Development and validation of a high-performance thin-layer chromatographic method for the simultaneous determination of levamisole and cocaine in seized cocaine sample

Abstract

Cocaine is the second most illicit drug worldwide. Levamisole, an anthelminthic drug, has been identified as a cocaine adulterant in the United States since the last decade. Now, its presence has increasingly been discovered in street cocaine samples seized in India. Recently, it has been observed in many street cocaine samples seized by investigation agencies in India. Due to the incidence of toxicity caused by this contamination which has been increasing rapidly since 2002, it is important to understand the chemical separation, identification, and quantification of this drug. In the present study, an attempt has been made to develop a new high-performance thin-layer chromatographic (HPTLC) method for the simultaneous discrimination and quantification of levamisole in seized cocaine samples. Chromatography was performed using a pre-coated silica gel aluminum plate as the stationary phase, and the mobile phase cyclohexane—toluene—diethyl amine (75:15:10) was able to discriminate between cocaine hydrochloride and levamisole hydrochloride significantly. Densitometric analysis was performed in the absorbance mode at 230 nm. The linear regression analysis of data for the calibration curve showed good linearity over a concentration range of 100–1200 ng per band and 200–2400 ng per band with a regression value of 0.997 and 0.995 for levamisole hydrochloride and cocaine hydrochloride, respectively. The developed method is used to quantify cocaine content as well as to estimate the concentration of adulterant levamisole. The method was validated according to the International Conference on Harmonization (ICH) guidelines and can be used in the identification and quantification of levamisole and cocaine in seized cocaine samples. The present method is simple, reproducible, and repeatable, which can easily be performed in any laboratory.