Analysis of ten abused drugs in urine by large volume sample stacking-sweeping capillary electrophoresis with an experimental design strategy.

A statistical tool equipped with Plackett-Burman design (PBD) and central composite design (CCD) was used for fast stacking analysis of ten frequently consumed drugs, namely codeine, morphine, methamphetamine, ketamine, alprazolam, clonazepam, diazepam, flunitrazepam, nitrazepam and oxazepam, by capillary electrophoresis (CE). This statistical design is expected to help quick analysis with few procedures, avoiding tedious work required because of the large number of variables or parameters. A large volume sample stacking (LVSS)-sweeping CE is developed for concentrating and analyzing the 10 abused drugs. First, phosphate buffer (50 mM, pH 2.3) containing methanol was filled into a capillary and then the extracted urine sample was loaded (1 psi, 200 s) to enhance sensitivity. The sweeping and separating steps were completed simultaneously by phosphate buffer (50 mM, pH 2.3) containing methanol and sodium dodecyl sulfate, within 15 min. Better resolution was obtained by the experimental design than the "one factor at a time" (OFAT) approach. During method validation, calibration plots were linear (r>0.998), over a range of 25-1500 ng/mL for the six benzodiazepines, methamphetamine and ketamine, and 50-3000 ng/mL for codeine and morphine. The RSD of precision and absolute RE of accuracy in intra-day and inter-day assays were below 14.54% and 16.61%, respectively. The minimum limits for detection (S/N=3) of analytes were in the range of 7.5-30 ng/mL. This stacking method increased sensitivity more than 200-fold and can be applied for detection of the presence of methamphetamine in an abuser's urine (3600 ng/mL), which was confirmed by GC-MS. The method is considered feasible for fast screening of abused drugs in urine.