Reaction mechanism of detection methods of SO2 and NH3 at workplace
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Abstract
The reaction mechanism of detection methods of SO2 with formaldehyde absorbing-PRA spectrophotometry and NH3 with Nessler reagent spectrophotometry is reviewed. There are two steps in the reaction of SO2 absorbed by formaldehyde buffer solution:SO2 dissolves in the water to form H2SO3 firstly and then H2SO3 reacts with HCHO to form HO-CH2-SO3H. It involves both nucleophilic and electrophilic addition. The color reaction involves diazo reaction mechanism. The interference of NOx is eliminated while H2SO3 reacts with HCHO to form diazonium ion. The pale-yellow complexes generated by reaction of nessler's reagent with ammonia are the dinuclear complex in which atoms of O and N act as intermediate base connecting two Hg center ion. Therefore, it is needed to control the proportion of materials to generateHgI42- while preparing the Nessler reagent.
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