Ultramicrosampling in Infrared Spectroscopy Using Small Apertures

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Abstract
A method for obtaining IR spectra from submicrogram quantities of polymeric materials, with minimum sample preparation, using small apertures, is described. Spectra were obtained for thin films and fibers with the use of three FT-IR instruments: a research-grade spectrometer and two low-cost “bench top” spectrometers. The quality of the spectra obtained are evaluated in terms of the instrument type, detector, accumulation times, and the dimensions of the aperture. A usable spectrum was obtained from as little as 2 ng of poly-(ethylene terephthalate) with the use of the research-grade instrument, which employed a cooled MCT detector. Spectra were readily obtained from the low-cost instrument with the use of a standard TGS detector from ∼500 ng of material and were of sufficient quality for identification purposes. It would seem that energy limitations, diffraction effects, and long accumulation times would limit the utilization of apertures of less than 10 microns in diameter.