Chronopotentiometric Stripping Analysis Research Articles

Disposable DNA electrochemical biosensors for environmental monitoring

Two disposable electrochemical biosensors are described; the first one is useful for the detection of the hybridization of DNA and the second one is able to detect low-molecular weight compounds (toxins, pollutants, drugs) with affinity for nucleic acids. Synthetic single-stranded oligonucleotides have been immobilized onto graphite screen-printed electrodes using adsorption at a controlled potential. The probes were hybridized with different concentrations of the complementary sequences. The hybrids formed on the electrode surface were evaluated by chronopotentiometric stripping analysis using daunomycin hydrochloride as an indicator of the hybridization reaction. The DNA sensor was able to detect 0.2 mg l −1 of a 21-base target sequence. The determination of low-molecular weight compounds with affinity for DNA was measured by their effect on the oxidation signal of the guanine peak of calf thymus immobilized on the electrode sensor and investigated by chronopotentiometric analysis. The DNA biosensor is able to detect known intercalating and groove binding compounds. Detection limits of 0.3, 0.2 and 10 mg l −1 were obtained for daunomycin, polychlororinated biphenyls (PCBs) and aflatoxin B1, respectively. Applicability to river water samples was demonstrated.

Effects of complexants and surfactants on the deposition and stripping steps in chronopotentiometric stripping analysis and anodic stripping voltammetry: implications for operationally defined speciation measurements

The influence of humic substances, Triton X-100 and red wine on the deposition and stripping steps in anodic stripping voltammetry and chronopotentiometric stripping analysis (CPSA) of Cu(II) and Pb(II) was investigated. Fulvic acid and Triton X-100 had an impact only on the stripping step; humic acid and red wine influenced both steps. Failure to establish the impact of matrix components on the individual deposition and stripping steps could result in erroneous interpretation of metal ion speciation.

Disposable DNA electrochemical sensor for hybridization detection

A disposable electrochemical sensor for the detection of short DNA sequences is described. Synthetic single-stranded oligonucleotides have been immobilized onto graphite screen printed electrodes with two procedures, the first involving the binding of avidin-biotinylated oligonucleotide and the second adsorption at a controlled potential. The probes were hybridized with different concentrations of complementary sequences. The formed hybrids on the electrode surface were evaluated by differential pulse voltammetry and chronopotentiometric stripping analysis using daunomycin hydrochloride as indicator of hybridization reaction. The probe immobilization step, the hybridization event and the indicator detection, have been optimized. The DNA sensor obtained by adsorption at a controlled potential was able to detect 1 μg/ml of target sequence in the buffer solution using chronopotentiometric stripping analysis.

Chronopotentiometric stripping analysis as a probe for copper(II) and lead(II) complexation by fulvic acid: Limitations and potentialities

Fulvic acid exerts its influence only in the stripping step of chronopotentiometric stripping analysis (CPSA). Oxidation of reduced metal accumulated at a mercury-drop electrode is facilitated in the presence of fulvic acid, thus causing a reduction in the stripping time relative to that for a ligand-free solution, even when the same total amount of metal is oxidised. Data must be interpreted with caution; use of the term `labile' metal can be very misleading. CPSA is a potentially powerful tool to probe metal ion complexation over a wide range of ligand-to-metal ratios, allowing independent variation of both the total amount of metal oxidised and its rate of oxidation. The characteristic stripping peak parameters (stripping time, peak potential, and peak half-width) give information on the apparent stability and heterogeneity of the complexes formed by fulvic acid with copper(II) and lead(II).

Constant Current Chronopotentiometric Stripping Analysis of Bioactive Peptides at Mercury and Carbon Electrodes

Constant current derivative chronopotentiometric stripping analysis (CPSA) was used to study bioactive peptides [Lys8]-vasopressin and angiotensin II at carbon paste electrode (CPE) and hanging mercury drop electrode (HMDE). Both peptides contain a single tyrosine residue which is oxidized at CPE close to +0.6 V (against Ag/AgCl/3 M KCl electrode) producing peak Y; this peak was by about 15 mV more positive in vasopressin than in angiotensin II. At HMDE vasopressin yielded peak S due to the reduction of the disulfidic bond in the peptide. No peak S was observed with angiotensin II as it does not contain any cystine/cysteine residues. Vasopressin produced different catalytic hydrogen reduction signals in media with cobalt ion and in media not containing any metal ion. The signal produced in the latter media (peak H), which appeared close to −1.7 V, was well separated from the background. No catalytic hydrogen reduction signal was obtained with angiotensin II. The above mentioned CPSA signals can be applied for the determination of the respective peptide at nanomolar concentrations. The least sensitive peak S appears which requires at least 100 nM vasopressin concentration at moderate accumulation time. By two orders of magnitude, higher sensitivities can be obtained with peaks Y and H. In measuring these peaks CPSA shows significant advantages over the voltammetric stripping techniques.

