Peroxydisulphate

We have shown that known reaction of luminol with peroxydisulphate at low luminol concentrations takes place in the regime of controlled generation of SO ion-radicals at spontaneous destruction of peroxydisulphate. The detection limit for various types of antioxidants in water using this reaction is varied from 10 to 10 M. It is possible also to determine some polluting admixtures present in the atmosphere. The reagent used is the mixture of the luminol, base and K S O, which, once prepai ed, could be used during a working day. 

Diammonium peroxydisulphate as SoOg Diatomaceous earth, see Silica, 1 ... 

Chromium (total and speciated chromium) in chromium plated mists Colorimetric field method using 1,5-diphenyl carbazide after oxidation with silver (1 (-catalysed peroxydisulphate 67... 

Discussion. Alkali persulphates (peroxydisulphates) can readily be evaluated by adding to their solutions a known excess of an acidified iron(II) salt solution, and determining the excess of iron(II) by titration with standard potassium permanganate solution. 

Persulphate (peroxydisulphate). Persulphate cannot be determined directly by reduction with iron(II) because the reaction is too slow ... 

INDUCED REACTIONS CAUSED BY ARSENIC(lv) INTERMEDIATES 2.2.1 Iron II)-arsenic III)-peroxydisulphate system In the absence of oxygen... 

The reaction between arsenic(iri) and peroxydisulphate is very slow, but is markedly accelerated in the presence of iron(II) as inductor. According to Kolt-... 

According to this mechanism only iron(II) reacts with peroxydisulphate and gives an SO4 radical. With respect to reactions of the SO4 radical, reaction (44) becomes insignificant compared with (45) at [As(III)]/[Fe(II)] ratios greater than two, and then Fj will no longer depend on the arsenic(III) concentration. 

The effect of copper(II) is essentially similar to that of iron(Ill). In reaction (48) copper(I) is formed which results either indirectly by reaction (49) or directly by reaction (50) in the reduction of a peroxydisulphate ion... 

In the presence of oxygen the arsenic(IV) formed is oxidized by the step (51) and reactions (52), (53), (54) and (58) take place as in the reaction initiated by the iron(II)-peroxydisulphate reaction. 

Arsenic III)-peroxydisulphate reaction catalyzed by iron Ill) and copper II)... 

The slow reaction between arsenic(III) and peroxydisulphate is first order with respect to peroxydisulphate In the presence of oxygen the rate of reaction increases. Values of the first order rate coefficient... 

The thermal decomposition of peroxydisulphate proceeds by two parallel paths, viz. 

In the absence of oxygen the addition of arsenic(Iir) has only a slight effect on the rate of reduction of peroxydisulphate. In the presence of air the rate of reduction of persulphate increases nearly fortyfold (Table 12). The oxidation of arsenic(III) by SO4 from reaction (62) is not a chain process, thus it need not be considered in the iron(III)- and copper(II)-catalyzed reaction between peroxydisulphate and arsenic(III). 

At high copper(ri) concentrations the rate of reduction of peroxydisulphate becomes independent of copper(n) concentration and is unaffected by the presence of oxygen. This can be explained by the occurrence of the termination reaction... 

As the concentration of copper(II) is increased the steady-state concentration of copper(I) is also increased, and the SO4 radical reacts with copper(I) rather than with arsenic(IV). In such a case the rate of reduction of peroxydisulphate, taking /c5o[Cu(I)]//c 6i > 1, can be given by... 

Polarographic behaviour of the system containing peroxydisulphate, arsenic-... 

Copper(II) ions in the presence of chloride ions are reduced at the dropping mercury electrode (dme) in two steps, Cu(II) -> Cu(I) and Cu(I) -> Cu(0) producing a double wave at -1-0.04 and 0.22 V versus sce half-wave potentials. In the presence of peroxydisulphate , when the chloride concentration is large enough, two waves are also observed the first limiting current corresponds to the reduction of the Cu(II) to Cu(I) plus reduction of a fraction of peroxydisulphate and the total diffusion current at a more negative potential is equal to the sum of the diffusion currents of reduction of Cu(II) to Cu(0) and of the peroxydisulphate. There is evidence that peroxydisulphate is not reduced at the potential of the first wave because of the adsorption of the copper(I) chloride complex at... 

The kinetic current, 4, of peroxydisulphate exalting the Cu(II) to Cu(I) wave is caused by a regenerative reaction consisting of the following steps... 

The reduction wave of peroxydisulphate at dme starts at the potential of the anodic dissolution of mercury. The current-potential curve exhibits certain anomalous characteristics under various conditions. At potentials more negative than the electrocapillary maximum, a current minimum can be observed this is due to the electrostatic repulsion of the peroxydisulphate ion by the negatively charged electrode surface. The current minimum depends on the concentration and nature of the supporting electrolyte, and can be eliminated by the adsorption of capillary active cations of the type NR4. ... 

A minimum different from the above can be observed on the polarographic wave of peroxydisulphate at about -1-0.1 Volt in the presence of both copper(II) and arsenic(ril) which does not occur with either constituent alone . The decrease in the current due to peroxydisulphate, 4, is kinetic in nature and caused... 

In the presence of sufficient arsenic(III) reaction (45) is so rapid that the termination reactions (72) and (70) can be left out of consideration. The decrease of the peroxydisulphate current, /, should be proportional to the rate of reaction (50), viz. 

Considering only termination by reaction (72) and assuming that stationary conditions are attained, the rate of reduction of peroxydisulphate in the chain process is given by... 

It should be mentioned that there is no decrease in the peroxydisulphate current in the presence of both iron(ril) and arsenic(III). Presumably, the iron(II)-peroxydisulphate reaction is too slow to compete with the reduction of peroxydisulphate at the DME at the given concentration. However, iron(III) reduces the kinetic current in the presence of copper(II) and arsenic(ril). This can be accounted for by the termination reactions... 

It is known that the permanganometric or cerimetric determination of hydrogen peroxide in the presence of peroxydisulphate furnishes too low results It has been shown by recent studies that the error is due to the reaction between hydrogen peroxide and peroxydisulphate, viz. 

Chain initiation is due to reaction (61), i.e. the thermal decomposition of peroxydisulphate into sulphate radicals, viz. 

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