Complementary use of capillary zone electrophoresis and micellar electrokinetic capillary chromatography for mutual confirmation of results in forensic drug analysis

The purpose of this work was to compare different CE separation modes, namely capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC), for the analysis of drugs of forensic interest in order to assess the mutual degree of independence and consequently the possibility of complementary use for mutual confirmation of results. A panel of drugs including caffeine, morphine, barbital, pentobarbital, codeine, nalorphine, lidocaine, procaine, heroin, flunitrazepam, acetylcodeine, papaverine, amphetamine, narcotine, cocaine, diazepam, tetracaine, narceine, 6-monoacetylmorphine acetylcodeine and thebaine, were separated according to a MECC and two CZE methods. The MECC separation was carried out in a bare silica capillary (50 mu-m I.D.) with a buffer composed of 25 mM borate (pH 9.24)-20% methanol-100 mM sodium dodecyl sulphate; the applied voltage was 20 kV. The first CZE method (CZE1) was carried out in 50 mM phosphate buffer (pH 2.35) at 20 kV with a bare silica capillary (50 mu-m I.D.), and the second (CZE2) with 50 mM borate (pH 9.24) at 12 kV with the same capillary. The three methods were effective in the separation of the test drug mixture, but MECC was the only able to resolve all the components. Relative (to flunitrazepam) migration time RSDs ranged from 0.3 to 2.8% for MECC, from 0.1 to 1.4% for CZE1 and from lt 0.1 to 0.5% for CZE2. The separation patterns (migration order) of the three methods were compared with Spearman's test and with principal component analysis. CZE1 and CZE2 were significantly and directly correlated (r = 0.749, p lt 0.002), whereas MECC and CZE2 were also significantly, but inversely correlated (r = -0.865, p lt 0.001). MECC and CZE1 (limitedly to the basic drugs) appeared non-correlated (r = -0.131, p = 0.630) and therefore the two techniques are suitable for combined use to increase the discriminatory power.