Mercury/ions/salts determination

A. Mercury(II) chloranilate method Discussion. The mercury(II) salt of chloranilic acid (2,5-dichloro-3,6-dihydroxy-p-benzoquinone) may be used for the determination of small amounts of chloride ion. The reaction is ... 

Many other variations of the stripping technique have been developed. For example, a number of cations have been determined by electrodeposition on a platinum cathode. The quantity of electricity required to remove the deposit is then measured coulometrically. Here again, the method is particularly advantageous for trace analyses. Cathodic stripping methods for the halides have also been developed in which the halide ions are first deposited as mercury(I) salts on a mercury anode. Stripping is then performed by a cathodic current. 

In principle, any ion which can be oxidized or reduced or which will form a stable complex or slightly soluble salt with mercury can be determined polarographically. A survey of the literature indicates that the polarographic behavior of some 80 elements has been described and analytical determinations of most of these have been accomplished. Accordingly, polarography should be useful for determining most of the cations and indeed a number of anions of interest to water analysts. 

The most common species determined by cathodic stripping voltammetry are anions such as halides or sulphide, at a mercury electrode. This involves formation of a film of mercury(I) salts on the electrode in the deposition step. The anodic oxidation process involved in the deposition step is in fact the oxidation of mercury metal to mercury(I) ions. These immediately precipitate insoluble mercury(I) salts with the halide ion etc, on to the surface of the electrode. The anodic deposition potential required depends on the anion concerned. The subsequent cathodic stripping peak for the mercury(I) salt of each anion has at its own individual potential. 

Determination of silver as chloride Discussion. The theory of the process is given under Chloride (Section 11.57). Lead, copper(I), palladium)II), mercury)I), and thallium)I) ions interfere, as do cyanides and thiosulphates. If a mercury(I) [or copper(I) or thallium(I)] salt is present, it must be oxidised with concentrated nitric acid before the precipitation of silver this process also destroys cyanides and thiosulphates. If lead is present, the solution must be diluted so that it contains not more than 0.25 g of the substance in 200 mL, and the hydrochloric acid must be added very slowly. Compounds of bismuth and antimony that hydrolyse in the dilute acid medium used for the complete precipitation of silver must be absent. For possible errors in the weight of silver chloride due to the action of light, see Section 11.57. 

During the anodic polarization of a dropping mercury electrode the chloride, bromide, iodide, cyanide, thiocyanide and sulphide ions form slightly soluble salts or stable complexes with mercury. In the presence of these substances so-called anodic oxidation waves appear on polaro-graphic curves. The polarographic determination of chloride has received most attention. In many cases the dilution of the sample with 0.1 N H2SO4 is satisfactory and the solution can be polarographed directly [3]. 

With the liquid level above the analyte solution, some contamination i>f the sample is inevitable. In most instances, the amount of contamination is too slight to be of concern. In determining ions such as chloride, potassium, silver, and mercury, however, precaution must often be taken to avoid this source of error. A common w-ay is to interpose a second salt bridge between the analyte and the reference electrode this bridge should contain a noninierfering electrolyte, such as potassium nitrate or sodiujn sulfate. Double-junction electrodes based on this design are offered by several manufacturers. 

Cationic polymerization of diethyleneglycol divinyl ether and butanediol divinyl ether in the presence of oniiim salts was induced by y-irradiation. The mechanism for the initiation process involves the reduction of onium salts either by organic free radicals or solvated electrons depending on the reduction potentials of the onium salts. The reduction potentials of sulfonium salts was determined by polarography at the dropping mercury electrode. Only solvated electrons were capable of reducing the salts with reduction potentials lower than approximately -100 kJ/mol. The redox process liberates the non-nucleophilic anion from the reduced onium salt and leads to the formation of a Bronsted acid or a stabilized carbenium ion. These species are the true initiators of cationic polymerization in this system. The y-induced decomposition of onium salts in 2-ethoxyethyl ether was also followed by measuring the formation of protons. An ESR study of the structure of the radicals formed in the y-radiolysis of butanediol divinyl ether showed that only a-ether radicals were formed. 

AC voltammetry using the fundamental and second harmonic wave of Ti at a semistationary mercury drop electrode has been used for the direct determination of Ti [29]. This method has the distinct advantage of being able to tolerate large quantities of metal ion impurities. In another method, Ti salts were chelated with dihydroxyazo dyes, adsorbed onto a hanging mercury drop electrode, and then determined... 

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