Determination of the pesticide Chlorpyrifos by cathodic adsorptive stripping voltammetry

The adsorption behavior and differential pulse cathodic adsorptive stripping voltammetry of the pesticide Chlorpyrifos (CP) were investigated at the hanging mercury drop electrode (HMDE). The pesticide was accumulated at the HMDE and a well-defined stripping peak was obtained at –1.2 V vs Ag/AgCl electrode at pH 7.50. A voltammetric procedure was developed for the trace determination of Chlorpyrifos using differential pulse cathodic adsorptive stripping voltammetry (DP-CASV). The optimum working conditions for the determination of the compound were established. The peak current was linear over the concentration range 9.90 × 10^–8– 5.96 × 10^–7 mol/L of Chlorpyrifos. The influence of diverse ions and some other pesticides was investigated. The analysis of Chlorpyrifos in commercial formulations and treated waste water was carried out satisfactorily Received: 10 July 1997 / Revised: 1 April 1998 / Accepted: 6 April 1998     

Determination of selenium in sea water by adsorptive cathodic stripping voltammetry

A procedure is presented for determining Se(IV) and total dissolved Se in sea water using cathodic stripping voltammetry in the presence of added copper. Experiments using cyclic voltammetry indicate that the preconcentration step consists in adsorption of a Cu(I)₂Se complex species on the hanging mercury drop electrode. The optimized analytical conditions include a copper concentration of 40 μM and a solution pH of 1.6. Differential pulse modulation is used. Interference caused by organic surface-active substances present in natural waters in eliminated by UV photolysis of the sample. Cadmium interferes with the determination of Se only when present at a concentration 100 times higher than normal. UV photolysis at pH ≈ 8 is used to convert Se(VI), which is the electroactive species. The response is linear for Se concentrations between 0 and 200 nM. The limit of detection is 0.01 nM Se when a deposition time of 15 min is used.     

Determination of aluminium in tree samples by cathodic adsorptive stripping voltammetry

This paper presents a method of determination of aluminium in tree samples (wood, leaves, roots) based on the cathodic adsorptive stripping voltammetry. Al(III) complexed with alizarin S was determined by ASV method using a hanging mercury drop electrode. Optimal conditions were found to be: accumulation time 30-90 s, accumulation potential - 0.70 V versus SCE, supporting electrolyte 0.1 M ammonia-ammonium chloride buffer at pH 8.2 and concentration of alizarin 1 x 10(-5) M. The response of the system, a linear current-concentration relationship was observed up to 8 x 10(-6) M. The developed method has been tested by analysing international reference materials (BCR 62 Olive leaves and BCR 101 spruce needles).     

Determinationation of kanamycin by square-wave cathodic adsorptive stripping voltammetry

A square-wave cathodic adsorptive stripping voltametric (SWCASV) method for the determination of kanamycin was developed on a thin-film mercury electrode (TFME). The optimal working conditions for the application of the method were found to be pH 8.0, provided by a Britton-Robinson (B.R.) buffer, and an adsorption potential of +0.30 V during 300 s. The equilibration time was applied during 10 s, and potential scans were performed at a scan rate of 40 mV/s, with a square-wave frequency of 100 Hz. The measuring-system response was linear over the kanamycin concentration range from 1.2 × 10⁻⁹ to 5.0 × 10⁻⁸ M and the detection limit achieved was 4.8 × 10⁻¹⁰ M. The relative error and relative standard deviation obtained were 1.20 and 4.67%, respectively. The voltammetric procedure was applied successfully to give a rapid and precise assay of kanamycin in kanamycin sulfate injection form. Published in Elektrokhimiya in Russian, 2008, Vol. 44, No. 12, pp. 1433–1437. The text was submitted by author in English     

Trace determination of molybdenum by adsorptive cathodic stripping voltammetry

Molybdenum is determined by adsorptive cathodic stripping voltammetry in 0.15 M nitric acid solution containing 15 μM 2′,3,4′,5,7-pentahydroxyflavone (morin) as a ligand. In this medium, molybdenum is preconcentrated on a hanging mercury drop electrode and stripped cathodically in square-wave voltammetry mode, with a peak potential of -350 mV vs. Ag/AgCl (saturated KCl). The effect of various parameters (ligand concentration, supporting electrolyte composition, accumulation potential and collection time) on the sensitivity and linear range of the calibration curve are discussed. With controlled accumulation for 1 min, the detection limit (3σ) was 0.45 ng ml^?1 molybdenum and the calibration curve is linear up to 70 ng ml^?1. The procedure is applied to the determination of molybdenum in real samples with satisfactory results.     

