Constant Current Stripping Research Articles

Chronopotentiometric Stripping Analysis of Proteins and Their Interactions

Chronopotentiometric constant current stripping analysis (CPS) is a highly sensitive method for protein analysis that does not require modification or labeling. During the CPS analysis, proteins yield the so-called peak H, resulting from the catalytic hydrogen evolution reaction. This peak is sensitive to both local and global changes in protein structure, allowing the study of individual proteins, as well as their complexes. CPS analysis has been utilized in studying biomedically important proteins involved in neurodegenerative diseases and cancer. In this article, we describe the development of CPS protein analysis and its progress over the past decade. We also demonstrate the versatility of the method and its potential applications.

Sulfide-binding to Cu(II) in wine: Impact on oxygen consumption rates

This study investigates the relationship between the two main forms of Cu in wine and their impact on the rate of oxygen consumption. The Cu forms were differentiated by medium exchange constant current stripping potentiometry, which classified the Cu as either bound to sulfide or not. Oxygen consumption rates were determined in red, white and model wines after saturation with oxygen. The results for white wines showed that the oxygen consumption was sensitive to the non-sulfide-bound Cu concentration when ascorbic acid was present, and the first order rates ranged from 0.02 to 0.11 h−1. However, the same was not true for wines without added ascorbic acid that showed little influence of Cu form on oxygen decay rates. Cu forms were also found to significantly change in some wines during the oxygen decay experiment. Ascorbic acid is critical in enabling the form of Cu to significantly influence the oxygen reaction rate in wine.

Measurement of labile copper in wine by medium exchange stripping potentiometry utilising screen printed carbon electrodes

The presence of copper in wine is known to impact the reductive, oxidative and colloidal stability of wine, and techniques enabling measurement of different forms of copper in wine are of particular interest in understanding these spoilage processes. Electrochemical stripping techniques developed to date require significant pretreatment of wine, potentially disturbing the copper binding equilibria. A thin mercury film on a screen printed carbon electrode was utilised in a flow system for the direct analysis of labile copper in red and white wine by constant current stripping potentiometry with medium exchange. Under the optimised conditions, including an enrichment time of 500s and constant current of 1.0μA, the response range was linear from 0.015 to 0.200mg/L. The analysis of 52 red and white wines showed that this technique generally provided lower labile copper concentrations than reported for batch measurement by related techniques. Studies in a model system and in finished wines showed that the copper sulfide was not measured as labile copper, and that loss of hydrogen sulfide via volatilisation induced an increase in labile copper within the model wine system.

Determination of Lead(II) by Constant Current Stripping Chronopotentiometry Using Bismuth Film Electrode after Extraction of the Bromide Complex into Propylene Carbonate

AbstractA selective and simple method is presented for the determination of Pb(II) by constant current stripping chronopotentiometric analysis (CCSCP) using bismuth film electrode. This method is based on the extraction of the bromide complex into propylene carbonate, followed by CCSCP measurements in the organic phase. CCSCP studies revealed that Pb(II) gave a characteristic response at about −0.52 V vs. Ag/AgCl on the stripping chronopotentiogram (dt/dE curve) after recording a potential vs. time curve at 3.0 μA. The peak height of Pb(II) response was directly proportional to the initial metal concentration of the aqueous phase in the ranges of 1.0–22.0 μg dm−3 (correlation coefficient 0.997) when the optimized parameters were used. A detection limit (S/N=3) of 0.0880 μg dm−3 Pb(II) was obtained at 180 s deposition time. The relative standard deviation was 3.2% on replicate runs (n=12) for the determination of 10.0 μg dm−3 Pb(II). Analysis of certified reference materials has confirmed the applicability of the proposed method for determination of Pb(II) in soil and water samples.

Bismuth Film Electrode in Metal Complexation Studies: Stripping Analysis of the Pb(II)‐, Cd(II)‐, and Zn(II)‐Binding with Phthalate

AbstractThe possibilities of bismuth film electrode for complexation studies by anodic stripping voltammetry (ASV) and constant current stripping chronopotentiometry (CCSCP) are tested for Pb(II), Cd(II), and Zn(II) in the presence of phthalate. In all cases, labile complexes are detected. The regular signals obtained for the Pb(II)‐phthalate system allow an accurate determination of stability constants by means of the DeFord‐Hume method. As for Cd(II)‐ions, the two overlapping signals usually present in the absence of ligands suffer a similar evolution with the addition of phthalate. Then, the use of an intermediate potential between both signals allows a reasonable estimation of stability constants. In contrast, the two overlapping signals obtained for Zn(II) behave in a quite irregular way in the presence of phthalate, thus hindering any quantitative analysis of the formed complexes.

