Oxygen isotope analysis of quartz by neodymium–yttrium aluminium garnet laser–fluorination

Abstract

Oxygen isotope measurements of powdered quartz samples have been performed following liberation of oxygen by a fluorination reaction induced by heating the sample with radiation from a neodymium–yttrium aluminium garnet laser (wavelength 1064 nm). The fluorination reagent used was chlorine trifluoride. In order to effect absorption of the laser energy by the sample, nickel powder was mixed with the quartz. Sodium chloride was also mixed with the sample, which is important in reducing the incidence of problematic species generated during fluorination. The amount of sample analysed was normally less than 1 mg. Analytical parameters such as the choice of chemicals for flux, flux-to-sample ratio, amount of nickel powder, pressure of chlorine trifluoride and power of the laser were examined in detail using a quartz standard. Sodium chloride has proved to be a better flux than potassium chloride, not showing any strong dependence of δ¹⁸O with any of the parameters and producing oxygen yields ranging from 70 to 90% of the expected value. Although the δ¹⁸O values obtained by this technique, with 1 mg samples, were lighter than expected by about 0.8‰, the precision was good (0.1‰), enabling a correction to be applied to the measured value.