match the instrument capabilities to the expected applications. Instrument speed and resolution are the first parameters to consider. They generally depend on the control of interferometer mirror speed and the scan range. Sensitivity depends largely on the choice of detector, whether cooled or room temperature. However, instrument noise may depend on the region of the spectrum being acquired. 1T-IR presents the· greatest noise-reduction advantages in the mid-IR and far-IR regions of the spectrum. The advantage isn't as great in the near-IR region, Wilkins says, because in addition to detector noise there is significant source noise. Source noise can actually be made worse by FT modulation because the interferometric conversion can spread the error from a narrow band all over the derived spectrum. The UV-vis region is strongly limited by source noise. Another consideration is the type of sample that will be run in the instrument and what kinds of sample cells, interfaces, or accessories will be needed. GC/FT-IR requires a gas flow-through tube; liquids may require various types of specialized sample cells for techniques such as attenuated total reflectance, which is often used for analyzing aqueous solutions. Solids may be accommodated either by the traditional method of grinding them with KBr and pressing the mixture into pellets or by methods such as diffuse reflectance, PAS, or IR microscopy, all of which may be used to analyze an intact sample in situ. These three methods are growing in popularity, especially for products such as semiconductors and coatings. IR microscopy has also been used to increase sensitivity for GC detection. The eluent is trapped on ZnSe, an IR-transparent and water-inert support material, and the IR beam scans down and through the sample for chemical imaging. Wilkins says the future of FT-IR instrumentation may well be a higher degree of specialization to accommodate the increase in routine use, particularly on industrial process lines. Dedicated instruments for a particular routine application are cheaper to make and require fewer adjustments than general-purpose spectrometers that may be required to perform a large variety of hyphenated or advanced techniques. For routine methods, he says, "Eventually the trade-off will be cost versus performance. Specialized is the way to go—there's no point in paying for extra features that you aren't going to use." Deborah Noble
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