Fast Scan Differential Pulse Voltammetry Research Articles

Fast scanning voltammetric detector for high performance liquid chromatography

This article describes the application of fast scan differential pulse voltammetry on a glassy carbon electrode as a working electrode in a wall-jet arrangement in combination with a high performance liquid chromatography. During the characterization of electrochemical detection, the separability, the repeatability, and the concentration characteristics for determination of common antioxidants in standard solutions were found. Finally, as an application of the technique, the optimized procedure has been used for the first time to determine antioxidants contained in tea samples by applying a simple extraction procedure.

Differentiation between phenol- and amino-substances in voltammetry determination of synthetic antioxidants in oils

Abstract The paper describes a method of voltammetric determination of antioxidants in lubricating oils developed with the use of Linear Sweep Voltammetry (LSV) and Fast Scan Differential Pulse Voltammetry (FSDPV). Experimental conditions have been found for simultaneous determination of phenol-based antioxidants and amino-antioxidants: the phenols can be electrochemically oxidized using the polarisation of gold disc electrode (AuDE) in the potential range of 0–1400 mV in 0.2 M H2SO4 in the presence of ethanol and acetonitrile at the ratio of 3:1. Secondary aromatic amines can be determined directly in this supporting electrolyte; the presence of phenolic antioxidants does not interfere with this analysis. On the other hand, secondary aromatic amines interfere with the determination of phenolic substances; therefore, the amines present have to be eliminated in a suitable way. A procedure for masking the aromatic amines using their reaction with nitrous acid has been suggested and optimised. The nitrosamines thus formed can be used for sensitive and selective determination of amino-antioxidants by means of cathodic reduction on the hanging mercury drop electrode (HMDE) using Fast Scan Differential Pulse Voltammetry. The method was applied in analysis of real samples of lubricating oils.

Electrochemical Reduction of 6-Benzylaminopurine at Mercury Electrodes and Its Analytical Application

The commercial exploitation of modern, in vitro plant micropropagation methods, featuring synthetic cytokinins as essential components of the cultivation media, is rapidly increasing. Thus, development of rapid, inexpensive and less labour-intensive methods for monitoring cytokinin levels could help to optimise media consumption and reduce costs. Therefore, we studied the electrochemical behaviour of the highly active and widely used cytokinin, 6-benzylaminopurine (BAP), in aqueous solutions by DC polarography, cyclic and differential pulse voltammetry and constant potential coulometry. The BAP molecule undergoes a six-electron irreversible reduction process that starts with four-electron reduction of the protonated pyrimidine skeleton. As a result of elimination of the amine from the side chain, the N1=C6 electrochemically active bond is re-established and the last two-electron step follows. The intermediates of constant potential electrolysis were identified using mass spectrometric analysis. The dissociation constant (pKa) of BAP was found, spectrophotometrically, to be 4.16. BAP concentrations were measured using two voltammetric techniques, fast-scan differential pulse (FSDPV) and adsorptive stripping voltammetry (AdSV). The relative standard deviations for these two methods were lower than 4.5% (c < 28.7 ng ml-1) and 1.2% (c < 20 ng ml-1), while the detection limits were 7.88 and 0.80 ng ml-1, respectively. Using these techniques, BAP was determined in two types of nutrition media used for the micropropagation of plants in vitro (Gerbera and banana media). In the case of media samples containing the interfering agent adenine (i.e. Gerbera plant medium), the analyte was preconcentrated by ion-exchange chromatography and immunoaffinity chromatography. This preconcentration process gives 92% recovery. In contrast, it was possible to determine BAP levels in simple banana cultivation medium directly, without any pre-purification process. Both methods, reported here (FSDPV and AdSV), were found to be useful for rapidly monitoring BAP consumption by plants during their growth under in vitro conditions.

Electrochemical reduction of chloridazon at mercury electrodes, and its analytical application.

The electrochemical behavior of the herbicide chloridazon, I (pyrazon), at different pH is described. The electrode reaction (one wave in acidic media and another in alkaline media), investigated using direct current and pulse voltammetry, controlled-potential coulometry, and HPLC-MS, is a combination of the electroreduction (two-electron in the first step) and a kinetic process as a result of which simple compounds (HCl, NH3) are released and, moreover, a five-membered pyrrole cycle is formed in strongly acid media. Products of the kinetic reaction are further reducible. The dissociation constant of I, pKa = 2.96, was found spectrophotometrically. Fast-scan differential pulse voltammetry (FSDPV) was used for determination of I; the detection limit was 2.7 x 10(-8) mol L(-1) (0.006 microg L(-1)) at pH 2.3. Chloridazon was determined in spiked drinking and river water.

