Measurement of Li-7/Li-6 isotope ratios by resonant Doppler-free two-photon diode laser atomic absorption spectroscopy in a low-pressure graphite furnace

Resonant two-photon absorption spectroscopy with laser diodes is applied fo r isotope selective analysis of Li-6 and Li-7 in a low-pressure graphite fu rnace atomizer. The detection limits for both isotopes and the selectivity in form of the relative absorption sensitivity for Li-6 are determined unde r large optical saturation conditions with co-propagating laser beams as we ll as for small optical saturation with counter-propagating beams. The infl uence of collisional energy transfer and radiative processes are studied an d taken into account. Absolute detection limits lower than 1 pg are found f or both isotopes. The selectivity for Li-6 is approximately 4.8 x 10(3) in the high saturation and approximately 4.6 x 10(4) in the low saturation cas e. The isotope ratio of a highly Li-7 enriched stock solution was measured and found to agree with previous results obtained by wavelength modulation diode laser atomic absorption spectrometry of the Li resonance lines. (C) 2 000 Elsevier Science B.V. All rights reserved.