It is often necessary to determine the net amounts of the participating cupferron in both the aqueous and the organic phases of the extraction system of metals. A precipitation titration of the cupferron was carried out with a standard copper (II) sulfate solution by using Variamine Blue B as an indicator. The procedure is as follows : An aqueous solution containing 3 to 60 mg of cupferron is taken in a 300 ml conical beaker; 3 ml of 2 M hexamethylenetetramine buffer solution (pH 5.5) and 3 ml of 1 M potassium thiocyanate solution are added; the solution is diluted to about 100 ml with water; about 50 mg of Variamine Blue B, which is diluted with sodium chloride in a 1 : 100 weight ratio, is put into the solution; the solution is titrated with 0.01 M copper (II) sulfate solution till the solution turns purplish blue. For the ordinary extraction system involving cupferron, the aqueous phase is separated from the organic phase. According to the procedure presented above, 10 ml of the aqueous phase with the cupferron is titrated. The cupferron in 10 ml of the organic phase is completely transferred to the aqueous phase by shaking the organic phase with 20 ml of the ammonium buffer solution (pH 9.2) for about 30 sec. The buffer solution is then neutralized with hydrochloric acid, and is titrated. The distribution ratios which was the ratio of concentration of cupferron in one of various organic solvents to that in the aqueous phase was evaluated, where cyclohexane, carbon tetrachloride, ethyl ether, benzene, methyl isobutyl ketone, nitrobenzene, chloroform, butyl acetate or ethyl acetate was used as the organic solvent. The decomposed quantity of cupferron in either 1 M hydrochloric acid, 0.5 M sulfuric acid, 1 Macetic acid, or 1 M nitric acid, was also evaluated by determining the undecomposed cupferron in these acids. For the metal chelate-extraction system, the aqueous phase is also separated from the organic phase. In order to determine the cupferron combined with the metal as the cupferrate in 10 ml of the aqueous phase, the cupferron is isolated by adding some chelating agents more tightly combinable with the metals; CyDTA is perferable to Pb, Cu, In, Zn, and Co, while KHF2 to Fe and Al; the pH of the solution is then adjusted to 4.0 with the acetate buffer solution. The uncombined cupferron is extracted twice with each 10 ml of chloroform and reextracted with 40 ml of ammonium buffer solution (pH 9.2) from all the chloroform extracts. This buffer solution is titrated. To determine the cupferron combined with the metal as the cupferrate in 10 ml of the organic phase is shaken for about 5 minutes with 20 ml of ammonium buffer solution (pH 9.2) containing CyDTA or KHF2. The aqueous solution is nutralized with hydrochloric acid, and the pH is adjusted to 4.0 with the acetate buffer solution. The cupferron is extracted with two portions of 10 ml of chloroform and reextracted again from all the chloroform extracts into 40 ml of the ammonium buffer solution (pH 9.2). This buffer solution is titrated. The amounts of cupferron in both the aqueous phase and the organic phase of the chelate-extraction system involving Pb (II), Cu (II), In (III), Fe (III), Ni (II), Zn (II) or Co (II) were determined by the above procedure. © 1973, The Japan Society for Analytical Chemistry. All rights reserved.