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.     

A Microcell for Stripping Analysis with Glassy Carbon and Mercury-Plated Glassy Carbon Electrodes

Abstract

A microcell has been constructed for stripping analysis in solution volumes as low as 5 μl, employing a glassy carbon or mercury-plated glassy carbon working electrodes and a three electrode system. Using normal d.c. stripping techniques, as little as 100 picograms of mercury and 10 picograms of lead can be determined. With the more sensitive second harmonic a.c. voltammetric technique, this limit is lowered to 10 picograms of mercury and 1 picogram of lead.     

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.     

Applications of charge stripping/charge exchange spectra of organic ions

The application of a new technique which involves the combination of charge stripping and charge exchange processes has been investigated. Ions are charge-stripped in the second field-free region of a triple-sector mass spectrometer (BEE geometry), and then subjected to a charge exchange reaction in the third field-free region. The resulting charge stripping/charge exchange (CS/CE) spectrum is free from interference, which is otherwise common in charge stripping spectra. Comparisons between charge stripping and CS/CE spectra are made in cases where both kinds of spectra are obtainable. In order to assess the applicability of this new technique to studies of isomeric ion structures, species for which charge stripping spectra have previously been unobtainable have been chosen. CS/CE spectra of [C₆H₆]⁺˙, [C₆H₅]⁺, [C₈H₁₀]⁺˙ and [C₇H₇O]⁺ ions from a variety of precursors are recorded: in most cases, sufficient differences are observed to permit distinction between isomeric structures (or mixtures of structures). Previous studies which have shown that stable doubly charged molecular ions of ethane cannot be formed by the charge stripping technique are confirmed from its CS/CE spectrum.     

Determination of Trace Amounts of Copper by Adsorptive Stripping Voltammetry

ABSTRACT

A technique is presented for the determination of trace amounts of copper(II) by adsorptive cathodic stripping voltammetry. The procedure is based on adsorptive accumulation of copper(II)-Alizarin Red S (ARS) complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the reduction current of the adsorbed complex at -0.16 V (vs. Ag/AgCl). The height of the copper -ARS reduction peak is linearly dependent upon the copper(II) concentration between 0.2-15 and 15-500 ng.ml^?1. The detection limit of the technique is 0.05 ng.ml^?1 copper(II) for a collection time of 1 minute. The method is free from most interferences. The procedure has been successfully applied to the determination of trace amounts of copper(II) in some analytical grade salts.     

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.     

Determination of Cobalt Ions in Natural Waters Using Differential Pulse Adsorptive Stripping Voltammetry

Abstract

Differential pulse adsorptive stripping voltammetry using dimethylglyoxime complexes in the presence of triethanolamine and ammonium chloride can be applied to the determination of cobalt (II) ions in natural waters with high sensitivity. The limit of detection is about 3 ppt. Actual analysis of estuary water are reported. In this particular case of natural water, the factors influencing the use of differential pulse adsorptive stripping voltammetry for the determination of cobalt are described in detail.     

Adsorptive Stripping Voltammetry of Phytohemagglutinin

Abstract

The adsorptive stripping voltammetric behaviour of the lectin, phytohemagglutinin, has been optimised with respect to accumulation time, accumulation potential, pulse amplitude, scan rate and drop size. Adsorptive stripping voltammetry has also been used to study the interaction of this protein with nannose, galactose and N-acetyl-D-galactosamine.     

Determining Trace Concentrations of Copper in Water by Cathodic Film Stripping Voltammetry with Adsorptive Collection

Abstract

A technique is presented for the determination of trace concentrations of copper (II) in natural water samples by cathodic stripping voltammetry of a film of copper-catechol complex ions adsorbed on the hanging mercury drop electrode. The peak height of the copper-catechol reduction peak is linearly dependent upon the copper (II) concentration between 10^?10 and 10^?7 M. The detection limit of the technique is below 10^?10 M copper (II) for a collection time of 3 minutes, but the sensitivity can be further increased four-fold by collecting for 15 minutes. The sensitivity is reduced by high concentrations of competing trace metals and of surfactants, which necessitate the use of standard additions to the sample.     

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.     

Diagnosis of Metal Poisoning and Evaluation of Chelation Therapy by Differential Pulse Anodic Stripping Voltammetry Coupled to a Novel Digestion Procedure

Abstract

Differential pulse anodic stripping voltammetry, coupled to a closed acid digestion system, has been proven to be an efficient tool for rapid diagnosis of metal poisoning and for evaluating the progress of chelation therapy. This technique and system has been used to determine total zinc, cadmium, lead, bismuth, copper, and thallium in urine, blood, hair, teeth, feces, bone and other tissue for medical management and post-mortem studies. The technique lends itself to determining minute changes in metal concentrations, while its low detection limits provide for the analysis of liquid samples as small as 10 μl. A procedure for rapidly removing metal contaminants from reagents and electrolyte systems was tested and found to be effective for this highly sensitive technique.     