Signal splitting in the stripping analysis of heavy metals using bismuth film electrodes: Influence of concentration range and deposition parameters

The stripping signals of Pb(II), Cd(II) and Zn(II) in a bismuth film electrode (BiFE) ex situ plated on glassy carbon support were studied by differential pulse anodic stripping voltammetry and constant-current stripping chronopotentiometry. Regular signals were measured for Pb(II), with a good linearity inside a wide concentration range. In contrast, Cd(II) and Zn(II) produce two overlapping signals, one predominating at low metal concentrations and the other at high metal concentrations. For the detailed study of such peak splitting, multivariate curve resolution by alternating least squares has been used concluding that the total area becomes linear with metal concentration in both situations. The reasons of the peak splitting seem to be related to the accumulation of the reduced metal on BiFE in different ways. Even with that complication, the fact that the linear relationship total area versus concentration is hold reinforces the applicability of BiFE for the determination of total concentrations of metal ions inside a wider concentration range than that initially expected. However, the coexistence of signals at different characteristic potentials anticipates important difficulties in the analysis of potential shifts caused by heavy metal complexation.

Adsorptive accumulation in constant current stripping chronopotentiometry as an alternative for the electrochemical study of metal complexation by thiol-containing peptides

Abstract Constant current chronopotentiometric stripping analysis using adsorptive accumulation and negative current (AdSCP) was applied as an alternative for the study of metal complexation of glutathione (GSH) or (γ-Glu-Cys)2-Gly (PC2) with zinc ions on hanging mercury drop electrode. The behavior of the formed Zn-complexes was studied using voltammetric and chronopotentiometric methods. A multivariate curve resolution method by alternating least-squares (MCR-ALS) applied to DP voltammetric and chronopotentiometric measurements of Zn–PC2 system made possible the formulation of a complexation model. Moreover, the use of small currents in AdSCP allows one to obtain acceptable sensitivities and signal separation at very low concentrations, which is important in peptide studies under conditions similar to these of natural media.

Constant Current Stripping Chronopotentiometry for the Study of Adsorbing Inert and Electrochemically Nonreversible Metal Complexes at Low Concentrations: Application to Cd and Zn Metallothioneins

Constant current chronopotentiometric stripping analysis using adsorptive accumulation and negative stripping current (AdSCP) was applied for the study of behavior of rabbit liver Cd-Zn and Zn metallothionein (Cd-Zn-MT, ZnMT) on hanging mercury drop electrode. Electrochemically inert or labile behavior of complexes can be distinguished with the application of high (1000 nA) or low (100 to 20 nA) current. Using high current, no influence of added Cd2+ or Zn2+ ions on the reduction of Cd(II) or Zn(II) complexed within MT molecule was observed, except of additions of Cd2+ to ZnMT, where bound Zn(II) was substituted by cadmium ions. With lowering of stripping current and increasing concentration of added Cd2+ or Zn2+ ions in solution progressive formation of reorganized complex with labile behavior is observed. Parallel measurement using DC voltammetry with different rates of polarization or differential pulse voltammetry were in agreement with AdSCP measurement. However, only chronopotentiometric method combines good sensitivity and signal separation at μM concentrations, inevitable in MT studies.

Application of the Bismuth Film Electrode for Catalytic Adsorptive Stripping Potentiometric Determination of Cobalt in Dimethylglyoxime‐Nitrite System

The application of bismuth film electrodes to the determination of cobalt by constant current adsorptive stripping potentiometry with exploitation of a catalytic effect is presented. The addition of NaNO2 to the solution containing ammonia buffer and dimethylglyoxime results in a 25‐fold enhancement of the adsorptive stripping potentiometric cobalt signal. Several key parameters of the potentiometric stripping mode were optimized, including the composition of the supporting electrolyte, the stripping current, the accumulation potential, and the accumulation time. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=1.4% for a Co concentration of 2 µg L−1), low detection limit (0.07 µg L−1), and good linearity (up to 10 µg L−1, R2=0.998) with a deposition time of 60 s and a stripping current of 10 µA. The method enables the determination of Co in the presence of high excesses of Ni or Zn.

