Complexation and determination of palladium (II) ion with para-Cl-phenylazo-R-acid spectrophotometrically

The complexation of para-Cl-phenylazo-R-acid azo dye with Pd(II) has been studied spectrophotometrically. Protonation constant (pKa) of the ligand has been calculated and the stability conditional constants of para-Cl-phenylazo-R-acid ligand with palladium ion has been determined at a constant temperature (25.0°C), where the molar ratio of this complex is 1:1 (metal:ligand) with log β1=3.75, and 1:2 with log β2=8.55. Solid complex of para-Cl-phenylazo-R-acid has been prepared and characterized on the basis of elemental analysis and FTIR spectral data. A procedure for the spectrophotometric determination of Pd(II) using para-Cl-phenylazo-R-acid as a new azo chromophore is proposed where it is rapid, sensitive and highly specific. Beer’s law was obeyed in the range 0.50–10.00 ppm at pH 5.0–6.0 to form a violet–red complex (ε=7.7×104 l−1 mol−1 cm−1 at λmax=560 nm). Metal ions such as Cu(II), Cr(III), La(III), Yb(III), Y(III), and Rh(III) interfere with the complex. Ammonium salt of trimellitic acid is used to precipitate some of the interfering ions and a scheme for separation of Pd(II) from a synthetic mixture similar in composition to platinum ore or deposit was made.