Subject polarography

The Production Department was not amused, because lower values had been expected. Quality Control was blamed for using an insensitive, unse-lective, and imprecise test, and thereby unnecessarily frightening top management. This outcome had been anticipated, and a better method, namely polarography, was already being set up. The same samples were run, this time in duplicate, with much the same results. A relative confidence interval of 25% was assumed. Because of increased specificity, there were now less doubts as to the amounts of this particular heavy metal that were actually present. To rule out artifacts, the four samples were sent to outside laboratories to do repeat tests with different methods X-ray fluorescence (XRFi °) and inductively coupled plasma spectrometry (ICP). The confidence limits were determined to be 10% resp. 3%. Figure 4.23 summarizes the results. Because each method has its own specificity pattern, and is subject to intrinsic artifacts, a direct statistical comparison cannot be performed without first correcting the apparent concentrations in order to obtain presumably true... 

At the beginning of Section 3.3 a distinction was made between voltammetric techniques with non-stationary and stationary electrodes the first group consists of voltammetry at the dme or polarography, already treated, and voltammetry at hydrodynamic electrodes, a later subject in this section however, we shall now first consider voltammetry at stationary electrodes, where it is of significance to state whether and when the analyte is stirred. 

Moreover, it is difficult to find one s way in the overwhelming amount of literature on this subject because the major part of it is focussed on d.c. polarography and thus to the mass transfer problem at the dropping mercury electrode (DME). Neglecting the sphericity, the expansion of the drop has still to be accounted for in the diffusion equation for a species i. Equation (19b), which we have adopted thus far, should therefore be replaced by [11, 147]... 

The sensitivity of this technique is excellent and its accuracy is greater than that of conventional polarography. This method has found wide application in analytical chemistry. For addnl info on this subject see Refs 6,7,8,10,12,14,16,17,18,19,20,21,22,24,25,26 28,29,30,31 32... 

The ability of adenine and cytosine to undergo reduction in aqueous medium is at least partially retained at the level of oligo- and polynucleotides. In both acid and neutral media, such residues in single-stranded RNA, DNA and synthetic polynucleotides, when subjected to d.c. polarography, undergo irreversible reduction in a protonated, adsorbed, state with the transfer of four electrons to adenine... 

A comprehensive review of the use of polarography and voltammetry for drug analysis is beyond the scope of this article. (See Section Bibliography for reviews on the subject.) The analytical range of the methods is also well illustrated in the references. " ... 

Part IV is devoted to electrochemical methods. After an introduction to electrochemistry in Chapter 18, Chapter 19 describes the many uses of electrode potentials. Oxidation/reduction titrations are the subject of Chapter 20, while Chapter 21 presents the use of potentiometric methods to obtain concentrations of molecular and ionic species. Chapter 22 considers the bulk electrolytic methods of electrogravimetry and coulometry, while Chapter 23 discusses voltammetric methods including linear sweep and cyclic voltammetry, anodic stripping voltammetry, and polarography. 

Because these methods are so deeply rooted in the polarographic tradition and even now are frequently used with polarographic electrodes, we begin with a discussion of phenomena at dropping mercury electrodes and then develop the subject through conventional polarography and into various forms of pulse voltammetry. 

An interesting method, though limited in scope, for improving the sensitivity of conventional polarography makes use of catalytic eflFect of a desired ion on some component of the solution. Thus the catalytic eflFect of uranyl ions on nitrate reduction was used by Korkisch and coworkers (30) however, this method is subject to many interferences. 

What is known of second coordination sphere structure The term is an old one, first introduced by Werner (3) in the nineteenth century. Most of the examples which have been studied involve ion pairing of one kind or another. Work in this area has involved spectroscopic methods, polarography, the use of ion exchange resins, and a variety of other techniques (4). In spite of this, many of the details of the subject are not well understood. Turning to nonionic outer sphere complexes, the situation is much worse. Further, nonionic complexes are certainly most important in homogeneous catalysis since this usually occurs in non-aqueous and nonpolar solvents. In all probability, nonionic ligands are also of considerable significance in enzymatic reactions. 

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