Improved dispersive liquid–liquid microextraction based on the solidification of floating organic droplet method with a binary mixed solvent applied for determination of nicotine and cotinine in urine

Abstract

A fast, simple and environmentally friendly method to determine nicotine and cotinine in urine has been developed using dispersive liquid–liquid microextraction based on solidification of floating organic droplet (DLLME-SFO) with a binary mixed extractant as the pretreatment method and high performance liquid chromatography with an ultraviolet detector (HPLC-UVD) as the analysis system. The nicotine and cotinine in urine samples were extracted using the binary mixed solvent of undecanol and CHCl₃ (v/v = 1 : 1) during the DLLME-SFO procedure. The employment of the mixed solvent had significantly improved the extraction efficiency of cotinine. Several crucial experiment parameters were evaluated, including the type and volume of extract solvent, type of dispersive solvent, pH of the aqueous phase, concentration of sodium chloride in the urine samples and extraction time. Under the optimal conditions, good linearity was observed in the range of 0.01–5.00 μg mL⁻¹ for nicotine and cotinine with correlation coefficients of 0.9993 and 0.9996 respectively, and the method detection limit (MLD) was 0.002 μg mL⁻¹ for both analytes. The proposed method was applied to urine sample analysis and the spiked recoveries of nicotine and cotinine were in the range of 78.0–105.0% and 72.0–86.7% respectively, with the relative standard deviations (RSDs) in the range of 6.02–7.28% and 2.94–8.43% respectively.