Spectrophotometric determination of strong chelating agents in water by the ligand exchange extraction of copper (II) chelate with sodium diethyldithiocarbamate

Abstract

Determination of total strong chelating agents in water and waste water was performed. The method consisted of the dissolution of equivalent copper (II) oxide with the chelating agents to be determined and the subsequent spectrophotometry of dissolved copper (II) with sodium diethyldithiocarbamate (NaDDTC). A sample solution containing strong chelating agents (less than 2 × 10^-6 mol), 3 cm³ of 0.05 mol dm^-3 CuSO₄ and 2 cm³ of saturated NaCl were put into a beaker. After the pH was adjusted to 10.0 ± 0.2 with 0.2 mol dm^-3 Na₂CO₃, the solution was evaporated to about 40 cm³. To obtain a good coagulation of the precipitate, 2 cm³ of 0.05 mol dm^-3 KAI (SO₄)₂ was added. After cooling the sample was transferred into a 50 cm³ measuring flask and diluted with water. After centrifuged for 30 min, 25 cm³ of the supernatant was taken into a separating funnel which contained 2 cm³ of 0.05 mol dm^-3 NaDDTC and 10.0 cm³ of CCl₄. Then the mixture was shaken for 10 min and the absorbance of the CCl₄ phase was measured at 436 nm. Usual foreign cations and anions did not interfere.