Julia Arcos

Horseradish peroxidase electrode for the analysis of clozapine

Abstract A horseradish peroxidase (HRP) immobilized electrode was developed for the assay of the antipsychotic compound clozapine (CLZ). The biosensor was made of HRP crosslinked with glutaraldehyde and bovine serum albumin (BSA) and blended in the electrode matrix. The latter was a carbon paste based on solid paraffin and graphite particles. A dialysis membrane was secured at the tip of the enzyme based electrode. Cyclic voltamperometry at the solid carbon paste electrode (sCPE) permitted to point out a reversible pattern for CLZ electrooxidation attributed to a relatively stable nitrenium ion. The formation of the latter and of a newly generated species, was inferred at the biosensor. The electroreduction of these generated species was performed at the biosensor at an applied potential of 0.0 V vs. Ag/AgCL 3 M KCl. Several experimental parameters influencing the biosensor response were studied such as pH, buffer composition, and detection potential. The resulting biosensor offered, at pH 4.5 in Britton–Robinson buffer (BRb) in the presence of 0.1 mM H2O2 and at 0.0 V vs. Ag/AgCl, a linear response in the concentration range comprized between 1.0 × 10−6 M and 1 × 10−5 M with a detection limit of 1.7 × 10−7 M and a quantification limit of 5.6 × 10−7 M. In addition to the mechanistic information provided, the biosensor was found useful for the determination of CLZ in tablets. The accuracy of the assay was checked by capillary electrophoresis (CZE).

Multiple standard addition with latent variables (MSALV): Application to the determination of copper in wine by using differential-pulse anodic stripping voltammetry

Abstract MSALV, multiple standard addition with latent variables, is a new method designed to overcome the difficulties presented by the determination of an analyte in a complex sample in which equilibria exist whose displacement may alter the response of the sensors when the analyte is added in a multiple addition. MSALV has been used to quantify the Cu content in samples of wine using differential-pulse anodic stripping voltammetry (DPASV) with a mercury electrode and ethylenediaminetetraacetic acid (EDTA) and KCl as complexing agents. The existence of the EDTA-Cu(II) complex and Cu(I)-chloride complex intermediate leads to a change in the sensibility of the sensors when Cu(II) is added, which must be born in mind during construction of the multiple addition model. The use of latent variables calculated by partial least squares (PLS) provides a solution which is both quantitatively adequate and chemically interpretable. The results of four repeated determinations of Cu in samples of red wine are shown. In each case the latent variables were calculated from the intensities recorded at fifteen potentials in eight voltammograms corresponding to the successive additions of wine and/or copper.

Voltammetric determination of Celiptium with carbon paste and lipid-modified carbon paste electrodes

Abstract The electrooxidation of the antitumour drug 2-methyl-9-hydroxyellipticinium (Celiptium) was investigated by cyclic, differential-pulse and adsorptive voltammetry at carbon paste (CPE) and lipid-modified carbon paste electrodes (LM-CPE). The influence of the paste composition, i.e., the ratio of graphite to binder, was studied in order to elucidate the nature of the accumulation process at the surface of the CPE. The electrode surface coverage at saturation was calculated. A.c. measurements at the CPE and at the LM-CPE during the accumulation of Celiptium demonstrated an increased differential double layer capacity of the LM-CPE. The influence of several parameters that affect the adsorptive step at the CPE was investigated, such as pH, ionic strength and interfering ions. Improved signals were obtained at the CPE and the detection limit in 0.1 M sodium perchlorate (tacc.=3 min) was found to be 2 × 10−10 M. Measurements of the drug in dilute standard serum samples were done using the medium-exchange technique.

Spectrophotometric and electroanalytical study of minoxidil

Abstract Polarographic reduction of minoxidil (1×10−5- 5×10−4 M) and spectrophotometric study were carried out at different pH.s pK values of the acid-base equilibria were calculated using both techniques. In addition, detection limits and sensitivity were determined using electrochemical (tast, differential pulse and pseudoderivative pulse polarography) and spectrophotometric techniques. A simple method is described for the determination of this compound in pharmaceutical formulations. Electrochemical oxidation was also performed at carbon paste and at lipid modified carbon paste electrodes.

Electrochemical behaviour of acemetacin

Acemetacin or l-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indole-3-acetic acid carboxymethyl ester is an efficient anti-inflammatory compound, and a derivative of indomethacin. Synthesis [l, 21, metabolism and pharmacokinetics [3, 41 of acemetacin have been well established. In the field of quaptitative analysis of acemetacin, thin layer chromatographic [5], liquid chromatographic [6], UV-spectroscopic [5], and fluorimetric [5] methods have been reported. No references on its electrochemical behaviour and related analytical methods have been found. However the electroactivity of acemetacin can be predicted because one reducible C = 0 group is present in the molecule. The general model for the reduction of amides to a-hydroxyamines can be applied in this case. The aim of this work was to verify that possibility and to develop some polarographic quantitative procedures based on it. In the examination of the nature and features of the electrodic process tast polarography, linear sweep voltammetry and potential controlled coulometry were used; as a quantitative analytical technique, pulse polarography was also considered.

Electroanalytical study of the reduction of Sb(III) in tartrate medium

Abstract A systematic study on the reduction of Sb(III) on a mercury electrode in aqueous solution of tartrate ion has been carried out. The nature of the electrode reactions has shown to be a function of the acidity of the solution. Results from polarographic, coulometric and voltammetric experiments allow us to outline a model of electrode reaction according to which different Sb-tartrate complex ions can be reduced. Sensitivity and detection limits for the polarographic determination of Sb(III) in tartrate medium are given using several polarographic waves obtained at different pH. In this way, the selection of the basic medium is vindicated.