Determination of trace europium by adsorptive cathodic stripping voltammetry after complexation with cupferron

This article describes the determination of Eu by adsorptive cathodic stripping voltammetry after complexation with N-nitroso-N-phenylhydroxylamine (cupferron). The accumulation of the complex at the HMDE was performed at 0.0 V and the subsequent potential scan was made in the square wave mode. The analyte signal occurred at −0.88 V. The detection limit is 0.06 nmol dm⁻³. The effect of instrumental and chemical parameters on the peak height and potential was investigated. The same technique can be used for the determination of ytterbium and of the other rare earth elements (REEs) after separation.     

Determination of secnidazole in tablets and human serum by cathodic adsorptive stripping voltammetry

The electrochemical reduction of secnidazole was carried out in BR buffer solutions in the pH range 2.0–11.8 by dc polarography. The polarograms exhibited two irreversible reduction waves in acidic media and one wave in alkaline media, corresponding to the reduction of nitro group in the drug. The cathodic adsorptive voltammetric behavior was studied on glassy carbon electrode to optimize an analytical method for determination of secnidazole. The drug was determined in the range between 4.0 × 10^?6 and 1.2 × 10^?4 mol L^?1. The proposed method was successfully applied to the determination of the drug content in tablets with mean recovery and relative standard deviation of 100.91% and 1.82%, respectively. It was also applied to human serum with a good precision and accuracy.     

Determination of trichlorobiphenyl by adsorptive stripping voltammetry

Trichlorobiphenyl is determined in the concentration range 0.004–1 mg l^?1 by adsorptive stripping voltammetry at a hanging mercury drop electrode. Preconcentration is achieved by adsorption at a potential of ?0.40 (V (vs. Ag/AgCl), and desorption at ?1.10 V. Biphenyl interferes with the determination only when present in 5-fold molar amounts compared to trichlorophenyl. The interference of DDT is eliminated by prior treatment of the sample solution with sulphuric acid. The method was applied for the analysis of waste and natural waters, the relative standard deviation being <5%.     

Determination of gallium by adsorptive stripping voltammetry

A procedure for the determination of gallium by differential pulse adsorptive stripping voltammetry (DPADSV), using different complexing agents (ammonium pyrrolidine dithiocarbamate (APDC), pyrocatechol violet (PCV) and diethyldithiocarbamate (DDTC)), has been optimized. The selection of the experimental conditions was made using experimental design methodology. Under these conditions, the calibration was made and the detection limit was determined for each gallium-ligand complex. A robust regression method was applied which allowed the elimination of anomalous points. The detection limit, with α=β=0.05, for gallium-APDC complex was 5.0×10⁻⁸ mol dm⁻³, for gallium-PCV complex was 9.9×10⁻⁹ mol dm⁻³, and the lowest detection limit (1.3×10⁻⁹ mol dm⁻³) was obtained with DDTC. For this reason, DDTC was selected for the determination of the gallium concentration in a certificate sample and in a spiked tap water sample. The linear dynamic range for gallium-APDC complex was from 5.0×10⁻⁸ to 2.7×10⁻⁷ mol dm⁻³, for gallium-PCV complex was from 5.0×10⁻⁹ to 4.8×10⁻⁷ mol dm⁻³, and for gallium-DDTC complex was from 1.0×10⁻⁹ to 2.1×10⁻⁷ mol dm⁻³.     

Determination of uranium by adsorptive stripping voltammetry

A voltammetric method for the determination of uranium in natural waters in the concentration range from 0.4 μg 1⁻¹ to 0.2 mg 1⁻¹ is described. The method is based on adsorptive accumulation of the uranium(VI)—pyrocatechol complex on the hanging mercury drop electrode followed by the reduction of the absorbed complex.     

