Determination of copper in the presence of a large excess of bismuth by differential-pulse anodic-stripping voltammetry without preliminary separation

Conditions have been found which make possible the determination of copper in the presence of a large excess of bismuth by differential-pulse and anodic-stripping voltammetry without preliminary separation. The electrochemical activity of the bismuth, which usually interferes in the determination of copper, is inhibited by using tetrabutylammonium chloride (TBAC) as surfactant. In 0.2M EDTA and 0.01M ascorbic acid at pH 4.5 as supporting electrolyte without the surfactant present, trace levels of copper (1.5 x 10(-8)M) can be determined accurately if the molar ratio of bismuth to copper is not higher than 3, but if the electrolyte also contains TBAC at 0.01M concentration, bismuth can be tolerated in concentrations up to 10(-4)M, and the height of the copper peak is unaffected.     

A pyrolytic carbon film electrode for voltammetry-III Application to anodic-stripping voltammetry

The potential applicability of a pyrolytic carbon film electrode in the differential-pulse anodic-stripping voltammetric determination of cadmium and lead in sea-water is demonstrated. The performance at the 10⁻¹⁰M level is compared with that of a satisfactory glassy-carbon electrode. The two types of electrode display comparable behaviour in anodic-stripping voltammetry, but the pyrolytic carbon film electrode needs less pretreatment.     

A contribution to the problem of increasing fhe sensitivity of anodic-stripping voltammetry

A brief discussion of problems connected with increasing the sensitivity of anodic-stripping determinations is presented. A new microcell for anodic-stripping voltammetry in solution volumes down to about 0.01 ml was constructed. The effect of the solution volume, the mercury-drop electrode size, and of the pre-electrolysis time and potential on the sensitivity of determinations was studied and the reproducibility of results for determinations of lead in mineral acids is given. It was found that nanogram amounts of heavy metals can easily be determined in this way. In determination of 2 ng of Pb(2+) in 0.02 ml of solution the results were 2.00 +/- 0.13 ng (95% confidence limits), the mean relative deviation being 6.3%. For determination of copper in KNO(3), stripping microanalysis was compared with atomic-absorption spectrophotometry. Advantages and disadvantages of stripping voltammetry on the macro- and micro-scales are discussed.     

Determination of alprazolam in serum by adsorptive stripping voltammetry

The surface-active properties of alprazolam at a hanging mercury drop electrode allow their sensitive determination by differential-pulse adsorptive stripping voltammetry. Detection limits are 0.07 ng/ml for accumulation in water (accumulation time 240 s) and 0.3 ng/ml for accumulation in serum extract (accumulation time 30 s). Coefficients of variation at 5 ng/ml (10 determinations) were typically <2%.     

Determination of trace metals by anodic-stripping voltammetry with a new kind of mercury electrode: The long-lasting sessile-drop electrode

A new kind of semi-stationary mercury drop electrode is described, which can be used for the determination of trace metals in natural waters by differential-pulse anodic-stripping voltammetry. Results are reported for the determination of zinc in potassium chloride and in samples of sea-water. The reproducibility of the electrode and of the results obtained with it for zinc at the 10(-8)M level are very satisfactory.     

Linear sweep voltammetry at the tubular electrode

The theory of linear sweep voltammetry at the tubular electrode has been developed for reversible electrode processes. The convective diffusion differential equations have been transformed to an integral equation which is solved numerically. The theoretical current—potential curves at different velocities of the solution have been calculated. Comparison with experiments using a tubular electrode shows satisfactory agreement.     

Studies of pretreatments in the determination of Zn, Cd, Pb, Cu, Sb and Bi in suspended particulate matter and plankton by differential-pulse anodic-stripping voltammetry with a hanging mercury drop electrode

The determination of Zn, Cd, Pb, Cu, Sb and Bi by differential-pulse anodic-stripping voltammetry has been applied to samples of plankton and suspended particulate matter after decomposition of organic matter by two methods: low-temperature ashing with microwave-activated oxygen and wet-ashing in pressurized Teflon crucibles. The loss of these elements, and contamination, were studied with a standard reference material. The relative merits of these oxidation techniques are discussed.     

