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Dithizone spectrophotometry
Key words: dithizone spectrophotometry; US instrumentation ; UV-1800
Dithizone spectrophotometry is a method in which dithizone is used as a chelating agent to react with metal ions to form a colored substance, and then the metal ion is determined spectrophotometrically. This is an indirect, extraction spectrophotometric method commonly used in environmental monitoring. Among the water quality standards, there are three standard methods using dithizone spectrophotometry. 1 Determination of lead: In the reducing medium of ammonia citrate-pH of 8.5-9.5, lead and dithizone form a reddish dithizone lead chelate which can be extracted by chloroform, at a wavelength of 510 nm. Spectrophotometry was carried out to determine the content of lead. 2 Determination of cadmium: In the strong alkaline solution, cadmium ions and dithizone red chelate compound, chloroform extraction, spectrophotometric determination at 518nm wavelength, quantified by standard curve method. The measured concentration range is from 1 to 60 μg/L. The method is suitable for the determination of cadmium in natural water and wastewater contaminated by cadmium. The water sample contains lead 20mg/L, zinc 30mg/L, copper 40mg/L, manganese and iron 4mg/L, which does not interfere with the determination; when the magnesium ion concentration reaches 20mg/L, it needs to be masked with potassium sodium tartrate. . 3 Determination of zinc: In an acetate buffer medium having a pH of 4.0-5.5, zinc ions form a red chelate with dithizone, and after extraction with carbon tetrachloride, spectrophotometry is carried out at a wavelength of 535 nm. When there are a small amount of metal ions such as lead, mercury, copper, cadmium, nickel, cobalt, antimony, zinc, palladium, printing, dental tin, etc. in the water sample, there is interference with the determination of zinc, but sodium thiosulfate can be used as a masking agent and control. The pH is eliminated. The minimum detection limit of lead by dithizone spectrophotometry is 0.010mg/L, and the upper limit concentration is 0.30mg/L (GB7470-87). The minimum detection limit of cadmium detection is 1μg/L, the upper limit concentration is 50μg/L (GB7471-87); the minimum detection limit of zinc measurement is 5μg/L, and the upper limit concentration is 50μg/L (GB7472-87). 4 Determination of mercury, the water sample was digested with a solution of potassium permanganate and potassium persulfate (oxidant) in an acidic medium at 95 ° C. After converting inorganic and organic mercury into divalent mercury, the excess was reduced with hydroxylamine hydrochloride solution. The oxidant is added with a dithizone solution, reacted with mercury ions to form an orange chelate compound, extracted with chloroform or carbon tetrachloride, and then added with an alkali solution to wash off the excess dithizone in the extract, and measured at a wavelength of 485 nm. Absorbance was quantified by the standard curve method. Key words: dithizone spectrophotometry; US instrumentation ; UV-1800
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