Electroanalytical study of salazosulfapyridine and biseptol components at the mercury electrode

The voltammetric behaviour of two sulfonamides, salazosulfapyridine (I) and sulfamethoxazol (II), and trimethoprim (III) was investigated in aqueous medium at various pH using classical and tast DC-polarography and fast scan differential pulse voltammetry (FSDPV) at a mercury dropping and a static drop electrode. Substance I, which contains an azo group, is reduced to a hydrazine derivative. The reduction of II takes place, with difficulty, by a radical mechanism. In case of III the reduction is a two- or four-electron process (depending on the acidity) that leads to the di- or tetra-hydropyrimidine derivative as a final product. The determination of these susbstances was performed using FSDPV and adsorptive stripping voltammetry (AdSV). It is dependent on the pH-value of the medium. For concentrations less than 60 ng/ml in model samples the relative standard deviations were smaller than 5% and the detection limits calculated from regression analyses were in the range 0.2–0.5 ng/ml. The determination of I–III was performed in tablets, too; the results were in accordance with data supplied by the manufacturers.

Voltammetric behaviour of some nitropesticides at the mercury drop electrode

Classical DC-polarography and fast scan differential pulse voltammetry (FSDPV) were applied to study the reduction mechanism of five nitropesticides (trifluralin, benfluralin, pendimethalin, bromofenoxim, fluoroglycofen-ethyl) at a dropping mercury electrode (DME) and at a static mercury drop electrode (SMDE) in a medium of 47–49% (v/v) alcohol or 10–20% (v/v) dimethylformamide. The nitro groups were reduced to hydroxylamine derivatives or further to the corresponding amines depending on the type of compound and of solution acidity. The determination of nitropesticides was performed using FSDPV and adsorptive stripping voltammetry (AdSV) in model samples. The relative standard deviations were smaller than 4.5% for concentrations higher than 2 ng/ml. The detection limits were found both experimentally and calculated from regression analyses. According to the experimental conditions their values were in the range 17–160 ng/ml or 0.1–2.8 ng/ml for FSDPV or AdSV, respectively. The nitropesticides in artificially contaminated soils were determined after two to three times extraction with acetone. The recovery was about 96%.

Polarographic behaviour of some s-triazine herbicides and their determination by adsorptive stripping voltammetry at the hanging mercury drop electrode

The electrochemical behaviour of six triazine herbicides (atrazine, terbutylazine, desmetryne, prometryne, terbutryne and methoprotryne) was studied by fast scan differential pulse voltammetry (FSDPV) at a static mercury drop electrode and by constant potential coulometry. The adsorption of these compounds at the mercury electrode was employed for their determination by adsorptive stripping voltammetry (AdSV) in Britton-Robinson buffers. The detection limits calculated from regression analyses ranged between 0.1 and 0.9 μg/l. Preconcentration (solid phase extraction on a C18 column) was used for the determination of very low contents in water samples. The recovery was 97–99.6%.

Determination of Acridine, Benz[c]acridine and Dibenz[a,h]acridine by Fast Scan Differential Pulse Voltammetry and Adsorptive Stripping Voltammetry

The behaviour of the title compounds in fast scan differential pulse voltammetry and adsorptive stripping voltammetry was studied and the optimum conditions were found for their determination by FS DPV over the concentration region of (2 - 100) .10-7 mol l-1 and by AdSV over the concentration regions of (2 - 10) .10-8 mol l-1 for acridine and dibenz[a,h]acridine and (2 - 100) .10-9 mol l-1 for benz[c]acridine. Practical applicability of the methods to the monitoring of the chemical efficiency of destruction of the carcinogens with potassium permanganate was tested.

Polarographic and Voltammetric Determination of 1-(2'-Nitrophenyl)-3,3-dimethyltriazene

The polarographic behaviour of 1-(2'-nitrophenyl)-3,3-dimethyltriazene in mixed aqueous-methanolic solvent was investigated by tast polarography, differential pulse polarography, and fast scan differential pulse voltammetry at a hanging mercury drop electrode. A mechanism is suggested for the reduction of the compound investigated. The optimum conditions were found for the determination of this analyte by tast polarography over the concentration region of 100 to 2 μmol l-1 and by differential pulse polarography or fast scan differential pulse voltammetry at a hanging mercury drop electrode over the region of 100 to 0.2 μmol l-1. Additional sensitivity increase in the last-mentioned technique was achieved by adsorptive accumulation of analyte on the hanging mercury drop surface, owing to which the concentration region was depressed to 0.1 - 0.02 μmol l-1.

