Determination of traces of Cs, Li and Rb in rocks by laser enhanced ionization spectrometry without preconcentration

Abstract

Methods for lithium, cesium and rubidium determinations in rock samples using a laser spectrometer for laser enhanced ionization (LEI) with flame atomization were developed. The analyte atoms were excited with one- and two-step schemes from both the ground state and excited states. The schemes yielded detection limits down to 10 −1 pg ml in aqueous solutions. The effect of sample macrocomponents on the analytical signal was shown to be mainly the appearance of additive multiphoton ionization background due to CaOH molecules in the flame. The CaOH ionization-excitation spectrum was produced to permit the selection of the atom excitation schemes which are optimum with respect to the background. The detection limits in rocks are 0.002, 0.001 and 0.5 ppm for cesium, lithium and rubidium, respectively. The absence of chemical interferences permits the calibration to be conducted with aqueous standard solutions. Cesium, Li and Rb determinations were made in a standard magnesian basalt, low-alkali tholeiite basalt, alaskite granite, trap and some other samples. The accuracy of the analysis was tested by the standard addition method and by comparision with the certified values obtained by atomic absorption spectrometry and other techniques, where available.