Zinc coulometric

An assay for the determination of vitamin K3 (2-methyl-1,4-naphthoquinone) by a combination of both constant-potential and constant-current cou-lometry has been reported [13]. The assay requires the two-electron reduction of the compound to the corresponding hydroquinone at a mercury pool electrode (E = -0.60 V vs. SCE) in acetate buffer, pH 5.9, followed by the coulometric titration of the reduction product with electrogenerated Ce(VI). This method is preferable to the standard method requiring preliminary reduction to the hydroquinone by zinc dust in acid medium, followed by titration with standard Ce(IV) solution. It is capable of low-level determination (1-2 mg) of this vitamin in pharmaceuticals, biological fluids, and foods. 

The three samples (Ci, C2, and C3) taken from the calendering machine have been studied by coulometric titration and dehydrochlorination. Taking into account the calcium stearate and the zinc stearate and... 

Owing to metal chlorides titration by the coulometric method, and carboxylic acid titration by the potentiometric method, it is possible to follow the metal soaps consumption during thermomechanical heat treatments. This new technique provides a better understanding of the stabilization mechanisms of PVC with the calciumr-zinc system, and offers a better explanation of synergistic effects between metal soaps and secondary stabilizers such as epoxidized soya-bean oil, a-phenylindole, and butanediol-p-aminocroto-nate. The influence of these last stabilizers on zinc chloride formation enables us to classify them into short- and longterm stabilizers. 

During heat treatments, zinc and calcium stearates react with hydrogen chloride that has evolved from the polymer or with labile chlorine atoms to liberate zinc and calcium chlorides. These compounds are titrated by a coulometric method in tetrahydrofuran (7) using a generator of Ag+ ions that are precipitated in the presence of chloride ions. When zinc and calcium stearates are used together, both chlorides are titrated at the same time, and they are not differentiated. 

To study the influence of secondary stabilizers on zinc chloride formation, we have prepared PVC sheets on a rolling mill with the different binary mixtures zinc stearate and a-phenylindole, epoxidized soya-bean oil, or /3-aminocrotonate esters, and we have followed the zinc chloride formation by coulometric titration of chloride ions. In Figure 5 we have combined the percentage of zinc chloride that may be liberated with respect to the initial amount of zinc stearate in the presence of a-phenyl-indole (Curve 1 )> epoxidized soya-bean oil (Curves 2 and 3), and butane-diol- -aminocrotonate (Curve 4) during heating in a stove at 180°C. 

Alfonsi (9,10,11,12,13) has carried out an extensive investigation of the controlled-potential separation and determination of antimony in alloys containing combinations of lead, tin, bismuth, and copper. Tanaka (14, 15), working mainly with synthetic samples, reports conditions for the separation of antimony from gold, silver, mercury, copper, bismuth, cadmium, zinc, and vanadium in a variety of common electrolytes. Very recently, Dunlap and Shults (18) have developed two coulometric procedures which permit the determination of antimony in each of its oxidation states as well as the total antimony present. After pre-reduction of antimony (V) with hydrazine hydrate, the antimony (III) is reduced to the amalgam at a mercury cathode with a potential of —0.28 V vs. SCE in a supporting electrolyte 0.4 m in tartaric add and 1 m in hydrochloric acid. In the... 

Zinc may also be coulometrically determined by the oxidation of zinc amalgam (265). This process may be carried out either with an... 

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