Determination of Lead and Cadmium by Stripping Voltammetry After Separation from Humic Acid by Thin-Layer Chromatography

Abstract

Interferences resulting from the presence of humic acid (HA) and other surface-active substances in a sample matrix decrease the reliability of Pb and Cd determinations obtained by square-wave anodic stripping voltammetry (SWASV). The implementation of thin-layer chromatography (TLC) prior to SWASV minimizes the effect of these interferents by physically separating Pb and Cd from the sample matrix prior to analysis. The determination of both Pb and Cd was shown to be feasible after TLC separation from laboratory standards spiked with 100 ppm humic acid and from a lake water sample spiked with 1 ppm of Pb and Cd.     

Differential Pulse and Cathodic Stripping Voltammetric Methods for the Determination of Aromatic Sulfones

Abstract

A cathodic stripping voltammetric method for the determination of aromatic sulfones was developed. The technique involved a conversion of the sulfone to a sulfinate by controlled potential electrolysis at a mercury pool electrode and a subsequent determination of the sulfinate by cathodic stripping at a silver electrode. The detection limit was 2 × 10^?7 M sulfone in 4:1 DMSO-H₂O.

The differential pulse polarographic method utilized direct reduction of the sulfone in a 3:2 DMSO-benzene solvent. Although the detection limit (4.6 × 10^?7 M) was higher than in the stripping method, the linear dynamic range was greater (500 vs. 25), the typical precision was better (0.5 v. 7% relative standard deviation) and the determinations were more rapid (20 vs. 90 min). In addition, fewer interferences are anticipated for the pulse polarography method.     

Adsorptive Stripping Voltammetry of Some Triazine- and Nitro Group-Containing Pesticides

Abstract

The application of adsorptive stripping analysis in combination with differential pulse voltammetry for the determination of some triazine- and nitro group- containing pesticides like Dinobutone, DNOK, Ametryne and Prometryne is described. Conditions for determinations in the concentration range from approx. 0.1 to 50 ppb are given.     

Batch-injection stripping voltammetry (tube-less flow-injection analysis) of trace metals with on-line sample pretreatment

The most essential limitation of batch-injection analysis (BIA) methodology compared to other flow methods (CFA, FIA, SIA) is the lack of possibility of on-line sample processing in the measuring system. Some procedures of on-line sample pretreatment in BIA are possible by changing the plastic tip of the automatic micropipette used for sample injection into a flow-through reactor, e.g. by packing it with a bed of a solid sorbent. This concept is employed in the voltammetric stripping determinations of trace metals using a bed of commercial chelating resin Chelex-100. It was found that, besides the electrochemical preconcentration of analytes in the form of amalgams on the surface of mercury thin film electrodes, an approximately 10-fold additional preconcentration can be achieved on the packed sorbent bed by using different volumes of aspirated sample solution and eluent. This procedure allows also efficient elimination of some matrix effects.     

Determination of Cadmium in Plant Tissues by Electrothermal Atomisation Atomic Absorption Spectrometry with Matrix/Analyte Modification and Smith-Hieftje Background Correction

Abstract

Pressure decomposition in a microwave oven provides a rapid means of sample preparation for plant tissue analyses. The use of delayed atomisation cuvettes, Smith-Hieftje background correction and matrix/analyte modification enables accurate determinations of cadmium concentrations in plant materials to be made. However, care should be taken to restrict the concentrations of modifier used, as too high a concentration may lead to problems with both tube life and over-correction by the Smith-Hieftje background correction system.     

Determination of trace amounts of copper in water samples by flame atomic absorption spectrometry after preconcentration on octadecyl-bonded silica membranes modified by a Di-Schiff base ligand

A simple method for rapid extraction-preconcentration and determination of trace amounts of copper(II) ions in water samples by using octadecyl-bonded silica membranes modified by a Schiff base, named bis(5-chloro-2-hydroxyacetophenone)-1,2-propanediimine (L), followed by flame atomic absorption spectrometry (FAAS) is described. The effect of parameters influencing the extraction efficiency, i.e. pH of the sample solution, amount of the modifier, type and volume of stripping reagent, and sample and stripping reagent flow rates were evaluated and optimized. The detection limit and the concentration factor of the presented method are 10.2 ng/L and greater than 400, respectively. Under optimum experimental conditions the capacity of the membrane disks modified by 4 mg of the ligand was found to be 142.8 (±0.2) μg of copper. The method was applied to the enrichment and determination of copper content in different natural water samples.     