The Polarographic and Voltammetric Determination of N,N-Dimethyl-4-amino-3'-nitroazobenzene

The polarographic reduction of N,N-dimethyl-4-amino-3'-nitroazobenzene was studied by tast polarography and differential pulse polarography, constant potential coulometry and cyclic voltammetry and mechanism was proposed for the reduction. Optimal conditions were found for the determination of the test substance using tast polarography in concentration range 1 . 10-4 - 2 . 10-6 mol l-1, differential pulse polarography at classical dropping mercury electrode and fast scan differential pulse voltammetry at a hanging mercury drop electrode in range 1 . 10-4 - 2 . 10-7 mol l-1 and linear scan voltammetry at a hanging mercury drop electrode in range 1 . 10-5 - 2 . 10-8 mol l-1. A further increase in the sensitivity was achieved through adsorptive accumulation of the test substance on the surface of the working electrode, permitting the determination to be carried out in the concentration range 1 . 10-7 - 2 . 10-9 mol l-1.

The Polarographic and Voltammetric Determination of 1-(3'-Carbamoylphenyl)-3,3-dimethyltriazene

A study was made of the polarographic reduction of the title triazene, a mechanism was proposed for this process and optimal conditions were found for its analytical application using tast polarography in the range 1 . 10-4 - 2 . 10-6 mol l-1, differential pulse polarography in the range 1 . 10-4 - 2 . 10-7 mol l-1 and fast scan differential pulse voltammetry at a hanging mercury drop electrode in the range 1 . 10-4 - 2 . 10-7 mol l-1. The sensitivity of the latter technique was increased through adsorptive accumulation of the test substance on the surface of the working electrode, permitting determination in the concentration range 1 . 10-7 - 2 . 10-9 mol l-1.

The Polarographic and Voltammetric Determination of 1(4'-Carbamoylphenyl)-3,3-dimethyltriazene

A study was made of the polarographic behaviour of 1-(4'-carbamoylphenyl)-3,3-dimethyltriazene and optimum conditions were found for its determination by tast polarography and differential pulse polarography at a static mercury drop electrode and by fast scan differential pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 . 10-4 to 2 . 10-7 mol l-1. A further increase in the sensitivity can be achieved through adsorptive accumulation of the test substance on the surface of a hanging mercury drop, permitting the determination to be extended to the concentration range 1 . 10-7 - 2 . 10-9 mol l-1.

Polarographic and Voltammetric Determination of Chlorobenzene, Benzyl Chloride and Melphalan

Conditions were found for the determination of chlorobenzene and benzyl chloride in dimethylformamide and of Melphalan in ethanol-water medium (4 : 1) using tast polarography at a classical dropping mercury electrode in the concentration range 1 . 10-3 - 2 . 10-5 mol l-1. Differential pulse polarography permits the range for the determination of benzyl chloride to be extended to 1 . 10-5 - 2 . 10-6 mol l-1. The use of fast scan differential pulse voltammetry and linear scan voltammetry at a hanging mercury drop electrode did not lead to an increase in the sensitivity of the determination because of the very negative half-wave potential values and high irreversibility of the processes involved.

Vitamin B 12 as coordinating agent for the voltammetric determination of nitrite in natural waters

The determination of trace amounts of nitrite in aqueous solutions is possible in the presence of vitamin B 12 (added in the form of cyanocobalamin) as coordinating agent via adsorptive accumulation of nitric coordinated to vitamin B 12 at a stationary mercury drop electrode, followed by fast-scan differential-pulse voltammetry. The calibration graph is linear in the concentration range of nitrite from 0.1 to 100 μmol l −1, with a detection limit calculated as 0.02 μmol l −1 or 1 μg l −1 of nitrite. Nitrate, chloride, sulphate and phosphate do not interfere but sulphite, dithionate and cadmium(II) do. The method was applied to the determination of nitrite in drinking and river waters.

