How to determine mercury in water by dithizone spectrophotometry.

Principle of determination of mercury in water by dithizone spectrophotometry: Digest the sample with potassium permanganate and potassium persulfate at 95℃, convert all the mercury contained into bivalent mercury, reduce excess oxidant with hydroxylamine hydrochloride, react mercury ions with added dithizone solution to form orange chelate under acidic conditions, extract with organic solvent, wash off excess dithizone with alkali solution, determine absorbance at 485nm wavelength, and calculate the mercury content in water by standard curve method. For the determination of mercury in water by dithizone spectrophotometry, please refer to Determination of Total Mercury in Water (GB 7469-87). The sample was digested with potassium permanganate and potassium persulfate at 95℃, and all the mercury contained in it was converted into bivalent mercury. Excess oxidant is reduced by hydroxylamine hydrochloride. Under acidic conditions, mercury ions react with the added dithizone solution to form an orange chelate, which is extracted with an organic solvent and then washed away with an alkaline solution. The absorbance was measured at 485nm, and the mercury content in water was calculated by standard curve method. Chloroform or carbon tetrachloride can be used as organic solvent as extractant, and the former is widely used because of its low toxicity. The minimum detection concentration of mercury in this method is 2pg/L, and the upper limit is 40pg/L ... It is suitable for monitoring industrial wastewater and surface water polluted by mercury. This method requires strict control of determination conditions. In particular, there are requirements for the purity and dosage of reagents. It should also be noted that mercury is a highly toxic substance, and the chloroform solution containing mercury dithizone after extraction should not be discarded. Sulfuric acid should be added to destroy the colored chelate, and chloroform should be recovered by re-steaming after it is separated from other impurities in the water phase. The remain waste liquid containing mercury is adde into sodium hydroxide solution to be neutralized to be slightly alkaline, and then sodium sulfide solution is added under stir to completely precipitate that mercury, and the precipitate is recovered or otherwise treated. How to determine methylmercury in water? Methylmercury in water can be determined by gas chromatography. See Determination of Methyl Mercury in Environment by Gas Chromatography (GB/T17132-1997) for details. This method is suitable for the determination of methylmercury in surface water, drinking water, domestic sewage, industrial wastewater, sediments, fish, human hair and human urine. (For more technical information about quality inspection, analytical testing, chemometrics and reference materials, please refer to the national reference material www.rmhot.com. Firstly, the water sample was pretreated to enrich the methylmercury content to the determination requirements, and then the methylmercury content in the sample was determined by gas chromatograph (electron capture detector). Different samples have different pretreatment methods and minimum detection concentrations. Methylmercury in water, sediment and urine was determined by pretreatment with sulfhydryl gauze and sulfhydryl cotton, and the detectable concentrations were 0.0 1 ng/L, 0.02 ug/kg and 2 ng/L respectively. Methylmercury in fish and human hair was determined by hydrochloric acid solution extraction pretreatment method, and the detectable concentrations were 0. 1pg/L and 1ug/kg, respectively.