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).     

Adsorptive Stripping Voltammetric Determination of Trace Uranium with a Bismuth‐Film Electrode Based on the U(VI)→U(V) Reduction Step of the Uranium‐Cupferron Complex

This work reports the use of adsorptive stripping voltammetry (AdSV) for the determination of uranium on a preplated rotating‐disk bismuth‐film electrode (BiFE). The principle of the method relied on the complexation of U(VI) ions with cupferron and the subsequent adsorptive accumulation of the complex on the surface of the BiFE. The uranium in the accumulated complex was then reduced by means of a cathodic voltammetric scan while the analytically useful U(VI)→U(V) reduction signal was monitored. The experimental variables as well as potential interferences were investigated and the figures of merit of the method were established. Using the selected conditions, the 3σ limit of detection for uranium was 0.1 μg L^?1 at a preconcentration time of 480 s and the relative standard deviation was 4.7% at the 5 μg L^?1 level for a preconcentration time of 120 s (n=8). The accuracy of the method was established by analyzing a reference sea water sample.     

Determination of caprolactam by adsorptive voltammetry after separation by thin-layer chromatography

Caprolactam (2-oxohexamethyleneimine) can be determined in wastewaters and natural waters by adsorptive stripping voltammetry after separation of the product of the reaction between caprolactam and p-(N,N-dimethylamino)benzene-p′-azobenzoyl chloride. When a hanging mercury drop electrode is used with an accumulation time of 60 s in stirred solution, caprolactam can be determined from a lower limit of 0.2 μg ml^?1. With a 360-s accumulation time, linear calibration plots are obtained for 8 × 10^?10?8 × 10^?9 mol l^?1 caprolactam. The effect of interfering sample components is eliminated by the TLC separation.     

Electrocapillary Activity and Adsorptive Accumulation of U(VI)‐Cupferron and U(VI)‐Chloranilic Acid Complexes on Mercury Electrode

Interfacial activity of uranium(VI)‐cupferron and uranium(VI)‐chloranilic acid (CAA) complexes (in 0.1 M acetate buffer pH 4.6 or 0.1 M NaClO₄ respectively) on polarized mercury electrode at 110 mV, 10 mV or ?240 mV respectively vs. saturated calomel electrode (SCE), and under conditions of the application of adsorptive stripping voltammetric techniques was studied. It revealed a competitive effect of interfacial activity of the mentioned complexes consisting in a nonmonotonous effect of the bulk concentration of U(VI) on the adsorption of the mentioned complexing reagents at their constant concentrations. At concentrations lower than 5×10^?5 mol L^?1 the complexes U(VI)‐cupferron or U(VI)‐CAA exhibited a relatively strong electrosorption providing the adsorption coefficients β of the order 10⁴ L mol^?1, the maximum surface excess Γ_m ≈ 5 to 10 μmol m^?2 and average Frumkin interaction coefficients reaching their absolute values 2 to 2.6.     

The Cyclic Renewable Mercury Film Silver Based Electrode for Determination of Uranium(VI) Traces Using Adsorptive Stripping Voltammetry

The new cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of uranium(VI) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) is presented. The Hg(Ag)FE electrode with a surface area adjustable from 1.1 to 12 mm² is characterized by very good surface reproducibility (≤2%) and long‐term stability (more than 2 thousand measurement cycles). The mechanical refreshing of mercury film is realized in the simple constructed device, in a time shorter than 1–2 seconds. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 0.4 nM (95 ng L^?1) to 250 nM (60 μg L^?1) for an accumulation time of t_acc=20 s, with correlation coefficient of 0.9996. For a Hg(Ag)FE with a surface area of 2.7 mm² the detection limit for an accumulation time of 120 s is as low as 12 ng L^?1. The repeatability of the method at a concentration level of the analyte as low as 2.4 μg L^?1, expressed as RSD is 2.5% (n=7). The proposed method was successfully applied and validated by studying the recovery of U(VI) from spiked river water and sediment samples.     

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.     

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.     

