Constant Current Stripping Analysis Research Articles

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.

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.

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).

Determination of copper, zinc, and selenium in human plasma and urine samples by potentiometric stripping analysis and constant current stripping analysis

Potentiometric stripping analysis and constant current stripping analysis are proposed as routine methods for analysis of copper, zinc and selenium in plasma and urine samples. The analytical performance of these methods is comparable with that reported for atomic absorption spectrometry. However the low cost, greater simplicity of the apparatus, and the facility of execution make this methodology a valid candidate for routine application in Clinical Chemistry laboratories.

Measurement of Copper in Sea-water by Constant Current Stripping Analysis (CCSA) With a Rotating Gold Disk Electrode

A chronopotentiometric stripping method [constant current stripping analysis (CCSA)] using a rotating gold disk electrode for measurements of copper in sea-water is described. Compared with a CCSA method using a stationary gold film electrode, the new method has a sensitivity 2.5 times higher and a detection limit of 11 ng l–1 after a 5 min deposition time, and eliminates from the analysis the time needed for gold plating. The precision and accuracy of this method agree well with those obtained by other techniques. Vertical profiles of copper obtained by two different chronopotentiometric stripping methods, CCSA and potentiometric stripping analysis (PSA) in west Brittany coastal waters show that the measurement of copper by CCSA coupled with a gold disk electrode appears to be less affected by organic matter than those made by PSA with a mercury electrode.

Determination of tin in canned fruit juices by stripping potentiometry

The total tin concentration in five different kinds of canned fruit juices has been determined by using constant current stripping analysis on a gold film electrode, and potentiometric stripping analysis on a mercury film electrode, the concentration in the samples ranging between 40 and 80 mg l −1. The total time for one determination, including sample preparation, is approximately 10 min and the relative precision around 8%. The results obtained by the two electroanalytical techniques agreed satisfactorily with those results obtained by flame atomic absorption spectrophotometry.

Studies on the second reciprocal derivative constant-current stripping analysis

Theoretical and experimental investigation have been made on a method called the second reciprocal derivative constant-current stripping analysis (SRD-CCSA). The SRD-CCSA is based on the measurement of the d 2 t/d E 2 signal given by the curve of (d 2 t/d E 2) versus the electrode potential ( E). The d 2 t/d E 2- E curve gives a maximum value (d 2 t/d E 2) max and a maximum value ((d 2 t/d E 2)) min, which show as two peaks on the curve. Either of the heights of the peaks and the sum of absolute values of the two peaks are proportional to the bulk concentration of the analyte in solution, and they are much larger than (d t/d E) p in the first reciprocal derivative constant-current stripping analysis (FRD-CCSA). The ratio of peak-peak height in the SRD-CCSA to peak height in the FRD-CCSA is about 43n (where n represents the number of electrons transferred during the electrode process for the analyte). Potential difference ( W pp) between the two peaks is 48.2 mV n −1 at 25°C in the SRD-CCSA, which is noticeably smaller than the half-height width W p/2, 65.5 mv n −1, in the FRD-CCSA. The theory was verified with a home-made multireciprocal derivative measuring instrument. The experimental results were in good agreement with the theoretical ones.

Derivative chronopotentiometric stripping analysis of insulin

AbstractPorcine insulin was analyzed in the presence of dissolved oxygen by constant current stripping analysis (CCSA) and potentiometric stripping analysis (PSA). The CCSA analysis involves the constant current reduction of mercuric insulin thiolate following its potentiostatic accumulation on a hanging mercury drop electrode. The CCSA response was quantitatively enhanced in the presence of dissolved oxygen. The PSA analysis involves the oxidation, by dissolved oxygen, of sulfhydryl groups in reduced insulin following its accumulation on the HMDE at −900mV (vs. SCE).