The Use of an Automated Device in the Direct Simultaneous Determination of Heavy Metals in Commercial Coca Cola By DPASV

Abstract

The performance of a polarographic analyser equipped with a long-lasting, sessile-drop mercury electrode is described in the direct, simultaneous determination of heavy metals (cadmium, copper and lead) in some Coca Cola samples (drawn from commercial bottles or tins). The determinations were performed by the differential pulse anodic stripping voltammetric technique using a programmed fully automated sequence (i.e., deposition-stripping-recording). The results obtained (1-3, 6-25 and 1.5-3.3 ppb for cadmium, copper and lead, respectively) as well as those previously obtained in the stripping analysis of some sea-waters and mineral-waters samples suggest that the proposed automated device ensures sufficient sensitivity and accuracy to be employed in the DPASV determination of toxic metals (at trace and subtrace levels) in natural waters and beverages.     

Stripping Analysis of Trace Metals at a Flow-Through Reticulated Vitreous Carbon Electrode after the Preconcentration by Supported Liquid Membrane Technique

Abstract

The performance of a flow-through mercury coated reticulated vitreous carbon (RVC) electrode in the potentiometric stripping analysis (PSA) of trace metals has been examined. A wall-jet glassy carbon cell was used for the comparative experiments. Experimental parameters influencing the stripping signals have been optimised in order to use the stripping analysis after the preconcentration and matrix isolation by supported liquid membrane (SLM) technique. The SLM with di-2-ethylhexyl-phosphoric acid (DEHPA) as the extractant in the membrane liquid for proton driven transport of trace metals across the membrane has been chosen. Results presented for lead determination in river water demonstrate the analytical advantages of coupled technique SLM-PSA.     

Flow-injection potentiometris stripping analysis — a new concept for east trace determinations

Flow-injection potentiometric stripping analysis is introduced as a highly versatile technique for micro and trace determinations of heavy metals. The simple instrumentation used, with extremely short residence times (below 1 s), permits a simple throughput of 200 h^–1. Up to four elements can be determined simultaneously at lower μgl^? levels up to % levels. On-line sample manipulation (e.g., dilution and matrix modification is possible with one- and two-channel flow systems. The utility of f.i.p.s.a. is evaluted by comparing response, sensitivity, and practical aspects of four different flow-through cells. The method is successfully applied to the fast sequential measurements of zinc, lead and copper in tap water and to the direct determination of lad and cadmium in acid digests of biological samples without further treatment.     

New Protocol for Determination of Rifampicine by Adsorptive Stripping Voltammetry

For determinations of organic compounds by adsorptive stripping voltammetry till now the same material of the electrode has been used for the accumulation and stripping steps. This paper describes a new protocol for extending the range of organic compounds, which can be determined by adsorptive stripping voltammetry. In the proposed procedure the accumulation step was performed on the electrode modified by a lead film, which assures adsorption of the studied species on the modified electrode and then the stripping step of the accumulated substance was performed on the support of the lead film electrode. As an example rifampicine was accumulated by adsorption at the lead film electrode while in the stripping step lead film and then the accumulated rifampicine were oxidized at a glassy carbon electrode. Using an acetate buffer as a supporting electrolyte a calibration graph for rifampicine in the range from 2.5×10^?10 to 1×10^?8 mol L^?1 was obtained. The detection limit for rifampicine following 60 s accumulation time was equal to 9×10^?11 mol L^?1. The obtained detection limit was comparable or lower than reported previously for other stripping voltammetric procedures. The proposed procedure was applied to rifampicine determination in pharmaceutical preparation.     

