Dithizone indicator, commonly known as lead reagent, is the most widely used organic color reagent in colorimetric analysis. It can be used to determine trace heavy metal ions such as Pb2+, Hg2+, Zn2+, Cd2+, etc. Its molecular formula is C6H5NHNHCSN=NC6H5. The appearance is a purple black crystalline powder. Difficult to dissolve in water and inorganic acids. Soluble in chloroform and carbon tetrachloride, with chloroform having a higher solubility and the solution appearing green. Slightly soluble in hydrocarbon solvents. One active hydrogen atom in the dithizone molecule is replaced by a metal, and the nitrogen atom forms a coordination bond with the metal ion, forming a chelate compound. The solution appears orange or red, and the reaction is very sensitive. Easy to be oxidized by air, can be protected by adding sulfur dioxide aqueous solution.
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Chemical Formula |
C9H7NO2 |
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Exact Mass |
161.05 |
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Molecular Weight |
161.16 |
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m/z |
161.05 (100.0%), 162.05 (9.7%) |
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Elemental Analysis |
C, 67.08; H, 4.38; N, 8.69; O, 19.85 |
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Form |
Crystalline |
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Color |
Black Powder |
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Melting point |
168 °C ( dec. ) ( lit. ) |
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Boiling point |
376.1 ± 25.0 °C ( Predicted ) |
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Density |
1.2578 ( rough estimate ) |
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Acidity coefficient ( pKa ) |
pK1 : 4.50 ; pK2 : 15 ( 25 °C ) |
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Flash point |
> 230 ° F |
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Refractive index |
1.5700 ( estimate ) |
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Dithizone indicator (chemical name diphenylthiocarbazone, molecular formula C ₁∝ H ₁₂ N ₄ S) is a purple black crystalline powder with unique chemical properties: easily soluble in chloroform and carbon tetrachloride (solution appears green), slightly soluble in alcohols, and almost insoluble in water; The sulfur and nitrogen atoms in its molecular structure can form stable chelates with various metal ions, accompanied by significant color changes. This characteristic makes it widely applicable in fields such as analytical chemistry, environmental governance, industrial production, and biomedical research.
Analytical Chemistry: A "Sensitive Probe" for Heavy Metal Detection
Its core application lies in the qualitative and quantitative analysis of heavy metal ions. The chelates formed between it and metal ions have bright colors, high stability, and comply with Beer's law. High sensitivity detection can be achieved through colorimetric methods.
It has extremely high selectivity for lead ions (Pb ² ⁺) and can form orange red complexes with a sensitivity of up to micrograms (detection limit of 0.01 μ g/mL). In environmental monitoring, the dithizone chloroform system is widely used for screening lead pollution in water, soil, and food. For example, the Chinese standard GB 5009.12-2017 stipulates the use of the dithizone colorimetric method to determine lead content in food. The operating steps include sample digestion, color development of dithizone solution, and measurement with a spectrophotometer. This method can eliminate the interference of copper, zinc, and other ions under pH 8.5-9.0 conditions.
Multi metal ion stepwise detection
By controlling reaction conditions such as pH value and type of masking agent, stepwise detection of multiple metal ions can be achieved
Mercury ion (Hg ² ⁺): Under strong acidic conditions of pH 1-2, it forms a red complex with mercury and is used for monitoring mercury pollution in industrial wastewater.
Copper ion (Cu ² ⁺): In acetic acid buffer solution with pH 4-5, it forms a yellow green complex with copper, which is suitable for evaluating the treatment effect of electroplating wastewater.
Zinc ion (Zn ² ⁺): In an ammonia buffer solution with pH 9-10, it forms a pink complex with zinc and is commonly used for alloy composition analysis.
It can be used as an endpoint indicator for complexometric titration, for example, in the EDTA titration method to determine cobalt (Co ² ⁺), the solution before the titration endpoint is the red color of the dithizone cobalt complex. At the endpoint, EDTA captures cobalt ions, and the solution color changes to the blue black color of the dithizone itself, indicating the completion of titration.
