Direct titration of other reducing substances with iodine is an indirect iodometric method. VC and other substances are determined by the oxidation of iodine, iodine is obtained by the oxidation of iodine ions by oxidizing substances, and then titrated with sodium thiosulfate standard solution, so that the concentration of oxidants with medium oxidation intensity such as iron ions can be determined.

Iodometric method can be used in a wide pH range, as long as the pH is less than 9, and generally there is no need to adjust the pH value (indirect iodometric method should be careful not to be too acidic, and thiosulfate ions are unstable under acidic conditions). Generally, the adjustment of pH is to add acid directly, and what acid to add and how much to add should be judged according to the specific situation.

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