Potentiometric Stripping Analysis Research Articles

Determination of lead in microliter amounts of whole blood by stripping potentiometry

AbstractLead in whole blood is determined using a commercial potentiometric stripping analyzer in combination with a portable personal computer and a new electrode design permitting rotation of the sample. A 70 μL blood sample is added to 200 μL distilled water contained in a disposable test tube. After mixing, 400 μL of a matrix‐modifying solution containing hydrochloric acid, mercury (II) ions, Triton X‐100, and bismuth (III) as an internal standard, is added to the sample which is then transferred to the sample holder. Lead amalgam is deposited on the glassy carbon electrode by means of a pulsed potential cycle for 3 minutes after which lead is reoxidized by means of a constant current. The complete electroanalytical procedure, including result evaluation by means of the internal standard, and graphical display is under computer control. For ca. every 15th sample, the instrument is recalibrated, if necessary, using two whole blood standards. The relative precision is ca. 10% and the detection limit 3.5 μg/L. The stripping potentiometry results agree well with the results obtained by inductively coupled plasma mass spectrometry in the analysis of whole blood from individuals occupationally exposed to lead and with the results obtained by graphite‐furnace atomic spectroscopy in the analysis of whole blood from 141 school children.

Determination of metals in animal tissues by potentiometric stripping analysis without chemical destruction of organic matter

Metal (Cu, Pb, Cd) ions contents of various animal tissues have been determined by potentiometric stripping analysis (PSA) from lyophilized samples. The organic matter destruction, which is the classical preliminary step of such determinations, is circumvented by the use of sodium dodecylsulfate (DOC) and sodium desoxycholic acid (SDS) solutions, in a reflux process and with the aid of sonication. The efficiency of the digestion is tested by comparison with total mineralisation with the low temperature ashing (LTA) method. The digesting medium is adapted to PSA measurements by the aid of a mixed (aqueous-organic) electrolyte. Operating PSA parameters have been studied in the final medium to optimize analytical conditions in the goal of adapting the entire process for routine analysis in environmental control studies. The inherent advantages of a no-current electrochemical method are demonstrated. The process uses classical instrumentation and can be conducted, from the lyophilized sample, in approximately 3–4 h of operation. The relative standard deviation obtained by standard additions method is ±5% for Cd and Pb, and ±3% for copper. The study is conducted with various samples of heifer and fish livers obtained from the commercial distribution circuit and by fishing sampling.

Flow injection potentiometric and voltammetric stripping analysis using a dialysis membrane covered mercury film electrode

Flow injection stripping analysis using a cellulose triacetate (CTA) polymer-modified mercury film electrode is described for the determination of lead in environmental and clinical samples. Commercially available CTA dialysis membranes were secured to a glassy carbon disc electrode using a Plexiglas cap in a wall-jet flow cell. Optimization of the flow cell dimensions and the stopped-flow protocol are described. Flow injection Osteryoung square-wave anodic stripping voltammetry and flow injection potentiometric stripping analysis (FI-PSA) are demonstrated to be effective for determining low ppb levels of lead in tap water, river water and sea-water. FI-PSA is also shown to be effective for urine and whole blood sample matrices. Bovine whole blood samples (10 µl) were pre-treated by dilution (1 + 29) with 5% v/v HCl or by using the commercially available Metexchange M reagent. Lead was determined in certified whole blood samples (188 ppb) with a precision of 10.6% and an accuracy of 4.91%(n= 8). The analysis time was 6 min per sample.

