Small-scale analyses of volatiles in minerals and glasses provide
information on how volatiles influence high-temperature geologic
processes and low-temperature alteration processes. Four techniques for
determining the C-O-H volatile contents of andesitic glasses are
compared: manometry, secondary ion mass spectrometry, micro-Fourier
transform infrared spectroscopy, and a technique where the H2O content
is calculated using the difference between electron microprobe analysis
totals and 100% sum. We present a method to determine the H content of
a wide range of glass and mineral compositions using secondary ion mass
spectrometry and a model for calibration factors. The extinction
coefficients for H-O volatile contents in intermediate composition
synthetic glasses are determined, and it is demonstrated that C-O
speciation changes as total H2O content increases, with molecular CO2
decreasing, CO32- increasing, and carbonate peak splitting increasing.
For glasses with low H2O content and oxy-substituted minerals, the
methods of choice for volatile analysis are secondary ion mass
spectrometry or micro-Fourier transform infrared spectroscopy.