Review of Polarography

Electroanalytical chemistry has found wide application in recent years for the chemical analysis of various components in iron and steel. It has developed., as in the case of the spectrochemical methods, many instrumental methods and has made the extensive improvements of the classical methods of the chemical analysis of iron and steel. Polarographic method is one of the methods which is used widely in this field. This method can afford the simulataneous determination of the several elements or the determination of microamount of element contained in iron and steel samples. The main difficulty encountered in applying this method is due to the discharged wave of ferric iron which is reduced at very positive potential at DME. Various methods to eliminate this interference is summarized and also reviewed. The utilization of polarographic method has much advantage for the determination of tungsten, titanium, or niobium in stainless steel or high alloyed steel. The potentiometric titration is generally used for the determination of the elements commonly present in iron and steel and the application of the ammperometric titration and the coulometric titration in this field are increasing. A conductometric or a coulometric determination of carbon, sulfur or oxygen is the method recently developped in iron and steel analyses. These methods make it possible to apply an automatic recording system for the rapid and accurate determination of microamount of these elements (fig. 1) Electrolytic separation of the metallic compound or non-metallic compound in steel is a principal way of phase analysis which is very importrant in the field of metallographic study of iron and steel. Either acidic or neutral electrolytes are used, depending on the properties of the metallic compounds to be isolated, and the further analysis of the isolated compounds is submitted to the usual chemical analysis including many electrochemical methods. The elctrolytic cell and the condition of the electrolytic solution are also discussed in this review. (Table 1, Fig. 2.3.4 and 5)

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Electron paramagnetic resonance (EPR) spectra of electrolytically generated nitrobenzen derivative anion radicals and the polarographic behavior of nitrobenzene derivatives are reviewed. Complete reduction by the electrolysis outside the cavity is desirable, because many of the radicals undergo rapid electron exchange reactions with their precursors that broaden the lines in the spectrum. Intra muros technique with the mercury pool cathode within the microwave cavity has the advantages of simplicity and ease of operation. Tetraalkyammonium salt must be employed for the supporting electrolyte which are less likely to form tight complexes with the anion radicals than alkali ions. Dissolved oxygen must be removed completely, because it plays a remarkable negative role in diminishing the proton hyperfine lines by the magnetic dipole-dipole interaction. The polarographic half wave potentials of nitrobenzene derivatives are correlated to the nitrogen coupling constants of nitrobenzene derivative anion radicals. Twisting of nitro group to the ring plane reduces the conjugation of the nitro group with the ring. Consequently, coupling constant at the nitro group increases with the decrease of the hydrogen coupling constant at the ortho, meta and para position of the benzene ring. Fraenkel proposes localized solvent complexes with the functional group of the radical ion to explain the solvent effect which nitrogen coupling constant increases markedly and hydrogen coupling constants are practically unchange. The strange phenomena of line broadening and anisotropy in EPR spectra of nitrobenzene derivative anion radicals are found in the presence of phenol derivatives or lithium ion. Very strong exchange interaction between electrolytically generated benzonitrile negative ion and the parent benzonitrile is described. The electron interchange reactions between highly reactive radicals (for instance, nitrobenzene negative ion) and normal ground state substance (for instance, paranitrobenzenitrile) are discussed. Several examples of unusual electrode reaction are described, such as the formation of unsubstituted nitrobenzene anion radical from the electrolysis of iodonitrobenzene or ortho-bromonitrobenzene.

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