Electroanalytical study of the antidepressant sertraline

Aflowinjection squarewave cathodic stripping voltammetric method has been developed for the determination of sertraline in a pharmaceutical preparation. The method shows linearity between peak current intensity and sertraline concentration for the interval between 0.20×10−6 and 1.20×10−6 mol L−1. Limits of detection and quantification were found to be 1.5×10−7 and 5.0×10−7 mol L−1, respectively. Up to 70 samples per hour can be analysed with a good precision (R.S.D. = 2.5%). The proposed method was successfully applied to the determination of sertraline in a commercial product. In the voltammetric determination of sertraline in flow, a high sample rate is obtained at reduced costs, opening the possibility to compete with the chromatographic methods generally used for this analysis.

Activated Copper Cathodes as Sensors for Nitrite Analysis

The increased surface area of copper electrodes upon applying a suitable potential protocol was characterized by atomic force microscopy images. Scanning electrochemical microscopy was used to demonstrate the enhanced reactivity of the generated surface. The modified electrode showed excellent catalytic activity towards nitrite reduction in acidic medium (pH 2). This new platform was used in the development of a fast and simple voltammetric method for nitrite determination. Commercial and rainwater spiked samples were analyzed and the data showed an excellent agreement with those obtained with a reference spectrophotometric method (Griess reaction) at a confidence level of 95% (Student`s t-test).

Graphite-silicone rubber composite electrode: Preparation and possibilities of analytical application

Composite electrodes were prepared using graphite powder and silicone rubber in different compositions. The use of such hydrophopic materials interned to diminish the swallowing observed in other cases when the electrodes are used in aqueous solutions for a long time. The composite was characterized for the response reproducibility, ohmic resistance, thermal behavior and active area. The voltammetric response in relation to analytes with known voltammetric behavior was also evaluated, always in comparison with the glassy carbon. The 70% (graphite, w/w) composite electrode was used in the quantitative determination of hydroquinone (HQ) in a DPV procedure in which a detection limit of 5.1 x 10(-8) mol L-1 was observed. HQ was determined in a photographic developer sample with errors lower then 1% in relation to the label value. (c) 2007 Elsevier B.V. All rights reserved.

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.

Characterisation of gold electrodes modified with self-assembled monolayers of l-cysteine for the adsorptive stripping analysis of copper

Electrochemical sensors for copper ions in environmental samples were prepared by modifying gold electrodes with l-cysteine by self-assembly. The adsorption of l-cysteine on gold electrodes was studied by electrochemical reductive desorption in 0.5 M KOH, and the interaction of l-cysteine with copper ions was investigated by cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy. At low concentrations the ratio of l-cysteine to bound Cu(II) is 2:1. At higher concentrations (0.1 M) copper reacts with adsorbed cysteine forming copper sulfide on the electrode surface. On a modified l-cysteine gold electrode, Osteryoung square wave voltammetric determination of Cu(II) with a detection limit below 5 ppb has been demonstrated.

Copper Hexacyanoferrate Formation on the Modified Silica Surface with DAB-Am-16 Dendrimer

The third generation (G-3) polypropylenimine hexadecaamine dendrimer (DAB-Am-16) was grafted onto the silica gel surface. The modified silica interacts easily with Cu(2+) and then with potassium ferrocyanide to form copper hexacyanoferrate. The modified silica was characterized by the following techniques: Nuclear Magnetic Resonance (NMR), FTIR spectroscopy, Energy Dispersive X-ray (EDX) and Cyclic Voltammetry. The modified silica containing copper hexacyanoferrate (CuHCFSD) was tested for a voltammetric determination of nitrite using a modified graphite paste electrode.

Eletroanálise de corantes alimentícios: determinação de índigo carmim e tartrazina

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Desenvolvimento de métodos electroquímicos de quantificação de fármacos em amostras de água contaminadas

