Sensitive analysis of two barbiturates in human urine by capillary electrophoresis with sample stacking induced by moving reaction boundary

An on-line stacking method based on moving reaction boundary (MRB) was developed for the sensitive determination of barbital and phenobarbital in human urine via capillary electrophoresis (CE). The optimized conditions for the method are: 60 mmol L−1 pH 11.0 Gly-NaOH as the background electrolyte, 10 mmol L−1 pH 5.5 Gly-HCl as sample buffer, secobarbital as the internal standard (IS), 12.5 kV, 1.4 psi 10 s sample injection, 75 μm ID 60.2 cm total length (50 cm effective length) capillary and 214 nm detect wavelength. Under the optimized conditions, the method can well stack and separate barbital and phenobarbital in urine samples and result in 20.5-fold and 22.6-fold improvement in concentration sensitivity for barbital and phenobarbital, respectively. Furthermore, the method holds: (1) good linear calibration functions for the two target compounds (correlation coefficients r > 0.999), (2) low limits of detection (0.27 μg mL−1 for barbital and 0.26 μg mL−1 for phenobarbital), (3) low limits of quantification (0.92 μg mL−1 for barbital and 0.87 μg mL−1 for phenobarbital), (4) good precision (R.S.D. of intra-day and inter-day less than 5.38% for barbital and 1.67% for phenobarbital, respectively) and (5) high recoveries at three concentration levels (90.27-106.36% for barbital and 93.05-113.60% for phenobarbital in urine). The method is simple, sensitive and efficient, and can fit to the need of clinical and forensic toxicology.