Nafion-coated Mercury Film Electrode Research Articles

Determination of Lead and Cadmium in the Presence of Quercetin–5’–sulfonic Acid by Adsorptive Stripping Voltammetry with a Hanging Mercury Drop Electrode and a Nafion–coated Mercury Film Electrode

Determination of Lead and Cadmium in the Presence of Quercetin–5’–sulfonic Acid by Adsorptive Stripping Voltammetry with a Hanging Mercury Drop Electrode and a Nafion–coated Mercury Film Electrode

Voltammetric Studies of Cadmium‐ and Zinc‐Containing Metallothioneins at Nafion‐Coated Mercury Thin Film Electrodes

AbstractVoltammetric studies of rabbit liver metallothioneins (MTs, containing both Zn and Cd ions) and Zn7‐MT were carried out at Nafion‐coated mercury film electrodes (NCMFEs). The accumulation of MT molecules into the NCMFEs enhances the voltammetric signals and the electrostatic interaction between the Nafion membrane and MT facilitates facile electron transfer reactions. Two well‐defined redox waves, with reduction potential (Epc) values at −0.740 and −1.173 V, respectively, were observed. The peak at Epc =−0.740 V is attributable to the reduction of the Cd‐MT complex, whereas that at Epc=−1.173 V was assigned to the reduction of the Zn‐MT complex. Zn7‐MT exhibits only one redox wave with Epc=−1.198 V. The NCMFE was found to be more advantageous than thin mercury film electrode (MFE), because the pristine metal ions in MTs (e.g., Cd2+ and/or Zn2+) are not significantly replaced by Hg2+. The NCMFE is also complementary to Nafion‐coated bismuth film electrode in that it has a greater hydrogen overpotential, which allows the reduction of the Zn‐MT complex to be clearly observed. Moreover, intermetallic compound formation between Cd and Zn appears to be less serious at NCMFEs. Consequently, the amounts of Cd and Zn deposited into the electrode upon the reduction reactions can be quantified more accurately.

Nafion-Coated Bismuth Film and Nafion-Coated Mercury Film Electrodes for Anodic Stripping Voltammetry Combined On-Line with ICP-Mass Spectrometry

Nafion-coated bismuth film electrodes (NCBFEs) and Nafion-coated mercury film electrodes (NCMFEs) were used to electrochemically preconcentrate metal analytes for subsequent analysis by inductively coupled plasma-mass spectrometry (ICP-MS). Either type of electrodes is part of a thin-layer electrochemical flow cell that is positioned upstream of a microconcentric nebulizer for the ICP-MS. Performances of these electrodes were compared in terms of the analytical "figures of merit" (e.g., dynamic ranges, reproducibility, hydrodynamic stability, and elimination of matrix effects detrimental to ICP-MS). The coupled technique (ASV-ICP-MS) is found to possess a wide dynamic range (at least 4 to 5 orders of magnitude) and to be reproducible. Both electrodes are much more stable than the thin mercury film electrode (TMFE) traditionally used for ASV-ICP-MS, with the lifetime of the NCBFE exceeding 8 h. Adopting these electrodes for ASV-ICP-MS overcomes the problems associated with a TMFE, the erosion of which decreases the sample throughput, affects the analysis precision, and contaminates conventional glass nebulizers and spray chambers of the spectrometer. The medium exchange procedure inherent in ASV is successfully implemented with a two-valve flow injection system for the accumulation of trace Cd2+ into the electrode from a certified seawater sample, followed by stripping Cd into a solution that is compatible to the ICP-MS operation.

Nafion-Coated Mercury Film Electrodes for Square Wave Stripping Voltammetry Determination of Lead and Cadmium in Continuous Flow

Nafion-Coated Mercury Film Electrodes for Square Wave Stripping Voltammetry Determination of Lead and Cadmium in Continuous Flow

Application of Nafion-coated mercury film electrodes to the microdetermination of formaldehyde by differential-pulse voltammetry

Formaldehyde, after in situ conversion to an ionic derivative with Girard's reagent T, was first accumulated on a Nafion-coated mercury film electrode. The adsorbed derivative was then determined in aqueous solution using differential-pulse voltammetry. A single peak centred at –1.24 V (versus Ag–AgCl) was observed at pH 9.7 when using 0.4 mol l–1 NH4Cl–NH3 as the supporting electrolyte. The calibration graphs were rectilinear over the range from 2.0 × 10–7 to 1.0 × 10–5 mol l–1 formaldehyde. By incorporating a preconcentration step via the Nafion-modified electrode, the detection limit of the method for formaldehyde was calculated to be 3.4 × 10–8 mol l–1. The reproducibility and lifetime studies of the electrodes indicated that a newly prepared electrode could be repeatedly used for more than ten measurements with satisfactory precision. In addition, the method can be extended, without any modification, to the determination of acetaldehyde.

