An on-line stacking capillary electrophoresis method for the analysis of Δ(9)-tetrahydrocannabinol and its metabolites.

The objective of this study was to establish a practical and reliable analytical method for monitoring trace amounts of Δ(9)-tetrahydrocannabinol (THC) and its metabolites in biological samples. A novel on-line preconcentration capillary electrophoresis method combining large volume sample injection, anion selective exhaustive injection and sweeping was developed to enhance analytical sensitivity. A background buffer composed with 30mM phosphate buffer (pH 2.5) containing 40% methanol and 100mM SDS was used to suppress the electroosmotic flow of the uncoated fused silica capillary (40cm×50μm i.d.). High conductivity buffer (200mM phosphate, pH 2.5) was injected for analyte accumulation. The samples, prepared in phosphate buffer or Tris buffer, were introduced by hydrodynamic injection and electrokinetic injection. After sweeping, the separation was performed in micellar electrokinetic chromatography (MEKC) mode at -15kV. During the method validation, the coefficient of determination of the regression curve was measured at greater than 0.993, and the relative standard deviation and relative error were lower than 11.06% and 9.24%, respectively. Under optimized conditions, an improvement of up to 2000-fold higher sensitivity was achieved. This method was applied to the analysis of urine samples, indicating that it could be satisfactorily utilized in the toxicological and clinical monitoring of cannabis.