Determination of cocaine adulterants in human urine by dispersive liquid-liquid microextraction and high-performance liquid chromatography

This study aimed to determine simultaneously five major street cocaine adulterants (caffeine, lidocaine, phenacetin, diltiazem, and hydroxyzine) in human urine by dispersive liquid-liquid microextraction (DLLME) and high-performance liquid chromatography. The chromatographic separation was obtained in gradient elution mode using methanol:water plus trifluoroacetic acid 0.15% (v/v) (pH=1.9) at 1mLmin(-1) as mobile phase, at 25 degrees C, detection at 235nm, and analysis time of 20min. The effect of major DLLME operating parameters on extraction efficiency was explored using the multifactorial experimental design approach. The optimum extraction condition was set as 4mL human urine sample alkalized with 0.5M sodium phosphate buffer (pH 12), NaCl (15%, m/v), 300L acetonitrile (dispersive solvent), and 800L chloroform (extraction solvent). Linear response (r(2)0.99) was obtained in the range of 180-1500ngmL(-1) with suitable selectivity, quantification limit (180ngmL(-1)), mean recoveries (33.43-76.63%), and showing relative standard deviation and error (within and between-day assays) 15%. The analytes were stable after a freeze-thaw cycle and a short-term room temperature stability test. This method was successfully applied in real samples of cocaine users, suggesting that our study may contribute to the appropriate treatment of cocaine dependence or with the cases of cocaine acute intoxication.