Guerrero Serrano E.D., López-Rivadulla M.

Instituto de Medicina Legal, Servicio de Toxicología Forense, Facultad de Medicina, Universidad de Santiago de Compostela, Santiago de Compostela, Spain

The objective of this work is to present the analytical and statistical methodology that is used in forensic investigations in the local marketplace of heroin.
Methods. Analytical Procedures: the development of a method involving reversed-phase HPLC using PREOPT-W^® and a spreadsheet computer program, is described for the simultaneous qualitative and quantitative determination of heroin in illicitly manufactured street samples, containing by-products originating from opium (heroin, morphine, 6-monoacetylmorphine, acetylcodeine,noscapine, papaverine and acetylthebaol) and commonly occurring adulterants (piracetam, caffeine, acetaminophen), that have been found in Santiago de Compostela. The method utilizes simple sample dissolution followed by reversed-phase HPLC on a µ-Bondapack C18 column with methanol-water-perchloric acid as mobile phase. UV detection and quantification were carried out at 202, 230 and 252 nm with a PDA detector.
Statistical Procedures: Analytical data were processed using multivariate Chemometric techniques involving cluster analysis, principal component analysis (PCA), discriminant analysis, etc.
Results. The optimum linear gradient elution consisted of eleven steps with a total duration of 62 min. Excellent agreement between predicted and measured retention times with differences ranging from 0.5% to 10% was found. For calibration, all compounds showed a good linear relationship between peak area and concentration. With this method, the limits of absolute detection ranged from 0.014 µg/ml for acetylthebaol in the best case to 1.64 µg/ml for heroin in the worst case, depending on molar absorptivities. Subsequent statistical procedures are able to quickly identify sample relationships. PCA and cluster analysis revealed the occurrence of groupings between the analyzed samples according to their origin.
Conclusions. Arriving at an expert conclusion about the relationship between samples originating in the illegal local drug trade, requires consideration of a series of factors. The comparative chemical analyses together with the use of statisticals methods are the basis of this forensic application in a criminal prosecution.