The Spectrophotometric Determination of Palladium with Chromazurol S

Abstract

Abstract A simple spectrophotometric method for the determination of palladium was studied, using chromazurol S as a reagent. Palladium (II), in a slightly acidic or a nearly neutral solution, reacts with chromazurol S to form blue or red complexes, each consisting of one molecule of the reagent and one atom of palladium. The maximum absorption wavelengths of blue and red complexes are respectively 596 mμ and 500 mμ, against the reagent blanks. The color development of the blue complex formed in a slightly acidic medium is more sensitive, therefore, it was applied to the spectrophotometric determination of palladium. Several conditions for the color development were investigated; a calibration curve was made under the optimum conditions; and the influences of coexisting ions were also investigated. The blue complex gives a maximum absorbance at 596 mμ in the pH range from 4.3 to 5.3. About a 2-fold excess of the reagent over the palladium concentration is necessary in order to obtain the maximum color intensity. The color development is almost instantaneous, and the absorbance remains constant for at least 4 hr. The order of the addition of reagents has no effect upon the absorbance. The color system obeys Beer’s law over the concentration range up to 70 μg of palladium per 10 ml. The molar extinction coefficient at 596 mμ is 18600, which corresponds to a sensitivity index of 0.0058 μg/cm2 for an absorbance of 0.001. Sulfate, chloride, fluoride, phosphate and acetate ions do not interfere with the color reaction. Thiosulfate ion and polycarboxylate ions such as oxalate, citrate and EDTA etc. bleach the color of the complex. Cations such as Sc(III), Y(III), Th(IV), U(VI), Be(II), Al(III) and Cu(II) ions cause an over-estimation of palladium; the interference by these cations except copper, however, could be eliminated by the addition of appropriate amounts of either sodium fluoride or sodium phosphate as masking agent.