Resolving the copper interference effect on the stripping chronopotentiometric response of lead(II) obtained at bismuth film screen-printed electrode

As copper(II) is a common ion in a variety of analytical samples, its effect on the stripping response of lead(II) at bismuth film screen-printed carbon electrode (BFSPCE) was investigated. The study was conducted using a screen-printed three-electrode system (working, counter and reference electrodes), with the carbon-working electrode plated in situ with bismuth film. Copper present at significant concentration level in samples was found to affect the sensitivity of the electrode by reducing the constant current stripping chronopotentiometric (CCSCP) response of lead(II). Recovery of the lead stripping response at the BFSPCE in the presence of copper was obtained when 0.1 mM ferricyanide was added to the test solution. The ferricyanide added circumvents the detrimental effect of copper(II) by selectively masking the copper ions by forming a complex. The analytical utility of the procedure is illustrated by the stripping chronopotentiometric determinations of lead(II) in soil extracts.

Sensitive electrochemical determination of unlabeled MutS protein and detection of point mutations in DNA.

MutS protein plays an important role in the DNA repair system in prokaryotic and eukaryotic cells; it recognizes unpaired and mispaired bases in duplex DNA and can be used for detection of point mutations in vitro. We have shown that small amounts of this protein can be detected electrochemically at mercury and carbon electrodes without any labeling. Using constant current stripping analysis (CPSA) and mercury electrodes, tens of attomoles of this protein can be detected. The sensitivity of the determination at carbon electrodes is by more than 3 orders of magnitude lower. Using biotinylated DNA duplexes attached to magnetic beads, single-base mismatches and insertion/deletions were recognized by MutS. Picogram amounts of this protein were detected by CPSA after MutS releasing from the beads.

Measurement of total selenium and selenium(IV) in seawater by stripping chronopotentiometry.

We developed a stripping chronopotentiometric method (constant current stripping analysis, CCSA) with a mercury film electrode for selenium quantification in seawater. A sensitivity and detection limit of 222 ms ng(-1) l and 4 ng l(-1) (50 pM), respectively, were accomplished for a 3-min electrolysis time. Compared to the other chronopotentiometric methods available for a single selenium measurement only in natural waters, our procedure exhibits a ten times better sensitivity. It, therefore, allows one to reach the current concentration thresholds found in coastal and oceanic waters (30-200 ng l(-1)). Moreover, a simple change in operating conditions enables one to also quantify Se(IV), a toxic dissolved species. With respect to the other electrochemical methods of current use, our procedure is beneficial because of its ease-of-use: it needs neither degassing step, nor catalyser.

Comparison of constant-current stripping chronopotentiometry and anodic stripping voltammetry in metal speciation studies using mercury drop and film electrodes

Capabilities for heavy metal speciation of anodic stripping voltammetry (ASV) and constant-current stripping chronopotentiometry (SCP) in both mercury drop (HMDE) and mercury film rotating disk (MFE-RDE) electrodes are compared. For this purpose, the Cd(II)–glycine and Cd(II)–polymethacrylate (PMA) systems are used as models of simple labile and macromolecular labile complexes adsorbing onto the electrode, respectively. The results suggest that SCP could be a valuable alternative to the more widespread ASV in this kind of study. Concerning the electrode, the MFE-RDE is less user-friendly than the HMDE, but presents a better definition of both the hydrodynamic conditions during the deposition step and the stripping regime during the oxidation. An important interference in SCP is the dissolved oxygen, which can be minimised by combining relatively large oxidation currents and low stirring rates. Moreover, for Cd–PMA, double peaks have been observed in both ASV and SCP, which seems to be due to the lack of enough ligand excess to complex the metal ions released by the amalgam oxidation. Anyway, this problem can be minimised by optimising the rotation rate of the electrode and ensuring enough ligand excess.

Stripping chronopotentiometric detection of copper using screen-printed three-electrode system—application to acetic-acid bioavailable fraction from soil samples

Single-use sensors, incorporating a three-electrode configuration (graphite carbon-working electrode; carbon-counter electrode and silver/silver chloride-reference electrode), have been fabricated on a polyester substrate using low cost screen-printing (thick-film) technology. These electrodes coupled with constant current stripping chronopotentiometry (CCSCP), has provided a convenient screening tool for on-site detection of trace levels of copper. Modification of the graphite carbon surface based on in situ deposition of mercury film has been carried out. By appropriate choice of supporting medium and applied constant stripping current, well-resolved and reproducible response for copper was obtained. The stripping response for copper following 2 min deposition was linear over the concentration range examined (10–2000 ppb) with detection limit of 6 ppb using 2 M hydrochloric acid (HCl). Successful applications of the sensing device to acetic-acid bioavailable fraction of a certified reference material (CRM 601, a lake sediment) and soil samples are demonstrated.

