ナイルブルーによるオレイン酸ナトリウムの比色定量法

非硫化鉱物に対するオレイン酸ナトリウム吸着量測定法

抄録

The spectrophotometric determination method of sodium oleate, which was developed by R. Goiffon and M. Couchoud, has been modified to determine the amounts of sodium oleate adsorbed on nonsulfide minerals.
The method by R. Goiffon and M. Couchoud was based on a fact that sodium oleate prevents the color change of Nile blue solution from blue to red at pH 11. On the other hand, the new method is founded on a phenomenon that sodium oleate fades the blue color of Nile blue solution at pH 8. The difference in absorbance of Nile blue solution at pH 8 between the absence and the presence of sodium oleate is maximum at 594 nm of wave length.
The difference in absorbance at 594 nm increases with the concentration of Nile blue, but it does not vary within several hours. Although the relationship between the difference in absorbance at 594 nm and the concentration of sodium oleate is not a linear one, sodium oleate can be determined at the concentration ranging from 5 x 10^-6 to 3 x 10^-5 mole/ l. Namely, the sensitivity limit of this method is about one tenth of that of the method by R. Goiffon and M. Couchoud.
The difference in absorbance at 594 nm is not affected by the presence of pyrophosphate, phosphate, sulfate, carbonate, oxalate, chloride or nitrate, up to 10^-2 mole/1 and by the presence of silicate ion, up to 10^-3mole/1. In the presence of hexametaphosphate ion, the difference in absorbance at 594 nm increases as hexametaphosphate ion concentration increases up to 10^-4 mole/1 and remains constant at the concentration range from 10^-4 to 10^-2 mole/1. Therefore, in the case where hexametaphosphate ion is contained in sample solutions, sodium oleate can be determined by adding 10^-4 to 10^-2 mole/1 sodium hexametaphosphate to a standard solution.
Based on the above results, the amounts of sodium oleate adsorbed on hematite surface are determined from the difference between initial and equilibrium concentration.