Determination of abscisic acid by cathodic stripping square wave voltammetry

In this paper a study is accomplished on behavior in a mercury electrode, of the phytohormone abscisic acid and of the conditions of accumulation in a HMDE. A mechanism is proposed of reduction based on its electrochemical behavior and proving the product of the reduction through mass spectrometry of bulks. A method is proposed for the determination of Abscisic acid (ABA) with a quantification limit of 58 ng ml(-1). The procedure is applied wing determination of ABA in pears through the combination of high performance liquid chromatography (HPLC) with electrochemical quantification.     

Determination of metallothionein in Daphnia magna by modified square wave cathodic stripping voltammetry

Metallothioneins (MTs) are widely used as biomarkers in environmental studies. However, eliminating interfering factors for MT determination in vivo by electrochemical detection is difficult. In this study, NO₃⁻ and Cl⁻ were found to negatively affect MT determination in Daphnia magna by square wave cathodic stripping voltammetry (SWCSV). The relevant mechanism was analyzed, and results were used to modify the original electrochemical testing parameters and environmental conditions. This modified SWCSV achieved accurate MT concentrations in D. magna, leading to detection limits as low as picomolar levels.     

Determination of sulfur species by cathodic square wave stripping voltammetry; Compounds relevant to natural sulfur mineralization

The feasibility of rapid analysis of a number of environmentally important sulfur compounds by cathodic square wave stripping voltammetry at a mercury electrode has been investigated. For cysteine/cystine a relatively anodic peak was identified, which is ascribed to the stripping of a mercurous species. The dependence of the peak currents on pH was found to be different for cysteine and cystine. Methionine and thioproline gave similar stripping peaks to those for cysteine. It is proposed that they arise from species deposited by oxidative hydrolysis. A complex ion is proposed to cause the stripping peak of thiosulfate and tetrathionate, while polysulfides give both a HgS stripping peak and a non-adsorptive reduction peak. Limits of detection are in the 10(-8)-10(-9)M range.     

Determination of ketorolac in human serum by square wave adsorptive stripping voltammetry

The adsorption behavior of ketorolac on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The square wave voltammetric response of ketorolac depends on the parameters of the square wave voltammetry excitation signal as well as on the pH of the medium and the accumulation time. The drug was accumulated at HMDE and a well-defined peak was obtained at -1.41 V versus. Ag/AgCl (saturated KCl) in acetate buffer of pH 5.0. A square-wave adsorptive stripping voltammetric method for the quantitative determination of ketorolac was developed. The linear concentration range was 1x10(-10)-1x10(-8) when using 300 s accumulation at -0.8 V. The detection limit of ketorolac was 1.0x10 (-11)M . The precision was excellent with relative standard deviation of 3.85% at concentration of 5x10 (-8)M after 60 s accumulation time. Applicability to serum samples was illustrated. A detection limit of 14 ng per ml of serum was obtained.     

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.     

Direct determination of molybdenum in seawater by adsorption cathodic stripping square-wave voltammetry

A reliable and very sensitive procedure for the determination of trace levels of molybdenum in seawater is proposed. The complex of molybdenum with 8-hydroxyquinoline (Oxine) is analyzed by cathodic stripping square-wave voltammetry based on the adsorption collection onto a hanging mercury drop electrode (HMDE). This procedure of molybdenum determination was found to be more favorable than differential pulse cathodic stripping voltammetry because of inherently faster scan rate and much better linearity obtained through the one-peak (instead of one-of-two peaks) calibration. The variation of polarographic peak and peak current with a pH, adsorption time, adsorption potential, and some instrumental parameters such as scan rate and pulse height were optimized. The alteration of polarographic wave and its likely mechanism are also discussed. The relationship between peak current and molybdenum concentration is linear up to 150 mug l(-1). Under the optimal analytical conditions, the determination limit of 0.5 mug l(-1) Mo was reached after 60 s of the stirred collection. The estimated detection limit is better than 0.1 mug l(-1) of Mo. The applicability of this method to analysis of seawater was assessed by the determination of molybdenum in two certified reference seawater samples (CASS-2 and NASS-2) and the comparison of the analytical results for real seawater samples (study on a vertical distribution of Mo in the seawater column) with the results obtained by Zeeman-corrected electrothermal atomization atomic absorption spectrometry (Zeeman ETAAS). A good agreement between two used methods of molybdenum determination was obtained.     

The determination of aluminium in seawater and freshwater by cathodic stripping voltammetry

Dissolved aluminium in seawater and freshwater is determined by cathodic stripping voltammetry (c.s.v.) preceded by adsorptive collection of complex ions with 1,2-dihydroxyanthraquinone-3-sulphonic acid (DASA) on the hanging mercury drop electrode. Complexation of aluminium by DASA is rapid and no waiting period or heating of the sample is required. Optimal conditions are a DASA concentration of 10^?5 M, a solution pH of 7.1–7.3 and an adsorption potential of ?0.9 V; the c.s.v. scan is done in the differential-pulse mode. The limit of detection is 1 nM aluminium for an adsorption time of 45 s. The total time needed, including 50min deaeration and a standard addition, is 10–15 min per sample. No serious interferences were found; u.v. irradiation is recommended for samples containing high levels of organic materials.     

Determination of pyrithione in natural waters by cathodic stripping voltammetry

A method was developed to determine the biocide pyrithione in natural waters. The method is based on cathodic stripping voltammetry (CSV) in the presence of Triton-X-100, which is used to separate the peak from interfering thiol compounds. Optimised conditions include a Triton-X-100 concentration of 4 ppm and a pH adjusted to 9 using ammonia buffer. The adsorption potential for pyrithione was −0.10 V and the peak occurred at −0.2 to −0.3 V. Detection was by differential-pulse CSV. The detection limit in UV-digested seawater was 1.5 nM for a deposition time of 60 s. In principle, this limit of detection could be lowered by extending the adsorption time, but in practice this may not be possible due to interferences by other organic compounds (surfactants and thiol compounds) in natural waters.     