Environmental Governance: Precise Adsorbents for Heavy Metal Pollution
Traditional methods for treating heavy metal wastewater, such as precipitation and adsorption, suffer from high costs and poor selectivity. However, through functional modification, highly selective adsorption materials can be prepared, significantly improving treatment efficiency.
Dithizone graft chelating gel
Patent CN103801271B discloses a preparation method of graft gel with polyacrylamide as the matrix and dithizone as the functional monomer: dissolve the polyacrylamide gel in distilled water, adjust the pH to 9, add the formaldehyde solution, drop the dithizone solution, react at 24 ℃ for 2 hours, and obtain the product after separation and drying. The adsorption capacity of the gel for mercury ions (Hg ²+) is 120mg/g, and it maintains high adsorption efficiency within the pH range of 2-8, which is suitable for the advanced treatment of acid mine wastewater and electroplating wastewater.
By modifying it on the surface of Fe3O4 nanoparticles, magnetic adsorbents can be prepared. For example, by covalently bonding dithizone to the surface of Fe ∝ O ₄ @ SiO ₂ core-shell structure with silane coupling agent, the adsorption selectivity coefficient (Ksel) of the obtained material for lead ions (Pb ² ⁺) reaches 85.6, which is much higher than that of unmodified material (Ksel=12.3), and can be quickly separated and recovered by an external magnetic field, achieving the recycling of the adsorbent.
Dithiazone imprinted polymer
Molecular imprinting technology (MIT) combined with the chelating ability of dithizone can prepare adsorbent materials with "memory effect" on specific metal ions. For example, using dithizone copper complex as a template, imprinted polymers were prepared by free radical polymerization. The adsorption capacity of copper ions was 3.2 times that of non imprinted polymers, and the copper ion recovery rate reached 92.7% in a mixed metal solution of 10mg/L (containing Cu ² ⁺, Zn ² ⁺, Cd ² ⁺).
Industrial production: a "separation and purification assistant" for high-purity substances
Dithizone indicator chelating properties make it a key reagent for metal ion separation and purification in industrial production, especially widely used in the fields of precious metal recovery and semiconductor material preparation.
In the treatment of electronic waste, it can be used for selective extraction of precious metals such as gold (Au ³ ⁺) and silver (Ag ⁺). For example, by adjusting the acid leaching solution of the crushed circuit board to pH 1-2 and adding a solution of dithizone chloroform, gold ions are extracted into the organic phase, while base metals such as copper and iron remain in the aqueous phase, achieving efficient enrichment of precious metals. The gold recovery rate of this method reaches 98.5%, and the dithizone can be recycled through reverse extraction regeneration.
Purification of semiconductor materials
In the preparation process of silicon (Si) single crystals, it can be used to remove impurities such as copper and iron from the raw materials. For example, mixing silicon powder with a solution of dithizone toluene and stirring at 80 ℃ for 2 hours, copper ions form a complex with dithizone and are extracted. The purity of silicon powder is increased from 99.9% to 99.999%, meeting the requirements of semiconductor grade.
In processes such as electroplating zinc and nickel, dithizone can be used as a purifying agent to remove harmful impurities such as lead and cadmium from the plating solution. For example, adding a dithizone ethanol solution to a zinc plating solution containing 0.5mg/L lead causes lead ions to precipitate as dithizone lead complexes. After filtration, the lead content in the plating solution decreases to below 0.01mg/L, significantly improving the quality of the coating.
The dithizone indicator we provide is a substance with a purity of 98%. The reagent is achieved through our own technology. Prepare according to the following steps.
(1) Preparation of Phenylhydrazine Dithioformate Phenylhydrazine Salt. Dissolve 13g of phenylhydrazine in 60ml of ether and add 5.2ml of carbon disulfide dropwise. Filter out the generated white precipitate and wash it with ether to obtain about 15g.
