Nessler's reagent spectrophotometry
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Why is the pH adjusted to around 10.5 after adding zinc sulfate and sodium hydroxide during the pre-treatment flocculation and precipitation process? Also, why are the values obtained using the Nessler’s reagent spectrophotometric method higher than those obtained by the distillation method?
Adjusting the pH to 10.5 causes zinc sulfate to hydrolyze, producing flocculent zinc hydroxide precipitates, which serves a flocculating and precipitating role. As for the issue of method error, it is recommended that you conduct a comparative test using standard samples.
I conducted several sets of comparative tests, and the Nessler spectrophotometric method yielded higher results than the distillation method. I don’t know why; could it be an error in the method itself? But by definition, they all react with free ammonia and ammonium salts in the sample.
Reply to 3# 15049139054: Have you tried drawing the curve again? It is normal for different methods to have certain errors; the method should be chosen based on actual needs.