Polarography pulse

Pulse polarography has enjoyed increasing popularity because of the availability of commercial instruments. Furthermore, there is general agreement that the differential form of the method provides the greatest analytical sensitivity in the electrochemical field. Review articles provide more detail of the method and its applications.12 13,17-20 

This method is classified into normal pulse polarography and differential pulse polarography, based on the modes of applied voltage [5]. 

7) Although not dealt with in this chapter, AC impedance measurements (sometimes called electrochemical impedance spectroscopy) are important in studying electrode dynamics. Generally in this method, a sinusoidal voltage (10 2 to 105 Hz) is applied to the cell, the phase angle and the amplitude of the response current are measured as a function of 

10 mV) (upper) and the faradaic current (solid curve) and the charging current (dashed curve) (lower) in SW polarography. The currents after attenuation of the charging current (shown by small circles) are sampled. 

This method is the most sensitive of the polarographic methods now available and the lower limit of determination is 5 x 10-8 M. It is fairly sensitive even for substances that undergo irreversible electrode reactions. DPP is very useful in trace analyses. 

Voltammetry and Related New Techniques - Methods that Electrolyze Electroactive Species Only Partially (3) 

Maximum suppressors. Gelatin is widely used as a maximum suppressor in spite of the fact that its aqueous solution deteriorates fairly rapidly, and must therefore be prepared afresh every few days as needed. Usually a 0.2 per cent stock solution is prepared as follows. Allow 0.2 g of pure powdered gelatin (the grade sold for bacteriological work is very satisfactory) to stand in 100 mL of boiled-out distilled water for about 30 minutes with occasional swirling warm the flask containing the mixture to about 70 °C on a water bath for about 15 minutes or until all the solid has dissolved. The solution must not be boiled or heated with a free flame. Stopper the flask firmly. This solution does not usually keep for more than about 48 hours. Its stability may be increased to a few days by adding a few drops of sulphur-free toluene or a small crystal of thymol, but the addition is rarely worth while and is not recommended. 

A gelatin concentration of 0.005 per cent, which corresponds to 0.25 mL of the stock 0.2 per cent solution in each 10 mL of the solution being analysed, is usually sufficient to eliminate maxima. Higher concentrations (certainly not above 0.01 per cent) should not be used, since these will distort the wave form and decrease the diffusion current markedly. 

Triton X-100, like gelatin, suppresses both positive and negative maxima, but, unlike gelatin, its aqueous solution is stable. A stock 0.2 per cent solution is prepared by shaking 0.20 g of Triton X-100 thoroughly with 100 mL of water. About 0.1 mL of this solution should be added to each 10 mL of the sample solution to give a Triton X-100 concentration of 0.002 per cent. 

As already indicated, quantitative conventional d.c. polarography is limited at best to solutions with electrolytes at concentrations greater than 10-5M, and two different ions can only be investigated when their half-wave potentials differ by at least 0.2 V. These limitations are largely due to the condenser current associated with the charging of each mercury drop as it forms, and various procedures have been devised to overcome this problem. These include  

These modified procedures involve the use of specially constructed polarographs. 

CHARACTERISTICS OF VOLTAMMETRIC METHODS FOR TRACE METAL ANALYSIS 

Technique Working. Electrode Detection Limit, M Speed (time per cycle), min 

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Potential-excitation signals and voltammograms for (a) normal pulse polarography, (b) differential pulse polarography, (c) staircase polarography, and (d) square-wave polarography. See text for an explanation of the symbols. Current is sampled at the time intervals indicated by the solid circles ( ). 

When either pulse polarography or anodic stripping voltammetry can be used, the selection is often based on the analyte s expected concentration and the desired... 

The concentration of As(III) in water can be determined by differential pulse polarography in 1 M HCl. The initial potential is set to -0.1 V versus the SCE, and is scanned toward more negative potentials at a rate of 5 mV/s. Reduction of As(III) to As(0) occurs at a potential of approximately —0.44 V versus the SCE. The peak currents, corrected for the residual current, for a set of standard solutions are shown in the following table. 

Peak currents in differential pulse polarography are a linear function of the concentration of analyte thus... 

Differential pulse polarography and stripping voltammetry have been applied to the analysis of trace metals in airborne particulates, incinerator fly ash, rocks. 

Miscellaneous Samples Besides environmental and clinical samples, differential pulse polarography and stripping voltammetry have been used for the analysis of trace metals in other samples, including food, steels and other alloys, gasoline, gunpowder residues, and pharmaceuticals. Voltammetry is also an important tool for... 

Garda-Armada, P. Losada, J. de Vicente-Perez, S. Cation Analysis Scheme by Differential Pulse Polarography, /. 

The amount of sulfur in aromatic monomers can be determined by differential pulse polarography. Standard solutions are prepared for analysis by dissolving 1.000 mb of the purified monomer in 25.00 mb of an electrolytic solvent, adding a known amount of S, deaerating, and measuring the peak current. The following results were obtained for a set of calibration standards... 

Zinc can be used as an internal standard in the analysis of thallium by differential pulse polarography. A standard... 

Differential pulse polarography is used to determine the concentrations of lead, thallium, and indium in a mixture. ... 

The following data were collected for the reduction of Pb + by normal pulse polarography... 

The following sources provide additional information on polarography and pulse polarography. 

DETERMINATION OF TRACE ELEMENTS IN ALCOHOLIC DRINKS BY DIFFERENTIAL PULSE POLAROGRAPHY... 

Raki, a Turkish alcoholic drink was also analyzed by differential pulse polarography and copper, iron and zinc could be determined. For the arsenic content in beer a more sensitive method had to be applied. For this method a new catalytic method is established and the arsenic content was determined by using this new method. 

An important feature of pulse polarography is the sampling of the current at definite points in the lifetime of the mercury drop, and it is essential to... 

In just the same way as differential pulse polarography represents a vast improvement over conventional polarography (see Section 16.10), the application of a pulsed procedure leads to the greatly improved technique of differential pulsed anodic (cathodic) stripping volammetry. A particular feature of this... 

Differential pulse polarography, 68, Diffusion, 4, 8, 129 Diffuse layer, 19... 

Redox switching, 126 Reference electrodes, 100, 105, 142 Reflectance spectroscopy, 44 Resistance, 22, 105 Resolution 50, 71 Reverse pulse polarography, 68 Reversible systems, 4, 31 Reticulated vitreous carbon, 114, 115 Riboflavin, 37... 

The complexation of Pu(IV) with carbonate ions is investigated by solubility measurements of 238Pu02 in neutral to alkaline solutions containing sodium carbonate and bicarbonate. The total concentration of carbonate ions and pH are varied at the constant ionic strength (I = 1.0), in which the initial pH values are adjusted by altering the ratio of carbonate to bicarbonate ions. The oxidation state of dissolved species in equilibrium solutions are determined by absorption spectrophotometry and differential pulse polarography. The most stable oxidation state of Pu in carbonate solutions is found to be Pu(IV), which is present as hydroxocarbonate or carbonate species. The formation constants of these complexes are calculated on the basis of solubility data which are determined to be a function of two variable parameters the carbonate concentration and pH. The hydrolysis reactions of Pu(IV) in the present experimental system assessed by using the literature data are taken into account for calculation of the carbonate complexation. 

Differential pulse polarography, oxidation state analysis of dissolved Pu ions.319, 326-27... 

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