Flow constant-current stripping analysis for antimony(III) and antimony(V) with gold fibre working electrodes : Application to Natural Waters

Antimony(III) is determined by means of electrolysis at ?0.40 V vs. Ag/AgCl on a gold-coated gold fibre electrode for 0.5–10 min in a redox buffer containing 0.01 M iron(II) in 0.10 M hydrochloric acid, and subsequent stripping with a constant current of 0.50μA either in 2 M hydrochloric acid or in 4 M hydrochloric acid/4 M calcium chloride. Antimony(V) is determined by the same procedure in 4 M hydrochloric acid medium. Bismuth(III) is masked by the addition of iodide to the sample prior to electrolysis. Antimony(III) and antimony(V) are determined by standard addition methods; the whole procedure including digital and graphical evaluation of the results is fully automated. The antimony(V) concentrations in the river water reference sample SLRS-1 and the seawater reference sample NASS-1 were found to be 0.63 and 0.31 μg l^?1 with standard deviations of 0.046 and 0.051 μg l^?1, respectively (n=15). The certified value for SLRS- 1 is 0.63±0.05 μg l^?1; no certified value is available for NASS-1.     

Determination of lead in whole blood with a simple flow-injection system and computerized stripping potentiometry

An automated (24 samples/hour) procedure is described for the determination of lead (0–1000 μg l^?1) in human blood based on flow-injection stripping potentiometry. The samples are diluted 20-fold with 0.5 M hydrochloric acid containing 100 mg l^?1 mercury and 40 μg l^?1 cadmium (II), and a 1.1 ml aliquot is injected into the flow system. With a mercury-coated carbon fibre as working electrode, lead (II) is determined by using cadmium (II) as internal standard and a calibration graph prepared from bovine blood. Analyses of two human blood reference samples yielded results of 335±37 and 691±24 μg l^?1 lead, the certified values being 332 and 663 μg l^?1, respectively.     

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l^?1 Cu, 0.38 μg l^?1 Pb, 0.01 μg l^?1 Cd and 0.95 μg l^?1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.     

Simultaneous determination of mercury(II), copper(II) and bismuth(III) in urine by flow constant-current stripping analysis with a gold fibre electrode

Urine samples are treated with concentrated nitric acid and potassium permanganate ar 70°C for 10 min prior to injection. The flow electrode system consists of a 10-μm diameter gold fibre working electrode, a glassy carbon reference electrode and a platinum counter electrode. In the fully automated constant-current stripping procedure, the gold fibre is first covered with a fresh gold film after which the sample is electrolyzed for 1 min prior to stripping in 0.1 M hydrochloric acid with a current of 0.1μA. The procedure is repeated on a spiked sample after which the sample analyte concentrations are evaluated and presented digitally and graphically on a printer/plotter. The results obtained for bismuth, copper and mercury in a urine reference sample were 36.9, 39.7 and 47.7 μg l^?1 with standard deviations (n=10) of 3.2, 4.2 and 2.1, respectively. The certified values for copper and mercury were 45 and 51 μg l^?1; no certified value was available for bismuth.     

Determination of uranium(VI) in seawater by means of automated flow constant-current cathodic stripping at carbon fibre electrodes

Uranium(VI) is determined in an automated flow system by means of constant-current reductive stripping with a mercury film-coated carbon fibre electrode and catechol as adsorptive reagent at pH 8.6 Interference from iron(III) is eliminated by addition of sulphite. Increased linear range between stripping signal and sample uranium(VI) concentration can be obtained by adding, in the computer, several stripping curves, each obtained after a short period of adsorptive accumulation. It is shown that the hanging mercury drop electrode can be used for the determination of uranium(VI) by means of computerized constant current stripping without the need for inert gas bubbling. The results obtained for uranium(VI) in two reference seawater samples, NASS-1 and CASS-1, were 2.90 and 2.68 μg l^?1 with standard deviations (n = 8) of 0.57 and 0.75 μg l^?1, respectively.     