Gold ultramicroelectrodes for on‐site monitoring of trace lead

AbstractGold and gold‐coated cylinder microelectrodes are used as stripping‐based microsensors for trace lead. These gold ultramicroelectrodes exhibit a favorable stripping performance, similar to that observed at common mercury ultramicroelectrodes. Such use of “mercury‐free” electrodes greatly facilitates the development of disposable sensors for lead blood screening programs. Potentiometric stripping analysis at these gold ultramicroelectrodes yields reproducible results for parts per billion (μg/L) concentrations of lead, following short preconcentration periods and using static, nondeaerated solutions. Numerous experimental variables have been characterized and optimized. Repetitive assays of 200‐μl sample drops yield a relative standard deviation of 2.2% (n = 20). The application of the gold ultramicroelectrodes for assays of various real samples is demonstrated, and prospects for their use in decentralized testings are discussed.

Reductive potentiomeric stripping analysis of manganese with potassium hexacyanoferrate(II) as reducing agent on a glassy carbon electrode

The reductive potentiometric stripping analysis (RPSA) of managenese with potassium hexacyanoferrate(II) as reducing agent on a glassy carbon electrode was investigated. This method is more sensitive, more reproducible, more precise and more convenient than the RPSA method for manganese with hydroquinone as reducing agent on a platinum working electrode. The technique was applied satisfactorily to determine micro amounts of manganese in artificial human hair sample solution and vegetables. The pretreatment of the glassy carbon electrode, the processes of anodic preconcentration and subsequent RPSA and interferences are discussed.

Elimination of zinc/copper intermetallic interference in the determination of zinc in wastewaters and seawater by potentiometric stripping analysis

AbstractA new approach to the elimination of Zn/Cu intermetallic interference in the determination of zinc by potentiometric stripping analysis is described. The method is based on the use of several enrichment/ stripping cycles, with each cycle using an enrichment time of 10 seconds or less and the stripping signal from each cycle being added to give the total stripping signal. The additive method compares favorably with the traditional “third element” approach based on the use of gallium, and it is demonstrated that, for an industrial sample containing oil and grease, the additive method has significant advantages over the gallium method. The advantages of potentiometric stripping analysis in monitoring zinc in industrial wastes and the applicability of the technique to zinc speciation studies are described.

Mercury-free disposable lead sensors based on potentiometric stripping analysis of gold-coated screen-printed electrodes

Gold-coated screen-printed electrodes offer reliable quantitation of trace lead in connection with potentiometric stripping analysis (PSA). Such replacement of mercury-based sensors, with gold-coated ones, avoids environmental contamination associated with the disposal of mercury electrodes in connection with large-scale screening for lead poisoning. The PSA operation obviates the need for oxygen removal, offers low background contributions, and minimizes surfactant interferences. Changes in the peak intensity and position (vs mercury-coated strips) offer new selectivity dimensions. Various experimental parameters are optimized to allow convenient monitoring of micrograms per liter lead concentrations following short deposition periods. Applicability to urine and drinking water samples is illustrated. The highly stable response of these screen-printed electrodes makes them very attractive for both single-use and multiple applications.

Effect of model organic compounds on potentiometric stripping analysis using a cellulose acetate membrane-covered electrode

The effects of model surfactants (sodium dodecyl sulfate, Triton X-100), proteins (ovalbumin, gelatin), and carbohydrates (agar, starch) as well as D-camphor and humic acid on a cellulose acetate dialysis membrane-modified mercury film electrode (CM-MFE) in potentiometric stripping analysis (PSA) are described. The CM-MFE (1000 amu molecular weight cutoff) minimized interference by these compounds to the PSA measurement. The constant current stripping analysis (CCSA) mode was found to provide a more stable response than the used of Hg(II) as chemical oxidant with the CM-MFE

Potentiometric stripping analysis and the speciation of heavy metals in environmental studies

Potentiometric Stripping Analysis (PSA) is applied to a wide variety of acidic dissolution reagents to investigate the inherent possibilities of this method in heavy metal speciation studies using various specific extraction media. The nature and the concentration of the acids, pH and ionic strength effects are studied in the pH range 0–6.5 and with ionic strengths ranging from 10 −4 to 5 M. PSA offers serious advantages over other electrochemical methods based on current measurements: the method gives correct analytical signals in a wide pH range (0–6.5) for all types of acidic reagents and in the whole range of ionic strengths. The study is conducted in the goal of permit routine measurements of heavy metal determinations in speciation studies of environmental samples: cadmium, lead and copper ions have been chosen as heavy metal ions and mercury(II +) is the chemical oxidizing agent and the precursor in mercury film formation onto the glassy carbon working electrode.