Continuous flow and flow injection stripping voltammetric determination of silver(I), mercury(II), and bismuth(III) at a bulk modified graphite tube electrode

The epoxy-impregnated graphite tube electrode bulk modified with 2-mercaptobenzoxazole, employed in a wall-jet configuration, was found to be useful for the continuous flow and flow injection stripping voltammetric determinations of Ag^I, Hg^II and Bi^III. For continuous flow, detection limits for Ag^I, Hg^II and Bi^III were 1.8 × 10⁻¹⁰ M, 1.9 × 10⁻⁹ M and 9.5 × 10⁻⁹ M, respectively (10 min accumulation, S/N = 3). Precisions for 5.00 × 10⁻⁹ M Ag^I, 1.00 × 10⁻⁸ M Hg^II and 1.00 × 10⁻⁷ M Bi^III were 10.5%, 5.77 % and 7.90% (relative standard deviations, n = 6), respectively. In the case of flow injection stripping, with a 500 μL injection loop, detection limits of 0.59 ng, 2.0 ng and 120 ng were obtained for Ag^I, Hg^II and Bi^III, respectively (S/N = 3). Selected metal ions, inorganic and organic substances were investigated for interferences. The electrode was tested with a certified sample and then applied to the determinations of the metal ions in a urine and a sea-water sample.     

A Fluorescence Spot Test for Salicylate Determination

Abstract

A procedure based on a spot test for salicylate is presented. The method is simple, rugged and is based on the salycilate native fluorescence measurement on the surface of a filter paper by using optical fibers for light conduction. The fluorescence was linear at concentration range of 0.01–0.4 mmol l^?1. The relative standard deviation of 5% (n=10) was observed. Detection and quantification limits were 4 and 14 µmol l^?1, respectively. The results obtained in pharmaceutical salicylate determinations showed that practically no statistical difference existed with the pharmacopeical method (95% confidence level). The recovery studies in biological samples spiked with salicylic acid at overdose concentration levels showed that the matrix sample did not interfere in the method.     

Preparation of a Chelating Polymeric Membrane and Application to Uphill Transport

Abstract

Modification of an anion-exchange membrane by (1-(2-arsono-phenylazo))-2-hydroxy-3,6-naphthalenedisulfonic acid (thoron) results in a membrane that can chelate metals. The high affinity of the disulfonate for the anion-exchange sites together with molecular adsorption of the aromatic thoron onto the polymers yields a system that is stable in strong acids at or below 1 M. By employing a relatively high pH sample (5-9) in conjunction with an acidic stripping solution (0.2 - 1.0 M HCl), uphill transport of Cu(II) and Zn(II) was accomplished. The transport rate was increased by means (lower chelating capacity and the use of a chelate-forming aid on in the stripping solution) of promoting the volume diffusion mechanism of membrane transport. With a 0.05 mmol per dry gram chelating capacity and a 0.1 M EDTA stripping solution (pH 6.5), an enrichment factor of 16 was observed in a one-hour experiment with a 200 mL sample, 11 cm² membrane, and 5 mL stripping solution. This value compares favorably with those obtained by other uphill transport modes under the same conditions.     

Determination of Trace Elements in Pharmaceutical Tablets Using Anodic stripping Voltammetry

Abstract

Anodic stripping voltammetry is applied for measurement of copper and zinc in pharamaceutical formulations. Because of the inherent sensitivity and selectivity of stripping voltammetry toward amalgam forming metals, no sample preparation is required (except for acidic dissolution). Copper-zinc intermetallic interferences are eliminated by the addition of an excess of gallium or through utilization of a dual working electrode approach. Automation of this procedure is indicated from flow injection measurments at a rate of 15 per hour.     

Direct Determination of Lead in Whole Blood Using Electrothermal Vaporization Inductively Coupled Plasma Atomic Emission Spectrometry

Abstract

A carbon rod atomizer was used for sample introduction into a commercial inductively coupled plasma for the determination of lead in whole blood. Samples of known lead concentration were either treated with Triton-X or nitric acid or diluted 1+5 with distilled water and analyzed by comparison against graphs obtained using aqueous solutions and using the standard additions method. Both approaches produced similar results indicating no appreciable matrix influence. The Pb concentration values obtained were in close agreement with those previously determined by ETA-AAS, Delves′ cup-FAAS and anodic stripping voltammetry. Signal integration and careful selection of the measurement period were critical to obtain accurate results. Derived concentrations were shown to be essentially independent of the heating rate of the vaporization unit and the length of tubing used to transport the material into the plasma. Using a 1 μg ml^?1 lead aqueous standard, a signal to background ratio of 5.5 was obtained under optimized conditions. Relative standard deviations of the blank and the analytical signal were 0.2 and 1.8%., respectively. An aqueous solution detection limit of 0.007 μg ml^?1 was calculated for lead.     

