobile phases up to 80% and 60%, respectively, in volume of organic modifier from initial aqueous buffer pH and buffer concentration (before adding the organic modifier) between 0.001 and 0.01 mol L-1. From both the estimated pH values of the mobile phase and the estimated pKa of the ionisable analytes, it is possible to predict the degree of ionisation of the analytes and therefore, the interpretation of acidbase analytes behaviour in a particular hydroorganic buffered mobile phase. Nitromethane has several properties that make it an interesting solvent for capillary electrophoresis especially for lipophilic analytes that are not sufficiently soluble in water. In the present thesis we investigated the change of electrophoretically relevant analyte properties (mobilities and pKa values) in nitromethane in dependence on the most important experimental conditions determined by the background electrolyte: the ionic strength and the pH. Sertindole, an atypical antipsychotic drug, was separated by capillary electrophoresis from its two main metabolites norsertindole and dehydrosertindole. The low solubility of the analytes in water was overcome by the use of methanol and acetonitrile as solvents for the background electrolyte. "