Ultraviolet spectrophotometric determination of bismuth by perchloric acid

Abstract

This report deals with the results of an investigation of the ultraviolet spectrophotometric determination of bismuth using perchloric acid as a reagent.
Absorption spectra of bismuth perchlorate under various concentrations of perchloric acid were obtained, and it was observed that the bismuth ion (hydrated) showed the maximum absorbance at 222 mμ (Fig. 1). Absorption spectra of bismuth salts in weak acidic medium (pH 13) were also measured, and it was observed that two isosbestic points exist; and it was presumed that the change of spectra with pH may be attributed to the change of equilibrium between bismuth aquo ion and hydroxo complex ion (Fig. 2 and 3). In the spectrophotometric determination, the calibration curves were made by the usual and by the differential method; and then the effects of the temperature and diverse ions were investigated. The following results were obtained:
1. The use of a wave length of 222mμ and a 1.0N perchloric acid was chosen as the working conditions.
2. Beer's law is followed up to 15 ppm by the usual method, and up to 70 ppm by the differential method. The errors in these were found to be 0.110.18% (Fig. 4 and 5).
3. The temperature coefficient of absorbance was 0.0009/°C.
4. The presence of iron(III) gave a considerable positive error.
5. It was found that the specific absorption spectrum appeared when aluminum ion was present with bismuth, and it was presumed that a specific interaction occurs between the two ions in the perchloric acid medium (Fig. 6).
Thus, the proposed method has the features of not requiring a special coloring reagent as in the organic one, besides having the merits of simplicity of operation and of giving good accuracy of results.