8 – Multivariate Calibration Methods Applied to Quantitative FT-IR Analyses

Theoretical and practical aspects of short open tubular columns at subambient pressures in gas chromatography/mass spectrometry

Diffuse-reflectance Fourier-transform infrared spectroscopic studies of the stability of aluminum nitride powder in an aqueous environment

Heteropoly oxometalates containing tungsten aŕe active and selective heterogeneous catalysts for the conversion of methanol. The methanol interacts with both peripheral and bulk protons to form protonated methanol which, at higher temperatures, leads to the methylation of the heteropoly anions, the precursor to the formation of carbon-carbon linkages. In contrast, the isostructural molybdenum-containing heteropoly oxometalates when supported on silica are effective for the oxidation of methane. The presence of protons is shown to be essential for the oxidation process, evidently assisting in the production of oxygen vacancies.

Catalysis by solid state oxometalates

Chemical intermediates in heterogeneous catalysis

Photoacoustic Spectroscopy (PAS) is now well-established as a useful technique for obtaining optical absorption spectra from strongly scattering and/or opaque materials which are difficult to study by conventional photometric methods. However, its quantitative application to solids in the UV-visible region has been somewhat restricted by the phenomenon of photoacoustic (PA) signal saturation, in which the intensity of the stronger bands in the spectrum becomes insensitive to changes in analyte concentration. By comparison, with the recent advent of Fourier Transform Infrared Photoacoustic Spectroscopy (FT-IR/PAS), this problem is expected to be much less serious in view of the low absorptivities characteristic of IR bands. Indeed, recent work in our laboratory has shown that when NH3 is sorbed stepwise into the bulk of 12-tungstophosphoric acid, H3PW12O40, the base is quantitatively converted to NH4+ ion, and the calibration curve of the analyte peak area (standardized against a reference band of the substrate) vs. analyte concentration is virtually linear up to stoichiometric loading. With the use of this method, several salts of the parent acid were found to exist in partial (Bronsted) acid form, and adjusted molecular formulae thus calculated were consistent with those obtained in dependently by elemental analysis.

J. B. Moffat

Papers

The Influence of Experimental Conditions in Quantitative Analysis of Powdered Samples by Fourier Transform Infrared Photoacoustic Spectroscopy