Indirect polarographic and cathodic stripping voltammetric determination of cefaclor as an alkaline degradation product

Cefaclor is not reducible at a mercury electrode, but it can be determined polarographically and by cathodic stripping voltammetry as its initial alkaline degradation product which is obtained in high yield by hydrolysis of cefaclor in Britton-Robinson (B-R) buffer pH 10 at 50 degrees C for 30 min (reduction peak at pH 10, -0.70 V). Differential pulse polarographic calibration graphs are linear up to at least 1 x 10(-4) mol l(-1). Recoveries of 93% of the cefaclor (n = 3) were obtained from urine spiked with 38.6 mu g ml(-1) using this polarographic method with 1 ml urine made up to 10 ml with pH 10 buffer. Using cathodic stripping voltammetry and accumulating at a hanging mercury drop electrode at -0.2 V for 30 s, linear calibration graphs were obtained from 0.35 to 40 mu g ml(-1) cefaclor in B-R buffer pH 10. A relative standard deviation of 4.2% (eta = 5) was obtained, and the limit of detection was calculated to be 2.9 ng ml(-1). Direct determination of cefaclor in human urine (1 ml of urine was made up to 10 ml with pH 10 buffer) spiked to 0.39 mu g ml(-1) was made (recovery 98.6%). (C) 1999 Elsevier B.V. B.V. All rights reserved.

Voltammetric assay of albendazole in pharmaceutical dosage forms

A simple, rapid inexpensive voltammetric method have been developed for the quantitative determination of albendazole (ABZ) as the pure assay, by direct dissolution of commercial tablets in HCl solutions. Studies with linear sweep (LSV), square-wave (SWV) and differential pulse voltammetry (DPV) were carried out ABZ in aqueous medium at a glassy carbon electrode. A well defined irreversible oxidation peak current was obtained at 1,00V vs. SCE. The method permits a precise quantitative determination of ABZ using the standard addition method. The detection limits for the three voltammetric techniques were found to be 3.0 x 10(-5) M (LSV), 6.2 x 10(-5) M (SWV) and 4.0 x 10(-5) M (DPV).

Determination of nickel in fuel ethanol using a carbon paste modified electrode containing dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 x 10(-9) to 5.0 x10(-7) mol(-1) was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 x 10 mol(-1) and 5.2 x 10(8) mu A mol(-1) L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 x 10(-8) to 6.9 x 10(-8) mol(-1). A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.

Studies of the voltammetric behavior and determination of diazo reactive dyes at mercury electrode

The electrochemical reduction of two reactive dyes: Procion Red HE-3B 9 (RR120) and Procion Green HE-4BD (RG19) was investigated using cyclic voltammetry, differential pulse and DC, polarography, chronoamperometry and controlled potential electrolysis at mercury electrodes. The bis-azo groups of the RR120 dye are reduced together in one single step of four electrons, the bis-azo groups of the RG19 dye are reduced in two steps owing to the difference in the electron densities promoted by the different substituents in the benzene rings adjacent to the azo groups. The bis-monochlorotriazine reactive groups in both dyes are reduced only in acidic medium in their protonated form, leading to the reduction of the triazine groups. The reduction mechanism of both reactive dyes is discussed. Both dyes can be quantified in aqueous medium by differential pulse polarography in the concentration range of 1 x 10(-7) mol L-1 to 1 x 10(-5) mol L-1 by monitoring the reduction of the chromophore group or the reactive group.

Electroanalysis and determination of acetaldehyde in fuel ethanol using the reaction with 2,4-dinitrophenylhydrazine

The voltammetric reduction of acetaldehyde was studied in 0.1 M LiOH: LiCl (60: 40 v/v). Welldefined waves can be seen at -1.77 and -1.60 V with the use of hanging mercury and glassy carbon electrodes. Acetaldehyde was shown to react at room temperature with the 2,4-dinitrophenylhydrazine and the product exhibited a differential pulse voltammetric peak at -0.90V, which was well separated from the peaks of the derivative. This allowed the indirect determination of acetaldehyde in the presence of 0.1 M ethanol/tetrabutylammonium perchlorate after 10 min of reaction. Calibration graphs were obtained for 1.00 x 10(-6)-1.00 x 10(-4) M of acetaldehyde. The detection limit is 8.14 x 10(-7) M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment.

