Spectrophotometric Determination of Small Amounts of Palladium(II) with 5, 10, 15, 20-Tetrakrs [4(trimethylammonio)phenyl] porphyrin

Abstract

Complex formation of a water soluble porphyrin, 5, 10, 15, 20-tetrakis[4-(trimethylammonio)phenyl]porphyrin (ttmapp), with palladium(II) was studied. Although the reaction was very slow at room temperature, it was greatly accelerated to yield a Pd(II)-ttmapp complex in the presence of sodium L-ascorbate. When the sodium L-ascorbate concentration was over 0.05%, the reaction proceeded quantitatively in a pH range 3.9-5.9 within 2 min at room temperature. The complex was stable in a pH range 0.2-13. The soret peaks of ttmapp and the Pd(II) complex at pH 1.2 were 432 nm (ε=5.14×10⁵) and 409 nm (ε=3.06×10⁵), respectively. The recommended procedure for palladium(II) determination is as fol lows. To a sample solution containing palladium(II) 0-9.2 μg in a 50 cm³ measuring flask are added 1 cm³ of 2 mol⋅dm^-3 acetate buffer solution (pH =5), 1 cm³ of 9×10^-5 mol⋅dm^-3 ttmapp solution, and 1 cm³ of 10% sodium L-ascorbate solution. After standing for 5 min at room temperature, 5 cm³ of 5 mol⋅dm^-3 nitric acid is added to the solution followed by dilution to 50 cm³. The absorbance at 432 nm is measured against water. Tolerance limits are given for 28 metal ions and 6 anions. No metal ion interfered seriously with the determination. A linear calibration curve was obtained up to 184 ppb of palladium(II) and the sensitivity (Sandell index) was 0.205 ng Pd(II) cm^-2. The relative standard deviation was 0.56%(n=20). The present method exhibits a high selectivity and the highest sensitivity fot palladium(II). This method was applied to the determination of palladium and copper in dental alloy samples.