Boy Hoyer

Electrostatic spraying: a novel technique for preparation of polymer coatings on electrodes.

A liquid flow emerging from a tip or a thin tube under the influence of a strong electric field will, due to charging of the dielectric liquid, break up into small droplets. Thus, if a polymer material is dissolved in the liquid, this electrodeposition technique can be utilized for producing polymer coatings on electrodes. The method was applied for in situ formation of ultrathin (∼3000 Å) cellulose acetate (CA) phase inversion membranes on glassy carbon electrodes. The purpose of the membrane was to protect the electrode surface from fouling by macromolecular species. The spraying liquid consisted of CA, acetone, and aqueous magnesium perchlorate as pore former, and the spraying voltage was 14 kV. Profilometric measurements showed that the thickness of the spray-cast membranes was much more uniform than that of similar membranes formed by solvent casting. By using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method, it was found that the membranes prepared by spray casting offered better protection against interference from poly(ethylene glycol) (PEG) 6000 than those prepared by solvent casting. Also, the interference from PEG 2000 was significantly reduced. Experimental details of the electrostatic spraying technique are given.

Suppression of surfactant interferences in anodic stripping voltammetry by sodium dodecyl sulfate

Abstract It was investigated whether interferences from surfactants in anodic stripping voltammetry (ASV) could be remedied by the anionic surfactant sodium dodecyl sulfate (SDS) which causes little or no interference in itself. Cadmium and lead were used as test analytes, and measurements were performed in acetate buffer as well as in 0.1 M HNO3. One hundred parts per million of the interfering surfactant was added. SDS eliminated severe interference from the non-ionic surfactants Triton© X-100 and dodecyl octaethylene glycol ether as well as from the polymer polyethylene glycol 6000 and from the cationic surfactant cetyl trimethyl ammonium bromide. SDS could not remedy the extraordinarily severe interference from the cationic surfactant cetyl pyridinium chloride. Two anionic surfactants were also tested as interferents but they had little detrimental effect on the ASV signals. The effect of SDS was explained by the formation of mixed micelles which scavenge the interferent in the bulk solution and by competitive displacement of the interferent at the electrode surface.

Signal stability of Nafion-coated thin mercury film electrodes for stripping voltammetry

The signal stability of the Nafion-coated thin mercury film electrode (NCTMFE) was studied by using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method. In particular, the effect of the casting solvent and the curing procedure employed in the preparation of the polymer film was examined. Best results were obtained with N,N-dimethylacetamide as casting solvent and a two-step curing procedure in which the polymer was evaporated to dryness at 55 degrees and cured at 105 degrees with a hot-air gun. Mercury plating was performed ex situ. An NCTMFE prepared in this manner has a better signal stability than ex situ-plated as well as in situ-plated conventional mercury film electrodes.

Use of sodium dodecyl sulfate as an antifouling and homogenizing agent in the direct determination of heavy metals by anodic stripping voltammetry

The effectiveness of the anionic surfactant sodium dodecyl sulfate (SDS) for suppressing adsorption interferences in anodic stripping voltammetry (ASV) was investigated. The samples included fruit juices, wine, beer, milk powder and waste water, and the analytes were cadmium, lead and copper. In most of the samples, the ASV signals were severely depressed or even absent due to electrode fouling, but addition of SDS in concentrations up to 10 g L(-1) proved effective in restoring the ASV response. By using SDS as an interference suppressor, the content of lead and copper in a milk powder reference material was determined, and the results were in agreement with the certified values. In this determination, which could not have been performed without SDS, the surfactant also served as a homogenizing agent, preventing separation of the sample components. The effect of SDS was explained by the interaction of the surfactant with the electrode surface and with the constituents of the sample matrix.

Suppression of protein interferences in anodic stripping voltammetry by sodium dodecyl sulphate

The anionic surfactant sodium dodecyl sulphate (SDS) can effect desorption of proteins from surfaces, and this mechanism has been exploited for suppressing adsorption interferences in anodic stripping voltammetry (ASV). Using cadmium and lead as test analytes, and albumin and lysozyme as model interferents, it was found that ASV signals strongly depressed by proteins regain their initial magnitude (prior to protein addition) when SDS is added in a concentration above a threshold value. Also, SDS protected against protein interference when the surfactant was added prior to the protein. SDS in itself caused little or no interference.

Phase-inversion cellulose acetate membranes for suppression of protein interferences in anodic stripping voltammetry

The phase-inversion (PI) method was used to cast permselective cellulose acetate membranes on glassy carbon electrodes with the aim of suppressing protein interferences in anodic stripping voltammetry (ASV). By using cadmium and lead as test analytes and differential pulse ASV as detection method, it was found that the modification of the electrode greatly reduces the interference from albumin. Cellulose acetate membranes prepared by the PI method give better protection against protein interference and have more reproducible permeability characteristics than membranes of comparable thickness prepared by the base hydrolysis method. An optimization study of the PI coating procedure was undertaken.

Effect of the Pretreatment of Recast Nafion Membraneson Their Rejection of the Albumin Interferencein Anodic Stripping Voltammetry

The title subject was examined using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method. Ultrathin (ca. 0.3 µm) Nafion coatings were deposited on glassy carbon by electrostatic spray deposition. This technique proved far superior to evaporative casting with respect to the uniformity of the polymer layer. Overall, it was found that the pretreatment of the Nafion coating had a major effect on the extent of the albumin interference. Swelling of the Nafion coating in nitric acid and lithium hydroxide significantly reduced albumin interference, whereas treatment with sodium hydroxide and cesium hydroxide did not have an effect. Heat treatment (140 °C) of Nafion in the H+ form worsened the albumin interference, and the same trend was seen for the Na+ and Cs+ forms but not for the Li+ form. These results show that the degree of albumin interference is determined not only by the permeability of the coating but also by adsorption onto the outer surface of the membrane. The experimental results are explained in terms of the conformational changes of Nafion induced by the pretreatments.

Evaluation of single-point calibration in flow potentiometric stripping analysis

The use of a single-point calibration in flow potentiometric stripping analysis has been evaluated. For a number of sample matrices, the results obtained by calibration methods agree with those obtained by using standard addition. The most serious source of systematic error is inhibition in the deposition step, caused by organic surfactants and chelating agents in the sample matrix. Consequently, the use of the calibration method should be restricted to samples which have been totally mineralized. It is shown that most sources of systematic error in the calibration method will result in underestimation of the analyte concentration.

Annotation paper Interference by volatile nitrogen oxides in the determination of mercury by flow injection cold vapor atomic absorption spectrometry.

The determination of mercury by the title method with sodium tetrahydroborate as reducing agent can be interfered with by volatile nitrogen oxides which inhibit the reduction of mercury by scavenging the reducing agent. The nitrogen oxides are formed as reduction products of nitric acid during sample decomposition. The interference effect was encountered in the determination of mercury in sewage sludge digests, and the main symptom was poor reproducibility of the shape of the mercury peak. The area of the mercury peak is more resistant to the interference than the peak height. The nitrogen oxide interference did not cause any systematic error in the mercury determination when calibration was done by standard addition. The interference can be easily remedied by purging the sample with argon.

Application of the generalized standard addition method to correction for the effects of peak overlap and intermetallic compound formation in potentiometric stripping analysis

Abstract Applications of the generalized standard addition method in potentiometric stripping analysis are presented. Accurate quantitative results can be obtained, even when the analytical signals are strongly affected by peak overlaps or by the formation of intermetallic compounds. The possibilities and limitations of the approach are discussed. An optimized experimental procedure for correction of the copper-zinc intermetallic interference is introduced.