Extraction and preconcentration of residual solvents from herbal medicines by headspace-micro solid phase extraction combined with deep eutectic solvent-based dispersive liquid–liquid microextraction

In this study, a headspace-micro solid phase extraction method combined with dispersive liquid–liquid microextraction was utilized in the extraction of residual solvents from herbal-based medicine samples. A home-made extraction device was used for headspace-micro solid phase extraction by transferring a proper amount of the samples into the device and adsorption of the analytes onto octadecylsilane from the headspace of sample solution. The adsorbed analytes were eluted by dimethylformamide. The eluate was mixed with a few microliters of tetrabutylammonium chloride: p-aminophenol: linalool deep eutectic solvent [1:1:1, mol: mol: mol]. It was used in the microextraction step to preconcentrate the analytes. The enriched analytes were determined by gas chromatography equipped with flame ionization detector. Under optimized conditions, the method validation was done by International Council of Harmonization protocol and the limits of detection and quantification were in the ranges of 0.81–1.2 and 2.8–4.1 ng g−1, respectively. Wide linearity was obtained with a correlation coefficient ≥ 0.994 for the calibration curves. Relative standard deviation values for the repeated analyses in the same day (n = 6) and different days (n = 4) were ≤ 4.9% at a concentration of 5.0 ng g−1 of each analyte. The method was successful in determination of the analytes in herbal medicines at trace levels (ng g−1).