Square-wave adsorptive stripping voltammetric determination of antihypertensive agent telmisartan in tablets and its application to human plasma

The adsorptive stripping voltammetry of telmisartan was investigated with a hanging mercury drop electrode. This compound produced a catalytic hydrogen wave at ?1.5 V in Britton Robinson buffer of pH 10.38, and the peak current increased with adsorptive accumulation at the electrode. Adsorptive stripping voltammetry with the catalytic hydrogen wave could provide a sensitive novel method for the determination of telmisartan. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for telmisartan determination. Under these optimized conditions the square-wave adsorptive stripping voltammetric (SW-AdSV) peak current showed a linear dependence on drug concentration over the range 0.05–3.00 μg/mL (1 × 10^?7?6 × 10^?6 M) (r = 0.999) with accumulation for 120 s at ?1.0 V vs. Ag/AgCl. The proposed electrochemical procedure was successfully applied for the determination of telmisartan in pharmaceutical tablets and human plasma. The results of the developed SW-AdSV method were comparable with those obtained by reported analytical procedures.     

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.     

Differential-pulse anodic stripping voltammetry of mercury with gold-film micro-electrodes

Cylindrical gold film micro-electrodes are easily produced by plasma-sputtering of gold onto carbon fiber electrodes. The micro-electrodes produced were found to maintain their cylindrical geometry indefinitely, unlike gold wire electrodes of similar dimensions. Application of these electrodes in differential-pulse anodic stripping voltammetry provides a method for quantifying trace levels of mercury(II). Up to 100 μg l^?1 Hg(II) the area of the mercury stripping peak varied linearly with mercury concentration; the detection limit was 3.7 μg l^?1. With more than 100 μg l^?1 Hg(II) a new mercury stripping peak grows in at less positive potentials; its peak height is linear with Hg(II) concentration.     

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.     

Potentiometric stripping analysis for lead in urine

Potentiometric stripping analysis is based on the preconcentration of analytes by means of potentiostatic reduction and amalgamation at a thin-film mercury electrode. After preconcentration, the potentiostatic circuitry is disconnected and the amalgamated metals are oxidized either by mercury(II) ions or by dissolved oxygen. Lead can be determined in acidified urine samples by potentiometric stripping analysis after the addition of Triton X-100. In deaerated samples the detection limit is 1 μg l^?1, and in non-deaerated samples 12 μg l^t-1, the preconcentration time being 16 min.     

Bismuth film electrode for simultaneous adsorptive stripping analysis of trace cobalt and nickel using constant current chronopotentiometric and voltammetric protocol

Bismuth film electrode (BiFE) is presented as a promising alternative to mercury electrodes for the simultaneous determination of trace cobalt and nickel in non-deoxygenated solutions. The preplated BiFE was employed under adsorptive stripping constant current chronopotentiometric and adsorptive stripping voltammetric conditions in the presence of dimethylglyoxime complexing agent. BiFE exhibited well-defined and undistorted signals with favorable overall resolution for cobalt and nickel cations, with the signals for both metal cations being practically independent of each other. The stripping performance of BiFE is characterized by good reproducibility (RSD 1.4% for Co(II), and 4.3% for Ni(II)), low detection limits of 0.08 μg l⁻¹ for Co(II) and 0.26 μg l⁻¹ for Ni(II) employing a deposition time of 60 s, in addition to good linearity. The non-toxic character of bismuth imparts the possibility of tailoring disposable and one-shot electrochemical sensors for decentralized environmental, clinical and industrial monitoring of trace cobalt and nickel.     

Automated determination of total arsenic in sea water by flow constant-current stripping analysis with gold fibre electrodes

Total arsenic in sea water is determined in a fully automated flow system, by means of potentiostatic deposition for 4 min at a 25-μm gold fibre electrode and subsequent constant-current stripping in 5 M hydrochloric acid. Previously the sample is acidified with hydrochloric and arsenic(V) is reduced to arsenic(III) with iodide. During stripping, the potential vs. time transient is recorded with a real-time measurement rate of 26.5 kHz and a potential resolution of 1 mV. Cleaning and regeneration of the gold electrode are fully automated. The total arsenic concentrations in two reference sea waters (NASS-1 and CASS-1) were evaluated by single-point standard addition and found to be 1.58 and 1.14 μg l^?1 with standard deviations of 0.39 and 0.28 μg l^?1, respectively; certified values are 1.65 ± 0.19 and 1.04 ± 0.07 μg l^?1. The arsenic(III) content in these samples was below the detection limit (0.15 μg l^?1).     