Direct determination of bismuth and antimony in sea water by anodic stripping voltammetry

A method based on anodic stripping voltammetry at the mercury-coated graphite electrode has been developed for the direct determination of bismuth and antimony at their natural levels in sea water. Bismuth plated at -0.4 V from sea water made 1 M in hydrochloric acid gives a stripping peak proportional to concentration at -0.2 V without interference from antimony or other metals normally present. Antimony may be plated from sea water made 4 M in hydrochloric acid and gives a stripping peak at -0.2 V proportional to the sum of bismuth and antimony. By use of the standard addition technique, satisfactory results were obtained for sea water samples with concentration ranges of 0.02–0.09 μg kg^?1 for bismuth and 0.2–0.5 μg kg^?1 for antimony.     

Differential preconcentration of arsenic(III) and arsenic(V) with thionalide loaded on silica gel

2-Mercapto-N-2-naphtylacetamide (thionalide) on silica gel is used for differential preconcentration of μg l^?1 levels of arsenic(III) and arsenic(V) from aqueous solution. In batch experiments, arsenic(III) was quantitatively retained on the gel from solutions of pH 6.5–8.5, but arsenic(V) and organic arsenic compounds were not retained. The chelating capacity of the gel was 5.6 μmol g^?1 As(III) at pH 7.0. Arsenic retained on teh column was completely eluted with 25 ml of 0.01 M sodium borate in 0.01 M sodium hydroxide containing 10 mg l^?1 iodine (pH 10). The arsenic was determined by silver diethyldithiocarbamate spectrophotometry. Arsenic(V) was subsequently determined after reduction to arsenic(III) with sulphite and iodide. Arsenic(III) and arsenic(V) in sea water are shown to be < 0.12 and 1.6 μg l^?1, respectively.     

Stripping voltammetry of aluminum based on adsorptive accumulation of its solochrome violet RS complex at the static mercury drop electrode

A very sensitive electrochemical stripping procedure for aluminum is reported. Accumulation is achieved by controlled adsorption of the aluminum/solochrome violet RS complex on the static mercury drop electrode. Optimal experimental parameters include an accumulation potential of ?0.45 V, solochrome violet RS concentration of 1 × 10^?6 M, and a linear-scan stripping mode. The detection limit is 0.15 μg l^?1, the response is linear over the 0–30 μg l^?1 concentration range, and the relative standard deviation (at the 10 μg l^?1 level) is 2%. Most cations do not interfere in the determination of aluminum. The interference of iron(III) is eliminated by addition of ascorbic acid. Results are reported for snow samples.     

Automated determination of molybdenum(VI) in seawater by means of constant-current reduction of the adsorbed 8-quinolinol complex in a computerized flow potentiometric stripping analyzer

Molybdenum(VI) in seawater is determined by means of potentiostatic adsorption of the 8-quinolinol complex onto a mercury film electrode at ?0.2 V vs. SCE and subsequent reduction of the complex by means of constant-current stripping in 5 M calcium chloride medium with a fully automated stripping analyzer. A single stripping peak at –0.42 V vs. SCE was obtained. The molybdenum(VI) concentration in reference seawater NASS-1, with a certified value of 11.5 ± 1.9 μg 1^?1, was found to be 8.9 ± 1.3 μg 1^?1 (n = 10).     

Flow potentiometric and constant-current stripping analysis for arsenic(V) without prior chemical reduction to arsenic(III): Application to the Determination of Total Arsenic in Seawater and Urine

Arsenic(V) is reduced to elemental arsenic on a gold-coated platinum-fibre electrode at electrolysis potentials below ?1.60 V vs. Ag/AgCl and subsequently re-oxidized, either by means of a constant current, or chemically, with gold(III) as oxidant. Total arsenic in acidified seawater can be determined by means of electrolysis for 60 s at ?1.80 V vs. Ag/AgCl and subsequent stripping in 4 M hydrochloric acid containing 2.5 M calcium chloride. The detection limit obtained after 60 s of electrolysis (ca. 0.1 μg1^?1) is about ten times lower than that obtained by the electrochemical stripping methods for arsenic(III) reported hitherto. Total arsenic in urine is determined after digestion with nitric acid and hydrogen peroxide.     

