Considerations on the Colorimetric Determination with Dye as a Weak Acid-Weak Base Reaction.

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Considerations on the colorimetric determination with dye as a weak acid-weak base reaction have been described. Other applications in the pharmaceutical fields are suggested. Several equations were derived on which are based the following five items : 1) Some of organic acids may be determined by colorimetry with a basic dye as well as with organic bases. 2) The dye which combined with sample reaches maximum value at a certain pH value. 3) Dissociation constants of a sample and of a dye should preferably be as large as possible. 4) The calibration curve is linear. 5) In general, the ratio of combination of a sample and a dye is nearly in integral ratio, such as 1 : 1.