Interactions of antitumor drug daunomycin with DNA in solution and at the surface

The interaction of the antitumor drug daunomycin with double-stranded (ds) calf thymus DNA was studied in solution and at the electrode surface by means of cyclic voltammetry and particularly by constant-current chronopotentiometric stripping analysis (CPSA) with the carbon paste electrodes (CPE). As a result of intercalation of this drug between the base pairs in dsDNA, the CPSA daunomycin peak δ decreased and a new more positive shoulder δ b appeared. This shoulder was attributed to the oxidation of the drug intercalated in DNA. Under the same conditions almost no changes in the DNA peak G ox (due to oxidation of guanine residues) were observed. It was shown that daunomycin adheres strongly to the bare CPE (resisting washing) so that a daunomycin-modified electrode can be easily prepared. Daunomycin immobilized at CPE interacted with DNA on immersion of the modified electrode into the dsDNA solution, showing a decrease of peak δ and a well-separated peak δ b instead of the shoulder (which resulted from the interaction of DNA with daunomycin in solution). When the DNA-modified CPE was immersed into a daunomycin solution the peak G ox increased in dependence on daunomycin concentration or on the time of interaction of daunomycin with dsDNA at the electrode surface. Such changes in peak G ox were observed only at submicromolar concentrations of daunomycin. At higher daunomycin concentrations or at longer interaction time intervals a daunomycin peak appeared, which was substantially smaller and more positive than the peak of free daunomycin. The increase of the DNA peak G ox was attributed to interaction of daunomycin from the side of the DNA double helix not contacting the electrode surface. Such binding may induce changes in the DNA structure including bending of the DNA molecule which may result in the increase of peak G ox. Our results thus suggest that the interaction of daunomycin with DNA anchored at the surface may significantly differ from that with DNA in solution. The prospects of using of electroanalytical methods in studies of DNA–drug interactions are discussed.

Chronopotentiometric stripping of DNA at mercury electrodes

AbstractDenatured (single‐stranded, ss) and native (double‐stranded, ds) DNAs were studied by constant current chronopotentiometric stripping analysis (CPSA) at a hanging mercury drop electrode (HMDE). In agreement with the previous voltammetric studies at neutral pH values ssDNA produced CPS cathodic peak CA (due to reduction of cytosine and adenine) and anodic peak G (due to oxidation of the guanine reduction product) at dt/dE against E curves. The same peaks produced by dsDNA were substantially smaller. Differences in heights (areas) of peaks G and CA produced by ss and dsDNAs at partial and full electrode coverage are compared and discussed. Using CPSA a well‐developed and symmetrical peak CA was obtained at low DNA concentrations compared to a poorly measurable inflection produced by differential pulse or linear sweep voltammetries under the same conditions. The CPS peak CA can be used also in adsorptive transfer stripping (AdTS, medium exchange) experiments. In the previous AdTS voltammetric measurements only peak G was exploited while the voltammetric peak CA was poorly defined to be of any use in combination with DNA‐modified electrodes. CPS peaks were measured in the presence and in absence of air. It was shown that in the presence of air peak CA is enhanced while peak G decreased. We compared the CPSA of ssDNA at the mercury and carbon paste electrodes (CPE). The CPS peak G (obtained with HMDE) seems to be the best choice for the electrochemical determination of DNA in highly diluted solution. With 10 min adsorptive preconcentration a detection limit below 20 ng of ssDNA per mL was obtained at HMDE. At CPE the limit of detection (of the same ssDNA) was at least two‐fold higher.

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.

Trace measurements of plasmid DNAs by adsorptive stripping potentiometry at carbon paste electrodes

Supercoiled, linear and denatured forms of plasmid pUC19 DNA can be adsorbed at carbon paste (CPE) and pyrolytic graphite (PGE) electrodes and detected by constant current chronopotentiometric stripping analysis (PSA) at low bulk concentrations. The determination is based on the PSA peak at about 1.0 V (against Ag|AgCl) due to the oxidation of guanine residues in the DNA. In agreement with earlier voltammetric data obtained with chromosomal DNAs at carbon electrodes, the denatured DNA produces a higher signal than linear and supercoiled DNAs. Compared with voltammetry, the sensitivity of PSA is higher by several orders of magnitude. PSA detection limits (obtained with a CPE) are about 100 ng ml −1 for supercoiled and linear DNAs and 15 ng ml −1 for denatured DNA. This great increase in sensitivity of the analysis at carbon electrodes offers new possibilities for electrochemical research, involving various forms of plasmid DNA.

