Polarographs square-wave

The technique of controlled-potential cathodic deposition followed by anodic stripping with a linear potential sweep has been applied to the determinations of a number of metals (e.g., Bi, Cd, Cu, In, Pb, and Zn) either alone or in mixtures (Figure 11.8.5). An increase in sensitivity can be obtained by using pulse polarographic, square wave, or coulostatic stripping techniques. Other variants, such as stripping by a potential step, current step, or more elaborate programs (e.g., an anodic potential step for a short time followed by a cathodic sweep) have also been proposed (68-74). 

The realization that current sampling on a step pulse can increase the detection sensitivity by increasing the faradaic/charging ratio is the basis for the development of various pulse voltammetric (or polarographic) techniques. Also, the pulses can be applied when it is necessary and can reduce the effect of diffusion on the analyte. Figure 18b. 11 shows the waveform and response for three commonly used pulse voltammetric techniques normal pulse voltammetry (NPY), differential pulse voltammetry (DPV), and square-wave voltammetry (SWV). 

The analytical sensitivity of classical polarographic or voltammetric methods is usually quite good at about 5 x 10 mol dm . At the lowest concentrations of analyte, however, the currents caused by double-layer effects or other non-faradaic sources causes the accuracy to be unacceptably low. Pulse methods were first developed in the 1950s to improve the sensitivity of the polarographic measurements made by pharmaceutical companies. At present, two pulse methods dominate the analytical field, i.e. normal pulse and differential pulse . Square-wave methods are also growing steadily in popularity. 

Iron Estimations. These were carried out by extracting the iron with "iron-free HC1 (/—0.2 p.p.m.), followed by measurement using a square w ave polarograph. Reproducibility and accuracy on samples in which known amounts of ferric acetylacetonate had been placed were poor (zb50%). Wet combustion techniques followed by estimations using the square wave polarograph gave worse results than the procedure described. 

Eletrochemical detection has been used for the detection of synthetic dyes. Fogg et al. (226) described a method for the qualitative and quantitative determination of several synthetic dyes using polarographic detection. The system was a stationary mercury drop electrode operated in the differential-pulse mode. Ashkenazi et al. (131) used fast-scan square-wave voltammetry for the polarographic detection of five synthetic dyes. The voltametric mode was observed to be much faster than the differential-pulse method. Another advantage is that the experimental measurement produces, in addition to the peak current, the redox potential of the dye, which can serve to identify the analyte further. 

Refs [i] Osteryoung J, O Dea JJ (1986) Square-wave voltammetry. In Bard A] (ed) Electroanalytical chemistry, vol. 14. Marcel Dekker, p 209 [ii] Bond AM (1980) Modern polarographic methods in analytical chemistry. Marcel Dekker, pp 391-399 [iii] LovricM (2002) In ScholzF (ed) Electroanalytical methods. Springer, Berlin, pp 111-136 [iv] Mirdeski V, Komorsky-Lovric S, Lovric M (2007) Square-wave voltammetry. In Scholz F (ed) Monographs in Electrochemistry. Springer, Berlin... 

Analytical Applications of the Barker Square-wave Polarograph, Part II. 

Hamm, R.E. Square-wave Polarograph. Anal. Chem. 30, 350 (1958). 

Kambara, T. Polarographic Diffusioii Currents Obtained with Square Wave... 

The electrochemical behavior, in non-aqueous solvents, of some mono- and bis-Cp oxo homo- and heteropoly-nuclear titanium derivatives containing oxo bridges between different metals is described (Scheme 592). Cyclic voltammetry, square wave voltammetry, and polarographic studies have been used to elucidate and compare the redox properties of these compounds.829... 

Various polarographic techniques have been successfully used to measure elemental sulfur, S , and sulfide (H2S and HS ) concentrations in laboratory solutions [116], salt water [117], saline lake [118], freshwater [119], lake porewaters [120], salt marsh sediments [109,120], and marine porewaters [121], Using stripping square wave voltammetry, researchers have been able to measure sulfide species at nanomolar concentrations [118-120, 122,123], Recently, cyclic and linear sweep voltammetries have been used to quantify elemental sulfur S , hydrogenosulfide (HS ) and polysulfides (S ) with fast scan rates (IV s ) [124] for example, in estuarine sediments (from Rehoboth Bay, an inland bay located in Delaware), the sulfur speciation was found to change throughout a core profile, with dominant in the top layers (0-6 cm), dominant... 

We will consider five subtopics tast polarography and staircase voltammetry, normal pulse voltammetry, reverse pulse voltammetry, differential pulse voltammetry, and square wave voltammetry. Tast polarography, normal pulse voltammetry, and differential pulse voltammetry form a sequence of development rooted historically in polarography at the DME. To illustrate the motivating concepts, we will introduce each of these methods within the polarographic context, but in a general way, applicable to both the DME and SMDE. Then we will turn to the broader uses of pulse methods at other electrodes. Reverse pulse voltammetry and square wave voltammetry were later innovations and will be discussed principally outside the polarographic context. 

Square wave voltammetry is normally carried out at a stationary electrode such as an HMDE, and involves the waveform and measurement scheme shown in Figure 7.3.13. As in other forms of pulse voltammetry, the electrode is taken through a series of measurement cycles however there is no renewal of the diffusion layer between cycles. In contrast to NPV, RPV, and DPV, square wave voltammetry has no true polarographic mode. The waveform can be viewed as a special case of that used for DPV (Figure 7.3.9), in which the preelectrolysis period and the pulse are of equal duration, and the pulse is opposite from the scan direction. However, the interpretation of results is facilitated by considering the waveform as consisting of a staircase scan, each tread of which is superimposed by a symmetrical double pulse, one in the forward direction and one in the... 

NIES biological CRMs Zn Cd Pb Cu Digest with FlNOs, in a Fligh Pressure Asher [WDCCV] Measure square wave ASV with polarographic analyzer with HMDF [SWASV] [WDCCV- SWASV] Wtirfels 1989... 

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