Ion pairs of 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione with cationic surface-active substances as analytical reagent for determination of copper(II)

摘要

A new organic reagent, 5,5-dimethyl-2-(2-hydroxy-3,5-disulfophenylhydrazo)cyclohexane-1,3-dione (H_2L), was synthesized by azo coupling of diazonium salts of 2-hydroxy-3,5-disulfoaniline with dimedone. The dissociation constants of H_2L were determined by potentiometric titration, being pK_1=5.90±0.03 and pK_2=9.67±0.04. The interaction in systems of H_2L and cationic surface-active substances (CSAS), cetylpyridinium chloride (CPCl), cetylpyridinium bromide (CPBr), or cetyltrimethylammonium bromide (CTABr) was studied in the presence and absence of Cu(II). It was found that the detection limit of Cu(II) using H_2L-CSAS pairs decreases in accord with the stability of associates H_2L(CPCl)_2>H_2L(CPBr)_2>H_2L(CTABr)_2 and their copper(II) complexes Cu[(HL) (CPCl)_2]_2>Cu[(HL)(CPBr)_2]_2>Cu[(HL)(CTABr)_2]_2. The effects of foreign ions and masking substances on the complexation were studied and showed that the reaction of Cu(II) with H_2L in the presence of CSAS is more selective. Based on these observations, a procedure for the spectrophotometric determination of copper(II) in soils polluted by oil, seawater, igneous rock, and nickel-based alloys was developed.