Electrochemical oxidation and voltammetric determination of the antimalaria drug primaquine

Primaquine, an antimalarial drug, presents a well-defined oxidation peak around +0.6V vs SCE at a glassy carbon electrode that can be used for its determination. Calibration graphs were obtained for primaquine in B-R buffer pH 4.0 from 3.00 x 10(-5) mol L-1 to 1.00 x 10(-2) mol L-1 using linear-scan voltammetry and 3.00 x 10(-5) mol L-1 to 1.00 x 10(-2) mol L-1 using differential pulse or square-wave voltammetry. The correspondent detection limits was 9.4 mu g mL(-1); 4.2 and 1.8 mu g mL(-1), respectively. All the voltammetric methods were applied with success in direct determination of the primaquine in commercial tablets without separation or extraction procedures.

Electrochemical reduction of azo-based chlorotriazine reactive dyes

The reduction process of the azo dyes reactive red 120 and reactive green 19 was investigated in B-R buffer pH 2-12 by differential pulse polarography, cyclic voltammetry and controlled potential electrolyse. The reactive red 120 presents two azo groups reducible in a single step of 8 electrons followed by simultaneous reduction of the two clorotriazine groups. The reduction of reactive green 19 is complicated by the presence of azo groups and chlorotriazine moyeties in a non symmetrical molecule. The peaks can be monitored for dyes determination in concentration level up to 1x10(-7) mol/L and 1x10(-9) mol/L using differential pulse polarography or cathodic stripping voltammetry.

New Ni(II)-sulfonamide complexes: Synthesis, structural characterization and antibacterial properties. X-ray diffraction of [Ni(sulfisoxazole)(2)(H2O)(4)] center dot 2H(2)O and [Ni(sulfapyridine)(2)]

The synthesis, structural characterization, voltammetric experiments and antibacterial activity of [Ni(sulfisoxazole)(2)(H2O)(4)] center dot 2H(2)O and [Ni(sulfapyridine)(2)] were studied and compared with similar previously reported copper complexes. [Ni(sulfisoxazole)(2)(H2O)(4)] center dot 2H(2)O crystallized in a monoclinic system, space group C2/c where the nickel ion was in a slightly distorted octahedral environment, coordinated with two sulfisoxazole molecules through the heterocyclic nitrogen and four water molecules. [Ni(sulfapyridine)(2)] crystallized in a orthorhombic crystal system, space group Pnab. The nickel ion was in a distorted octahedral environment, coordinated by two aryl amine N from two sulfonamides acting as monodentate ligands and four N atoms (two sulfonamidic N and two heterocyclic N) from two different sulfonamide molecules acting as bidentate ligands. Differential pulse voltammograms were recorded showing irreversible peaks at 1040 and 1070 mV, respectively, attributed to Ni(II)/Ni(III) process. [Ni(sulfisoxazole)(2)(H2O)(4)] center dot 2H(2)O and [Ni(sulfapyridine)(2)] presented different antibacterial behavior against Staphylococcus aureus and Escherichia coli from the similar copper complexes and they were inactive against Mycobacterium tuberculosis. (c) 2007 Elsevier B.V. All rights reserved.

A New Indirect Electrochemical Method for Determination of Ozone in Water Using Multiwalled Carbon Nanotubes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Synthesis and characterization of ruthenium complexes immobilized on poly(4-vinylpyridine)

The [Ru(NH3)5(H2O)]2+ and trans-[Ru(NH3)4SO2(H2O)]2+ complexes ions were immobilized on poly(4-vinylpyridine) (4-PVP) through reactions in aqueous solutions. The stability of the imobilized complexes was checked in aqueous solution in the pH 2.0-8.0 range. The number of pyridinic nitrogens in the polymer 4-PVP is 2.80±0.05 mmol/g according to nitrogen elemental analysis. Potentiometric titration experiments showed that the accessible nitrogen, in aqueous medium, was 0.94±0.02 mmol/g with a p Ka value of 7.4±0.2. In addition, ruthenium and sulfate analysis has demonstrated that about 15% of the accessible nitrogen sites are able to coordinate to the metal centers. The characterization of the immobilized complexes was made through diffuse electronic and infrared spectroscopies and differential pulse and cyclic voltammetries. © 1993 Plenum Publishing Corporation.

