ELECTROCHEMICAL SENSORS AS SIMPLE AND CHEAP DEVICES FOR RAPID DETERMINATION OF VARIOUS SPECIES IN ENVIRONMENTAL SAMPLES

The electrochemical methods are very good tool for determination of trace concentrations of various species in water samples. The analysis carried out using these methods are usually simple, fast and also the cost of the required equipment is much lower comparing to other instrumental methods. Furthermore, the electroanalytical methods are easy to automate and computerize. Among five major groups of these methods (potentiometry, voltammetry, coulometry, conductometry and dielectrometry), potentiometry and voltammetry attract the greatest attention of researchers. In this paper, experimental results of research related to development of procedures (voltammetric and potentiometric) for the determination of elements in environmental water samples were presented. Due to their common occurrence in environment and possible toxic effects on living organisms, vanadium and nitrate ions were selected for investigation. Optimization of voltammetric procedure for V(V) determination were carried out in matrix containing different surfactants and humic acids, using lead film electrode as a working electrode. Results showed that only nonionic surfactant Brij-35 did not interfere with the voltammetric signal. Other surfactants as well as humic acids reduced the signal, and possibility of their elimination with suitable resins were also investigated. Potentiometric measurements were consisted of preparation and determination of analytical properties of nitrate ion-selective electrodes with solid contact. The results showed that among three different membrane composition, the best response was achieved by membrane containing: Ni(Phen)2, THTDPCl, PVC and NPOE in the ratio of 1:2:33:64 wt. %, respectively. With the detection limit of 2.8 × 10^-6 mol L^-1, the working concentration range from 5 × 10^-5 to 1 × 10^-1 mol L-1 and a slope of -55.1 mV per decade, this electrode showed good selectivity to sulfate, acetate, carbonate, dihydrogen phosphate, fluoride and chloride ions, and also good potential reversibility

Riboflavin (Vitamin B2) Assay by Adsorptive Cathodic Stripping Voltammetry (Adcsv) at the Hanging Mercury Drop Electrode (HMDE)

In this study the interactions of Riboflavin (Vitamin B2) with a mercury surface are investigated. Firstly, by using Cyclic Voltammetry, it is demonstrated that Riboflavin can be efficiently accumulated, by adsorption from buffered solutions containing an excess of NaClO4, onto the mercury drop of a HMDE. Secondly, it is shown that the adsorbed Riboflavin can be reduced through an electrochemical reaction whose stoichiometry is extricated by confronting simulated with experimental CV voltammograms acquired in a range of pH between about four and nine. Finally, the cathodic current, sustained by the surface reduction of Riboflavin, is exploited for assaying Riboflavin via Differential Pulse Adsorption Cathodic Stripping Voltammetry (DP AdCSV) within the frame of the standard additions calibration procedure. By applying the suggested DP AdCSV procedure with standard voltammetric equipment, typical DP settings and pre-electrolysis time of about 10 s, a linear response is maintained if Riboflavin concentration in the electrolysed solution does not exceed about 2 mg/l. On the other side, a limit of detection (expressed as the concentration of Riboflavin in the electrolysed solution) of 7 μg/l has been achieved with a pre-electrolysis time of 68 s

Electrochemical and microfabrication strategies for remotely operated heavy metal sensor networks for water analysis : the dual challenges of calibration-less measurement and sample pretreatment.