Determination of trace amounts of estriol and estradiol by adsorptive cathodic stripping voltammetry.

Estriol and estradiol are electroinactive in the potential range from -200 to -1000 mV versus a silver-silver chloride electrode at a mercury electrode. The conversion of these estrogens into electroactive nitro derivatives of estrogens, which are used for voltammetric determination, was studied. Such nitro derivatives give a well defined cathodic stripping wave at -600 mV in pH 10.5 borate buffer. Estriol and estradiol are determined in the ranges 1 x 10(-9)-1.5 x 10(-6) and 5 x 10(-9)-2 x 10(-6) mol dm-3, respectively, by differential-pulse adsorptive stripping voltammetry at a hanging mercury drop electrode. Some steroids, such as estrone, interfere because the three estrogens have almost the same molecular structure and have similar nitro derivatives, but progesterone does not interfere and is reduced at significantly more negative potentials than the nitrated estrogens. It can be determined simultaneously with estriol or estradiol. A method was developed for the assay of estriol in pharmaceutical preparations.     

Determination of palladium by adsorptive stripping voltammetry

 Adsorptive accumulation of the Pd(II) complex with dimethylglyoxime was evaluated for stripping voltammetry with respect to different parameters. The sensitivity of the method and the linearity between the peak current and the concentration of Pd(II) depends on the ionic strength, the electrode area, the preconcentration time, the transport rate to the electrode, and the potential scan rate. The most appropriate medium was 0.1 mol/L acetate buffer between pH 3.5 and 4. Using 2 min of preconcentration at a 2.6 mm² electrode and the differential pulse mode, a detection limit of 0.05 μg/L Pd was achieved for liquid samples and 50 ng/g for solid samples. Different aqueous and solid samples were analysed and the recovery from biological and inorganic materials investigated. Received: 29 February 1996/Revised: 29 July 1996/Accepted: 1 August 1996     

Determination of azinphos-methyl by adsorptive stripping voltammetry

A very sensitive electrochemical stripping procedure for azinphos-methyl (Guthion) is reported. Accumulation is achieved by adsorption of the compound on a hanging mercury drop electrode. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte and other variables. The determination limit is 0.2 ng ml^?1 after 300 s accumulation and 0.4 ng ml^?1 after 180 s accumulation. The procedure was applied to spiked river water.     

Determination of Captropril using adsorptive cathodic differential pulse stripping voltammetry with the HMDE

A voltammetric method for the determination of 3-mercapto-D-2-methylpropanoyl-L-proline, a hypotensive drug whose pharmaceutical name is Captopril (CPT), in the concentration range from 9.0×10⁻¹⁰M to 3×10⁻⁶M, is described. In this range the peak current increases linearly with drug concentration even when different collection periods are used. A self-cleaning Hanging Mercury Drop Electrode (HMDE) was used and a negative Differential Pulse potential (DP) was applied to the indicator electrode. The stripping peak of CPT splits into two peaks as soon as the concentration is increased over about 10⁻⁵M; in the oxidation DP scan, instead, this splitting is observed at a concentration of 2.0×10⁻⁴M. Some attempts were made to verify the suitability of other techniques such as Alternating Current polarography (AC) and the use of a different electrode, the Wax-Impregnated Graphite Electrode (WIGE).     

Determination of trace amounts of thallium by adsorptive cathodic stripping voltammetry with xylenol orange.

Trace amounts of thallium(I) can be determined using adsorptive cathodic stripping voltammetry in the presence of Xylenol Orange (XO). The reduction current of the thallium(I)-XO complex ion was measured by square-wave cathodic stripping voltammetry. The peak potential was at -0.44 V vs. Ag/AgCl. The effect of various parameters (pH, ligand concentration, accumulation potential and collection time) on the response are discussed. The response was linearly related to the thallium concentration in the range 0.5-110 ng ml(-1) and 110-2000 ng ml(-1). The limit of detection was 0.2 ng ml(-1). The relative standard deviation for the determination of 80 ng ml(-1) thallium was 2.8%. Many common anions and cations did not interfere with the determination of thallium. The interference of lead was reduced by the addition of 0.003 M sodium carbonate. The voltammetric procedure was then successfully applied to the determination of thallium in various complex samples.     