Current Response and Determination of Traces of Coenzyme I At a Silver Microelectrode

Abstract

A useful current response of nicotinamide coenzyme I at a silver microelectrode was obtained and, therefore, an electrochemical method has been developed for the determination of traces of the coenzyme by square wave adsorption stripping voltammetry. Under optimum conditions the proposed method provides a linear response over the coenzyme concentration in the range of 0.5～7.5 μmol/L. The detection limit was 0.2 μmol/L. The relative standard deviation was 3.5% for 6 successive determinations of the coenzyme at 1.0 μmol/L. In view of the merits of the electrochemical techniques and this microelectrode, this method will be of great usefulness in the biochemical and clinical fields in the future.     

Optimisation of a Gas Stripping Concentration Technique for Trace Organic Water Pollutants

Abstract

The application of gas stripping for the concentration prior to analysis of organic water pollutants at the parts per million and parts per billion level has been studied. Solutes are stripped from solution by a stream of inert gas and subsequently adsorbed onto active carbon from which surface they are taken up in a solvent for analysis.

The method is shown to be applicable to the analysis of a wide range of compounds including pesticides and polychlorinated biphenyls. The effect of gas flowrate, the time of stripping, adsorbent particle size, and desorbing solvent on the percentage recovery of a range of organic compounds has been measured.

Problems of contamination of aqueous solutions by absorption of atmospheric vapours prior to analysis are considered, and the analysis of a typical water sample is demonstrated.     

Determination of cadmium with a sequential injection lab-on-valve by anodic stripping voltammetry using a nafion coated bismuth film electrode

This work exploited a sequential injection lab-on-valve (LOV) system for the determination of cadmium by anodic stripping voltammetry (ASV). A miniaturized electrochemical flow cell (EFC) was fabricated in LOV, in which a nafion coated bismuth film electrode was used as working electrode. The cadmium was electrodeposited on the electrode surface in bismuth solution, and measured with the subsequential stripping scan. Under optimal conditions, the proposed system responded linearly to cadmium concentrations in a range 2.0-100.0 μg L⁻¹. The detection limit of this method was found to be 0.88 μg L⁻¹. By loading a sample volume of 800 μL, a sampling frequency of 22 determinations h⁻¹ was achieved. The repeatability expressed as relative standard derivation (R.S.D.) was 3.65% for 20 μg L⁻¹ cadmium (n = 11). The established method was applied to analysis of trace cadmium in environmental water samples and the spiked recoveries were satisfactory.     

Speciation of Arsenic by Potentiometric Stripping Analysis Using Gold(III) Solution as Chemical Reoxidant and a Wall‐Jet Flow Cell

A simple procedure is described for the potentiometric stripping of arsenic with a wall‐jet cell by means of potentiostatic co‐deposition of gold and arsenic at a glassy‐carbon electrode and subsequent chemical stripping with Au(III). Optimum medium containing 160 mg L^?1 of Au(III) in HCl 0.1 M, where it is possible to speciate As(III) and As(V). As(V) was electrodeposited directly without prior chemical reduction at working electrode. As(III) was first determined at an electrodeposition potential of ?0.1 V. Afterwards, total arsenic was determined by an electrodeposition potential of ?0.7 V, from the area of peak obtained of the differential stripping potentiogram by using the standard addition method. The original As(V) concentration in the sample was calculated by difference. The possibilities of the optimized method were demonstrated by determinations of As(III), As(V) and total arsenic in samples of polluted water.     

Determination of trace arsenic on hanging copper amalgam drop electrode

Hanging copper amalgam drop electrode has been applied for trace determination of arsenic by cathodic stripping analysis. Detection limit for As(III) as low as 0.33 nM (0.02 μg/L) at deposition time (240 s) could be obtained. For seven successive determinations of As(III) at concentration of 5 nM relative standard deviation was 2.5% (n = 7). Interferences from selected metals and surfactant substances were examined. Absence of copper ions in sample solution causes easier optimization and makes method less vulnerable on contamination. The developed method was validated by analysis of certified reference materials (CRMs) and applied to arsenic determinations in natural water samples.