Automated square-wave anodic-stripping voltammetry with a flow-through cell and matrix exchange

An extremely sensitive and versatile instrument is described that performs square-wave anodic-stripping voltammetry. The instrument incorporates a flow-through cell and is capable of changing the solution matrix between the deposition and stripping steps. The working electrode is a static mercury drop electrode constructed in the authors' laboratories. The entire system is controlled by a microcomputer that allows the usual variation of the square-wave parameters, as well as setting of the initial and final scan potentials, the deposition time, the scan-rate, the instrument sensitivity and the drop size. To show the performance of the instrument, calibration graphs for Cd in the ranges 0.2-40 and 0.1-1 ng/ml are described and the reproducibility of the drop is discussed. Analysis of a NaCl sample for Cd is given as an example of application of the method.     

Evaluation of differential pulse anodic-stripping voltammetry at a stationary mercury-film electrode with stirred solution

Differential pulse anodic-stripping voltammetry at a stationary mercury-film electrode with the solution stirred during the deposition step has been investigated. The sensitivity achieved by using such a simple set-up is similar to that obtained with a mercury-film rotating disk electrode. The effects of various experimental parameters on the peak current are described. Lead and cadmium were used as test systems, and gave detection limits of around 1 x 10(-10)M with 5-min deposition times.     

Determination of trace amounts of thorium by electroanalytical techniques

Trace amounts of thorium have been determined in the presence of uranyl nitrate and ammonium diuranate (as interferents) by cyclic voltammetry, differential-pulse polarography, differential-pulse voltammetry, square-wave voltammetry and anodic-stripping voltammetry. The determination is based on the substitution of thorium for copper, lead and cadmium in their EDTA complexes and voltammetric measurement of the displaced metal ion. The detection limits ranged between 2 x 10(-7) and 1 x 10(-6)M (r.s.d. 2-7%) for solutions free from the uranium compounds, and between 8 x 10(-7) and 5 x 10(-6)M (r.s.d. 3-5%) in the presence of the uranium compounds at concentrations up to about 1000 times that of thorium. The detection limits depend on both the particular technique and the EDTA complex employed. Anodic-stripping voltammetry gave detection limits of 8 x 10(-8) and 10(-7)M in the absence and presence of uranium respectively.     

Flow injection system for stripping voltammetry

A flow system for quantifying traces of heavy metals by anodic stripping voltammetry (a.s.v.) is described. This system is optimized for simplified, rapid sample processing using either linear-sweep or differential-pulse stripping waveforms. The linear-sweep excitation signal can be used effectively for concentrations in the ng ml^?1 range at a rate of approximately 30 samples per hour. The differential-pulse waveform lowers the detection limits to concentrations as low as 20 pg ml^?1, in a sample volume of 1 ml at a rate of approximately 9 samples per hour. The advantages of the system include improved efficiency of sample preconcentration during the deposition step (especially for sub-milliliter samples), simplified operation, ready adaptability to automation and online monitoring, no sample deoxygenation, minimal sample pretreatment, and easy matrix exchange between the deposition and stripping steps. The utility of this system is demonstrated with indium and for the determination of lead in blood.     

Determination of thallium in bismuth by differential pulse anodic-stripping voltammetry without preliminary separation

The determination of trace levels of thallium in bismuth and bismuth salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent, in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte in the absence of surfactant, bismuth at concentrations below 10(-4)M does not interfere. When the electrolyte also contains tetrabutylammonium ions at 0.01 M concentration, bismuth can be tolerated at concentrations up 0.05M, and the height of the thallium peak is unaffected. It is thus possible to determine 1 nM Tl(I) in the presence of 0.05M Bi(III), i.e., Tl at the 1 x 10(-6)% level in bismuth. The precision of the determination and the recovery are satisfactory. Neither an 800-fold ratio of Cu(II) nor a 10(7)-fold ratio of Pb(II) to Tl(I) interferes in the determination. Other cations such as Zn(2+), Cd(2+), In(3+), Hg(2+), Fe(3+), Sb(3+) and Sn(4+) in 10(4)-fold molar ratio to Tl(I) have no effect on the determination. Thallium has been determined in bismuth metal and in bismuth nitrate of various degrees of purity.     

Differential-pulse anodic-stripping voltammetric determination of traces of lead in high-purity copper after its separation by ion exchange

Trace amounts of lead in copper can be determined by differential-pulse anodic-stripping voltammetry after separating it from the matrix. Lead was quantitatively retained on a small Dowex 1-X4 ion-exchange column, without retaining copper when present as a copper-amine complex in solutions containing 0.2 M sodium hydroxide. Subsequent desorption was done with 2 M nitric acid. After deposition for 1 min on a hanging mercury drop electrode and subsequent stripping, the limit of detection was 2 ng ml^?1 and the limit of quantification was 6.6 ng ml^?1. Recoveries of lead were checked by standard addition to copper solution.     

