Use of arylidenerhodanines for the determination of Cu(II), Hg(II) and CN−

Arylidenerhodanines have been synthesized as reagents for the spectrophotometric determination of Cu(II) and Hg(II). 5-(4-Hydroxy-3-methoxybenzylidene)rhodanine (HMBR) and 5-(3,4-dihydroxybenzylidene)rhodanine (3,4-DHBR) form colored complexes of maximum absorbance with these metal ions, in the presence of polyvinylpyrrolidone (PVP) and cetyltrimethylammonium bromide (CTAB), respectively. In the pH ranges 9.7−10.6 and 9.6−10.6, the molar absorptivities of Cu- and Hg-HMBR-PVP systems are 4.55 × 104 and 9.52 × 104 l mol−1 cm−1 at 535 and 525 nm, respectively. The corresponding Cu- and Hg-3,4-DHBR-CTAB ternary complexes are formed in the pH ranges 9.8−10.4 and 9.9−10.8 with molar absorptivities of 5.4 × 104 and 1.05 × 105 1 mol−1 cm−1 at 562 and 535 nm. The effect of reagents, PVP and CTAB concentrations, pH, standing time and diverse ions have been studied. The ionization constants of reagents, and the stoichiometry and stability constants of complexes were evaluated. The proposed methods have been used to determine copper in aluminium metal, aluminium and gold alloys, steels and waters, and to the determination of mercury in muscle tissue of Mackerel fish. Moreover, indirect methods for determining CN− have been developed, based on measuring the decrease in absorbance of Hg-HMBR-PVP and Hg-3,4-DHBR-CTAB systems by the addition of CN−. The calibration graphs are rectilinear for 0.02−0.40 ppm of CN−. The methods have been used to determine total cyanide in industrial wastewater.