Comparison of potentiometric stripping analysis and square-wave voltammetry with respect to the influence of Triton X-100

Potentiometric stripping analysis (PSA) is less sensitive to the presence of electroinactive surface-active substances than anodic stripping square-wave voltammetry (ASSWV). Influences of the non-ionic detergent Triton X-100 on the responses of Tl +, Pb 2+, Cu 2+, Cd 2+, Bi(III) and In(III) obtained by direct and derivative PSA, square-wave voltammetry, d.c. polarography and ASSWV are compared.

Present potentials and limitations in the determination of trace elements by potentiometric stripping analysis

The determination of trace elements such as Zn, Cd, Pb, Cu, Ni, Co, Tl, Bi and Sn by potentiometric stripping analysis (PSA) in various matrices is described. With natural water samples only simple acidification to a pH of about 2 is sufficient to liberate the trace elements. In more complex matrices like waste waters, whole blood or other liquid samples the pH, time and deposition potential play an important role for the liberation of some trace elements. The data of interlaboratory comparisons about the determination of lead in whole blood and wine samples by PSA after simple sample preparation are presented.

Interlaboratory quality control for lead determination in wine by potentiometric stripping analysis

Computerized potentiometric stripping analysis (PSA) was used for the determination of lead in wine samples. With this analytical method the sample preparation is limited to dilution with an appropriate supporting electrolyte (0.5 mol/l HCl and 40 mg/l Hg2+). Due to very high sensitivity the time needed for one determination can be reduced to 2 min. This method for lead determination in wine was compared with results from voltammetry and ETAAS from various laboratories participating in two BCR studies. With PSA it is possible to determine cadmium, lead and copper in wine after a single dilution with an appropriate supporting electrolyte. For other elements such as Bi, Tl, Hg, Sn, As, Zn determination procedures are under development.

Potentiometric stripping analysis of selected heavy metals in biological materials

Different biological materials such as edible oils, refined and unrefined cane and beet sugar and tea (black and green) leaves were assayed for the heavy metals cadmium, copper, lead and zinc. The results revealed significant differences in heavy metal contents within each class of the biological materials (P < 0.05). Cadmium was not detectable in sugar samples. Among the oils, highest amounts of copper (0.263 microgram/g) and lead (0.154 microgram/g) were in corn oil and zinc in olive oil (3.01 micrograms/g) whereas cadmium exhibited a narrow range (0.023-0.033 microgram/g). The samples of beet-sugar generally contained higher levels of the heavy metals than cane-sugar. Black and green tea leaves contained 0.411-0.908 microgram Cd/g, 6.500-9.220 micrograms Cu/g, 2.200-5.238 micrograms Pb/g, and 14.500-25.180 micrograms Zn/g.

Direct Determination of Cadmium and Lead in Whole Blood by Potentiometric Stripping Analysis

The commercially available equipment for potentiometric stripping analysis (PSA) was tested for routine lead and cadmium determination in whole-blood samples. In contrast to anodic stripping voltammetry, PSA is not subject to background interferences from organic electroactive constituents in the sample or to the presence of dissolved oxygen (i.e., oxygen removal is not necessary). To determine lead and cadmium by PSA, it is sufficient to dilute the blood sample with an appropriate supporting electrolyte (0.5 mol/L HCl). The detection limit changes with deposition time and volume of blood sample used. For 1 mL of blood and a 1-min deposition time, the detection limit is 1 microgram/L for both elements. If the deposition time increases to 10 min, cadmium can be determined at its normal concentration in blood (the detection limit is improved to < 0.1 microgram/L). Procedures for routine determination of lead and cadmium in whole blood are presented.

