Dispersive liquid-liquid microextraction based on solidification of floating organic drop and high-performance liquid chromatography to the analysis of cocaine's major adulterants in human urine

Abstract

A simple method has been proposed for the determination of cocaine's major adulterants (caffeine, levamisole, lidocaine, phenacetin, diltiazem, and hydroxyzine) in human urine by dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) in combination with high-performance liquid chromatography - photodiode array detector (HPLC-PDA). The reversed-phase chromatographic separation was obtained with a column C18 extended (250×4.6mm; 5μm; 80Å) in gradient elution mode using acetonitrile-trifluoroacetic acid 0.026% (v,v) (pH=2.5) at 1mLmin^-1 as mobile phase, at 25°C, and detection at 235nm. The analysis time was 25min. This condition had the best resolution factors (>1.15), retention factors (>0.68), number of plates (>2094.9), and separation factors (>1.05) for all targets, indicating a good separation. The kind of extraction and dispersive solvent were investigated for unifactorial design. The buffer pH, the volume of extraction and disperser solvent, and the amount of salt were optimized for full factorial design. Under optimum conditions, human urine samples were alkalized with 0.5M sodium phosphate buffer (pH 10) and added to sodium chloride (20%m/v). Acetonitrile (150μL) and 1-dodecanol (30μL) were used as dispersive and extraction solvent, respectively. The method presented linear range of 312.5-3125ngmL^-1 to caffeine and levamisole and 187.5-1875ngmL^-1 to lidocaine, phenacetin, diltiazem, and hydroxyzine. The limit of quantification was 187.5ngmL^-1 to lidocaine, phenacetin, diltiazem, and hydroxyzine and 312.5ngmL^-1 for caffeine and levamisole. The recovery mean values were between 6.0 and 42.6%. The method showed good precision and accuracy, with within- and between-run relative standard deviation and relative error less than 15%. The samples were stable after freeze-thaw cycle and short-term room temperature stability tests. Besides, this method was satisfactorily applied in urine of cocaine users. It is expected that this method, which was the first to combine the use of DLLME-SFO and HPLC-PDA for the determination of cocaine's major adulterants in human urine, will contribute to the accuracy in the diagnosis of acute intoxication, the proper planning of therapeutic measures, as well as to the favorable prognostic of cocaine intoxicated patients.

Keywords: Dispersive liquid-liquid microextraction based on solidification of floating organic drop; Drug adulteration; Liquid chromatography; Street cocaine; Urine toxicology analysis.