An extraction procedure has been developed for beta-agonists in liver samples using combined MSPD-C-18 SPE clean-up. The procedure is suitable for the determination of compounds from both beta-agonist classes, the substituted aniline-type compounds (e.g., clenbuterol) and the phenolic-type compounds (e.g., salbutamol), at levels below 1 ng g(-1). The procedure is more robust than the method recently reported from this laboratory in that it does not rely on the special properties of one particular brand of C-18 material. In this instance, the procedure has been evaluated using two major commercial brands of C-18 material. For both C-18 materials similar results were obtained for salbutamol, clenbuterol and mabuterol in fortified and incurred liver samples.

An electrochemical study of three important beta-agonist drugs at unmodified and Nafion-modified carbon paste electrodes was carried out. All the compounds are oxidized irreversibly st high positive potentials at a bare carbon paste electrode, giving rise to sharp, well-defined peaks. A secondary oxidation process was observed at pH values above 6.0. The rate-determining step was investigated for each compound at two concentration levels. Electrochemical activation procedures were optimized to ensure reproducible signals for the construction of calibration graphs. The modification of the carbon paste surface with a Nafion film allowed a preconcentration process to take place for all compounds, such that higher sensitivities were achieved compared with the bare surface. Such modifications resulted in limits of detection for the compounds down to 2.5 X 10(-8) mol dm(-3). Optimum accumulation was obtained at low pH values (2-3). Cyclic voltammetry at two Nafion film thicknesses demonstrated that a diffusion-controlled process exists within the Nafion layer. Salbutamol showed a higher affinity for Nafion than the other two compounds, both in terms of longer linear accumulation and linear accumulation at higher concentrations.

A procedure for the extraction of salbutamol including conjugated forms of the drug, from liver samples, is described. It combines matrix solid-phase dispersion with radioimmunoassay for the measurement of salbutamol residues at the sub-ppb level. Inter- and intra-assay validation, carried out on fortified liver samples, show good recoveries over the range 1-5 ppb of salbutamol. An enzyme hydrolysis procedure was optimized for the deconjugation of incurred residue. The developed procedure is shown to be suitable for the extraction and determination of other P-agonists such as clenbuterol, mabuterol, terbutaline, and cimaterol at residue levels of less than 1 ng g(-1).

The preconcentration of fenoterol on a Nafion-modified carbon paste electrode and its subsequent determination using differential pulse voltammetry is described. The effect of pH and percentage Nafion concentration on the accumulation behaviour of fenoterol was studied, and accumulation curves, calibration graphs and reproducibility studies at two different Nafion concentrations have been carried out in the range 2.5 × 10−8−5.0 × 10−7 M fenoterol. A limit of detection in aqueous solutions, calculated using a signal-to-noise ratio (S/N) of 3, was 9.0 × 10−9 M. Application of the electrode to pharmaceutical preparations, without sample pretreatment, resulted in acceptable deviation from the stated concentration (RSD = ± 3.81%, n = 4). For more complex matrices, a suitable extraction procedure was developed, resulting in recoveries of >90% (urine) and >75% (serum).

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The anodic stripping voltammetry of selenium (IV) in a gold fiber electrochemical flow cell is described. The cell is simple to construct and flexible in its operation. The nonlinear diffusional mass transport characteristics of such small diameter electrodes influence the anodic stripping voltammetry of Se(IV) with the result that significant deposition of metal ions occurs during the scan period from the deposition potential to the peak potential. Therefore, an extremely short deposition period of the order of 20 seconds can be employed at the gold fiber electrode. The system described resulted in a linear working range from 0-15 ng/mL, a detection limit of 0.5 ng/mL Se(IV) and a relative standard deviation of 6% at 5 ng/mL (n = 7) in pure solution.