GC Determination of Methamphetamine in Urine with Solid Phase Extraction Optimized by Response Surface Method

Response surface analysis with 3 factors and at 3 levels was applied to the optimization of conditions of solid phase extraction (SPE) of methamphetamine (MPM) in human urine, and the optimum conditions found were as follows: ① acidity of the urine sample: pH 9.35 (PBS); ② flow-rate of sample introduction: 0.9 mL·min-1; ③ appropriate volume of ethyl acetate as eluant: 3.2 mL. The eluate obtained was evaporated to dryness by N2-blowing, and the residue was taken up with 100 μL of ethanol solution of the internal standard of SKF525-A, and the solution was used for GC analysis. Chromatographic separation was carried out on AB-5 capillary column with volume of sample introduction of 1 μL. Nitrogen-phosphorus detector was used in the determination. Linear relationship between values of peak area and mass concentration of methamphetamine was kept in the range of 0.10-10.0 mg·L-1 with detection limit (3S/N) of 0.062 mg·L-1. Values of within-day and inter-day RSD′s (n=6) obtained were same to be less than 5%.