抄録
In diethyl-p-phenylenediamine (DPD) method, used for the measurment of residual chlorine, KMnO4 solution is used as the colorimetric standard solution but is unsuitable in field measurement because of its unstability. The modified method described here indicates that Phenol Red solution can be used as a colorimetric standard solution because it is stable and its color tone is similar to tho colored solution of DPD. DPD reagent is a mixture of a buffer reagent and DPD in tablet or powder form, and becomes colored during storage, but it was found that a powder made separately is not colored even in long storage. Standard method of the American Public Health Association, etc. describes DPD method in detail, and directs the addition of disodium ethylenediaminetetraacetic acid (EDTA) to the reagent because it prevents coloring. In this procedure, the reagent is added to the sample water, and the reverse addition creates an error. This wrong order of addition often occurs in field measurement. The present method can prevent the error as a result of the use of cyclohexanediaminetetraacetic acid (CyDTA) instead of EDTA.
