FTIR.-Absorbance spectra were recorded on a BioRad FIS-60A spectrometer
equipped with a deuterated triglycine sulphate (DTGS) detector using the Digilab
attenuated total reflectance (ATR) accessory with a ZnSe crystal at an angle of incidence
of 45”. Samples, of particle sizes below 125 pm, were measured directly after pressing
the samples on the crystal. The spectra, obtained at a resolution of 4 cm-‘, were
averages of 400 scans, and were recorded against an empty cell as background. Spectra
were baseline-corrected at 1200 and 800 cm-’ by drawing a straight line. All spectra
were deconvoluted using techniques described by Cameron and Moffat [31] and
modified for use on the FTS-60A. A half-bandwidth of 15 cm-’ and an enhancement
factor of 1.5 with triangular apodization were employed. Intensity measurements were
performed on the deconvoluted spectra by recording the height of the absorbance bands
from the baseline. Instead of single-intensity measurements, ratios of absorbance
intensities were used to compensate for path-length differences between samples that
might arise from incomplete coverage of the ATR crystal.