Combining poly (methacrylic acid-co-ethylene glycol dimethacrylate) monolith microextraction and on-line pre-concentration-capillary electrophoresis for analysis of ephedrine and pseudoephedrine in human plasma and urine

A method based on poly (methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith microextraction (PMME) and field-enhanced sample injection (FESI) pre-concentration technique was proposed for sensitive capillary electrophoresis-ultraviolet (CE-UV) analysis of ephedrine (E) and pseudoephedrine (PE) in human plasma and urine. The PMME device consisted of a regular plastic syringe (1 mL), a poly (MAA-EGDMA) monolithic capillary (2 cm × 530 μm I.D.) and a plastic pinhead connecting the former two components seamlessly. The extraction was achieved by driving the sample solution through the monolithic capillary tube using a syringe pump, for the desorption step, an aliquot of organic solvent, which normally provided an excellent medium to ensure direct compatibility for FESI in CE, was injected via the monolithic capillary and collected into a vial for subsequent analysis by CZE. The best separation was achieved using a buffer composed of 0.1 M phosphate electrolyte (pH 2.5) and 10% acetonitrile (v/v). The combination of both pre-concentration procedures allowed the detection limits of the analytes down to 5.3 ng/mL and 8.0 ng/mL in human plasma and urine, respectively. Excellent method of reproducibility was found over a linear range 50–5000 ng/mL in plasma and urine sample. Plasma and urine samples from volunteers receiving pseudoephedrine have also been successfully analysed.