Calibration of a reflectance FTIR method for determination of dissolved CO2 concentration in rhyolitic glasses

A technique based upon infrared reflectance spectroscopy is developed as an alternative to the Fourier transform infrared (FTIR) transmission method f or the quantitative measurement of dissolved molecular carbon dioxide in al uminosilicate glasses. The technique has the advantage that only a single s ample surface need be polished, and no thickness measurement is necessary. The reflectance spectrum is analyzed by Kramers-Kronig relations or classic al oscillator analysis to yield the optical constants and the absorption co efficient at 2350 cm(-1), due to the asymmetric stretching (v(3)) vibration of molecular CO2. The value obtained is in excellent agreement with values obtained by the transmission FTIR technique for a suite of rhyolitic glass es. For practical application of the method to rhyolites, an empirical corr elation is developed between the normalized change in reflectance at 2350 c m(-1) and the CO2 content, up to similar to 0.40 wt%. Copyright (C) 2000 El sevier Science Ltd.