Theory of derivative and differential potentiometric stripping analysis and stripping chronopotentiometry

AbstractThe theoretical treatment of derivative potentiometric stripping analysis and differential potentiometric stripping analysis is presented. The latter term refers to the technique employing the derivative of time with respect to potential vs. the potential function as the measured signal. The mathematical expressions obtained were also verified experimentally.

Constant-current enhanced potentiometric stripping analysis

Constant-current enhanced potentiometric stripping analysis (CCEPSA) is similar to potentiometric stripping analysis (PSA) except that during the stripping step in CCEPSA a cathodic current is imposed on the electrode system. The freshly oxidized metal ions in the vicinity of the electrode surface are partially redeposited so that the stripping time is extended. The stripping time and potential-time equations for CCEPSA were derived and verified using the stripping of cadmium(II). Under the most favorable conditions, the sensitivity of cadmium(II) determination was enhanced by a factor of 15.

Lead determination in wine by potentiometric stripping analysis

Computerized potentiometric stripping analysis (PSA) was used for lead determination in wine samples. In this method sample preparation before determination is limited to dilution with an appropriate supporting electrolyte (0.5 mol/l HCl and 40 mg/l Hg2+). Due to the very high sensitivity, the time needed for one determination can be reduced to 2 min. The method was tested by lead determination in different wines, different concentration ranges and in one European interlaboratory comparison organized by BCR. Using PSA it is possible to simultaneously determine cadmium, lead and copper in wine. For other elements such as Bi, Tl, Hg, Sn, As, Zn the determination procedures are under development. The PSA equipment is available on the market, small in size, relatively cheap and it does not require any special installation such as gas or cooling water.

A Microcomputer Controlled System for Potentiometric Stripping Analysis

ABSTRACT The construction of an inexpensive microcomputer controlled potentiometric stripping analysis system is described. The system allows both cathodic or anodic preconcentration of metal ions, and the deposited material may be stripped either chemically or galvanically. The interface circuits and the units comprising the system are described and the main features of the control software are also presented. The system has been designed to support operation with a rotating glassy carbon disk as a working electrode and it can be used for the determination of several heavy metals at ppb concentration range. The system is flexible, expandable and suitable for general studies on the technique, allowing the development of new operating modes by simple modifications on the hardware and software.

Determination of germanium by potentiometric stripping analysis and adsorption potentiometric stripping analysis

Potentiometric stripping analysis was applied to determination of germanium(IV) in 0.2 M NH 3-NH 4Cl (pH 8.4) buffer solution at −1.8 V ( vs. Ag/AgCl), with dissolved oxygen or Hg(II) as oxidant. The sensitivity was 8.5 × 10 −9 M in the presence of 2.0 × 10 −5 M Hg(II) with plating for 15 min after deaeration for 20 min. Cyclic voltammetry revealed that GE(IV) å Ge at the surface of the mercury-film electrode in a one-step irreversible reduction reaction, and the Ge at the electrode was oxidized by dissolved oxygen in the solution. The presence of complexing agents such as Alizarin Red (ARS), which forms a Ge(IV) complex adsorbed at the electrode, improved the sensitivity by one order of magnitude. The presence of adsorption was revealed by the temperature coefficient, the electrocapillary curve and cyclic voltammetry. Ge-containing samples were analysed by the proposed methods and agreement with the results obtained by other methods was excellent.

Theory of potentiometric stripping analysis in the case of reversible and quasi‐reversible electrode reactions

AbstractThe theoretical treatment of potentiometric stripping analysis is presented for the cases of reversible and quasi‐reversible electrode reactions. The experimental results were found to be in good agreement with calculated data. Derivations based on different assumptions (e.g., stripping in stirred solutions, diffusion layer of constant thickness) are compared.