Determination of adenine by chronopotentiometric stripping analysis with nafion‐modified electrode

AbstractThe determination of adenine by chronopotentiometric stripping analysis with Nafion‐modified electrode is reported. Various conditions for the determination of adenine were explored. In the Britton‐Robinson (BR) buffer solution (pH 3.3), preconcentration was carried out at −0.2 V (vs. SCE) for 90 seconds by chronopotentiometric stripping analysis. The peak height was proportional to the adenine concentration between 2.5 × 10−7 and 8.0 × 10−6 mol/L. For 10 repetitive measurements, the relative standard deviation for 5 × 10−6 mol/L, adenine was 2.2%. The method was fairly free of interference, and the results of real samples were satisfactory.

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.

Determination of nickel and cobalt in natural waters and biological material by reductive chronopotentiometric stripping analysis in a flow system without sample deoxygenation

The instrumental set-up consists of a thin-layer cell with a glassy carbon working electrode and an inlet valve by means of which six different solutions can be sucked through the cell. The system is controlled by a microprocessor and suction is provided by means of a peristaltic pump. In the first step of the analytical cycle, a mercury film is plated onto the glassy carbon electrode and then the sample solution is allowed into the cell and nickel(II) and cobalt(II) are potentiostatically adsorbed onto the mercury film as their dimethylglyoxime complexes. Nickel(II) and cobalt(II) are then reduced in a medium of 5 M calcium chloride by means of constant current and simultaneously the microprocessor records the potential vs. time behaviour of the working electrode. Finally the mercury film is removed by mild oxidation in an iodine/iodide solution and the glassy carbon surface is cleaned with ethanol and sodium hydroxide prior to the next analytical cycle. The cobalt(II) and nickel(II) concentrations are evaluated by means of a standard addition procedure. The technique was applied to drinking, estuarine and sea water samples. The detection limits on the one sigma level after one minute of potentiostatic adsorption were 9 and 11 ng l −1 for nickel(II) and cobalt(II), respectively. Nickel(II) and cobalt(II) were determined in reference samples of bovine liver and sea-water sediments after acid digestion. In order to obtain correct cobalt values, it was necessary to reduce cobalt(III) species formed during the acid digestion with sodium tetrahydroborate.

Use of a single carbon fibre electrode for chronopotentiometric stripping analysis

The use of a single carbon fibre electrode for chronopotentiometric stripping analysis is described. In experiments using cadmium(II) it is shown that the carbon fibre electrode does not require the use of stirred solutions during plating and stripping. This effect is believed to be due to the fact that the diameter of the carbon fibre electrode is less than the diffusion layer thickness.The [mercury(II)] to [cadmium(II)] ratio is shown to have a significant effect on the magnitude of the measured stripping time. The effect on the stripping time of the concentration of cadmium(II) and the plating time have been examined.Mixtures of cadmium(II), lead(II) and copper(II) have been examined and it was found that the stripping times are longer in 0.11 than in 0.01 M hydrochloric acid.

Determination of thorium and scandium by indirect chronopotentiometric stripping analysis

A highly sensitive chronopotentiometric determination of thorium or of scandium is described. It is based on the substitution of thorium or scandium for lead (or zinc) in the lead—EDTA complex, and measurement of the liberated lead by deposition on a mercury film electrode, followed by a chemical oxidation stripping process during which the potential of the mercury electrode is monitored. Thorium has been determined at concentrations in the range 10 −5–10 −7 M by use of deposition times from 1 min to 1 hr.

1127. Glass curtains—handle with care!: Abel, R. R. (1966). Washing machine and fibreglass. Archs Derm.93, 78

Selenium is an element both toxic and essential for humans, animals and microorganisms. The selenium effect depends mostly on its chemical form and concentration. For the determination and monitoring of selenium content in different foodstuffs reliable and selective analytical method should be applied. In this work two modifications of the chronopotentiometric stripping analysis (CSA) using mercury film electrode were investigated and optimised. The first one included deaeration step (CSA-DEA) prior selenium deposition in the electrode, while applying medium-exchange technique (ME-CSA) time consuming deaeration step was avoided. Experimental parameters such as electrolysis potential, electrolysis time, dissolution current, linearity and the concentration of the CaCl2 were optimised in standard solutions of tetravalent selenium. Detection limits obtained for the CSA-DEA and ME-CSA modifications were 0.40 and 1.15 ppb, respectively. Interferences from copper, lead and iron were examined as well. For the methods verification standard reference material, wheat durum flour (RM 8436), was used. Two modifications of the chronopotentiometric stripping technique were applied for selective determination of total, Se6+, and the sum of Se0, Se2− and Se4+ in different samples of flour, garlic and sunflower seed. Recovery test as well as the analysis of the reference material confirmed the correctness of the defined methods. Selenium contents determined with two different modifications were in agreement.