Flow potentiometric and constant-current stripping analysis for silver(I) with carbon- and platinum-fibre electrodes

At concentrations above 50 μg l^?1, silver(I) is determined in nitric acid medium by means of potentiostatic deposition onto a platinum-fibre electrode and subsequent constant-current stripping in the sample or potentiometric stripping in a potassium permanganate medium. Interference from copper(II) is reduced by a pulsed potential procedure whereby copper deposited onto the fibre electrode is reoxidized intermittently. At concentrations below 50 μg l^?1, silver(I) is determined by using a mercury-coated carbon-fibre electrode and constant-current stripping in acetonitrile containing 0.20 M perchloric acid. Potentiostatic deposition for 30 min yielded a detection limit of 0.24 μg l^?1 silver(I) at the 3σ level.     

Determination of very low/levels of selenium(IV) in sea water by differential-pulse cathodic stripping voltammetry after extraction of the 3,3′-diaminobenzidine piazselenol

Selenium(IV) is determined by cathodic stripping voltammetry after the formation of a piazselenol with 3,3′-diaminobenzidine. The selenium is then accumulated as HgSe on a mercury electrode by deposition at ?0.45 V. The differential-pulse cathodic stripping peak allows a detection limit of 0.01 μg l^?1. For the determination of selenium in natural waters, interferences can be avoided by extraction of the piazselenol into toluene followed by a back-extraction into 0.5 M hydrochloric acid. The accuracy of the overall procedure was checked by analyses of a standard reference material. The method was applied to the determination of selenium(IV) in sea-water samples at levels as low as 20 ng l^?1 with a concentration factor of 10 during the extraction procedure.     

The determination of gold by anodic stripping voltammetry

A method is described for the routine determination of gold as its chloride or cyanide complex by anodic stripping voltammetry at a glassy carbon electrode coupled to a microprocessor-controlled voltammeter. The preferred supporting electrolyte is 0.1 M HCl/0.32 M HNO₃, with plating at ?200 mV or ?1200 mV (vs. Ag/AgCl). The stripping peak potentials range from 830 to 1150 mV (vs. Ag/AgCl) depending on concentration and plating time. Precision (percent relative standard deviation) is better than 5 % for a range of concentrations between 5 μg l^?1 and 1000 μg l^?1. The detection limit is about 5 μg l^?1 for a 5-min plating period. Interferences from Cu, Hg, Ag and other electroactive species are overcome by preliminary extraction with diethyl ether.     

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

In the proposed method As(III) is determined with a wall‐jet flow cell by means of potentiostatic co‐deposition of Au(III) and As(III) at a glassy‐carbon electrode and subsequent chemical stripping with Au(III). Factors affecting sensitivity and precision including acidity, Au(III) concentration, electrodeposition potential and flow rate were optimized. Optimum determination of As(III) in solutions containing 160 mg L^?1 and 1.2 M hydrochloric acid was accomplished with an electrolysis potential of ?0.1 V (vs. Ag/AgCl) and a flow rate of 0.59 mL min^?1. Different linear concentration ranges were achieved under these conditions with good precision and relative standard deviations between 6–9%. The detection limit obtained after 120 s of electrolysis was 0.55 μg L^?1.     

Redox Speciation of Inorganic Arsenic in Water and Saline Samples by Adsorptive Cathodic Stripping Voltammetry in the Presence of Sodium Diethyl Dithiocarbamate

This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(III)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na₂S₂O₅ and Na₂S₂O₃ in the concentrations 2.5 and 0.5 mg mL^?1, respectively, and the sample heating at 80 °C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 μg L^?1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 μg L^?1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 μg L^?1 and 15.0 μg L^?1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 μg L^?1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for As(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring.     

