Three different pretreatments followed by a spectrophotometric method have been developed to determine mercury at microgram levels in a variety of, inorganic and organic solutions and solids. Inorganic solutions are reacted with hot nitric acid to oxidize mercury to the (II) oxidation state. Inorganic solids are dissolved in acids or fused with potassium pyrosulfate. Organic materials or inorganic materials that contain organic matter are digested withTanitric-sulfuric acid mixture.nIn the spectrophotometric method, the mercury(ll) dithizone compiex is extracted into chloroform and measured at 495 mp. A single extraction of the complex from an EDTA-citrate masking medium is sufficient when the concentrations of copper and silver are below established limits. A double extraction increases the tolerance for copper. In this double extraction procedure, the complex is extracted into chloroform from either an acidic (<0.75N) medium or the. EDTA-citrate masking medium at. pH 2.85±0.35. Mercury is stripped from the chloroform phase with an acidic nitrite solution, the nitrite is destroyed with hydroxylamine and aniline, and mercury(ll) dithizonate is extracted a second time into chloroform.nThe method is highly selective. Of 35 metal ions and 8 nonmetal anions studied in the double extraction procedure, only silver(I) interferes at a molar ratio to mercury below 50 to 1.
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