Application of poly(methacrylic acid‐ethylene glycol dimethacrylate) monolith microextraction coupled with capillary zone electrophoresis to the determination of opiates in human urine

A novel poly(methacrylic acid‐ethylene glycol dimethacrylate) (MAA‐EGDMA) monolith microextraction method coupled with CZE was proposed for rapidly determining a mixture of opiates comprising heroin, 6‐monoacetylmorphine, morphine, codeine, papaverine, and narcotine in human urine. The extraction device contained a regular plastic syringe, the poly(MAA‐EGDMA) monolithic capillary tube (530 µm id×3 cm) and a plastic pinhead, which connected the monolithic capillary tube and the syringe without leakage. In the polymer monolith microextraction, the sample solution was ejected via the monolithic capillary tube by a programmable syringe pump, followed by desorption with an aliquot of appropriate solution, which was collected into a vial for the subsequent analysis by CZE. The best separation was achieved using a buffer composed of 0.1 M disodium hydrogen phosphate (adjusted to pH 4.5 with 1 M hydrochloric acid) and 20% methanol v/v with temperature and voltage of 25°C and 25 kV, respectively. By applying electrokinetic injection with field‐enhanced sample stacking, detection limits of 6.6–19.5 ng/mL were achieved. Excellent method of reproducibility was found over a linear range of 80–2000 ng/mL.