Determination of lithium in mineral water samples by X-ray fluorescence spectrometry.

A method is shown for the determination of trace amounts of lithium by X-ray fluorescence spectrometry (XRF) in natural mineral waters with various therapeutic effects originating in Poland. The method is an expansion of X-ray fluorescence spectrometry applications to the determination of a very light element. The direct determination of lithium by XRF is practically impossible due to the extremely low fluorescence yield and long-wavelength characteristic radiation of such a light element. The lithium is determined via iron after precipitation with stoichiometric potassium lithium periodatoferrate(III) complex. The solution obtained after dissolving the complex was pipetted onto Mylar foil for XRF analysis. As little as 1 μg Li may be determined with this method. Accurate lithium determinations can be obtained using simple calibration samples requiring only pipetting Fe solution in the range 8.0-28.0 μg onto the Mylar foil. The prepared samples are thin, which allows the errors resulting from self-absorption or matrix effects to be neglected. Our studies give essential information about the quality of the analyzed waters.