Polarographic research

The story of the development of polarography is sufficiently known and documented in text-books and review articles (for a recent review see (21) ). While the polarographic research consisted in its "classical" stage mainly in interpretations of current -voltage curves obtained with the dropping mercury electrode, the unique qualities of this electrode also spurred scientific development in other directions. In the following some examples of such researches are given. 

A critical review of polarographic researches on semicarba zones was given in the recently published article by Fleet and Zuman [164]. They showed that the four-electron reduction of semicarba-zones is preceded by protonation. They examined also quantitatively the effect of polar substituents on the reduction of aromatic aldehyde derivatives and found that in this series of compounds the values are relatively little sensitive to the effects of substituents (p =0.10 V). 

Many handbooks like the CRC Handbook of Chemistry and Physics provide, on behalf of electrochemistry investigation, values of standard reduction potentials, listed either in alphabetical order and/or in potential order. These must be considered as potentials of completely reversible redox systems. In current analytical practice one is interested in half-wave potentials of voltammetric, mostly polarographic analysis in various specific media, also in the case of irreversible systems. Apart from data such as those recently provided by Rach and Seiler (Spurenanalyse mit Polarographischen und Voltammetrischen Methoden, Hiithig, Heidelberg, 1984), these half-wave potentials are given in the following table (Application Note N-l, EG G Princeton Applied Research, Princeton, NJ, 1980). 

Aromatic substitution reactions are often complicated and multistep processes. A correlation, however, in many cases can be found between the charged attacking species and the electron density distribution in the molecule attacked during electrophilic and nucleoph c substitution. No such correlation is expected in radical substitution where the attacking particles are neutral, rather a correlation between the reactivities of separate bonds and a free valency index of the bond order. This allows the prediction of the most reactive bonds. Such an approach has been used by researchers who applied quantum calculations to estimate the reactivities of the isomeric thienothiophenes and to compare them with thiophene or naphthalene. " Until recently quantum methods for studying reactivities of aromatics and heteroaromatics were developed mainly in the r-electron approximation (see, for example, Streitwieser and Zahradnik ). The M orbitals of a sulfur atom were shown not to contribute substantially to calculations of dipole moments, polarographic reduction potentials, spin-density distribution, ... 

Shikata, Masuzo — (Aug. 10,1895, Tokyo, Japan - May 8, 1964, Kyoto, Japan) In 1920 Shikata graduated from the Department of Agricultural Chemistry of the Imperial University of Tokyo. In 1922 he went to Europe, and the next year joined - Heyrovsky, J. in Prague, Czechoslovakia. In 1924 Heyrovsky and Shikata [i] developed the first - polarograph - the first automatic instrument to record current-potential dependencies of a - dropping mercury electrode. For this invention, Heyrovsky was awarded the Nobel Prize in Chemistry in 1959. In 1924 Shikata was appointed Professor of the Imperial University of Kyoto (presently Kyoto University). In 1942 he was appointed Vice-President of the Research Institute of... 

NPV), differential pulse voltammetry (DPV) and SWV, and polarography methods (use of a mercury drop electrode) like normal (normal and pulse polarography (NPP)) and DPP, although sometimes these polarographic versus voltammetric terms are used interchangeably. These step methods do not typically use return scans and therefore often do not provide information about reversibility of the redox process and can sometimes give data that, unknown to the researcher, are characteristic of decomposition products. 

The amount of some gases, such as SO2 [73], CO [74], can be automatically continuously measured by polarographic analyzers [75]. Measuring electrodes with a constant surface, e.g. carbon, platinum, gold disks or rods are most often used. Present research is concentrated on the so-called coulometric analyzers [73]. The analysed gas is brought by the shortest route directly to the measuring electrode. The substance to be determined is completely reduced or oxidized electrochemically at a large area electrode. 

This book is based on the study of reactions of thermal electrons with molecules using the ECD, negative ion chemical ionization (NICI) mass spectrometry in the gas phase and polarographic reduction in aprotic solvents [18]. Only the complementary studies related to our research are considered here. 

Heyrovsky, J. and Shikata, M. (1925) Researches with the dropping mercury cathode. Part II. The Polarograph, Recueil des Travaux Chimiques des Pays-Eas, 44, 495 98. 

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... 

Several workers " studied the polarographic behaviour of nitrofurans. Nitrofurazone in animal feed has been quantitatively assayed by polaro-graphy. Polarographic assay of nitrofurans will require more basic research before it can be used on a large scale. However, the spectrophotometric assay of nitrofurantoin has been replaced by a polarographic assay in the first U.S. P. XVI supplement (U.S. Pharmacopoeia Convention, 1962). 

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