Spectrophotometric Determination of Trace Amounts of Copper in High-Purity Rare Earth with α,ß,γ,δ-Tetra-(4-Trimethylammonium-Phenyl) Porphine

Abstract

High-purity rare earth such as Y2O3 is a common material for the preparation of various solid-state luminescent materials. Since the luminescence is affected by the presence of trace copper impurities, attention has recently been given to the spectrophotometric determination of trace amounts of copper with porphyrin as spectrophotometric reagents, because of their high sensitivity and stability (1–3). In this paper, the complex reaction of water-soluble α,s,γ,δ-tetra-(4-trimethylammoniumphenyl)porphine T(4-TAP)P with copper(II) has been studied. This compound was synthesized according to the method proposed by Krishnamuthy (4). It was found to be a highly sensitive and selective reagent for the direct spectrophotometric determination of copper at ppb level. The soret band of the reagent was laid at 431 nm, which was well separated from that of the complex (411 nm). Apparent molar absorption coefficient of the reagent and sensitivity for 0.001 absorbance were 4.7×105 1 mol−l cm−l and 0.13 ng Cu cm−2, respectively, and that of the complex were 4.0×105 1 mol−l cm−l and 0.16 ng Cu cm−2, respectively (Fig. 1). The interference of many ions and salts has been examined and found to be minimal. Large amounts of rare earths do not interfere with the determination.