Nira Symposium July 7-8, 1982

Although Near Infrared Analysis (NIRA) as a technique can be traced back to the late 19th century, the first commercial instrumentation (Cary 14) was made available in the mid 1950's. Significant growth in the number of NIRA instruments used did not occur until the 1978-1982 period. During this time, the number of units utilized has grown at an annual compounded growth rate of well over sixty per cent. This phenomenal growth rate has been caused by: a) the enthusiasm and dedication, by leading researchers, of this technology; b) the financial resources of leading companies who have been convinced of the future market potential of NIRA; and c) by progressive users of the technology who have learned that NIRA methods, when applicable, can provide solutions more conveniently and more accurately than any other means of analysis. The number of industries presently utilizing this technology are in excess of 75 and continue to accelerate rapidly. The number of NIRA instruments installed worldwide is estimated to exceed 5,000. ABSTRACT Near infrared reflectance spectrometry has the main advantage that the detectors which are used are both very sensitive and operate at room temperature. The instrumentation for NIR is therefore very simple and rugged. On the other hard, mid infrared detectors are less sensitive than PbS and many have to be cooled, so that more sophisticated instrumentation is needed. Most mid infrared reflectance spectra have been measured using an FT-IR spectrometer with mercury cadmium telluride detection. Calculations will be shown to demonstrate that the use of an interferometer does not significantly improve the sensitivity of NIR measurements but is essential for good mid infrared data. Mid infrared reflectance should allow three types of sample to be studies which are not readily amenable to NIR analysis; (a) those with minor components absorbing in spectral regions where the major components do not have strong bands; (b) samples whose overtones and harmonics are too weak to permit near infrared detection; (c) samples which are too "black" for NIR analysis. Examples will 'be shown for which mid infrared analysis should be useful; these include the analysis of pharmaceutical compounds, both raw materials and final products, and coals. There are several problems intrinsic to diffuse reflectance spectrometry which appear to be more serious for mid infrared than for near infrared spectrometry. These include the nonlinearity of plots of the reflectance metric, whether this be –log 10 R or the Kubelka-Munk …