Cathodic Stripping Voltammetric Study of The Release of Inorganic Sulfide from Proteins in Alkaline Media

Abstract

The concentration of inorganic sulfide ion liberated from a wide range of proteins denatured in 0.2 M NaOH at 25° was measured using cathodic stripping voltammetry (CSV) directly and after separation of the H₂S by an isothermal microdiffusion technique. The sulfide produced in 0.2 M NaOH was equivalent to the number of protein disulfide bridges broken, and using several model proteins it was shown that only surface, or solvent-accessible disulfide bonds are attacked. The reaction obeyed first-order kinetics, and the rate was proportional to hydroxide ion concentration. Some simple disulfide compounds were also studied, and possible reaction mechanisms for the formation of sulfide ion are discussed. Normal and cancerous blood serum samples were analysed by CSV measurement of the sulfide released in alkali.     

Cathodic Stripping Voltammetric Study Of DL-N-Acetylhomocysteine Thiolactone (Citiolone)

Abstract

The behaviour of DL-N-acetylhomocysteine thiolactone (citiolone) at a hanging mercury drop electrode is studied by cathodic stripping voltammetry (c.s.v.) as an example for determination of thiolactones. Voltammetric response is only obtained at pH> 9.3, when the cyclic structure of thiolactone is open. A spectrometric study is made in order to ascertain this behaviour. Under the recommended conditions and at pH> 9.3, the sulfur containing group can form mercury complexes and citiolone can be determined from the stripping peak that appears at about -0.470 V within the concentration range 3.5 10^?7- 1 10^?9 mol l^?1. Calibration functions are reported and detection limits calculated. The interference of several organic compounds is reported.     

Disposable Screen-Printed Electrodes (Spe) Mercury-Free for Lead Detection

ABSTRACT

Strategies to modify screen-printed electrodes (SPE) for lead determination are reported. Dithizone was mixed with graphite ink to obtain a modified screen-printed strip to detect ppb levels of lead(II) (detection limit 12 μg/l) using square wave anodic stripping voltammetry (SWASV). In addition, screen-printed electrodes were also modified by casting a few μl of a Nafion® solution onto the working electrode surface. In this case, ppb levels of lead were detected (detection limit 15 μg/1), using potentiometric stripping analysis (PSA). The addition of an ionophore to Nafion® polymer was also investigated, but this did not yield a significant improvement.     

Voltammetric Behavior of Mifepristone (RU‐486) Using Square‐Wave and Adsortive Stripping‐Wave Techniques. Determination in Urine Samples

The behavior of Mifepristone (RU‐486) was studied by square‐wave technique, leading to two methods for its determination in aqueous samples and urine samples at pH 2. The application of the square‐wave (SW) without the adsorptive accumulation and stripping voltammetric (AdSV) show the maximum response at ?0.896 V using an accumulation potential of ?0.5 V. The effect of experimental parameters that affect this determination are discussed. For the stripping technique, Mifepristone proved to be more sensitive, yielding signals four times larger than those obtained by applying a square‐wave scan without the previous accumulation. The calibration plot to determine Mifepristone was linear in the range 2.4×10^?8 and 5.4×10^?7 M by stripping mode with an accumulation time t_acc of 30 s. The relative standard deviation obtained for concentration levels of Mifepristone as low as 2.0×10^?7 M with square‐wave was 1.17% (n=10) and with stripping square‐wave 2.02% (n=10) in the same day. The two proposed methods (SW and SWAdSV) were applied to the determination of Mifepristone in urine.     

The cathodic stripping voltammetric determination of traces of iodide with a hanging copper amalgam drop electrode

A hanging copper amalgam drop electrode (HCADE) is used for the determination of traces of iodide by cathodic stripping voltammetry. The cathodic stripping peak of copper(I) iodide from the HCADE is better defined than that of mercury(I) iodide from a hanging mercury drop electrode. Optimum conditions and interferences are reported. With a 3-min deposition time at ?0.1 V vs. SCE, the calibration plot is linear up to 2 × 10^?6 mol dm^?3 iodide. The detection limit for iodide with the HCADE under voltammetric conditions is 4 × 10^?8 mol dm^?3; this is lowered to 8 × 10^?9 mol dm^?3 by using the differential pulse stripping technique.     

Stripping chronocoulometry for the determination of pertechnetate

Stripping chronocoulometry is proposed as an alternative to linear-sweep anodic stripping voltammetry when the latter technique gives multiple stripping waves. Such complicated stripping waves are commonly observed at solid electrodes. The determination of pertechnetate (⁹⁹Tc) demonstrates the advantages of stripping chronocoulometry at a wax-impregnated graphite electrode.     

Application of the Bismuth Film Electrode for Catalytic Adsorptive Stripping Potentiometric Determination of Cobalt in Dimethylglyoxime‐Nitrite System

Abstract

The application of bismuth film electrodes to the determination of cobalt by constant current adsorptive stripping potentiometry with exploitation of a catalytic effect is presented. The addition of NaNO₂ to the solution containing ammonia buffer and dimethylglyoxime results in a 25‐fold enhancement of the adsorptive stripping potentiometric cobalt signal. Several key parameters of the potentiometric stripping mode were optimized, including the composition of the supporting electrolyte, the stripping current, the accumulation potential, and the accumulation time. The optimized procedure yields favorable and highly stable stripping responses with good precision (RSD=1.4% for a Co concentration of 2 µg L^?1), low detection limit (0.07 µg L^?1), and good linearity (up to 10 µg L^?1, R²=0.998) with a deposition time of 60 s and a stripping current of 10 µA. The method enables the determination of Co in the presence of high excesses of Ni or Zn.     

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.     

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.