A chemometric sensor for determining sulphaguanidine residues in honey samples

The inclusion complex of sulphaguanidine (SGN) in beta-cyclodextrin has been investigated. To avoid the problem of the low solubility of beta-cyclodextrin in water, solutions of beta-cyclodextrin in urea have been used. A 1:1 stoichiometry and an association constant of 450M(-1) have been established for the complex. A new spectrofluorimetric method has been developed for the determination of SGN residues in honey samples. This sulphonamide is widely employed for honey treatment. The method for the determination is based on second-order multivariate calibration, applying parallel factor analysis (PARAFAC). No previous separation or samples pre-treatment were required. The calibration solutions were prepared in water, with concentrations in the range from 0.02 to 0.20mugmL(-1) for SGN. The use of the second-order calibration method in the standard addition mode, using the excitation-emission matrices (EEMs) as analytical signal, allowed its determination in honey samples, even in the presence of interferences, with satisfactory results. The proposed procedure was validated by comparing the obtained results with a HPLC method, with satisfactory results for the assayed method.

Fluorimetric Determination of Sulphaguanidine and Sulphamethoxazole by Host-Guest Complexation in β-Cyclodextrin and Partial Least Squares Calibration

The host-guest inclusion complexes of sulphamethoxazole (SMTX) and sulphaguanidine (SGN) with beta-cyclodextrin, in aqueous solutions, have been investigated. A 1:1 stoichiometry of the complexes was established, the association constants were calculated by different methods, and the influence of several chemical variables on the complexation processes were established. According to the results obtained, a spectrofluorimetric method for the determination of these sulphonamides has been proposed. The individual and binary mixtures of both sulphonamides have been determined in human urine samples, at representative therapeutic ranges, by application of a first-order multivariate calibration partial least squares (PLS-1) model. The calibration set was designed with 9 samples, containing different concentrations of the two sulphonamides, and 8 blank urine samples, with the aim of modelling the variability of the background. The concentration ranges for the sulphonamides were up to 0.5 microg mL(-1) for SMTX and 1.0 microg mL(-1) for SGN. Figures of merit as selectivity, analytical sensitivity and limit of detection (LOD) were also calculated. The proposed procedure was validated by comparing the obtained results with a HPLC method, with satisfactory results for the assayed method.

Determination of sulphathiazole and sulphanilamide by photochemically induced fluorescence and first-derivative fluorescence

This manuscript reports the usefulness of the determination of sulphathiazole (ST) using photochemically induced fluorescence (RTPF) and RTPF coupling with first derivative (D1-RTPF), and the determination of sulphanilamide (SAN) by meaning first derivative of the emission spectrum. By irradiating 5 min, with intense UV radiation, sulphathiazole, in ethanol:water 20:80 (v/v) solutions at pH 4.5-5.0, show fluorescence emission at 342 nm (lambdaex=251 nm). Under these conditions, a linear relation, fluorescence intensity-ST concentration, was found between 0.23 and 3.00 microg mL(-1) of ST. The method was applied for determining ST in a pharmaceutical drug. ST was also determined in honey by using the D1-RTPF signal, applying the standard addition method, and measuring at 324.8 nm. Under the same experimental conditions of pH and solvent, a fluorimetric method for determining SAN in presence of ST is proposed. Calibration graphs for SAN determination were established using the amplitude of the first derivative of the emission spectrum measured at 324.4 nm, as the analytical signal. This method has been applied to determining SAN in a pharmaceutical formulation.

Development of a Micellar electrokinetic capillary chromatography method for the determination of three drugs employed in the erectile dysfunction therapy

A Micellar electrokinetic capillary chromatography method is proposed for the determination of sildenafil, vardenafil and tadalafil, which are employed in oral therapy for erectile dysfunction. Optimum conditions for the separation were investigated. A background electrolyte solution consisting of 10 mM phosphate buffer adjusted to pH 12.0, sodium dodecyl sulfate (SDS) 25 mM, hydrodynamic injection, and 25 kV as separation voltage were used. Relative standard deviations (R.S.D.s) were 1.0, 1.0, 0.4% and 2.9, 2.9, 1.9% for migration time and corrected peak area (CPA) (n = 9) for sildenafil, vardenafil and tadalafil, respectively. Detection limits obtained for the three drugs ranged from 0.19 to 0.61 mg L(-1). A linear concentration range between 1 and 20 mg L(-1) was obtained. A ruggedness test of this method was checked using the fractional factorial model of Plackett-Burman, in which the influence of six factors at three different levels was tested on different electrophoretic results: resolution and corrected peak area. The statistical evaluation of the electrophoretic results was achieved by Youden and Steiner method. The described method is rapid, sensitive and rugged and it was tested in the pharmaceutical formulations analysis obtaining recoveries between 98 and 107% respect to the nominal content.

Hydrogen peroxide sensitive amperometric biosensor based on horseradish peroxidase entrapped in a polypyrrole electrode

The enzyme horseradish peroxidase (HRP) has been entrapped in situ by electropolymerization of pyrrole onto a platinum electrode. The latter was previously coated by a polypyrrole layer for better adhesion of the biocatalyst film and in order to avoid the enzyme folding onto the Pt electrode. The biosensor allowed the determination of hydrogen peroxide in the concentration range comprised between 4.9 x 10(-7) and 6.3 x 10(-4) M. The biosensor retained more than 90% of its original activity after 35 days of use.