(2) Preparation of Diphenylenediamine Thiourea. Place the above product in a beaker and heat it in a water bath at 96-98 ℃. After the material melts, release hydrogen sulfide and turn into a pale yellow gel like substance. If ammonia gas is released, remove it from the hot bath and cool it with water. Then use ice cooling. Then cool it with ice, add 15ml of anhydrous ethanol, take it out of the ice bath, stir and heat it slightly. At this point, the gel like substance becomes a crystalline product, filter it, wash it with ethanol, and obtain about 7.5g.
(3) Preparation of dithizone. Add the obtained diphenylthiourea to a caustic potassium solution (6g potassium hydroxide dissolved in 60ml anhydrous methanol), reflux on a boiling water bath for 5 minutes, and remove and cool in an ice bath. Filter and acidify the filtrate with sulfuric acid until the Congo red test paper changes color and a dark blue precipitate is precipitated. Filter and treat the precipitate with caustic potassium solution and sulfuric acid. After filtration, wash with water until no sulfate ions are present. Drying at 40 ℃ yields about 3g of dithizone.
(4) Cool the mixture of phenylhydrazine and toluene to below 0 ℃, add carbon disulfide with stirring, and control the addition rate to maintain the reaction temperature at 60-70 ℃. Leave it for more than 10 minutes, then heat it up to 90-95 ℃, dissolve the crystals, and start the reaction.
(5) When a large amount of crystals precipitate and the lead acetate reagent turns slightly brown, the reaction is complete. After cooling, it is filtered and the crystals are washed successively with cold toluene and ethanol. The resulting white crystal is diphenylthiocarbazide.
(6) Then, add diphenylcarbazide to a methanol solution of potassium hydroxide, heat and reflux for 5-10 minutes, cool with ice water to around 30 ℃, and filter out insoluble substances.
(7) Add 0.5mol/L sulfuric acid aqueous solution to the filtrate while stirring until the solution is acidic to Congo red test paper. Wash the obtained crystals with cold water first, then dissolve them in 5% sodium hydroxide solution, filter out insoluble substances, and cool the filtrate with ice water.
(8) At the same time, acidify the Congo red test paper with cold 0.5mol/L sulfuric acid until it becomes acidic. After complete precipitation, filter it. Wash the filtered crystals thoroughly with ice water until the SO4 2- ion is qualified. After draining, dry at 40 ℃ to obtain the finished product diphenylthiocarbazone.
faq
How to prepare dithizone indicator?
Prepare the dithizone solution by dissolving 0.05 g dithizone in 100 mL of 95% ethanol in a 250-mL beaker. The solid may not completely dissolve, but upon stirring, a dark blue/green solution is obtained. This solution should be made fresh.
What is the use of dithizone in analytical chemistry?
Dithizone is defined as a chemical compound used in fluorescence sensing applications, particularly for detecting specific residues in samples such as vegetables and water, where it forms complexes that can be quantified through fluorescence quenching methods.
What is the dithizone test for lead?
The dithizone method measures lead in water and wastewater. The DithiVer Metals Reagent is a stable powder form of dithizone. Lead ions in basic solution react with 6 Lead, Dithizone Method (300 µg/L) Page 7 dithizone to form a pink to red lead-dithizonate complex, which is extracted with chloroform.
What is the dithizone method for cadmium analysis?
Colorimetric determination with dithizone (diphenylthiocarbazone) is a simple method that has been applied to analyze cadmium (Cd) ions in water. However, determining concentrations close to the environmental standard value (3 μgL-1) using this method is difficult because of its low sensitivity.
What is dithizone also known as?
Dithizone, also known as Diphenylthiocarbazone, is used to measure the purity of pancreatic islet preparations for transplantation into humans with type 1 diabetes. It is a ligand that forms complexes with several metals including mercury and lead.
What is the best test for cadmium?
The best screening and diagnostic test for chronic cadmium exposure is a 24-hour urinary cadmium level, normalized to creatinine excretion. Urinary metallothionein and β2-microglobulin excretion can be correlated with long-term cadmium exposure.
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