Dispersive liquid-liquid microextraction, an effective tool for the determination of synthetic cannabinoids in oral fluid by liquid chromatography-tandem mass spectrometry

Abstract

In the present work, dispersive liquid-liquid microextraction (DLLME) was used to extract six synthetic cannabinoids (JWH-018, JWH-019, JWH-073, JWH-200, or WIN 55,225, JWH-250, and AM-694) from oral fluids. A rapid baseline separation of the analytes was achieved on a bidentate octadecyl silica hydride phase (Cogent Bidentate C₁₈; 4.6 mm × 250 mm, 4 μm) maintained at 37 °C, by eluting in isocratic conditions (water:acetonitrile (25:75, V/V)). Detection was performed using positive electrospray ionization-tandem mass spectrometry. The parameters affecting DLLME (pH and ionic strength of the aqueous phase, type and volume of the extractant and dispersive solvent, vortex and centrifugation time) were optimized for maximizing yields. In particular, using 0.5 mL of oral fluid, acetonitrile (1 mL), was identified as the best option, both as a solvent to precipitate proteins and as a dispersing solvent in the DLLME procedure. To select an extraction solvent, a low transition temperature mixture (LTTM; composed of sesamol and chlorine chloride with a molar ratio of 1:3) and dichloromethane were compared; the latter (100 μL) was proved to be a better extractant, with recoveries ranging from 73% to 101 % by vortexing for 2 min. The method was validated according to the guidelines of Food and Drug Administration bioanalytical methods: intra-day and inter-day precisions ranged between 4 % and 18 % depending on the spike level and analyte; limits of detection spanned from 2 to 18 ng/mL; matrix-matched calibration curves were characterized by determination coefficients greater than 0.9914. Finally, the extraction procedure was compared with previous methods and with innovative techniques, presenting superior reliability, rapidity, simplicity, inexpensiveness, and efficiency.

Keywords: Dispersive liquid-liquid microextraction; Illicit drugs; Microextraction techniques; Silica C-based column; Synthetic cannabinoids.

Graphical abstract

Fig. 1

Structures, exact masses and log P of the synthetic cannabinoids selected for this study.

Fig. 2

Chromatographic separation of the selected cannabinoids on (A) a bidentate C₁₈ silica hydride phase and on (B) an end-capped C₁₈ stationary phase.

Fig. 3

Comparison between two DLLME procedures based on the use of chloroform and the deep eutectic solvent chlorine chloride(sesamol)₃ as extractants. In this case, the chlorinated solvent offers better recovery yields for most analytes. DLLME: dispersive liquid-liquid microextraction.