Determination of a basic drug, bambuterol, in human plasma by capillary electrophoresis using double stacking for large volume injection and supported liquid membranes for sample pretreatment.

In this work we show the potential of using a double stacking procedure based on field enhancement as a means to increase the concentration sensitivity in CZE analysis of human plasma extracted by the supported liquid membrane (SLM) technique. A basic drug, bambuterol, was used as a model substance. The low ionic strength of the SLM extract makes this pretreatment technique compatible with the double stacking sequence. No significant loss of separation performance was observed when 3 microliters of SLM extract was concentrated by the CZE double stacking sequence. Almost no visible difference was seen between the electropherograms after enrichment of a plasma blank and an aqueous blank. Good performance of the whole procedure was demonstrated and detection limits in the low nM range were obtained in spite of the relatively weak UV absorbance of bambuterol. The developed procedure was evaluated for both achiral and chiral separation. In the latter approach chiral selectivity was obtained by adding cyclodextrin to the separation electrolyte.