Comparison of sample preparation methods for zolpidem extraction from hair

The reported concentration of zolpidem in hair after a single administration is inconsistent between research papers by Villain et al. (Forensic Sci Int 143:157–161, 2004) in France (1.8–9.8 pg/mg) and Cui et al. (J Anal Toxicol 37:369–375, 2013) in China (135.0–554.6 pg/mg). In these two studies, the extraction methods used and ethnic origin of the hair samples were different. To address the differences in observed concentrations, tentative peak-area-based extraction efficiency of zolpidem from Japanese human hair was investigated using different sample pretreatment (cut into small pieces or powdered) and extraction methods. Both black and white hair samples derived from a gray-haired donor were analyzed separately. The method of micropulverized extraction (MPE) with 3.0 M ammonium phosphate (pH 8.4) resulted in the highest extraction efficiency. The extraction efficiency of the solid–liquid extraction method with 0.1 M sodium hydroxide was 77–89 % that of the MPE method for both cut and powdered samples. On the other hand, the extraction efficiency of the phosphate buffer (PB) method using solid–liquid extraction with 3.0 M ammonium phosphate (pH 8.4) was quite low (5.2–17 % of the MPE method) when pulverization was not performed prior to extraction. Therefore, the use of the PB method is discouraged for cut samples in the case of zolpidem analysis in hair. The observed tight interaction between zolpidem and Japanese black hair supports the reported high concentration of zolpidem in Asian black hair samples.