Polarographic methods comparison

Figure 2.3. The distribution of sample concentrations encountered in the comparisons of the colorimetric method without iodine with (a) the polarographic method and (b) the colorimetric method with iodine water. For convenience the line of the unit gradient is shown in both cases. In each case the precision (95% confidence level) for each measurement is shown for the most concentrated sample. In (b) the broken line divides on shore (A) and offshore ( ) samples. From [80]...

TABLE 3.1 Comparison of Polarographic Methods for Determination of Metal Ions... 

Regardless of the degree of reversibility of the electrode process, both reversible and irreversible processes can be used for qualitative identification (using fii/z) and the quantitative determination based on the Ilkovic equation. If the classical DC polarographic method is applied the lower limit of determination is in the region of 2 xlO moll . This sensitivity is not sufficient in comparison with the more advanced analytical methods. The evaluation is carried out by calibration curves or by standard addition. 

Table 7.27 shows the results obtained in determinations of acrylonitrile monomer in some copolymers by the polarographic procedure. Comparison of ftiese results with those obtained by the dodecyl mercaptan procedure show that acrylonitrile contents some 30 per cent higher are obtained by the latter method. 

Polarographic techniques have been used by Sturm and Hans to demonstrate that certain amino-thiadiazoles and -benzthiazoles exist in the amino form (cf. also references 62, 63). This method, which involves comparison of the polarographic rdeuction potentials of the potentially tautomeric substance with those of alkylated reference compounds, has not been applied often, but may well prove to be a means to obtain qualitative information quickly. There is a possibility that the method can be modified to yield quantitative data. ... 

Faradaic rectification polarographic studies have been carried out for a mixture containing several metal ions together and also for individual inorganic depolarizers so as to explore the applicability and limitations of the method and to determine kinetic parameters for some of them. For comparison, some of the dc and ac polarograms have also been recorded simultaneously. In the following, the details of the experimental technique used will be described and the potentiality of the technique in qualitative and quantitative analysis will be examined. The applicability of the method in the... 

Two principal methods are widely used for the assay of DPOs. For enzyme kinetic studies, the most appropriate methods are polarographic and use an 02 electrode (Basic Protocol), which allows the direct measurement of the rate of utilization of oxygen and a true comparison of different phenolic substrates. Minor disadvantages of this method are that it requires more specialized equipment and that assays can only be carried out one at a time. Nevertheless it has proven to be the basis of some excellent undeigraduate biochemical laboratory experiments. 

The detection of products derived from the N-oxygenation of C=N functionalities presents many problems, which illustrate difficulties that are associated with the isolation, identification and quantification of small amounts of water-soluble metabolites. Spectrophotometric methods19 as well as differential pulse polarographic techniques20 previously used to determine oximes, nitrones and N-oxides frequently lack sensitivity and/or specificity. Improved analytical methods for the quantification of these N-oxy compounds include chromatographic techniques taking into account the chemical peculiarities of the individual N-oxygenated C=N functionalities. These procedures usually require the chemical synthesis of authentic material for comparison with data obtained with the isolated metabolites, and also for the construction of calibration curves. 

Polarographic AC and pulse polarographic techniques as well as stripping analysis are effective tools for the determination of trace levels of metal ions. Table 3.1 provides a comparison of the sensitivity and usefulness of the various methods.12,21 23 For metal ions, stripping voltammetry usually is the method... 

As in many other analytical methods, polarographic quantitative determination is carried out by comparison with a standard of known composition. The absolute measurement of the concentration is possible but often inconvenient. Polarography is not only an analytical method, but also a method for the determination of stability constants of various complexes, and rate constants of many reactions sometimes, it can assist in determining the structure of an organic molecule. 

Comparison of the half-wave potentials of the oxidizable and reducible forms of the redox reactants with the potentiometrically determined value of the standard redox potential is the simplest method for proof of reversibility and agreement between these two sets of data provides strong support for reversibility of the process being studied. However, in many polarographic reactions, it is found that one form of the conjugate redox pair is not sufficiently stable to be prepared or to permit determination of E% potentiometrically. In some of these cases, auxiliary methods can be used, particularly where the reactive species is relatively stable when formed at the surface of the mercury electrode. Such methods include the commutator method, an anodic stripping technique which has recently been reviewed by Barendrecht, and oscil-lopolarographic and cyclic voltammetric techniques. 

Table 5.3 Determination of acrylonitrile comparison of polarographic and chemical methods ...

Table 7.27 - Determination of Acrylonitrile Comparison of Polarographic and Chemical Methods... 

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