Centrifuge microextraction coupled with sweeping–MEKC to analyze trace steroid hormones in urine samples

A novel method that combines two concentration techniques, off-line centrifuge microextraction (CME) and on-line sweeping, is used to determine trace steroids in urine by micellar electrokinetic chromatography (MEKC). The CME–sweeping–MEKC is a promising technique, which has a variety of merits such as high sensitivity, rapid operation, minimal cost, and high sample throughput capability. Using CME–sweeping, over a 500-fold increase in sensitivity could be obtained as compared with the normal hydrodynamic injection without sample stacking. The linear range was 0.05–1 μg mL−1 with the square of the correlation coefficients ranging from 0.9998 to 0.9999. Detection limits (S/N = 3) were 5–15 ng mL−1 using a photodiode array UV detection at a wavelength of 240 nm. The relative standard deviations were between 2.8% and 3.5% (n = 5, progesterone as the internal standard). The diode array UV spectrum used can distinguish the analytes from the interference in the complex sample matrix, which is useful in biological and clinical sample analysis.