HPCE Analysis of Illicit Drug Substances

HPCE has been applied to the analysis of drugs and pharmaceuticals (Altria, 1993). In fact, determinations of drugs in pharmaceutical formulations represent one of the most rapidly growing areas for HPCE. In addition, pharmaceutical drug analysis is the starting point for the application of HPCE in forensic toxicology and the forensic sciences (Thormann et al., 1994). 

Weinberger and Lurie (1991) first applied HPCE to an analysis of illicit drug substances. These authors used a micellar electrokinetic chromatography (MEKC, discussed in Chapter 3, Section 3.7.2) separation system in 50 pirn i.d. bare silica capillaries (length 25-200 cm) the buffer consisted of 8.5 mM phosphate and 8.5 mM borate at pH 8.5 and contained 85 mM sodium dodecyl sulfate (SDS) and 15% acetonitrile. The applied voltage was 25 to 30 kV, and detection was by UV absorption at 210 nm. 

These authors reported high efficiency separations of heroin, heroin impurities, degradation products, and adulterants (Fig. 8.1). Also discriminated were acidic and neutral impurities present in heroin seized by law enforcement agencies, as well as in illicit cocaine samples, with resolution of benzoylecgon-ine, cocaine, cis- and frans-cinnamoylcocaine. MEKC was also used with a broad spectrum of other compounds of forensic interest, including psilocybin, morphine, phenobarbital, psilocin, codeine, methaqualone, lysergic acid diethylamide (LSD), amphetamine, chlordiazepoxide, methamphetamine, lora-zepam, diazepam, fentanyl, phencyclidine hydrochloride (PCP), cannabidiol, and tetrahydrocannabinol (THC), which were all separated with baseline resolution. 

The successful use of MEKC for the analysis of illicit heroin and cocaine was also reported by Staub and Plaut (1994), who used 50 mM SDS in phosphate-borate buffer (10 and 15 mM, respectively) containing 15% of acetonitrile (pH 7.8). In 25 minutes, these authors achieved separation and determination of paracetamol, caffeine, 6-monoacetylmorphine (6-MAM), acetylcodeine, procaine, papaverine, heroin, and noscapine, although with peaks sometimes skewed. On-line recorded UV spectra of the peaks helped the identification of the individual peaks. 

The use of the cationic micellar agent CTAB (50 mM) in phosphate-borate buffer (10 mM of each salt), pH 8.6, with 10% acetonitrile was preferred because of a faster separation (about 15 min) of heroin and related substances. Because the cationic surfactant, which coats the capillary silica wall with a positively charged layer, reverses the electroosmotic flow (EOF), the voltage (-15 kV) must be applied with a reversed polarity (with the cathode at the injection point). Detection was by UV absorption at 280 nm. 

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