Two DFSA cases involving midazolam clarified by the micro-segmental hair analyses

Purpose In this study, an analytical procedure to identify trace amounts of drug in hair based on micro-segmental hair analysis was presented. The method also can be used to estimate the time of drug ingestion at daily precision by cutting a single hair into sub-millimeter segments which correspond to daily hair growth. Methods A method was established for efficient extraction of midazolam, one of the most frequently detected compound in drug-facilitated sexual assault (DFSA) cases, from each 0.4-mm hair segment and validated by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS/MS). Moreover, two DFSA cases were used to compare the micro-segmental hair analysis with the 1- cm segmental analysis method. Results The validation showed a lower limit of quantification of 0.5 pg/mm for midazolam, with intraday and interday accuracies (bias) from − 5.2 to 0.9%. The micro-segmental hair analysis method was applied to proximal 1-cm hair segment including hair bulbs in two DFSA cases. The micro-segmental hair analysis results in case 1 showed midazolam in the S15–S17 (5.6–6.8 mm from hair bulb) in a concentration range from 0.5 to 0.9 pg/mm, and the concentrations of midazolam in all hair micro-segments (0–1 cm from the scalp) in case 2 were from 0.5 to 2.0 pg/mm. Conclusions Comparison with the conventional method revealed that micro-segmental hair analysis may enhance the utility of hair drug testing and strengthen probative force in DFSA cases.