Miniaturized supported liquid membrane device for selective on-line enrichment of basic drugs in plasma combined with capillary zone electrophoresis.

A hollow fiber miniaturized supported liquid membrane (SLM) device for sample preparation is connected on-line with capillary electrophoresis and used for determination of a basic drug, bambuterol, in human plasma. The analyte is extracted from the outside of the hollow fiber (donor) through the liquid membrane (pores of the fiber impregnated with organic solvent) into the acceptor solution in the fiber lumen. The process is driven by differences in pH between the donor and acceptor solution. The whole volume of the acceptor solution can then be injected into the CZE capillary by using the double-stacking procedure for large volume-injection. Very clean extracts of low ionic strength are obtained from the SLM treatment, making this sample pretreatment method compatible with the CZE double-stacking procedure, which in turn makes it possible to inject large volumes of sample onto the separation capillary. Good performance of the whole procedure is demonstrated, and detection limits in the low nanomolar range were obtained in spite of the relatively weak UV absorbance of bambuterol. Extractions through the miniaturized SLM unit can be performed for 5-6 h without regenerating the fiber. The regeneration procedure was tested, and no relevant changes in the performance of the extraction could be found after seven regenerations, allowing the same fiber to be used for a week.

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.

Micro-CLC as an interface between SLM extraction and CZE for enhancement of sensitivity and selectivity in bioanalysis of drugs.

This work demonstrates the high selectivity and sensitivity obtainable in bioanalysis using the supported liquid membrane (SLM) technique coupled on line with capillary zone electrophoresis (CZE) through a micro-column liquid chromatography (CLC) interface. The system utilizes two selective, sequential enrichment steps before the third analyte focusing and separation step with double-stacking CZE. The enantiomers of bambuterol in human plasma can be concentrated about 40,000 times (approx. 6 times by the SLM treatment, approx. 17 times by micro-CLC focusing, and approx. 400 times by double-stacking CZE) on their way through the system, and extremely high selectivity is obtained. Determinations in the subnanomolar region are achievable for the enantiomers despite relatively weak UV absorbance. Good performance of the entire procedure is demonstrated and a method to increase the sample throughput is presented.

Sample preparation using a miniaturized supported liquid membrane device connected on-line to packed capillary liquid chromatography.

A miniaturized supported liquid membrane device has been developed for sample preparation and connected on-line to a packed capillary liquid chromatograph. The device consists of hydrophobic polypropylene hollow fiber, inserted and fastened in a cylindrical channel in a Kel-F piece. The pores of the fiber are filled with an organic solvent, in this study 6-undecanone, thus forming a liquid membrane. The sample is pumped on the outside of the hollow fiber (donor), and the analytes are selectively enriched and trapped in the fiber lumen (acceptor). With this approach, the volume of the acceptor solution can be kept as low as 1-2 µL. This stagnant acceptor solution is then transferred through capillaries attached to the fiber ends to the LC system. The system was tested with a secondary amine (bambuterol), as a model substance in aqueous standard solutions as well as in plasma. The best extraction efficiency in aqueous solution, with an acceptor volume of 1.9 µL, was 32.5% at a donor flow rate of 2.5 µL/min. At flow rates above 20 µL/min, the concentration enrichment per time unit was approximately constant, at 0.9 times/min, i.e., 9 times enrichment in about 10 min. The overall repeatability (RSD) for spiked plasma samples was ∼4% (n = 12). Linear calibration curves of peak area versus bambuterol concentration were obtained for both aqueous standard solutions and spiked plasma samples. The detection limit for bambuterol in plasma, after 10 min of extraction at a flow rate of 24 µL/min, was 80 nM.

Supported liquid membrane technique for selective sample workup of basic drugs in plasma prior to capillary zone electrophoresis.

The potential of using the supported liquid membrane (SLM) technique for pretreatment of plasma samples before analysis with capillary zone electrophoresis (CZE) has been investigated. A basic drug, bambuterol, was used as a model substance in a system, where either 6-undecanone or a mixture of di-n-hexyl ether (DHE) and tri-n-octyl phosphine oxide (TOPO) was used as membrane liquids. It was found that the electropherograms obtained after SLM enrichment of bambuterol in plasma samples were as clean as when aqueous samples containing the same substance were processed in the same way. The low ionic strength of the SLM treated blood plasma samples permitted subsequent sample stacking in the CZE step. The linearity of the detector signal for different concentrations of bambuterol in plasma was satisfactory from 50 to 1000 nmol/L with regression co-efficients of 0.997 using 6-undecanone as membrane liquid and 0.999 with the other liquid. In both systems, the confidence interval of the intercept included the origin. The detection limit was about 50 nmol/L. The long-term stability of the two membrane liquids proved adequate as a membrane lasted at least through the working day.