Effect of model organic compounds on potentiometric stripping analysis using a cellulose acetate membrane-covered electrode

The effects of model surfactants (sodium dodecyl sulfate, Triton X-100), proteins (ovalbumin, gelatin), and carbohydrates (agar, starch) as well as D-camphor and humic acid on a cellulose acetate dialysis membrane-modified mercury film electrode (CM-MFE) in potentiometric stripping analysis (PSA) are described. The CM-MFE (1000 amu molecular weight cutoff) minimized interference by these compounds to the PSA measurement. The constant current stripping analysis (CCSA) mode was found to provide a more stable response than the used of Hg(II) as chemical oxidant with the CM-MFE

Reciprocal derivative constant-current stripping analysis

Reciprocal derivative constant-current stripping analysis (RD-CCSA) is based on the measurement of d t/d E converted from a derivative signal, d E/d t, vs. electrode potential ( E) during the stripping of analyte under galvanostatic conditions from a mercury-film electrode after preconcentration. The potential transient signal ( E-t) in normal chronopotentiometric stripping analysis (CPSA) is converted in RD-CCSA into a stripping peak (d T/d E) p the height of which is proportional to the bulk concentration of analyte in solution. The theory of RD-CCSA has been derived, and validated by the good correlation obtained between the theory and experimental data. Compared with normal CPSA, RD-CCSA is more sensitive and has higher resolution. The detection limit for cadmium is 6 × 10 −10 M. Simultaneous determination of Cd 2+, In 3+, and Tl + (for which the differences between the stripping peak potentials are 58 and 50 mV, respectively) which is impossible for normal CPSA, voltammetry or differential pulse polarography, has become possible with RD-CCSA.

Constant-current stripping analysis for iron(III) by adsorptive accumulation of its Solochrome Violet RS complex on a carbon-fibre electrode

The optimum experimental conditions with respect to pH, adsorption potential and Solochrome Violet RS concentration for the constant-current stripping determination of iron(III) have been investigated. The suggested procedure has been used for the determination of iron(III) in tap water and the accuracy investigated both by analysing standard solutions and by comparison with results obtained by atomic-absorption spectrometry. The relative precision was 6–13% and the detection limit for iron(III), set by the reagent blank, was approximately 1 μg/l. The results obtained with a mercury-film coated carbon-fibre flow electrode have been compared with those obtained with a hanging mercury drop electrode. The advantages of measuring electrode potential vs. time instead of vs. current have been evaluated.

Computerized flow constant-current stripping analysis for some electroactive organic compounds: Application to the determination of erythromycin in urine

The possibility of determining various electroactive organic compounds, e.g., erythromycin and riboflavin, by adsorptive preconcentration at constant potential on a mercury-coated carbon-fibre electrode in a flow system prior to stripping with a reductive constant current, is demonstrated. The advantages of measuring the electrode potential vs. time instead of current vs. electrode potential during stripping, the possibility of operating with non-deoxygenated solutions, the increased linear calibration range is in the multiple scanning mode, and the possibility of using the technique for detection in liquid chromatography, are discussed. An analytical procedure for the determination of erythromycin at the 10 −6 M level in urine after extraction with diethyl ether is described.

Computerized flow constant-current stripping analysis for nickel(II) and cobalt(II) with carbon fibre and modified carbon fibre electrodes

Nickel (II) and cobalt (II) are determined by constant-current stripping analysis, with mercury- coated carbon fibre electrodes, in non-deoxygenated solutions after potentiostatic adsorptive accumulation of their dimethylglyoxime complexes. By adding several stripping scans, each obtained after a short period of potentiostatic deposition, instead of a single scan obtained after the same total time of potentiostatic adsorption, the linear range between the analytical signal and the analyte concentration can be extended. By using pulsed-potential procedures for adsorptive accumulation, cobalt (II) can be determined in the presence of a larger amount of nickel (II) and vice versa. Carbon fibre electrodes were modified by sucking ethanolic solutions of either dimethylglyoxime (of Nafion and dimethylglyoxime) through the electrodes; Nafion did not affect the general behaviour of this electrode. The background of the modified electrodes was lower than that of the unmodified electrodes. The accuracy of the method was confirmed by analysis of sea- water reference samples. The detection limit for nickel (II) was about 40 ng l −1 for a total potentiostatic deposition time of 100 s (5×20 s); the reagent blank was about 150 ng l −1 under these conditions.

