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

The measurement of large lithium isotope ratios by diode laser graphite fur nace atomic absorption spectroscopy was investigated using a low pressure a tomizer and 2f-wavelength modulation (WM) detection. The measurements were supported by computer simulations. Compared with a direct absorption measur ement, the relative absorption sensitivity for Li-6 is considerably reduced when 2f-WM is performed in the center of the Li-6 D1 fine structure compon ent, 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 calculat ed 2f-WM line strengths were used to deconvolute overlapping lines and enab led the measurement of Li-7/Li-6 isotope ratios as large as approximately 2 000. The Li content of a sample with a strong sodium chloride matrix was de termined by isotope dilution. (C) 1999 Elsevier Science B.V. All rights res erved.