Este trabalho teve como objectivo, o desenvolvimento de um método electroquímico, para quantificação do fármaco carbamazepina (CBZ) em águas contaminadas. Neste trabalho foram utilizados quatro métodos voltamétricos: a voltametria cíclica, a voltametria de varrimento linear, a voltametria de onda quadrada e a voltametria de impulso diferencial. Os eléctrodos de trabalho utilizados foram, o eléctrodo de mercúrio de gota suspensa, o eléctrodo de carbono vítreo clássico e um eléctrodo de carbono vítreo modificado com um filme de nanotubos de carbono de paredes múltiplas (MWCNTs). O eléctrodo de mercúrio de gota suspensa permitiu o estudo da redução da CBZ numa região de potencial mais catódico, e os eléctrodos de carbono vítreo, com e sem modificação, permitiram o estudo da oxidação da CBZ numa região de potencial mais anódico. Nas condições experimentais estudadas, o eléctrodo de mercúrio de gota suspensa revelou ser um sensor voltamétrico pouco eficaz na determinação quantitativa da carbamazepina, em amostras com uma matriz complexa. Entre os eléctrodos de carbono vítreo, o eléctrodo de carbono vítreo modificado com os MWCNTs revelou ser o sensor voltamétrico mais eficaz e sensível, na detecção e determinação da carbamazepina. Modificado com um filme de nanotubos de carbono de paredes múltiplas, que previamente foram dispersos em dihexadecilhidrogenofosfato (DHP) e água, este novo eléctrodo permitiu obter uma resposta electroquímica da CBZ, consideravelmente superior ao eléctrodo não modificado. Utilizando a voltametria de varrimento linear e as condições experimentais consideradas óptimas, o eléctrodo nanoestruturado permitiu obter uma relação linear entre o sinal medido e a concentração da CBZ no intervalo 0.13- 1.60 M (30.7- 378 g -1), com os limites de detecção e quantificação mais baixos, até à data reportados com métodos electroquímicos (0.04 e 0.14M, respectivamente). O eléctrodo modificado foi aplicado na quantificação da CBZ, em formulações farmacêuticas, em águas naturais tratadas e em amostras de águas residuais, ambas dopadas, obtendo-se taxas de recuperação consideravelmente elevadas (100.6%, 98.0%,95.8%, respectivamente). Os resultados obtidos, na análise da CBZ em amostras ambientais, com o eléctrodo modificado, foram comparados com resultados obtidos por HPLC-UV e LC­ ESI-MS/MS, validando o método electroquímico desenvolvido neste trabalho. ABSTRACT: The aim of this work was to develop a new electrochemical method for the quantification of carbamazepine (CBZ) in contaminated waters. ln this study, four voltammetric methods were used: cyclic voltammetry, linear sweep voltammetry, square wave voltammetry and differential pulse voltammetry. the working electrodes used were the hanging mercury drop electrode (HMDE), the classical glassy carbon electrode (GCE), and a glassy carbon electrode modified with a film of multi-walled carbon nanotubes (MWCNls). Using HMDE, the reduction of CBZ was studied in the cathodic potential region. the CGE sensors, with or without modification, allowed the study of CBZ oxidation in the anodic potential region. ln the tested conditions, the results obtained for the quantification of CBZ using the HMDE sensor were not very satisfactory, especially when more complex samples were analysed. When the MWCNls-dihexadecyl hydrogen phosphate (DHP) film­ coated GCE was used for the voltammetric determination of CBZ, the results obtained showed that this modified electrode exhibits excellent enhancement effects on the electrochemical oxidation of CBZ. the oxidation peak current of CBZ at this film­ modified electrode increased significantly, when compared with that at a bare glassy carbon electrode. The enhanced electrooxidation and voltammetry of CBZ at the surface of MWCNTs-DHP film coated GCE in phosphate buffer solution (pH 6.71) was attributed to the unique properties of MWCNTs such as large specific surface area and strong adsorptive properties providing more reaction sites. The proposed method was applied to the quantification of CBZ in pharmaceutical formulations, drinking water and wastewater samples with good recoveries and low limits of detection and quantification (0.04 and 0.14 M, respectively), and was positively compared with chromatographic techniques usually used in the quantification of pharmaceutical compounds in environmental samples. HPLC-UV and LC-ESI-MS/MS were also used in the quantification of CBZ in pharmaceutical formulations and wastewater samples to prove the importance and accuracy of his voltammetric method.

Automated voltammetric system for shipboard determination of metal speciation in sea water

An automated and semi-intelligent voltammetric system is described for trace metal analysis. The system consists of a voltammeter interfaced with a personal computer, a sample changer, 2 peristaltic pumps, a motor burette and a hanging mercury drop electrode. The system carries out fully automatically approximately 5 metal determinations per hour (including at least 3 repetitive scans and calibration by standard addition) at trace levels encountered in clean sea water. The computer program decides what level of standard addition to use and evaluates the data prior to switching to the next sample. Alternatively, the system can be used to carry out complexing ligand titration with copper whilst recording the labile copper concentration; in this mode up to 8 full titrations are carried out per day. Depth profiles for chromium speciation in the Mediterranean Sea and a profile for copper complexing ligand concentrations in the North Atlantic Ocean measured on board-ship with the system are presented. The chromium speciation was determined using a new method to differentiate between Cr(III) and Cr(VI) utilizing adsorption of Cr(III) on silica particles.

Voltammetric Sensors for the Determination of Pharmaceuticals

Electrochemical sensors are increasingly being investigated to perform measurements for single or multiple analytes. Demanded by modern medical diagnosis, advances in microfabrication technology have led to the development of fast, sensitive and selective electrochemical sensors for drug analysis. Electrochemical sensors for the measurement of analytes of interest in clinical chemistry are ideally suited for these applications, due to their high sensitivity and selectivity, simple-to-operate, rapid response time and low-cost. As part of the present investigations eight voltammetric sensors have been fabricated for six drugs such as PAM Chloride, Tamsulosin Hydrochloride, Hesperidin Methyl Chalcone, Guaiphenesin, Cephalexin and Amoxicillin trihydrate. The modification techniques adopted as part of the present work include multiwalled carbon nanotube (MWNT) based modifications, electropolymerization, gold nanoparticle (AuNP) based modifications and platinum nanoparticle (PtNP) based modifications. The thesis is divided into nine chapters

Voltammetric studies of titanium (IV) phosphate modified with copper hexacyanoferrate and electroanalytical determination of N-acetylcysteine

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Voltammetric Studies of Cobalt Hexacyanoferrate Formed on the Titanium (IV) Phosphate Surface and its Application to the Determination of Sulfite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)