Determination of copper in seawater by anodic stripping voltammetry

Copper in surface seawater has been determined using both hanging mercury drop and thin film electrodes. Total copper was found to be in the range 0.4–0.7 μg l^?1, and labile copper in the range 0.2–0.4 μg l^?1. Most of the copper present in seawater is complexed with or adsorbed on organic matter, and a smaller percentage is associated with inorganic colloids. Seawater contains both organic and inorganic compounds which will react with approximately 1×10^?8M added ionic copper. Because of the presence of the complexing agents, peak current-copper concentration calibration curves in seawater are non-linear, and care must be exercised in using spiked results in the calculation of the copper content. The thin film electrode (TFE) is more suitable than the hanging mercury drop electrode for determining copper in seawater, although the TFE results are more dependent on deposition potential, and suffer from interference by nickel if very negative deposition potentials are used.     

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     

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 traces of hemoglobin by square wave stripping voltammetry at a silver microelectrode

An electrochemical method was developed for the determination of traces of hemoglobin (Hb) by adsorption square wave voltammetric stripping at a bare silver microelectrode. Under optimum conditions the proposed method provided a linear response over the hemoglobin concentration range 5 to 100 nmol/L. The detection limit was 3 nmol/L. The relative standard deviation was 4.5% for 6 successive determinations at 50 nmol/L Hb. Other chemicals present in the sample did not interfere.     

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).     

An optimization procedure for determination of metallothionein by square wave cathodic stripping voltammetry: application to marine worms

Electrochemical determination of metallothionein (MT) is widely used for environmental studies. This article describes the development and optimization of the procedure for the quantification of metallothionein by square wave cathodic stripping voltammetry. The determination is based on the complexation of cisplatin and MT and the subsequent reduction of the complexes at the electrode. In order to achieve the highest possible sensitivity and resolution of the peak, an optimization of the experimental parameters has been carried out using experimental design methodology (response surface). Seven chemical and physical parameters, namely, pH, cisplatin concentration, buffer concentration, deposition potential, square wave frequency, amplitude of pulse, and step potential, have been optimized to give 9.0, 5.9 µM, 0.65 M, –0.2 mV, 229 Hz, 46 mV, and 2 mV, respectively. Method characterization has been performed, leading to a detection limit of 0.1 µg L^–1. Quantification of MT in polychaetes and comparison with the modified Brdika procedure were also carried out.     

Determination of total gaseous selenium in atmosphere by honeycomb denuder/differential pulse cathodic stripping voltammetry

A new analytical method has been developed for the determination of total gaseous selenium in the atmosphere by honeycomb denuder collection followed by differential pulse cathodic stripping voltammetry (DPCSV) measurement. Gaseous selenium was collected in a denuder coating solution containing 2% HNO(3) and 2% glycerine. The soluble product, selenious acid, was then extracted by water for DPCSV analysis. The collection efficiency for gaseous selenium was 99.1% at a flow rate of 1 l min(-1) for 3 h. Excellent linearity in DPCSV was maintained up to Se concentration of 40 ng ml(-1). This was equivalent to a working concentration of 220 ng m(-3) of selenium in the atmosphere. A precision of 1.26% RSD (n=5) for 5 ng Se was obtained, and the detection limit (3sigma) and the quantitative determination limit were estimated to be 0.96 and 3.19 ng m(-3). The average recovery of selenium in three standard samples prepared by independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 99.0%. The total content of gaseous selenium in the atmosphere of our laboratories was 3.2-4.4 ng m(-3).     

Determination of 2-amino-5-nitrothiazole by square-wave cathodic stripping voltammetry

An electrochemical method has been developed for the detection and determination of 2-amino-5-nitrothiazole (2,5-ANT) by adsorption square-wave voltammetric stripping. The best sensitivity/resolution ratio was obtained by adsorption at pH 8.0 using a phosphate buffer, an accumulation potential of –10 mV (vs. Ag/AgCl 3 mol/l) and an accumulation time of 15 s. Under these conditions, the proposed method provides a linear electrode response over the 2,5-ANT concentration range 5–300 ng ml^–1, and a detection and determination limit of 4 and 7.5 ng ml^–1, respectively. The method was applied to the determination of 2,5-ANT in bacon.     

Determination of selenium in freshwaters by cathodic stripping voltammetry after UV irradiation

An analytical method was developed for the determination of total dissolved selenium in fresh waters, using linear sweep cathodic stripping voltammetry (CSV) in combination with UV photolytic digestion. Both the CSV method, based on the electrodeposition and stripping of Cu(2)Se, and the UV irradiation procedure were investigated in detail. In the presence of dissolved organic substances, as in freshwaters, Se(VI) is reduced to Se(IV) by UV irradiation in 0.1M hydrochloric acid. Glucose can be used as the carbon source in samples low in natural dissolved organic carbon (DOC). The photolytic yields of Se(IV) were about 90% in both cases. Five freshwater samples were analysed for total selenium by CSV after UV photolysis, and by hydride generation atomic absorption spectrometry (HG-AAS) after oxidative digestion followed by reduction with hydrochloric acid. The results agreed well and the concentrations were in the range 70-190 ng/l., well above the detection limit of the CSV method at 2 ng/l.     

Determination of selenium in soils with square-wave cathodic stripping voltammetry

A new voltammetric method is elaborated for the trace determination of selenium in soils. The use of the square-wave cathodic stripping voltammetry in the determination step efficiently eliminates the interference of electroactive components. The detection limit is 0.75 g/l.