Search results for "Square wave"
showing 10 items of 16 documents
Layer-by-layer identification of copper alteration products in metallic works of art using the voltammetry of microparticles.
2010
An in situ technique for layer-by-layer electrochemical analysis of solid surfaces using the voltammetry of microparticles is presented. The method is based on the determination of several shape-dependent parameters for voltammetric curves recorded at a graphite pencil working electrode in contact with the sample, all immersed into aqueous electrolytes. Repetitive square wave voltammetry and sequential application of constant potential reductive steps and voltammetric scans yield discernible responses for the corrosion products distributed in stratified layers on metal-based surfaces. This methodology is applied to identify alteration products of copper and copper alloys distributed in diff…
Square wave voltammetric determination of the redox state of a reversibly oxidized/reduced depolarizer in solution and in solid state
2012
Abstract Square wave voltammetric measurements allows for determining the composition of system containing a reversibly reducible/oxidable electroactive species in two oxidation states. The method is based on recording the ratio of reverse to forward peak currents. That ratio can be correlated with the molar fraction of the oxidized (or reduced) form of the depolarizer. The method was compared with cyclic voltammetric methods suggested in literature and it was tested using Fe ( CN ) 6 3 - / Fe ( CN ) 6 4 - in solution phase. Application to solid state systems is illustrated by the dehydroindigo/indigo couple in synthetic Maya Blue-type specimens prepared from indigo plus different clays whe…
Thermal NDE of thick GRP panels by means of a Pulse Modulated Lock-In Thermography technique
2010
This work describes the development and implementation of an infrared thermal NDE procedure for the evaluation of subsurface defects. The approach is called Pulse-Modulated Lock-In Thermography (PMLT) and is based on the analysis of the frequency response of the measured temperature and comparison with the carrier frequencies launched by the external heat delivering source. The heat deposited on the object is in particular modulated as a train of square waves. This is easily achieved by periodically shuttering the heat source. The temperature is then sampled throughout the deposition of a few square waves. A lock-in algorithm is then implemented able to selectively filter out components at …
Sequential identification of organic dyes using the voltammetry of microparticles approach
2009
An electrochemical method for identifying indigoid, anthraquinonic, naphtoquinonic, flavonoid, pyrone, pyran, and other related dyes in microsamples from works of art is reported using the voltammetry of microparticles methodology. Products of solid state oxidation/reduction of dyes form a layer on the lateral faces of the dye crystals as suggested by ATR-FTIR and AFM data. This method is based on the sequential application of oxidative and reductive constant-potential polarization steps coupled with the record of square wave voltammograms to solid microsamples of dyes in contact with aqueous electrolytes.
A simulation and experimental study of electrochemical pH control at gold interdigitated electrode arrays
2021
Abstract In electroanalysis, solution pH is a critical parameter that often needs to be tailored and controlled for the detection of particular analytes. This is most commonly performed by the addition of chemicals, such as strong acids or bases. Electrochemical in-situ pH control offers the possibility for the local adjustment of pH at the point of detection, without the need for additional reagents. Finite element analysis (FEA) simulations have been performed on interdigitated electrodes, to guide experimental design in relation to both electroanalysis and in-situ control of solution pH. No previous model exists that describes the generation of protons at an interdigitated electrode arra…
Electrochemical identification of flavonoid dyes in solid work of art samples by abrasive voltammetry at paraffin-impregnated graphite electrodes.
2004
Abstract An electrochemical method for identifying flavonoid-type dyes in microsamples from works of art is reported. Square wave voltammograms of natural insoluble dyestuffs based on flavonoid structure dragoon's blood, weld, old fustic, gamboge, Brazilwood and logwood (Campeche wood) attached to paraffin-impregnated graphite electrodes in contact with 0.25 M HAc + 0.25 M NaAc aqueous buffer display characteristic peaks in the potential region between +0.85 and −0.85 V versus AgCl/Ag. Sequential experiments in contact with 0.05 M AlCl 3 and 0.05 M Na 2 MoO 4 plus HAc/NaAc and 0.05 M H 3 BO 3 + 0.10 M NaOH solutions also provide dye-characteristic signals allowing for an unambiguous identi…
NiO@Ni core shell for electrochemical detection of Hg ions
2018
Heavy metals are considered as one of the most dangerous chemicals for human health. Among heavy metals, mercury is one of the most dangerous one: few ppb of Hg can cause serious damages to brain, heart, lungs and kidney. The Environmental Protection Agency setted the maximum concentration of Hg in water as 2 ppb [1] . Nowadays is very important to develop new and novel sensors for heavy metals that could be cheap, easy to use and for in-situ and real-time analysis and in this context electrochemical sensors are perfect candidates [2] . The more powerful electrochemical tequinique is Square Wave Anodic Strippic Voltammetry (SWASV), a two step techinique were the heavy metals are first depos…
Ni/NiO thin film Sensors for Mercury ions detection by Square wave anodic stripping voltammetry
2018
Square wave anodic stripping voltammetry (SWASV) is considered a very interesting electrochemical method for heavy metals detection in comparison to conventional techniques [1]. The main features of this technique are the high sensitivity and reproducibility (standard deviation lower than 5%), besides, the limit of detection is in the ppb level so is comparable with standard techniques such as AAS or ICP, the instrumentation is very inexpensive and easy to use and the detection time is very low. Among heavy metals, mercury is one of the most toxic for both environment and humans. In fact, it may cause serious health problems to brain, kidney and DNA. The concentration limit imposed by US En…
Electrochemical Characterization of Archaeological Tin-Opacified Lead-Alkali Glazes and Their Corrosion Processes
2005
The electrochemical response of weathered and unweathered archaeological tin-opacified glazes attached to paraffin-impregnated graphite electrodes is described. Upon comparison with the square wave voltammetric response of SnO2, PbO and PbO2, Sn- and Pb-centered reduction processes can be characterized. Reduction of Sn(IV) involves the stepwise formation of solid Sn(II) and Sn metal, successively, at potentials of −0.08 and −0.55 V vs. AgCl/Ag. Reduction of network-modifier Pb(II) in glazes occurs at −0.5 V and is accompanied by the reduction of network-forming Pb(IV) at potentials ranging from +0.65 to +0.20 V, confirming the presence of such centers in glazes. Voltammetric data suggest th…
Electrochemical determination of boron in minerals and ceramic materials
2004
Abstract A method for quantitatively determining boron in minerals and ceramic materials is described. It is based on the abrasive attachment of mixtures of ZnO plus sample to PIGEs. After a reductive deposition step, square wave voltammograms recorded for those modified electrodes immersed into 0.10 M NaCl+0.25 M mannitol provide well-defined stripping peaks at −0.85 and −0.15 V vs. AgCl/Ag for the oxidation of Zn and B, respectively. The quotients between the peak areas and the peak currents for the stripping oxidation of B and Zn vary linearly with the molar ratio of B and Zn in the mixture, thus providing an electrochemical method for determining the boron content in solid samples. Resu…