Maxima, in polarography

Manganese, D. of - continued with magnesium and zinc, (ti) 334 Mannitol 299, 581 Masking agents 12, 312 Mass action law 16 applications to electrolyte solutions, 23 Matrix effects 733, 794 Maxima in polarography 597 suppression of, 597, 611 Mean deviation 134 relative, 134 standard, 134 Measuring cylinders, 87 flasks, 81... 

Techniques, Apparatus, and Analytical Applications of Controlled-Potential Coulometry, Jackson E. Elarrar Streaming Maxima in Polarography, Elenry El. Bauer Solute Behavior in Solvents and Melts, A Study by Use of Transfer Activity Coefficients, Denise Bauer and Mylene Breant... 

Sketch the appearance of current maxima in dc polarography and explain how these unwanted signals can be avoided. 

The polarographic behavior of all the bipyridines with the exception of the 3,4 -isomer has been investigated in aqueous solution. The difficulty of reduction increases in the order 4,4 -, 2,4 -, 2,3 -, 2,2 -, and 3,3 -bipyr-idine. Most of the work has been concerned with 2,2 - and 4,4 -bipyridines. Both isomers are reduced in aqueous solution by a two-electron process, sometimes observed as two separate one-electron steps, which is pH dependent because of the formation of a dihydro derivative. Complications in interpretation of the waves due to prewaves, catalytic hydrogen waves, wave maxima, and adsorption phenomena have frequently been observed. ° Polarography and cyclic voltammetry investigations have been extended to the study of 2,2 - and 4,4 -bipyridines... 

One advantage of the derivative-type polarogram is that individual peak maxima can be observed for substances with half-wave potentials differing by as little as 0.04 to 0.05 V in contrast, classical polarography requires a potential difference of about 0.2 V for resolution of waves. 

Mass spectrometry (22, 96,181, 530, 531) and NMR spectroscopy (65, 69,181,209,431) have been recorded. The UV spectra of the dienone alkaloids differ in the extinction maxima (proaporphine alkaloids at 220 nm (e 24800) and 285 nm (c 3000) promorphinane alkaloids 230 nm (e 24,000) and 285 nm (e 7500)). IR Spectroscopy reveals characteristic frequencies of the cross-conjugated dienone at 1655, 1630, and 1613 cm"i. On polarography the proaporphine and the promorphinane dienone compoimds are reduced (335) at a half-wave potential similar to that of aromatic aldehydes. 

There are several mechanisms that can lead to movement of the solution and the appearance of maxima. The subject is too complicated to be satisfactorily discussed here the origins of maxima are discussed fully in Reference [1], and methods of dealing with them to permit quantitative analysis are given in the general texts on polarography listed at the end of the chapter. One can, however, make the following generalizations ... 

We shall see later that a typical dc polarography result takes the form of a wave, (Fig. 1.3f). The normal result is shown together with anomalous maxima superimposed. Both of these maxima are due to an enhancement in the rate of mass transport of the analyte to the electrode caused by convective movements at the Hg/HzO interface. 

The most important point for analytical applications is to be able to remove these maxima. It has been known for a long time that small concentrations of surface active agents suppress these maxima. Examples of chemicals used in the early days of dc polarography are gelatine and methyl red. More recently the non-ionic detergent Triton X-100 (Rohm and Haas Co., Philadelpia, Penn) has become established as the material of choice. A concentration of <0.002% w/v is usually sufficient. This level of concentration should not be exceeded without checking for distortion of the polarographic waves produced. 

Kalvoda has reviewed different electrochemical methods suppression of polarographic maxima, eletrocapillary measurements, Kalousek commutator technique, differential pulse polarography and tensammetric methods for the determination of oily substances in various types of waters. These compounds are neither reducible nor oxidizable but are surface active. The study of oil fractions has shown that the Kalousek technique responds only to higher levels of dissolved petroleum fractions (0.02 to 100 mg/1) found only in pollution sources such as harbors and refinery effluents.Recent results indicate that the water pollution with petroleum can be determined by differential pulse tensammetry. Good calibration graphs were obtained with Diesel oil at a concentration from 30-50 /xg to 0.5 mg/1 and with Saratov petroleum from 0.1-0.2 to 3.3 mg/1. ... 

The Brdifika basic reaction is realized by simple procedures in which biological material, usually serum, is submitted to polarographic analysis, being added to cobalt solutions without any previous treatment by de-naturation, precipitation, filtration, or by enzymatic or electrophoretic procedures. The polarography of solutions containing Co salts yields polarographic curves with current maxima of cobalt, and after the addition of the serum the typical double wave is obtained. 

The so-called rapid polarography operates with very short drop-times (several milliseconds) produced under mechanical [47] or optical [48] control. This technique permits the application of scan rates up to several hundreds mV per second. The advantage of this technique is evident maxima are suppressed and formation of surface-blocking films is minimized the damping of oscillations is not necessary and the application in flowing and agitated media is possible. These favorable effects are devaluated by the decrease of the faradaic-to-charging current ratio. Therefore, the detection of electroactive substances in solutions below 10 " M is impossible [82]. 

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