Polarographic measurement

Explain the reason for including the time-consuming oxygen removal step in pulse-polarographic measurements of tin ion in juice samples. 

The electrochemical cell for the polarographic measurements had a four-electrode configuration equipped with a microsyringe, and was connected to a computer-assisted data-acquisition system [7]. On the other hand, the cyclic voltammetric measurements that are also assisted by a computer data-acquisition system were carried out using a gel electrode that contains the aqueous phase [8]. The cell structure was as follows ... 

Polarographic titration seems of limited application owing to the discontinuity of the dme moreover, the addition of the titrant increments requires stirring whereas the polarographic measurements require an unstirred solution. 

Cu(II) EPR signal in nitriles as solvent as well as by polarographic measurements 144>. Similarly, the EPR signal disappeared when Cu(OTf)2 was used for catalytic cyclo-propanation of olefins with diazoesters 64). In these cases, no evidence for radical-chain reactions has been reported, however. The Cu(acac)2- or Cu(hfacac)2-eatalyzed decomposition of N2CHCOOEt, N2C(COOEt)2, MeCOC(N2)COOEt and N2CHCOCOOEt in the presence of cyclopropyl-substituted ethylenes did not furnish any products derived from a cyclopropylcarbinyl - butenyl rearrangement128. These results rule out the possible participation of electron-transfer processes and radical intermediates which would arise from interaction between the olefin and a radical species derived from the diazocarbonyl compound. 

J.E. Doeller, T.S. Isbell, G. Benavides, J. Koenitzer, H. Patel, R.P. Patel, J.R. Lancaster Jr, V.M. Darley-Usmar, and D.W. Kraus, Polarographic measurement of hydrogen sulfide production and consumption by mammalian tissues. Anal. Biochem. 341, 40-51 (2005). 

The thermal decomposition of some 3,5-disubstituted-l,2,4-thiadiazoles has been studied and some nonisothermal kinetic parameters have been reported <1986MI239>. Polarographic measurements of a series of methylated 5-amino-l,2,4-thiadiazoles show that thiadiazoles are not reducible in methanolic lithium chloride solution, while thiadiazolines are uniformily reduced at 0.5 = — 1.6 0.02 V. This technique has been used to assign structures to compounds which may exist theoretically as either thiadiazoles or thiadiazolines <1984CHEC(6)463>. The photoelectron spectrum for 1,2,4-thiadiazole has been published <1996CHEC-II(4)307>. 

The reactions above provide the interpretation of very detailed polarographic measurements. The oxidation products of aryllead derivatives on Hg electrodes were identified in other studies on Ph4Pb, Ph3PbCl, Ph2PbCl2, Ph3PbOAc and Ph(OAc)3. These oxidations... 

The relevance to polymerisation kinetics of the Keele group s polarographic measurements on various triarylmethylium ions in different solvents 137 is explained. 

OH2 for which there is support from polarographic measurements at high acidity43. 

The analytical sensitivity of classical polarographic or voltammetric methods is usually quite good at about 5 x 10 mol dm . At the lowest concentrations of analyte, however, the currents caused by double-layer effects or other non-faradaic sources causes the accuracy to be unacceptably low. Pulse methods were first developed in the 1950s to improve the sensitivity of the polarographic measurements made by pharmaceutical companies. At present, two pulse methods dominate the analytical field, i.e. normal pulse and differential pulse . Square-wave methods are also growing steadily in popularity. 

As was already mentioned, the constitution of reagents 5 in ethereal solutions and of the complexes formed by them with a number of Lewis acids was investigated by electrochemical methods and the nature of existing ions and electroactive species was elucidated. It was also possible to evaluate the equilibrium constant for the Schlenk equilibrium for 5b, 5e and 5i in DME solutions from polarographic measurements . 

Therefore, for polarographic measurements at negative potentials, alkali metal salts are not suitable. Moreover, alkali metal ions often give unfavorable influences on electrode reactions (Section 11.1.3). 

The relevant data for the dicyclopentadienyl metals are given in Table V (109) only in the case of ferrocene and nickelocene are the results both well-defined and comparable, and the values of 0are in agreement with the electron configurations [ ]( )4( 2i/)° and f ]( 2 )4( 2w)2 in that nickelocene is the more easily oxidized. More recently, it has been found (110) that qualitative agreement is observed between the oxidation potentials of a series of para-substituted phenylferrocenes and the Hammett a constant of the substituent, although in this case polarographic measurements at a... 

Polarographic measurements have also been performed on [(NbeCl CL] -6 (q = 2, 3) in DMSO. While in aqueous solutions iodine causes a two-electron oxidation, only a one-electron oxidation was observed in DMSO. 

Basic Protocol 1 Polarographic Measurement of Oxygen Uptake C4.2.2... 

As seen in Figure C4.2.1, there are two obvious methods of readily measuring LOX activity, that is, by oxygen uptake and ultraviolet (UV) absorbance of the conjugated hydroperoxy-diene product. Basic Protocol 1 describes the polarographic measurement... 

BASIC PROTOCOL 1 POLAROGRAPHIC MEASUREMENT OF OXYGEN UPTAKE Oxygen electrode equipment is used to determine oxygen uptake as a function of time. After preparing the enzyme (see Support Protocol) and calibrating the instrument, substrate and enzyme are added sequentially to a buffered solution, and the rate of oxygen uptake is monitored by a recorder. 

The acidities of carbon acids have been extensively discussed before, especially by Cram5 who has constructed a scale of pK values based on the work of Mc-Ewan, Streitwieser, Applequist, and Dessy and known as the MSAD scale. Table 3 shows a selection of these pK values, and also values given by Reutov and co-workers6 derived from polarographic measurements. It is clear from the values shown in Table 3 that substituents such as a-phenyl, a-benzyl, and a-carbethoxy increase the extent of carbanion formation from carbon acids very considerably,... 

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