Computerized flow constant-current stripping analysis for gold(III) with carbon or platinum fibre electrodes

Gold(III) is determined in hydrochloric acid media to which 1–5 mg l −1 of mercury(II) and copper(II) (if not already present in the sample) have been added. Potentiostatic deposition of gold onto the carbon or platinum fibre electrode is achieved by means of pulsed-potential electrolysis; e.g., each pulse is composed of electrolysis for 9 s at −0.60 V vs. mercury drop electrode followed by oxidation of copper and mercury by applying a potential of 0.30 V for 1 s. For constant-current stripping (0.5−1μA), 2 M hydrochloric acid in 40% (v/v) ethanol is the best medium. A detection limit (three sigma level) of 1 μg l −1 gold is estimated for a total electrolysis time of 900 s.

Flow potentiometric and constant-current stripping analysis for silver(I) with carbon- and platinum-fibre electrodes

At concentrations above 50 μg l −1, silver(I) is determined in nitric acid medium by means of potentiostatic deposition onto a platinum-fibre electrode and subsequent constant-current stripping in the sample or potentiometric stripping in a potassium permanganate medium. Interference from copper(II) is reduced by a pulsed potential procedure whereby copper deposited onto the fibre electrode is reoxidized intermittently. At concentrations below 50 μg l −1, silver(I) is determined by using a mercury-coated carbon-fibre electrode and constant-current stripping in acetonitrile containing 0.20 M perchloric acid. Potentiostatic deposition for 30 min yielded a detection limit of 0.24 μg l −1 silver(I) at the 3σ level.

Flow potentiometric and constant-current stripping analysis for arsenic(V) without prior chemical reduction to arsenic(III): Application to the Determination of Total Arsenic in Seawater and Urine

Arsenic(V) is reduced to elemental arsenic on a gold-coated platinum-fibre electrode at electrolysis potentials below −1.60 V vs. Ag/AgCl and subsequently re-oxidized, either by means of a constant current, or chemically, with gold(III) as oxidant. Total arsenic in acidified seawater can be determined by means of electrolysis for 60 s at −1.80 V vs. Ag/AgCl and subsequent stripping in 4 M hydrochloric acid containing 2.5 M calcium chloride. The detection limit obtained after 60 s of electrolysis (ca. 0.1 μg1 −1) is about ten times lower than that obtained by the electrochemical stripping methods for arsenic(III) reported hitherto. Total arsenic in urine is determined after digestion with nitric acid and hydrogen peroxide.

Simultaneous determination of mercury(II), copper(II) and bismuth(III) in urine by flow constant-current stripping analysis with a gold fibre electrode

Urine samples are treated with concentrated nitric acid and potassium permanganate ar 70°C for 10 min prior to injection. The flow electrode system consists of a 10-μm diameter gold fibre working electrode, a glassy carbon reference electrode and a platinum counter electrode. In the fully automated constant-current stripping procedure, the gold fibre is first covered with a fresh gold film after which the sample is electrolyzed for 1 min prior to stripping in 0.1 M hydrochloric acid with a current of 0.1μA. The procedure is repeated on a spiked sample after which the sample analyte concentrations are evaluated and presented digitally and graphically on a printer/plotter. The results obtained for bismuth, copper and mercury in a urine reference sample were 36.9, 39.7 and 47.7 μg l −1 with standard deviations ( n=10) of 3.2, 4.2 and 2.1, respectively. The certified values for copper and mercury were 45 and 51 μg l −1; no certified value was available for bismuth.