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A packaging material was microtomed cryogenically and examined by optical microscopy. A photomicrograph of a cross section having a thickness of about 100 (xm is shown in Figure 9, which suggests seven layers, as illustrated in Figure 10 (not to scale). Both ATR and transmission infrared techniques were employed in the analysis using a 32X objective. The functionality of layer A was determined by transmission IR after delamination at the layer B/layer C interface. Layer B, which remained attached to layer A, was then examined by ATR-IR. The aluminum layer E dissolved in about a minute with a strongly basic solution made by dissolving one pellet of KOH in a few drops of deionized water. The exposed adhesive prime layers D and F were rinsed with deionized water and analyzed by using the IR(xs ATR objective. Finally, transmission spectra of layers C and G were obtained after the aluminum layer was removed. Note that layers A, C, and G were thick enough to examine normal to the surface of the cut so that components in the other layers caused no spectral interference.

An example of a problem solved by employing RAIRS involved the identifi­ cation of a smudge on a metal surface. The advantage of the IRJULS microscope in this analysis was the ability to move rapidly from one region to another until a sample of the proper thickness could be located. Once the critical spot was