ANALYTICAL APPLICATION OF PORPHYRINS .5. SPECTROPHOTOMETRIC DETERMINATION OF ULTRAMICRO AMOUNTS OF CADMIUM WITH ANIONIC PORPHYRINS IN THE PRESENCE OF PYRIDINE

It has been found that organic bases such as pyridine, δ-picoline or imidazole accelerate considerably the complexation of cadmium (II) with α, β, γ, δ-tetrakis(4-carboxy phenyl) porphine [T(4-CP)P] or α, β, γ, δ-tetrakis(4-sulfophenyl)porphine [T(4-SP)P] in aqueous solution. In 0.4% pyridine solution adjusted the pH to about 9, the complexation of cadmium (II) with T(4-CP)P is completed almost instantaneously and that with T(4-SP)P in lOmin even at room temperature. On the basis of these observation, two practical spectrophotometric methods for the determination of cadmium at the ppb level have been developed : one method using T(4-CP)P in the presence of pyridine and the other using T(4-SP)P instead of T(4-CP)P have been established. Straight-line calibration curves were obtained up to about 250 ppb of cadmium for both the methods. The sensitivity for 0.001 absorbance was 0.246 ng Cd/cm2 the T(4-CP)P method and 0.256 ng Cd/cm2 in the T(4-SP)P method. Interferences from other ions and salts in the T(4-CP)P method were examined and the tolerance limit was shown for each of them. Only zinc(II) interfered with the determination. © 1979, The Chemical Society of Japan. All rights reserved.