Adsorptive stripping voltammetric determination of ofloxacin

The fluoroquinolone antibacterial agent ofloxacin was studied by adsorptive stripping voltammetry. Controlled interfecial accumulation of ofloxacin on a static mercury drop electrode in the hanging mercury drop mode provides high sensitivity. The linear concentration range was 0.079–197.5 μg ml^?1 when using a 60-s preconcentration at ?1 V vs. Ag/AgCl in Britton-Robinson buffer of pH 6.00. The detection limit of ofloxacin was 1 ng ml^?1. The precision is excellent with a relative standard deviation of ca. 0.75% at a concentration of 0.848 μg ml^?1.     

Elimination of SAS Interferences in Catalytic Adsorptive Stripping Voltammetric Determination of Cr(VI) by Means of Fumed Silica

In the work the procedure of chromium(VI) determination by catalytic adsorptive stripping voltammetry (CAdSV) with application of fumed silica, is presented. Two variants of the method are proposed: in the first fumed silica is put directly to the electrolytic cell containing tested solution, in the second the silica is shaken with the sample and next centrifuged. The effectiveness of many surface‐active substances removal from synthetic solutions as well as natural water samples, is studied. In the experiments the fumed silica (Sigma‐Aldrich) of the specific surface area in the range 200–390 m² g^?1 was used. Two types of the working electrodes were applied, i.e., hanging mercury drop electrode (HMDE) and cyclic renewable mercury film electrode (Hg(Ag)FE). In the silica presence i) the relative standard deviation (RSD) for 0.1 μg L^?1 Cr(VI) is <2% (HMDE) and <5% (Hg(Ag)FE), n=7, ii) the detection limits estimated deposition time 20 s were respectively 14 ng L^?1 (HMDE) and 22 ng L^?1 (Hg(Ag)FE). The accuracy of the method was tested by studying the recovery of Cr(VI) from spiked natural water samples.     

Square-wave anodic stripping voltammetry with a mercury-plated reticulated vitreous carbon electrode

A rotating mercury-plated reticulated vitreous carbon (RVC) electrode is tested for square-wave anodic stripping voltammetry; RVC provides very large surface areas which are easily plated with mercury. Despite the ill-defined geometry of the electrode, the square-wave stripping peaks are very well defined; their behaviour conforms partly to known theory for square-wave stripping from mercury film electrodes. Fast analytical determinations of lead and cadmium in the μg l^?1 range are facilitated by the high efficiency of the preconcentration step and the high sensitivity given by the stripping waveform.     

Ex Situ Prepared Antimony Film Electrode for Electrochemical Stripping Measurement of Heavy Metal Ions

The antimony film electrode (SbFE) was prepared ex situ for anodic and adsorptive stripping voltammetric measurement of selected heavy metal ions. The electrode revealed good linearity for Cd(II) and Pb(II) in a nondeaerated solution of 0.01 M HCl in the examined concentration range from 25 to 80 μg L^?1 with limits of detection of 1.1 μg L^?1 for Cd(II) and 0.3 μg L^?1 for Pb(II) and an excellent reproducibility. The preplated SbFE was also preliminary tested for measuring low levels of Ni(II) using adsorptive stripping voltammetry exhibiting good linearity and sensitivity in combination with only a 30 s deposition step.     

Stripping Potentiometry of Lead,Cadmium and Copper at a Nafion Coated Glassy Carbon Electrode with Encapsulated Mercury Acetate

Abstract

The stripping potentiometric determination of lead, cadmium and copper with mercury film glassy-carbon electrodes coated with a Nafion membrane was investigated. The mercury film was plated using either mercury(II) acetate encapsulated within the Nafion membrane or a mercury(II) solution. Dissolved dioxygen was used as the stripping agent. The electrodes showed promising properties, particularly robustness and response repeatability. A linear dependence of the stripping time on concentration was found in the μg l^?1 concentration range (s.d. of intercept ≤ 0.3 μg l^?1, r.s.d. of slope ≤ 1%, for both lead and cadmium).