A comparative study of the forensic analysis of heroin by different capillary electrophoretic techniques

Abstract

The analysis of clandestine preparations of illicit or controlled drugs in an effort to identify the major components and also any trace components remains to be a common task for forensic science laboratories around the world. These determinations are important for intelligence purposes, such as to infer sources and pathways of production and to establish commonality of origin among different drug seizures. Gas chromatography (GC), high pressure liquid chromatography (HPLC) and capillary electrophoresis (CE), the last of which being an emerging technology, all have the versatility and ease of use to routinely analyse complex exhibits. In this study, three different modes of CE, these being capillary zone electrophoresis (CZE), micellar electrokinetic capillary chromatography (MECC), and microemulsion electrokinetic capillary chromatography (MEEKC) are evaluated and compared. Heroin was chosen as the drug for comparison, since it remains to be the most commonly abused substance in the world. The application of MEEKC to the analysis of heroin has not yet been reported. Average absolute and relative migration times and areas (RSD) were calculated on the basis of ten injections repeated sequentially on the same day. The results obtained from the three different modes of CE were compared and the best method was chosen based on migration time and repeatability and applied to street drug samples and biological fluids. The results showed that of all three methods studied, CZE at neutral pH offered the most suitable analysis time while MEEKC at high pH offered the best resolution. These best modes of CE were applied for limit of detection (LOD) studies and for the analysis of heroin in street and biological samples. The results showed that MEEKC at high pH gave a better LOD. Both modes were suitable for the separation of an extracted urine sample, which had been previously spiked with heroin, however with direct injection, MEEKC at high pH proved rather ineffective since there was co-elution of the analytes of interest with compounds present in the urine sample. This work confirms the suitability of CZE, MECC and MEEKC for the analysis of drugs of forensic interest, in particular heroin.