Determination of arsenic in polluted waters by differential pulse anodic-stripping voltammetry

Experimental parameters affecting the analytical response of arsenic in differential pulse anodic-stripping voltammetry (DPASV) have been examined. DPASV offers higher sensitivity than linear-scan anodic-stripping voltammetry for similar analysis times. Both techniques have been applied to the NBS Standard Reference Water (SRM 1643) and some polluted water samples. The results on polluted waters compared favourably with those obtained by graphite-furnace atomic-absorption spectroscopy.     

Determination of arsenic by cathodic stripping voltammetry at a hanging mercury drop electrode

Arsenic (III), respectively arsenic(V) after the reduction were determined in model solutions and some inorganic and organic materials by fast scan differential pulse cathodic stripping voltammetry and by direct current cathodic stripping voltammetry with a rapid increase of potential. The accumulation on a hanging mercury drop electrode followed by cathodic stripping was carried out in 0.7–0.8M HCl or 1–2M H₂SO₄ solutions containing Cu(II)-ions. Detection limits calculated from regression parameters was determined to be under 1 ng/ml for the samples containing very low arsenic concentrations. The relative standard deviation did not reach 8% for arsenic contents about of 5 ng/ml.     

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 mercury by differential-pulse anodic-stripping voltammetry with various working electrodes Application to the analysis of natural water sediments

Four types of working electrode (glassy-carbon and gold rotating-disk electrodes and two types of gold-film electrode) have been used in determination of traces of mercury by differential-pulse anodic-stripping voltammetry, and the analytical parameters of the procedures compared. The technique has been applied to the analysis of river sediments. The lowest limit of detection (0.02 μg/l.) was obtained with the gold rotating-disk electrode. Two procedures have been found optimal for analyses of sediment samples; determination with the gold rotating-disk electrode and solution-exchange after the preelectrolysis, and determination with the gold-film electrode prepared in situ in the sample extract. The sample pretreatment involved a separation of the 0.45–63 μm fraction, mineralization with a mixture of hydrochloric and nitric acids (3:1 or 1:3) under atmospheric pressure in a fused silica vessel, followed by irradiation with ultraviolet light, after addition of hydrogen peroxide (to destroy organic matter). The most serious interference is from iron; this can be prevented by adding fluoride or pyrophosphate. The procedure is an alternative to the AAS determination of the total mercury content in sediments, especially with heavily polluted samples (mercury concentrations up to 0.01%).     

Adsorptive stripping voltammetry of chlordiazepoxide at the hanging mercury drop electrode

Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10^?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10^?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10^?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C₁₈ cartridge.     

Anodic-stripping voltammetry of heavy metals in the presence of organic surfactants

The efficacy of fumed silica for removal of sorption interferences by organic surfactants in the anodic-stripping voltammetry of heavy metals is demonstrated. Appropriate addition of silica to the sample solution rapidly "purifies" it from interfering surfactants during the nitrogen purge step. Up to at least 6 ppm of gelatin, Triton X-100, albumin or Liqui-Nox then does not affect the stripping response of cadmium, lead and zinc at the hanging mercury drop electrode. A relative standard deviation of 5.5% is obtained for 20 successive measurements of 1 x 10(-7)M lead in the presence of 2 ppm Triton X-100. Analogous improvements are observed at the mercury film electrode (in the presence of up to 60 ppm of these surfactants). The use of silica thus possesses the advantages of speed, efficiency, simplicity and low cost compared to other schemes for dealing with surfactant interferences in anodic-stripping voltammetry.     

Cathodic stripping voltammetry of 2-mercaptoethanol

The behaviour of 2-mercaptoethanol at a hanging mercury drop electrode by cathodic stripping voltammetry (c.s.v.) is studied. The stripping curves are recorded by three scanning modes: rapid-scan direct-current, differential-pulse and fundamental harmonic alternating-current polarography. Under the recommended conditions, pre-electrolysis is done at a potential of 0.0 V vs. Ag/AgCl for 3 min in a medium of pH 6.7 or 8 (Britton-Robinson buffer). Then after 1 min, stripping is done at a scan rate of 6.6 mV s^?1 preferably in the differential-pulse mode. The stripping peak at about ?0.4 V is used to determine 2-mercaptoethanol within the concentration range 3 × 10^?8/2-8 × 10^?7 mol l^?1. Calibration functions are reported; the standard additions method is preferred near the limit of detection. The interferences of several organic compounds are described.