4 method for the determination of trace amounts of chloride ion in aqueous solution is described. The chloride is converted into phenylmercury(I1) chloride, which is extracted into chloroform and subsequently determined in ethyl acetate solution by means of atomic-absorption spectrophotometry. Alternatively, but less conveniently, the phenvlmercury (I I) chloride can be extracted into isopropyl acetate and this solution, after concentration, is sprayed into the spectrophotometer. As little as 0.015 p.p.m. of chloride can be detected in a 250-ml sample of water, and 0.1 p.p.m. of chloride can be determined with a relative mean error of 4.6 per cent. Interferences are minimal but bromide, iodide, thiocyanate and cyanide must be absent from the solution. The present method compares favourably with a previously described gasliquid chromatographic method, and is only slightly less sensitive.FEW procedures for the determination of chloride involving atomic-absorption spectrophoto-metry1-6 have been described in the literature. In all of these methods chloride was precipitated with silver ions, and either the excess of silver in solution, or that in the precipitate after dissolution in ammonia s ~l u t i o n , ~ was determined by atomic-absorption spectrophotometry.As described previ~usly,~ chloride has been determined at low levels by gas chromatography. The chloride ion is converted into phenylmercury(I1) chloride by reaction of an aqueous solution of the chloride with an aqueous solution of phenylmercury( 11) nitrate in a perchloric acid medium at about pH 1.5. In the present method phenylmercury(I1) chloride is quantitatively extracted with chloroform, which is then evaporated off and the residue re-dissolved in ethyl acetate. This solution is then aspirated into the atomic-absorption spectrophotometer. Alternatively, phenylmercury(I1) chloride can be quantitatively extracted into isopropyl acetate and this solution can be aspirated, after concentration if necessary, direct 1 y into the at omic-absorpt ion spec t ropho t ome t er .
EXTRACTION OF PHENYLMERCURY(II) CHLORIDE CHOICE OF SOLVENT-Conditions for the reaction of chloride ion with plienylmercury( 11) nitrate and extraction into chloroform of the phenylmercury (11) chloride formed have been established previ~usly.~ However, chloroform is not a suitable solvent for use in atomic-absorption spectrophotometry ; two possibilities were therefore examined. The first of these was the evaporation of the solution of phenylmercury(I1) chloride in chloroform to dryness and its re-dissolution in a suitable organic solvent, such as isobutyl methyl ketone or ethyl acetate. The well known properties of chloroform that are advantageous in solvent-extraction processes (e.g., high density, low solubility in water) do not extend to atomic-absorption spectrophotometry. Nevertheless, it is possible to remove the chloroform by evaporation and take up the residue in a suitable solvent. The concentration of this solution can then be measured by atomicabsorption spectrophotometry. It ...
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