Flame atomic emission determination of rubidium in mineral and well waters using methane–air flame as excitation source

The rubidium content of some well and mineral waters has been determined by flame atomic emission spectrometry using the methane–air flame. Effects of the flame and of instrumental parameters (flame composition, the observation height, spectral bandpass of the monochromator) on the emission of rubidium in methane–air flame was studied and optimized. The best results were obtained using the 780.0 nm rubidium line at the observation height of 11 mm, with the flame composition of 1.12 (relative stoichiometric units, RSU) and the slitwidth of 0.6 mm. The effect of Na, K, Ca and Mg on the emission of rubidium was studied too. The detection limit of 2.3±0.9 μg l−1 was obtained, in the presence of 200 mg l−1 Cs, at a significance level of 0.05, using the two-step Neyman–Pearson criterion. The rubidium content of waters has been determined directly using both external calibration curve and standard addition method. With background correction results agree between these two methods.