Determination of tryptophan and histidine by adsorptive cathodic stripping voltammetry using H-point standard addition method

A sequential method is proposed for the determination of tryptophane and histidine by adsorptive cathodic stripping voltammetry using standard addition and H-point standard addition method (HPSAM). The complexes of copper(II) with the amino acids were accumulated onto the surface of a hanging mercury drop electrode for 60 s. Then the preconcentrated complexes were reduced by square wave voltammetry and the peak currents were measured. The effect of various parameters such as pH, concentration of copper, accumulation potential, accumulation time and scan rate on the sensitivity were studied by one-at-a time and artificial neural network. Under the optimized conditions, the peak currents at about +0.05 to −0.30 V is proportional to the concentration of tryptophan and histidine over the concentration ranges of 5–220 and 100–1200 nM, respectively. Optimization of the parameters by one-at-a time showed that at accumulation potential of 0.10 V (versus Ag/AgCl reference electrode) the peak current is proportional only to the concentration of tryptophan and histidine does not have any contribution to the current. The optimization results by artificial neural network showed that at accumulation potential of −0.06 V (versus Ag/AgCl) the peak current is proportional to the both concentrations of tryptophan and histidine. Therefore, the method of H-point standard addition has been used for resolving overlap voltamograms for determination of histidine in the present of tryptophane. The method was successfully applied to the determination of tryptophan and histidine in synthetic and real samples.     

Determination of thiram in water and soils by cathodic stripping voltammetry based on adsorptive accumulation

Summary A very sensitive electrochemical stripping procedure for thiram is reported. Accumulation is achieved by adsorption of the compound on the hanging mercury drop electrode. Optimal experimental parameters include an accumulation potential of –0.2 V vs. Ag/AgCl, a 0.075 mol/l ammonia solution as supporting electrolyte and a differential pulse stripping mode. The detection limit is 0.3 ng ml^–1 after 120 s accumulation and 0.03 ng ml^–1 after 600 s accumulation. Results are reported for water and soil samples.

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Bestimmung von Thiram in Wasser und Böden mit Hilfe der Cathodic-Stripping Voltammetrie aufgrund adsorptiver Anreicherung

     

Determination of chitosan by cathodic stripping voltammetry.

A sensitive method for the determination of chitosan (CTS) by cathodic stripping voltammetry is presented. The method exploits a pair of oxidation-reduction peaks of CTS at -0.62 V (vs. SCE) and -0.54 V (vs. SCE), and an enhancement of the peak current of CTS observed in a 0.05 mol l(-1) potassium hydrogenphthalate buffer solution (pH 2.5). The peak current is linear with the concentration of CTS from 5.0 x 10(-7) to 1.5 x 10(-5) g ml(-1), and the detection limit is 1.0 x 10(-7) g ml(-1). We studied the characteristics and the mechanism of the electrode reaction, which proved that this process was diffusion controlled. This method was applied to determine the content of CTS in real samples with satisfactory results.     

The determination of platinum in sea water by adsorptive cathodic stripping voltammetry

The catalytic effect of the formazone complex with platinum on the development of hydrogen at a mercury electrode is used to provide a very sensitive method of determining dissolved platinum in fresh and sea water by adsorptive cathodic stripping voltammetry. The optimal analytical conditions include the addition of 0.012% (w/v) formaldehyde, 0.0015% (w/v) hydrazine and 0.5 M sulphuric acid to the sea water. The complex is adsorbed for 1–20 min at ?0.925 V on the hanging mercury drop electrode, followed by a differential-pulse scan in a negative direction. The hydrogen reduction peak catalysed by the platinum complex appears at ?1.045 V. The limit of detection is 0.04 pM Pt with an adsorption time of 10 min, which is quite sufficient to determine dissolved platinum in sea water. The interference of surface-active compounds is eliminated by ultraviolet irradiation of the acidified sample. The method is applied to several sea-water samples. Comparative experiments showed that stripping chronopotentiometry is not sufficiently sensitive to determine platinum in sea water without preconcentration.