Determination of Trace Amounts of Rubidium by Graphite Furnace Atomic Absorption Spectrometry and Its Application t o the Analysis of Natural Waters

Abstract

The procedure for the determination of trace amount of rubidium by graphite furnace atomic absorption spectrometry (GFAAS) has been examined and applied to the analysis of some natural waters including rain, lake, pond, river and hot spring water. The optimum spectral conditions for the rubidium determination are as follows: wavelength, 780.0 nm; spectral bandwidth, 1.4 nm (low); absorption signal, peak area. The t emperatures of ashing and atomization, and interferences of several acids and of coexisting major components to the absorbance of 10 ppb rubidium were examined. The most appropriate temperatures of ashing and atomization were found to be 400 °C and 1900 °C, respectively. Nitric acid and hydrochloric acid showed no significant influence on the absorbance of rubidium. The chloride interference could be suppressed by the addition of nitric acid and sodium ion into the sample solution; 0.2 mol dm-3 of nitric acid and 100 ppm of sodium ion overcame the interference up to 100 ppm of chloride. In this procedure, 20 id of the sample solution was used for one measurement and five measurements were repeated for each sample. The finally determined values were the averages of three data after the highest and lowest values were excluded. Relative standard deviation was less than 1.5% (n=40). The procedure was applied to the determination of rubidium in natural waters. Reliability of the data was examined by the addition of a certain volume of a standard rubidium solution into a natural water Whose rubidium content was already determined. The amount of rubidium in the water thus formed reached 96 to 99% of what was expected from the calculation, indicating that the data are fairly reliable. As for the samples with high rubidium contents, the results determined by the present procedure were in good agreement with those obtained by flame atomic absorption spectrometry. The detection limit was 0.03ppb (S/N = 3).