Analysis of drugs in hair is often used as a routine method to obtain detailed information about drug ingestion. However, few studies have been conducted on desposition of synthetic cannabinoids including cyclopropylindoles (UR-144 and XLR-11) and their metabolites in hair. UR-144 and XLR-11 have been widely abused and controlled in South Korea recently. Identification of metabolites in hair can be an important proof of synthetic cannabinoids use because it can exclude the possibility of passive smoke exposure. In this study, we described a quantitative method of UR-144 and XLR-11 and their metabolites(UR-144 N-5- hydroxypentyl, UR-144 N-pentanoic acid and XLR-11 4-hydroxypentyl) in hair by liquid chromatography with ESI-MS/MS.

The target drugs were extracted in hair by alkaline hydrolysis followed by liquid-liquid extraction(LLE) and solid phase extraction(SPE). After hydrolysis, 1mL of 0.1M sodium acetate buffer (pH 4.5) and 0.2mL of acetic acid were added into hair samples and the samples were extracted with 2mL of n-hexane:ethyl acetate (9:1). The organic extract was transferred into a disposable test tube and evaporated to dryness at 45°C under a gentle stream of nitrogen. The extract was reconstituted with 2ml acetate buffer and SPE was performed using automatic SPE equipment, using hydrophobic and cation exchange SPE column. The extract was evaporated, filtered and analyzed by UHPLC-MS-MS with electrospray ion source in positive-ionization mode. JWH-018-d₉ and JWH-018 N-(5-hydroxypentyl) metabolite-d₅ (50mL, 100pg/mL internal standard mixed solution) were used as internal standards for the parent drugs (UR-144 and XLR-11) and their metabolites, respectively.

Chromatographic separation was completed within 15min. No interferences were detected in 10 blank hair samples. In intra- and inter-assay precision and accuracy study, CV (%) and bias (%) were below 10. The limit of detection was 0.1 to 2pg/mg and the limit of quantification was 0.2 to 2pg/mg, respectively. The validation results proved that the method was selective, accurate and precise with acceptable linearity within calibration range. No significant variation was observed by different sources of matrices.

This method was applied to hair samples from 17 individual suspects of XLR-11 or UR-144 use. The range of concentration of XLR-11 and UR-144 were 267.8 ~ 5618.8pg/mg and 0 ~ 7.87pg/mg, respectively. The range of concentration of UR- 144 N-5-hydroxypentyl and UR-144 N-pentanoic acid were 1.2 ~ 299.5pg/mg and 0.5 ~ 127.8pg/mg, respectively. The range of concentration of XLR-11 4-hydroxypentyl was 0 ~ 11.21pg/mg. UR- 144 N-4-hydroxypentyl was not detected in all cases. We can assume that UR-144 N-5-hydroxypentyl and UR-144 N-pentanoic acid are the major detectable compounds in hair in case of XLR-11 intake.