Synthetic cannabinoids in hair – Pragmatic approach for method updates, compound prevalences and concentration ranges in authentic hair samples

Highlights: • Comprehensive method validation for 72 synthetic cannabinoids in hair. • Pragmatic approach for method re-validation after adding new compounds. • Semi-quantitative data of more than 160 positive authentic hair samples. • Concentration ranges and prevalence of 52 synthetic cannabinoids in hair. • Comprehensive interpretation of qualitative and semi-quantitative data. - Abstract: Since the first detection of synthetic cannabinoids (SCs) in so-called 'legal high' products (e.g. 'Spice') sold as legal alternatives to marihuana, the rapid development of this class of designer drugs poses a great challenge for analytical laboratories. The aim of this study was the comprehensive validation of an up-to-date LC-MS/MS method for detection of SCs in human hair for the purpose of drug abstinence testing and evaluation of a pragmatic re-validation approach for frequent method adaption. The validation demonstrated low quantification limits (0.5–5.0 pg mg⁻¹) and acceptable selectivity, linearity, accuracy, and precision for 72 SCs. High matrix effects have been taken into consideration as a major limitation of the method. The partial re-validation approach proved to be an appropriate compromise between reduced validation effort and sufficient control of the method performance enabling analysts to keep pace with the dynamics of the drug market. The analysis of 294 authentic samples resulted in 163 positive samples and showed a broad concentration range (−1) for 52 SCs in hair with up to 17 different compounds detected in a single hair sample. Periods of detection between one and 58 months were observed for single compounds in hair. Regarding the interpretation of analytical findings semi-quantitative concentrations were considered sufficient for a rough classification of the intensity of drug exposure in (i) passive exposure or exposure in the distant past (lower pg mg⁻¹ range), (ii) more intense exposure (elevated concentration range, >20 pg mg⁻¹ (upper 25th-percentile)), and (iii) heavy/recent exposure (>150 pg mg⁻¹).