Determination of arsenic at a gold-plated carbon paste electrode using constant current stripping analysis

A new stripping method for the determination of arsenic in water samples with a gold film-plated carbon paste electrode has been developed for the use in constant current stripping analysis (CCSA). In the novelized procedure, differentiation between As(III) and chemically pre-reduced As(V), the effect of Cu(II) on the response of arsenic, and the stability of sample solutions were studied in detail. Compared to the voltammetric approach, the method utilizing CCSA offers a more rapid procedure with improved analytical characteristics such as reproducibility, selectivity over the Cu(II) ions, or lower detection limit (3 ppb for As(III) and 0.5 ppb for As(V), respectively). The possibilities of the optimized method are demonstrated by determinations of As(III), As(V), and total arsenic in samples of polluted river water.

Simple and rapid determination of iodide in table salt by stripping potentiometry at a carbon-paste electrode.

A simple and rapid procedure, utilising constant-current stripping analysis (CCSA) at a carbon-paste electrode containing tricresyl phosphate as a pasting liquid (TCP-CPE), has been developed for the determination of iodide in table salt. Because of a synergistic accumulation mechanism based on ion-pairing and extraction of iodide in combination with electrolytic pretreatment of the TCP-CPE, the method is selective for iodide and enables direct determination of iodide in samples of table salt containing anti-caking agents such as K(4)[Fe(CN)(6)] (food additive "E 536") or MgO. The iodide content (calculated as KI) can be determined in a concentration range of 2 to 100 mg kg(-1) salt, with a detection limit (S/N=3) of 1 mg kg(-1), and a recovery from 90 to 115%. The proposed method has been used to determine iodide in several types of artificially iodised table salt and in one sample of natural sea salt. The results obtained agreed well with those obtained by use of three independent reference methods (titration, spectrophotometry, and ICP-MS) used to validate the CCSA method, indicating that the developed method is applicable as a routine procedure for rapid testing in salt production process control and in the analysis of marketed table salts.

Perspectives of carbon paste electrodes in stripping potentiometry.

The testing of various types of carbon paste electrodes (CPEs) for their use in stripping potentiometry was carried out by means of specially proposed procedures and by using various model analyte systems. CPEs containing three different pasting liquids (paraffin oil, silicone oil, tricresyl phosphate) were tested as supports for mercury- and gold films, and as substrates for electrolytic, adsorptive, ion-pair forming, and extractive accumulation. Test measurements in organic solvent-containing media and studies of some irreversible electrochemical reactions were performed as well. Individual examples to be studied allowed one to formulate and outline some perspectives of CPEs in potentiometric stripping analysis and related constant current stripping analysis.

Determination of metallothionein at the femtomole level by constant current stripping chronopotentiometry.

Metallothionein (MT) from rabbit liver was analyzed by differential pulse polarography, cyclic voltammetry, square wave voltammetry, and chronopotentiometric stripping analysis (CPSA) with a hanging mercury drop electrode under various conditions. The highest sensitivity of the MT determination was obtained with CPSA which produced a well-developed peak H due to catalytic hydrogen evolution at highly negative potentials. The highest peak H was obtained in borate buffer close to pH 8.0. In this medium, subnanomolar concentrations of MT were detectable. In the adsorptive transfer stripping (medium exchange) experiments, determination of few femtomoles of MT in 5-microL aliquots of the analyte was possible. CPSA determination of MT in various tissues of carp (Cyprinus carpio) yielded values in agreement with the published data.

Stripping potentiometry of indium in aqueous chloride solutions

Stripping potentiometry (SP) has been used effectively for the determination of trace levels of several metal species in solution. Indium ion, which can be readily reduced and has a high solubility in mercury, can be determined directly using SP. The reduction potential of indium is located between those of lead and cadmium, necessitating optimization of several experimental parameters for successful quantitative analysis. A method for the SP of In(III) is presented which utilizes constant current stripping analysis (CCSA) at a mercury-film glassy carbon electrode in KCl solutions in the presence of Pb(II) and Cd(II).

Stripping analysis of nucleic acids at a heated carbon paste electrode.

A new electrically heated carbon paste electrode has been developed for performing adsorptive stripping measurements of trace nucleic acids. Such coupling of electrochemistry at electrically heated electrodes with adsorptive constant-current stripping chronopotentiometry offers distinct advantages for trace measurements of nucleic acids. The application of increased temperatures during the deposition step results in dramatic (4-34-fold, depending on temperature applied) enhancement of the stripping signal. Such improvement is attributed to the accumulation step at the heated electrode. Forced thermal convection near the electrode surface facilitates the use of quiescent solutions and hence of ultrasmall volumes. Using an electrode temperature of 32 degrees C and a quiescent solution during the 1-min accumulation, the response is linear over the 1-8 mg/L range tested, with a detection limit of 0.5 mg/L. Such electrode heating technology offers great promise for various applications involving thermal manipulations of nucleic acids.