Enantioselective determination of (R)-zopiclone and (S)-zopiclone (eszopiclone) in human hair by micropulverized extraction and chiral liquid chromatography/high resolution mass spectrometry

- Micropulverized extraction was utilized for 5 mg of hair sample to minimize the degradation of zopiclone and for rapid and facile operation.
- An excellent chiral separation (Rs = 5.0) of zopiclone was achieved using a chiral stationary phase and a volatile mobile phase.
- Lowest limit of quantification for each zopiclone enantiomer was 0.50 pg/mg using 5 mg of hair sample.

Zopiclone and its (S)-enantiomer (eszopiclone) are commonly prescribed for insomnia. Despite the high demand for enantioselective differentiation, the chiral analysis of zopiclone in hair has not been reported. In this study, a method for the enantioselective quantification of zopiclone in human hair was developed. The extraction medium and duration were optimized using real eszopiclone-positive hair samples. Specifically, micropulverized extraction with 3.0 M ammonium phosphate buffer (pH 8.4) involving salting-out assisted liquid-liquid extraction with acetonitrile was utilized to minimize the degradation of zopiclone and for rapid and facile operation. On the other hand, recovery of the conventional solid-liquid extraction involved overnight soaking in 3.0 M ammonium phosphate buffer (pH 8.4) was only 0.58 ± 0.12% of the maximum recovery achieved by the present method due to the decomposition in the phosphate buffer. An excellent chiral separation (Rs = 5.0) was achieved using a chiral stationary phase comprising cellulose tris(3,5-dichlorophenylcarbamate) and a volatile mobile phase of 10 mM ammonium carbonate (pH 8.0)-acetonitrile (25:75, v/v). Detection was carried out using liquid chromatography/high resolution mass spectrometry (LC/HRMS) with electrospray ionization. A Q Exactive mass spectrometer equipped with a quadrupole-Orbitrap analyzer was used for detection. The concentration of 0.50 pg/mg was defined as the lowest limit of quantification using 5 mg of hair sample. Using the developed approach, the concentration of eszopiclone in hair after a single 2-mg dose was found to be 441 pg/mg, which was higher than all the reported values regarding a single administration of zopiclone. After daily administration of racemic zopiclone (3.75 mg/day), the concentrations of (R)-enantiomer and (S)-enantiomer in the black hair were 5.30-8.31 ng/mg and 7.96-12.8 ng/mg, respectively, and the concentration of the (S)-enantiomer was always higher than that of the (R)-enantiomer due to the enantioselective difference in the pharmacokinetics.