Determination of cocaine in spiked saliva using liquid-liquid extraction and gas chromatography- mass selective detector methods

Abstract

Over the past few years, there have been a rapid development in forensic drug testing in biological specimen. Urine and blood are the most commonly used biological matrices for detection of cocaine. However, there are some disadvantages such as invasive to the privacy and personal safety of the donor as well as the instability of the cocaine in that biological matrix. Therefore, in this study, saliva has been proposed as an alternative matrix since the collection of saliva is non-invasive and rapid. In this study, the liquid-liquid extraction (LLE) method was utilized to extract cocaine from saliva before the analysis was done using optimized conditions of gas chromatography and mass selective detector (GC-MSD). Diethylether: isopropanol with volume to solvent ratio 3:5 was used in this study. The optimized method was validated by evaluating calibration curve, linearity, limit of detection (LOD), limit of quantification (LOQ), percentage recovery and intra-assay and inter-assay precision accuracy. From the calibration curve (0.5-10 ppm), good coefficient of determination was obtained at r² = 0.9994. LOD and LOQ were obtained at 0.29 and 0.97 ppm respectively. From the precision and accuracy analysis of intra and inter-day, lower coefficient variance (intra: 1.96%; inter: 0.79%) and high accuracy were attained (intra: 102.33%; inter: 101.20%). A mean recovery of 85.20% with acceptable coefficient of variance (CV < 6%) were also acquired. Finally, the stability of cocaine in the saliva were studied for 13 days. The analysis found that cocaine can be recovered with a mean recovery > 70 % without addition of any preservatives or buffers. The study showed that the analysis of cocaine in saliva is robust, hence it can be used as an alternative matrix for forensic drug testing.