Analysis of methamphetamine in urine by GC/MS coupled with solid-phase dispersive extraction and solid-phase derivatization

In this study, we investigated a solid-phase dispersive extraction (SPDE) method and solid-phase derivatization method using the same solid-phase gel to extract methamphetamine (MA) from urine samples more efficiently and perform trifluoroacetic acid (TFA) derivatization for MA analysis by gas chromatography/mass spectrometry (GC/MS). N-Methylbenzylamine (NMe-BA) was added to the urine sample as a surrogate, and MA was extracted by SPDE using Oasis^® HLB gel as a solid-phase agent. After drying the solid-phase gel of the SPDE, anhydrous TFA was added to the MA-absorbed HLB gel in order to derivatize MA with TFA on the solid-phase, followed by elution of the TFA derivative from this gel using ethyl acetate. As a validation of the analytical method, the limit of detection (S/N = 3) and the limit of quantification (S/N > 10) of MA were 0.002 µg/mL and 0.01 µg/mL, respectively. And the average recovery rate was 97.6–100.1%, repeatability was 5.6–10.7%, and intermediate precision was 10.1–11.4% for low (0.02 µg/mL), intermediate (0.1 µg/mL), and high (1 µg/mL) concentrations of MA added in urine. The developed pretreatment method enabled continuous extraction, cleanup, and TFA derivatization of urinary MA on the same solid-phase. Thus, urinary MA can be analyzed easily, rapidly, and with high sensitivity and accuracy.