Hair analysis for methamphetamine, ketamine, morphine and codeine by cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography

Abstract

We established a capillary electrophoretic method with high sensitivity and specificity for testing hair taken from addicts. After pretreatment of hair sample, the cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-Sweep-MEKC) was used to test for the presence of abused drugs in human hair. These drugs include morphine (M), codeine (C), ketamine (K) and methamphetamine (MA). First, an uncoated fused-silica capillary (40 cm, 50 μm I.D.) was filled with phosphate buffer (50 mM, pH 2.5) containing 30% methanol, followed by high conductivity buffer (100 mM phosphate, 6.9 kPa for 99.9 s). Electrokinetic injection (10 kV, 600 s) was used to load samples and to enhance sensitivity. Stacking steps and separations were performed at −20 kV with detection at 200 nm, using phosphate buffer (25 mM, pH 2.5) containing 20% methanol and 100 mM sodium dodecyl sulfate. Using CSEI-Sweep-MEKC, the analytes could be simultaneously analyzed and have a detection limit down to the level of picogram per milligram hair. During method validation, calibration plots were linear ( r ≥ 0.999) over a range of 0.15–80 ng/mg hair for MA and K, 0.3–30 ng/mg hair for C and 0.5–50 ng/mg hair for M. The limits of detection were 50 pg/mg hair for MA and K, 100 pg/mg hair for C and 200 pg/mg hair for M (S/N = 3, sampling 600 s at 10 kV). Our method was applied for analysis of real hair samples taken from addicts. The addicts’ specimens were also analyzed by LC–MS, and showed good coincidence of results. This method has proven feasible for application in detecting trace levels of abused drugs in forensic analysis.