Brian M. Lynch

Attenuated Total Reflectance Spectra of Colloidal and Particulate Silica Samples in Aqueous Media

We have measured and compared ATR/FT-IR spectra of aqueous dispersions of colloidal silica, and aqueous suspensions of particulate silica, over ranges of bulk concentrations using CIRCLE® and Contact Sampler™ cells. Procedures are described for quantitative analyses of each silica type. Detection limits are approximately 0.001% for the particulate species. The spectra of particulates are distorted by refractive-index effects to low frequency of the main analytical bands around 1090 cm-1, but the distortions are proportional to concentration and do not interfere with the precision of analyses. We recommend either ATR cell, but the Contact Sampler™ is more convenient.

PROPOSED TECHNIQUES TO ENHANCE VIBRATIONAL SPECTRA OF COALS: ATR CONTACT SAMPLING, SOLVENT DISSOLUTION, AND MICROSPECTROMETRY

Publisher Summary This chapter presents techniques to enhance vibrational spectra of coals. The mid-infrared spectra of fossil fuels typically show broad features requiring curve-resolving manipulations to distinguish the presence and proportions of differing functional entities. Two accessory infrared techniques, photoacoustic spectroscopy (PAS), and attenuated total reflectance (ATR) spectroscopy, involve surface-sensitive signal transduction. The chapter focuses on ATR and describes a method to decrease the problems of peak broadening and overlapping of characteristic vibrations existing with infrared studies of solid coals. The chapter presents certain examples of matrix isolation in solution. Attenuated total reflectance accessories such as the Contact Sampler™ give excellent quality infrared spectra of dilute aqueous salt solutions, colloidal dispersions, and fine suspensions under anion-isolation conditions. The Contact Sampler™ device may be used to examine solid coal powders. Thus, fine grinding of a sample of Western Canadian bituminous coal preferentially reduces the particle size of the inorganic component, which coats the exterior of the coal particles.

Photoacoustic Infrared Fourier Transform Spectroscopy of Thermally and Chemically Modified Coals

Over the past four years, Photoacoustic Infrared Fourier Transform (PAIFT) spectra of coal samples have been acquired in our laboratory for a data base now amounting to some 6000 spectra. Various preliminary reports of our results have been presented (1-5).