Fig. 8. Polymer pellets in sample cup placed above desiccant cup.

V. FTIR-PAS METHODS FOR SPECIFIC ANALYSES

This section provides detailed information on how to measure spectra of important classes of samples and how to process and interpret photoacoustic spectra. All of the spectra were measured at a resolution of 8 cm^-1, maximum source aperture, and with a helium gas atmosphere in the detector. The spectra have been normalized by computing a ratio of the sample spectrum to the spectrum of an MTEC carbon black standard unless otherwise stated.

A. Qualitative Analysis of Macrosamples

1. Polymer identification by computer search

FTIR-PAS allows spectra of polymers in powder, pellet, sheet, and chunk form to be directly measured and searched against standard commercial spectral libraries. Figs. 4 and 8 show a chunk and pellets, respectively, that have been placed in the sample holder for analysis. Figs. 9-12 show commercial library spectra¹⁵ and photoacoustic spectra of four common polymers. The photoacoustic spectra have been converted to transmittance to be compatible with the Perkin-Elmer commercial SEARCH^TM program. Because different polymer specimens were used when the library and photoacoustic spectra were measured, there are some variations between them. The degree of band saturation at low values of transmission vary from spectrum to spectrum but is generally slightly more pronounced in the photoacoustic spectra since the library samples were in the form of thin films.