Effect of model organic compounds on square-wave voltammetric stripping analysis at the Nafion/chelating agent mercury film electrodes

The effect of various organic compounds on the Nafion/chelating agent mercury film electrodes (NCAMFEs) in square-wave anodic-stripping voltammetry (SWASV) is explored. Two chelating agents used to prepare the NCAMFEs are dimethylglyoxime and 2,2'-bipyridyl. Triton X-100, sodium dodecyl sulfate, albumin, gelatin, starch, camphor, and humic acid are used as model organic compounds, while cadmium, lead, and copper are used as test metal ions. The NCAMFEs are considerably more resistant to organic interferences than the Nafion-coated mercury film electrode. The implications of these interferences for the reliability and feasibility of stripping measurements using the NCAMFEs in real samples are discussed. Results presented for untreated urine and natural water samples demonstrate the analytical utility of the NCAMFEs in SWASV.

Square-wave voltammetric determination of lead(II) with a Nafion ®/2,2-bipyridyl mercury film electrode

A chemically modified electrode (CME) system consisting of a Nafion-coated mercury film electrode containing appropriate amounts of 2,2-bipyridyl for practical use in the analysis of lead(II) was investigated. The relative advantages of using square-wave stripping voltammetry (SWSV) in combination with the CME for the determination of the reversible lead(II)-2,2-bipyridyl complex was assessed. The main advantages of the CMe are better mechanical stability of the mercury film, and improved resistance to interference from both surface-active compounds and those metals which commonly interfere in anodic stripping measurements. For a 5-min preconcentration period in the presence of oxygen, a linear calibration curve from 1 to 100 μg l −1 was obtained, and the detection limit was 0.1 μg l −. A lower detection limit can be obtained when longer preconcentration times are used. The CME surface could be regenerated by exposure to acid. For 10 successive preconcentration/determination/renewal cycles, the SWSV response could be reproduced with 5% relative standard deviation. Rapid and convenient acid renewal allows the use of an individual modified electrode surface in continuous-monitoring environmental or clinical applications.

Models for studying the binding capacity of albumin to zinc by stripping voltammetry

The complexation capacity of albumin to zinc was studied by different voltammetric methods. Cyclic voltammetry was used with a hanging mercury drop electrode (HMDE) to diagnose qualitatively the electrode mechanisms occuring at a mercury electrode and to evaluate the charge-transfer rate constant of the electrochemcial reaction of zinc in the presence of different concentrations of albumin. The conditional stability constant of the zinc-albumin complex was determined pseudo-polarographically by differential-pulse anodic stripping voltammetry (DP-ASV) with a Nafion-coated mercury film electrode (Nf-MFE). This electrode permits the determination of free (labile) zinc and rejection of the interfering adsorption of free albumin on the glassy coarbon surface. A mean conditional stability constant of log β′=6.10±0.16 was obtained by this method. DP-ASV was used to calculate β′ by titrating an albumin solution with ZN(II) and by Ruzic data treatment. In this instance a mean of log β′=5.49±0.28 was found with the HMDE and Nf-MFE. The results are compared and discussed.

Comparison of physicochemical speciation procedures with metal toxicity to chlorella pyrenoidosa

Metal speciation as measured by anodic stripping voltammetry (ASV), adsorption on a resin with adsorbed hydrated aluminium oxide, and dialysis with receiving resins is compared with the toxicity of the metals to the freshwater green alga Chlorella pyrenoidosa Chick. In the presence of natural and synthetic ligands, similar labile fractions of metals were obtained for ASV at three electrodes (hanging mercury drop electrode, mercury film electrode and Nafion-coated mercury film electrode). The toxic fractions determined by ASV and bioassay were in reasonable agreement for zinc, cadmium and copper, and alteration of the analytical conditions provided some measure of agreement for lead. The resin with adsorbed hydrated aluminium oxide correlated well with bioassay for copper, but over-estimated lead toxicity and under-estimated cadmium toxicity. Dialysis with receiving resins under-estimated metal bioaccumulation in the presence of ligands. Metal speciation analysis for water samples gave higher toxic fractions for metals in samples of polluted river water and road runoff samples than those found in pristine river water.