Voltammetric behavior of nitrofurazone and its hydroxymethyl prodrug with potential anti-chagas activity

Chagas' disease is a serious health problem for Latin America. The situation is worsened by the lack of efficient chemotherapy. The two available commercial drugs, benznidazole and nifurtimox, are more effective in the acute phase of the disease. Nitrofurazone is active against Trypanosoma cruzi, however its high toxicity precludes its current use in parasitosis. Hydroxymethylnitrofurazone is a prodrug of nitrofurazone. It is more active against Trypanosoma cruzi than nitrofurazone, besides being less toxic. This work shows the voltammetric behavior of nitrofurazone and a comparison with those of metronidazole and chloramphenicol using cyclic, linear sweep and differential pulse voltammetries. For these drugs also the prediction of the diffusion coefficients using Wilke-Chang equation was performed. The reduction of nitrofurazone is pH-dependent and in acidic medium the hydroxylamine derivative, involving four electrons, is the principal product formed. In aqueous-alkaline medium and with a glassy carbon electrode pre-treatment the reduction of nitrofurazone occurs in two steps, the first involving one electron to form the nitro-radical anion and the second corresponding to the hydroxylamine derivative formation. Hydroxymethylnitrofurazone presented the same voltammetric behavior and electroactivity, indicating that the molecular modification performed in nitrofurazone did not change its capacity to be reduced. A brief discussion regarding the differences in biological activity between the two compounds is also presented. ©2005 Sociedade Brasileira de Química.

Electrochemical reduction and voltammetric determination of diloxanide furoate in non-aqueous medium

The electrochemical reduction of diloxanide furoate (DF) in acetonitrile on glassy carbon electrode was studied in this work. It was observed that DF is reduced after a reversible one-electron transfer followed by an irreversible chemical reaction, diagnosed as C-Cl bond cleavage. Its reduction was followed by linear (LSV), differential pulse (DPV) and square wave voltammetry (SWV). Analytical curves were obtained for DF determination using all the investigated voltammetric techniques. For LSV was obtained a linear range (LR) from 5.0 × 10-4 to 1.0 × 10-2 mol L-1, with detection limit (DL) of 1.5 × 10-4 mol L-1 and sensitivity (S) of 2.1 × 104 μA mol-1 L. The analytical parameters obtained by DPV were: LR = 5.0 × 10-4 to 2.2 × 10-3 mol L-1, DL = 7.8 × 10-5 mol L-1, S = 3.7 × 104 μA mol-1 L. For SWV were obtained a LR = 7.5 × 10-6 to 1.2 × 10 -3 mol L-1, DL = 5.5 × 10-6 mol L -1 and S = 2.8 × 105 μA mol-1 L. Thus, the SWV was the most sensible technique, which can be used for DF determination at low concentration levels. Statistics methods were used to evaluate the analytical procedure, where recovery around to 100% was obtained for all voltammetric techniques. Relative standard deviations were lower than 5.0% (N=5). The obtained t values evaluating all the three voltammetric methods were less than the tabulated ones, indicating that there are no evidences of systematic error. ©2005 Sociedade Brasileira de Química.

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; ν = 2.0 mV s-1 νs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L-1 was obtained. The detection limit was estimated to be 5 μg L-1. The precision for six determinations of 0.05 and 0.26 mg L-1 Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal. 2005 © The Japan Society for Analytical Chemistry.

Voltammetry of mercury (II) based on an organo-clay modified graphite electrode

Organo-clay complex of ligand-hexadecyltrimethylammonium with montmorillonite was made for the purpose of application as a preconcentration agent in a chemically modified carbon paste electrode for determination of mercury (II) in aqueous solution. It was found out that the adsorption of Hg(II) by organo-clay complex is independent of the pH of the solution. It was also found out that the adsorption of the remaining metals Cd(II), Ps(II), Cu(II), Zn(II), and Ni(II) was dependent on the changes in pH solutions and increased when it varies from 1 to 8. The resultant material was characterized by cyclic and differential pulse anodic voltammetry using a modified graphite paste electrode in different supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, possible interferences and other variables.

Recent applications of analytical techniques for quantitative pharmaceutical analysis: A review

The intension of this paper was to review and discuss some of the current quantitative analytical procedures which are used for quality control of pharmaceutical products. The selected papers were organized according to the analytical technique employed. Several techniques like ultraviolet/visible spectrophotometry, fluorimetry, titrimetry, electroanalytical techniques, chromatographic methods (thin-layer chromatography, gas chromatography and high-performance liquid chromatography), capillary electrophoresis and vibrational spectroscopies are the main techniques that have been used for the quantitative analysis of pharmaceutical compounds. In conclusion, although simple techniques such as UV/VIS spectrophotometry and TLC are still extensively employed, HPLC is the most popular instrumental technique used for the analysis of pharmaceuticals. Besides, a review of recent works in the area of pharmaceutical analysis showed a trend in the application of techniques increasingly rapid such as ultra performance liquid chromatography and the use of sensitive and specific detectors as mass spectrometers.