Dithizone, the scientific name diphenylcarbazone, appearance is a purple-black crystalline powder. It is difficult to dissolve in water and inorganic acids, slightly soluble in alcohol and ether, slightly soluble in hydrocarbon solvents, and soluble in sulfuric acid, alkali, and alkali metal carbonates, and quickly turns dark red. It is easy to dissolve in chloroform and carbon tetrachloride and presents green. It is more soluble in chloroform. Its solution is unstable and easy to be oxygenated. It can be protected by a layer of sulfur dioxide. An active hydrogen atom in the molecule is replaced by metal, and the nitrogen atom forms a coordination bond with metal ions, The chelate is formed. The solution is orange or red, and the reaction is very sensitive. It is easy to be oxidized by air and can be protected by adding sulfur dioxide aqueous solution.
Discovery history of it:
The typical colorimetric reagent is diphenyl thiocarbazone, which was discovered by Emil Fischer in 1882. He observed that is very easy to form colored compounds with metal ions, but he did not continue this research. In 1926, Helmut Fischer studied this compound and reported the possibility of using it for analysis, which was fully utilized in the 1930s.
Synthetic dithizone: prepare according to the following steps.
1.) preparation of phenylhydrazine dithiocarbamate. Dissolve 13g of phenylhydrazine in 60ml of ether, and add 5.2ml of carbon disulfide dropwise. Filter out the generated white sediment and wash it with ether to obtain about 15g.
2.) preparation of diphenyl Diaminothiourea. Place the above products in a beaker and heat them in a 96-98 ℃ water bath. After melting, the materials release hydrogen sulfide and turn into yellowish colloids. If ammonia gas is released, remove it from the hot bath and cool it with water. Cool with ice. Then cool it with ice, add 15ml of water absolute ethanol, take it out of the ice bath, stir and heat it slightly. At this time, the colloid turns into a crystalline product, filters it, and wash it with ethanol to obtain about 7.5G.
3.) preparation of it. Add the above-mentioned diphenyl diamino thiourea to caustic potassium solution (6g potassium hydroxide dissolved in 60ml anhydrous methanol), reflux on a boiling water bath for 5min, take it out and cool it in an ice bath. After filtration, the filtrate is acidified with sulfuric acid until Congo red test paper changes color and dark blue precipitates are separated out. Filter by suction, and then treat the sediment with caustic potassium solution and sulfuric acid. After filtration, wash with water until there is no sulfate radical. Drying at 40 ℃ gives about 3G.
Determination of mercury in water by spectrophotometry principle: digest the sample with potassium permanganate and potassium persulfate at 95 ℃, convert all the mercury contained into divalent mercury, and reduce the excess oxidant with hydroxylamine hydrochloride, under acidic conditions, mercury ions react with the added it solution to form orange chelate, extract with an organic solvent, wash off the excess with alkali solution, and measure the absorbance at the wavelength of 485nm, Calculate the mercury content in water by standard curve method. For the determination of mercury in water by spectrophotometry, see the determination of total mercury in water quality potassium permanganate potassium persulfate digestion spectrophotometry (gb7469-87). Digest the sample with potassium permanganate and potassium persulfate at 95 ℃, convert all the mercury contained into divalent mercury, and reduce the excess oxidant with hydroxylamine hydrochloride, under acidic conditions, the mercury ion reacts with the added solution to form an orange chelate, extract with organic solvent, wash off the excess with alkali solution, measure the absorbance at the wavelength of 485nm, and calculate the mercury content in the water with the standard curve method. Chloroform or carbon tetrachloride can be used as an organic solvent or an extractant. The former is widely used because of its low toxicity. The minimum detectable concentration of mercury is 2PG / L and the upper limit of determination is 40pg / L. It is applicable to the monitoring of industrial wastewater and surface water polluted by mercury. This method has strict requirements for the control of determination conditions. In particular, the purity and dosage of reagents are highly required. It should also be noted that Mercury is a highly toxic substance. The chloroform solution containing mercury dithizone after extraction should not be discarded. Sulfuric acid should be added to destroy the colored chelate and separated it from other impurities in the water phase, and then the chloroform should be recovered by re-steaming. The remaining waste liquid containing mercury is neutralized with sodium hydroxide solution until it is slightly alkaline, and then sodium sulfide solution is added under stirring to completely precipitate mercury, and the precipitate is recovered or otherwise treated. How to determine methylmercury in water? Methylmercury in water can be determined by gas chromatography. For details, please refer to the determination of methylmercury in the environment by gas chromatography (GB / T 17132-1997). This method is suitable for the determination of methylmercury in surface water, drinking water, domestic sewage, industrial wastewater, sediment, fish body, human hair, and urine. (for more technical information on quality inspection, analysis and testing, stoichiometry and reference materials, please refer to the national reference materials www.rmhot.com) first, the water sample shall be pretreated to enrich the content of methyl mercury to the requirements of determination, and then the content of methyl mercury in the sample shall be determined by gas chromatography (electronic capture detector). The pretreatment method and the minimum detection concentration are different for different samples. Methyl mercury in water, sediment and urine was determined by the pretreatment method of secondary enrichment with sulfhydryl gauze and sulfhydryl cotton. The detectable concentrations were 0.01ng/l, 0.02ug/kg, and 2ng / L respectively; Methylmercury in fish and human hair was determined by the pretreatment method of hydrochloric acid solution extraction. The detectable concentrations were 0.1pg/l and 1ug / kg, respectively.