Application of the 2f-wavelength modulation technique for the measurement of large lithium isotope ratios by diode laser graphite furnace atomic absorption spectroscopy

摘要

The measurement of large lithium isotope ratios by diode laser graphite furnace atomic absorption spectroscopy was investigated using a low pressure atomizer and 2f-wavelength modulation (WM) detection. The measurements were supported by computer simulations. Compared with a direct absorption measurement, the relative absorption sensitivity for ~6Li is considerably reduced when 2f-WM is performed in the center of the ~6Li Dl fine structure component, but it will be enhanced, when the center of modulation is tuned to the maximum in the red wing of the 2f-WM line profile. The results of calculated 2f-WM line strengths were used to deconvolute overlapping lines and enabled the measurement of ~7Li / ~6Li isotope ratios as large as approximately 2000. The Li content of a sample with a strong sodium chloride matrix was determined by isotope dilution.