A high-performance thin-layer chromatographic technique to screen cocaine in urine samples

Qualitative identification of cocaine and its metabolites in urine samples is generally carried out by an immunoassay technique followed by a gas chromatographic/mass spectrometric confirmation of presumptive positives. Nevertheless, other chromatographic techniques such as thin-layer chromatography or gas chromatography could also be used to screen several types of drugs of abuse especially for forensic and legal purposes. In the present work, the capability of high performance thin-layer chromatography (HPTLC) to detect cocaine in urine samples and discriminate it from interfering substances (local anaesthetic, caffeine and nicotine) was studied. Twenty urine samples of drug addicts were submitted to the HPTLC method. Unaltered cocaine present in the urine samples and cocaine obtained after methylation of benzoylecgonine (main cocaine metabolite) with diazomethane were detected in all tested samples. In conclusion, the proposed HPTLC method showed to be useful to detect cocaine in biological matrices.