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Figure 8.2 Multiwavelength and single-wavelength (195 nm) MEKC electrophero-grams obtained with the fractions of a two-step extraction of a patient sample, which tested positively for several classes of drugs. Peaks: 1, benzoylecgonine; 2, morphine; 5, codeine; 9, methaqualone; 13, 6-MAM.

Figure 8.2 Multiwavelength and single-wavelength (195 nm) MEKC electrophero-grams obtained with the fractions of a two-step extraction of a patient sample, which tested positively for several classes of drugs. Peaks: 1, benzoylecgonine; 2, morphine; 5, codeine; 9, methaqualone; 13, 6-MAM.

Thormann et al. (1993) have published an overview of the strategies for using MEKC to monitor drugs in body fluids (serum, urine, saliva); they discuss buffer selection and sample preparation (direct injection, ultrafiltration, solid phase extraction.

The comparative use of MEKC, CZE, and capillary isotachophoresis (CITP) for the determination of drugs in body fluids was reported by Caslavska et al. (1993). Salicylate, paracetamol, and antiepilectics in serum and urine were analyzed with the three techniques. In case of high drug concentrations, body fluids could be injected directly, or with simple dilution (for urine) or ultrafiltration (for serum). Extraction and concentration were necessary for drugs present in the low micrograms per milliliter levels, however. The authors concluded that MEKC and CZE could be applied more easily, whereas CITP required careful selection of buffers and, in general, was less sensitive.

The analysis of hair samples is gaining acceptance in the forensic toxicology environment as a tool for investigating past chronic exposure to illicit drugs (Tagliaro et al., 1993b; Kintz, 1995). The usual analytical strategy, after hair collection, extraction, and extract purification, is based on radioimmunologic screening followed by chromatographic (GC, GC-MS, HPLC) confirmatory analyses.

The use of HPCE for this purpose shows potential advantages related not only to the peculiar separation mechanism, but also to the minimal need of sample, which, for aesthetic reason, is scarce in hair analysis. In recent reports on the analysis of hair samples, Tagliaro et al. (1993a, 1993c) adopted a CZE mode because it appeared to be easier to use and therefore to offer greater possibility for replication by other investigators. The CE background buffer was composed of 50 mM borate, pH 9.2. Simultaneous detection of cocaine and morphine was accomplished at 200 nm wavelength, but a higher selectivity was obtained at the absorbance maxima of each analyte (i.e., 238 nm for cocaine; 214 nm for morphine. Tetracaine and nalorphine were adopted as internal standards for cocaine and morphine, respectively. The separations were highly efficient (up to 350,000 theoretical plates) and repeatable (migration time RSDs: <1% intraday, <3% interdays), and the determination were accurate and precise (intraday RSDs in the range of 3-5%).

Once again, because of the minute (nanoliter) volumes injected and the moderate concentration sensitivity of HPCE with UV detection (in the order of the low micrograms per milliliter), the limit of detection in hair was acceptable (<0.2 ng/mg) only if the hair extracts (from about 100 mg of sample) were reconstituted with 10 to 20 /xL of solvent, a procedure too delicate for routine applications. More recently (Tagliaro et al., 1995) reported the use of sample-stacking techniques to allow the injection of about 10 times larger volumes (i.e., about 50 nL), thus permitting reconstitution of the extracts with as much as 100 /xL of water, without sacrificing efficiency. The same paper described the application of MEKC to the analysis of hair extracts using a buffer containing 0.1 M SDS in 25 mM borate with 20% methanol. The sensitivity achieved was only slightly less than that obtained with CZE, but the selectivity was much higher because the SDS micelles were able to exploit the additional "reversed-phase-like separation mechanism.

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