Extraction, identification, and quantification of cocaine impregnated in rubber sheets: a forensic case study from Sri Lanka

Abstract

Cocaine trafficking in the form of textile impregnation into ordinary materials presents a significant challenge for forensic drug analysis and is routinely encountered as a concealment method. This article reports a forensic case study involving four rubber sheets received by the Government Analyst’s Department of Sri Lanka. Spectroscopy has been a popular and successful testing method used for in situ screening of cocaine in textiles and other matrices. The exhibits, marked HL₁, HL₂, CL₁, and CL₂, were examined for the presence of cocaine. Cocaine was extracted using a methanol:chloroform solvent system, identified by the Scott colour test, thin layer chromatography, and gas chromatography–mass spectrometry, and quantified using gas chromatography–flame ionization detection with tetracosane as the internal standard. The method was linear over a concentration range of 100ppm to 1000ppm with a coefficient of determination (R 2) at 0.975 and acceptable precision and accuracy. A simple and accurate GC-FID spectroscopy method for the analysis and quantification of a cocaine analogue impregnated in textiles has been developed using this case study. The primary impregnated sheets, HL₂ and CL₂, contained approximately 25.325% and 32.094% cocaine by weight, respectively, while HL₁ and CL₁ contained only trace-level contamination consistent with their use as covering sheets. The study determines that solvent extraction followed by confirmatory instrumental analysis provides a consistent approach for the forensic examination of cocaine concealed in rubber matrices. The method has the potential to be further developed and implemented in real world forensic cases.