The determination of 4-substituted derivatives of N-nitroso-N-methyl aniline by fast scan differential pulse voltammetry at a hanging mercury drop electrode

Optimum conditions were found for the determination of N-nitroso-N-methyl aniline and its derivatives substituted in the 4 position by -CH3, -OCH3, -Cl, -CN, -OH or -NO2 groups by fast scan differential pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 10-5-2 10-7 mol l-1. It was demonstrated that these techniques are useful for the analysis of a mixture of the test substances either directly or after separation by thin-layer chromatography and that false positive results can be eliminated by UV irradiation of the test sample. An attempt to further increase the sensitivity by adsorptive accumulation of the test substances on the surface of the hanging mercury drop electrode was not successful as the test N-nitroso compounds are practically not adsorbed on this electrode.

Polarographic and voltammetric determination of N,N’-dinitrosopiperazine

Polarographic reduction of the genotoxic N,N’-dinitrosopiperazine was studied and its mechanism was suggested. Optimum conditions were established for the determination of this substance by tast polarography over the concentration region of 1 . 10-3 to 1 . 10-6 mol l-1 and by differential pulse polarography on the conventional dropping mercury electrode or by fast scan differential pulse voltammetry and linear sweep voltammetry on a hanging mercury drop electrode over the concentration region of 1 . 10-3 to 1 . 10-7 mol l-1. Attempts at increasing further the sensitivity via adsorptive accumulation of the analyte on the surface of the hanging mercury drop failed. The methods are applicable to the testing of the chemical efficiency of destruction of the title chemical carcinogen based on its oxidation with potassium permanganate in acid solution.

Polarographic and voltammetric determination of 1-(2’-carbamoylphenyl)-3,3-dimethyltriazene

A study was carried out of the polarographic behaviour of the genotoxic substance 1-(2’-carbamoylphenyl)-3,3-dimethyltriazene and optimum conditions were found for its determination by tast polarography or differential pulse polarography at a static mercury drop electrode and by fast scan differential pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 . 10-4 -2 . 10-7 mol 1-1. The sensivity of the determination can be further improved through adsorptive accumulation of the test substance on the surface of the hanging mercury drop electrode; five-minute accumulation in unstirred solution permits determination in the concentration range (2-10 . 10-8 mol 1-1 and two-minute accumulation in stirred solution allows determination in the range (2-10) . 10-9 mol 1-1.

The voltammetric determination of 4-nitrobiphenyl

Optimum conditions were found for the determination of 4-nitrobiphenyl by fast scan differential pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 . 10-5 to 2 . 10-7 mol l-1. A further increase in sensitivity was attained by adsorptive accumulation of this substance on the surface of the working electrode, permitting determination in the concentration range (2 – 10) . 10-8 mol l-1 with one minute accumulation of the substance in unstirred solution or (2 – 10) . 10-9 mol l-1 with three-minute accumulation in stirred solution. Linear scan voltammetry can be used to determine 4-nitrobiphenyl in the concentration range (2 – 10) . 10-9 mol l-1 with five-minute accumulation in stirred solution, with the advantage of a smoother baseline and smaller interference from substances that yield only tensametric peaks.

The polarographic and voltammetric determination of 2,6-dichloro-4-nitro-2'-acetylamino-4'-diethylaminoazobenzene

The polarographic reduction of the title azo dye has been studied, a mechanism has been proposed and optimal conditions have been found for its analytical use. The detection limit using a classical dropping mercury electrode was 2 . 10-7 mol l-1 for TAST polarography and 1 . 10-8 mol l-1 for differential pulse polarography. Using a hanging mercury drop electrode, the detection limit was 9 . 10-9 mol l-1 for fast scan differential pulse voltammetry and 1 . 10-8 mol l-1 for linear scan voltammetry. Adsorption accumulation of the test substance on the surface of the hanging mercury drop electrode led to a further decrease in the detection limit to 1 . 10-9 mol l-1 for fast scan differential pulse voltammetry and 7 . 10-10 mol l-1 for linear scan voltammetry.

The polarographic and voltammetric determination of 2,6-dicyano-4-nitro-2'-acetylamino-4'-diethylaminoazobenzene

The polarographic reduction of the title azo dye was studied and optimal conditions were found for its analytical utilization in the concentration range 1 . 10-6 - 1 . 10-7 mol l-1 using differential pulse polarography and 1 . 10-6 - 1 . 10-8 mol l-1 using fast scan differential pulse voltammetry or linear scan voltammetry at a hanging mercury drop electrode. When the latter technique is combined with adsorptive accumulation of the studied substance on the surface of the hanging mercury drop, the determination limit can be further decreased to 3 . 10-9 mol l-1.