A sensitive spectrophotometric method for zinc has been established by reacting zinc with three salicylic acid azo dyes 2-hydroxy (Ia), 2-carboxy (Ib) and 4-(2-arsonophenylazo) salicylic acid (Ic) in universal buffer solution of pH 8.4, 7.1 and 6.0 respectively. The molar absorptivities are 1.16, 1.39 and 1.36 X 10 1/mol.cm at 515, 450 and 525 nm using reagents Ia, Ib and Ic respectively. The formed complexes have the molar ratios of zinc to ligands 1: 1 and 2: 1. Beer's law is obeyed upto 7.19 ppm of zinc whereas the optimum concentration range as evaluated by Ringbom's method is 0.5-7.00 ppm. Sandell sensitivities of the method are evaluated. The method has been used to determine zinc in various pharmaceutical products.
|