Current heavy metal monitoring in water utilizes sophisticated instrumental methods at centralized laboratories. For many applications, a preferable approach is the deployment of remote sensor networks. To this end, electrochemical methods in conjunction with microfabricated sensors potentially offer the required sensitivity and practical advantages including inexpensive sensors, reduced need for manual operation, reduced energy requirements, and also takes advantage of existing technologies such as communications networks for real-time data acquisition. The remote sensor platform developed herein consists of a photo-lithographically patterned gold electrode on SiO2 substrate within a custom stopped-flow thin-layer cell (TLC). Metal concentrations were evaluated by anodic stripping coulometry (ASC), where it was possible to pre-concentrate all dissolved metals from the finite TLC volume in about a minute. Unlike previously reported ASC approaches which rely on either linear sweep voltammetry or chronopotentiometry, the ASC variant described herein utilizes a potential step to simultaneously strip all deposited metals. The use of a double potential step ASC method also allowed in situ blank subtraction without the need for a separate blank solution. To achieve selectivity, several deposition potentials are used to pre-concentrate only those metals which can be reduced at a given potential. This method is demonstrated to be capable of measuring 500 ppb As(III) to better than 10% error even in the presence of high interferent levels (1.3 ppm Cu2+, 500 ppb Cd2+, 500 ppb Pb2+, and 5 ppm Zn2+). Similar performance was possible for As(III) spiked Ohio River water after pH adjustment. For more negatively reduced metals, dissolved oxygen (DO) reduction interferes with stripping analysis. An indirect in-line electrochemical DO removal device (EDOR), utilizing a silver cathode to reduce DO in a fluidically isolated chamber from the sample stream, was therefore developed. This device is capable of 98 % DO removal at flow rates approaching 50 µL/min with power consumption as low as 165 mW hr L-1. Besides our specific stripping application, this device is well suited for Lab on Chip (LOC) applications where miniaturized DO removal and/or regulation are desirable

Modified Electrodes for Determining Trace Metal Ions

Due to all the advantages of low cost, speed, and simplicity, electrochemistry has always represented a perfect choice to be selected in quantitative analysis particularly in the case of metal ions but with the drawback of specificity and sensitivity. With the arrival of nanomaterials, the problem of sensitivity and limit of detection has been overcome and a great variety of applications of electrochemistry especially in trace analysis are highlighted. Layers of materials can be arranged and manipulated to make the methods more specific to targeting analytes The opportunity is there for both older and newer methods to be beneficial in a large number of applications with superb analytical performance. This knowledge of modified electrodes can inspire newer and greater innovative applications of electrochemistry with the promising extension to other areas under current interests

Investigation of deposition of some heavy metals on heated gold-loop electrode in comparison with gold rotating disk electrode in various samples of water

The experiments include deposition and stripping voltammetry of some heavy metals in aqueous solutions on Au-loop electrode at both temperatures 60 °C and room temperature. The analytical signals on heated Au-loop electrode were recorded to be much better than those obtained at room temperature and on Au-RDE at unaffected signal-to-noise-ratio. Heated Au-loop electrode replace a classic UV-Irradiation proces for Determination some heavy metals in origin river water sample. Heated Au-loop electrode work to achieve a high greatly self-cleaning effectdue to eliminate the fouling effects

Electrodes modification with silver nanoparticles for the detection of arsenic

L'arsènic és un dels 10 productes químics de l'OMS (Organització Mundial de la Salut) de major preocupació per la salut pública. El límit actual recomanat d'arsènic a l'aigua potable és de 10 ppb. Les tècniques habituals per la seva quantificació són cares i utilitzen instruments grans i voluminosos que només són aptes per al seu ús en laboratori. En canvi, les tècniques voltamperomètriques són més simples, de baix cost i permeten la utilització d’equips portàtils capaços de determinar elements traça. Aquest és el cas dels elèctrodes screen printed (SPE). A més a més, la composició de la seva superfície pot ser fàcilment modificada amb l’addició de nanopartícules per millorar la sensibilitat. En aquest sentit, es va proposar detectar arsènic en solució mitjançant voltamperometria i SPEs modificats amb nanopartícules de plata, les quals es poden obtenir per diferents tipus de síntesi. En aquest treball s’han estudiat dos tipus de nanopartícules (NPs): de via sintètica de diferents formes i mides (llavors i nanoprismes de plata) i també NPs de síntesi respectuosa amb el medi ambient o “verdes”. Tots els tipus es van caracteritzar microscòpicament i es van utilitzar en la modificació de SPEs comercials de nanofibres de carboni. La determinació d’arsènic es va realitzar mitjançant voltamperometria de redissolució anòdica en el mode de pulsos diferencials (DPASV) i es van optimitzar els paràmetres experimentals. El millor resultat es va aconseguir amb les NPs sintètiques i més concretament, amb les llavors de plata, aconseguint un límit de detecció de 1,66 ppb per un rang lineal de fins 50 ppb. Finalment, es va aplicar a una mostra real (aigua de l’aixeta “spiked”) , de la qual s’ha pogut determinar la seva concentració amb una desviació d’un 1%

An electrochemical instrument for the analysis of heavy metals in water via anodic stripping coulometry for applications in remote sensing.