Preconcentration and Spectrophotometric Determination of Chromium (VI) and Total Chromium in Drinking Water by the Sorption of Chromium Diphenylcarbazone with Surfactant Coated Alumina

Abstract

A simple and inexpensive method for determining chromium (VI) in drinking water by spectrophotometry after preconcentration with sodium dodecyl sulphate (SDS) coated alumina column is described. Chromium(VI) is reacted with diphenylcarbazide (DPC) and the Cr-DPC complex is quantitatively adsorbed onto a SDS coated alumina column from 800 ml of sample solution. The complex is then eluted with a 8 ml mixture of methanol, acetone and hydrochloric acid and determined by spectrophotometry. Total chromium can be determined after oxidation of chromium (III) to chromium (VI) by KMnO₄. The relative standard deviation (10 replicate analyses) at the 10 μg l^?1 of chromium (VI) and 10 μg l^?1 of total chromium were 3.5% and 3.4% and corresponding limits of detection (based on 3 σ) were 0.040 μg l^?1 and 0.033 μg l^?1, respectively.     

The spectrophotometric determination of arsenic in sea water,potable water and effluents

Procedures are described for the determination of arsenic in sea water, potable waters and effluents. The sample is treated with sodium borohydride added at a controlled rate. The arsine evolved is absorbed in a solution of iodine and the resultant arsenate ion is determined photometrically by a molybdenum blue method. The time required for a complete analysis is about 90 min, but of this only 15 min is operator time. For sea water the range, standard deviation, and detection limit are 1–4 μgl^-1, 1.4 % and O.14 μg l^-1, respectively; for potable waters they are 0–800 μg l^-1, about 1 % (at 20μg l^-1 level) and 0.5μg l^-1, respectively. Silver and copper cause serious interference at levels of 0.5 mgl^-1, and nickel, cadmium and bismuth interfere at concentrations of a few tens of mg l^-1; however, these elements can be removed either by preliminary extraction with a solution of dithizone in chloroform or by ion exchange. Arsenic present in organo-arsenic compounds is not directly determinable, but can be rendered reactive either by photolysis with ultraviolet radiation or by oxidation with permanganate or nitric—sulphuric acid mixture. Arsenic(V) can be determined separately from total inorganic arsenic after extracting arsenic(III) as its pyrrolidine dithiocarbamate into chloroform.     

An improved method for the determination of trace levels of arsenic and antimony in geological materials by automated hydride generation—atomic absorption spectroscopy

An improved, automated method for the determination of arsenic and antimony in geological materials is described. After digestion of the material in sulfuric, nitric, hydrofluoric and perchloric acids, a hydrochloric acid solution of the sample is automatically mixed with reducing agents, acidified with additional hydrochloric acid, and treated with a sodium tetrahydroborate solution to form arsine and stibine. The hydrides are decomposed in a heated quartz tube in the optical path of an atomic absorption spectrometer. The absorbance peak height for arsenic or antimony is measured. Interferences that exist are minimized to the point where most geological materials including coals, soils, coal ashes, rocks and sediments can be analyzed directly without use of standard additions. The relative standard deviation of the digestion and the instrumental procedure is less than 2% at the 50 μg l^-1 As or Sb level. The reagent-blank detection limit is 0.2 μg l^-1 As or Sb.     

Cathodic stripping determination of halides in mixtures

Cathodic stripping voltammetry is evaluated for the simultaneous determination of chloride, bromide and iodide in mixtures. Results are similar to those obtained with ion-selective electrodes. Detection limits are 177 μg l^?1 for chloride, 40 μg l^?1 for bromide, and 8 μg l?1 for iodide. Dam water and human spinal fluid were analyzed satisfactorily.     

On-line determination of residual aluminium in potable and treated waters by flow-injection analysis

A portable, automated, flow-injection-based solid-state spectrophotometric field monitor for the determination of residual dissolved aluminium in potable and treated waters is described. Aluminium is determined by complexation with pyrocatechol violet to form a colloidal lake with a maximum absorbance at 580 nm. Interference from iron(III) is masked by reduction to iron(II) and complexation with 1,10-phenanthroline. The monitor operates on a 30-min analytical cycle, i.e., with 48 results per day, and each cycle includes an autocalibration step. Over the course of a 3-month field trial the reliability was greater than 90%. The performance conforms to industry specifications for both overall accuracy (bias < ± 10%) and repeatability (relative standard deviation < ± 10%), the linear range is 0–1000 μg l^?1 and the practical limit of detection is 45 μg l^?1.