High sensitivity analysis of oxprenolol in urine by capillary electrophoresis with C18 packed on-line preconcentrator

High sensitivity analysis of oxprenolol in spiked human urine has been performed by capillary zone electrophoresis (CZE) in ammonium formate buffer pH 2.5 using an uncoated capillary with 1 cm length C18 on-capillary preconcentrator at the inlet side. The preconcentrator was fabricated in laboratory using the packing method and not encapped C18 5 μm particles as stationary phase material. The packed path was retained into the capillary by sintered stationary phase frits. Before running the CZE analysis, the oxprenolol was eluted from the preconcentrator by injecting a short plug of acetonitrile/water mixtures. With respect to classical CZE, the use of on-line preconcentrator widely increased the method sensitivity allowing the detection of the drug at 0.5 ng/mL (injected concentration). The method showed a linear response in the range of 1-150 ng/mL oxprenolol standard compound. The intra-day repeatability (n = 11) R.S.D. values for migration time, peak area and normalized peak area were 0.72%, 3.96% and 3.66%, respectively, while inter-day repeatability (n = 5 days) R.S.D. values were 2.74%, 9.41% and 9.83%, respectively. The method was successfully applied to the analysis of oxprenolol in extracted urine spiked at 250 pg/mL (oxprenolol LOQ concentration in urine).