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Post-column Method of Organic Acids

The post-column method of organic acids uses the reagent (Shodex ST3-R), the mixing module and the visible detector of 430nm wave length . The detector detects the color which comes from organic acids. Organic acids in a sample are separated by the column for organic acid analysis (RSpak KC-811) using acidic solution (ex. perchloric acid) as the eluent. The pH indicator in the reagent (ST3-R) is adjusted to be dissociated state (I-+H+). When the pH indicator and the eluted solution from the column are mixed in the mixing module, the acidic substances (organic acids) will be free state (AH->A-+H+) and the pH indicator generate color by the reaction of I-+H+->IH.
Right figure shows the spectrum of the pH indicator.