From the high levels of arsenic in groundwater in Bangladesh to the lead contamination of drinking water in Flint, Michigan, there are incidents across the globe that highlight the need for a reliable instrument capable of monitoring heavy metals remotely and continuously in a variety of geographical locations. Typical instrumentation for water analysis, such as ICP and AAS, must be housed in a central lab and relies on an operator traveling to the collection site, obtaining a sample, and transporting it back to the lab. This analysis provides a snapshot of the water quality that is limited to the specific time and location of collection. Portable instruments overcome delayed sample analysis time but still require a technician who must travel to the field to operate the equipment. Remote sensing overcomes these limitations as instruments are installed on-site and function autonomously to collect data continuously. This work is focused on developing an electrochemical technique featuring in situ background correction for applications in remote sensing of heavy metals in water. The technique is based on exhaustive anodic stripping coulometry in a fixed-volume cell and the target analytes are As(III) and Pb(II). Herein, the electrochemical device was redesigned to improve the detection limits for As(III) using double potential step-anodic stripping coulometry (DPS-ASC) to meet the WHO limit of 10 ppb. Stamp-and-stick fabrication was performed to define and control the sample volume. The gold electrode area was manipulated by fabrication of microelectrode arrays. The DPS-ASC technique was then optimized for the detection of Pb(II) in water using gold macroelectrodes and microelectrode arrays. Furthermore, the interference of Cu(II) was explored and managed by developing an in-line pre-electrolysis device. The practicality of DPS-ASC for analysis of real samples was evaluated using Ohio River water and the stability of the sensor was evaluated over the course of two weeks by daily analysis of Pb(II) charge. Last, novel boron doped diamond electrodes were evaluated for DPS-ASC analysis of Pb(II)

Adsorptive stripping voltammetric determination of reactive dyes

The present study was mainly devoted to evaluate the applicability of differential pulse adsorptive stripping voltammetry (DPAdSV) for the determination of ultra-trace concentration levels of a range of reactive dyes. The studied reactive dyes were found to adsorb effectively onto the hanging mercury drop electrode (HMDE). This applied electroanalytical method was primarily based on the nonelectrolytic accumulation (adsorption) of the analyte of interest (reactive dye), followed by a cathodic reduction scan measurement. Consequently, the adsorptive stripping voltammograms of the analysed reactive dyes exhibited several useful electrochemical signals, corresponding to the cathodic reduction of the anthraquinone, azo and halo-striazine groups... cont'd

Determination of trace quantities of selenium and arsenic in canned tuna fish using electroanalytical techniques

Toxic metals are present in the environment and are known to be present in food. Selenium, which is considered an essential micronutrient, is recognized as a toxic metal at slightly higher concentrations. Arsenic is also recognized as a toxic metal. Selenium and Arsenic tend to accumulate in food, specifically fish and seafood. Fifteen brands and types of tuna fish were analyzed for selenium using differential pulse cathodic stripping voltammetry. The cans with the high and low concentrations of selenium were analyzed for arsenic using differential pulse polarography. Three samples with three percent recoveries and a blank were analyzed for each can of tuna fish. Four sample digestion methods with several variations of each were tested to determine the most reliable technique. An acid digestion procedure using HNO3 and Mg(NO3)2.6H2O with an 18 hour predigestion step gave the best results with an average recovery of 98.2 percent. The selenium concentration of the cans analyzed ranged from 0.034 to 1.20 µg/g with an average concentration of 0.68±0.268 µg/g. The arsenic concentrations of the two cans analyzed were 1.62 µg/g and 2.41 µeg in the low and high selenium cans respectively. The selenium concentrations found in the tuna fish are not excessively high and do not seem to pose a problem. The arsenic concentration of 2.41 µg/g does however approach the maximum allowable level set by the FDA at 2.6 ppm