Mid-infrared spectroscopy has proved to be a powerful method for the study of various samples and chemical media as found in different industrial processes. In general, the analysis of such samples takes advantage of the fact that multiple analytes can be quantified simultaneously and rapidly without the need for additional reagents. When compared to near-infrared spectroscopy, for which quartz fiber probes can be successfully applied, the application of previously used mid-infrared fiber materials was restricted due to deficiencies with regard to their optical transmission and mechanical properties. Progress in the quality of infrared transparent silver halide fibers and their extrusion with different cross-sections enabled us to construct several flexible fiber-optic probes of different geometries which are particularly suitable and inert for process monitoring. Transmission and attenuated total reflection measurement techniques have mainly been employed for the analysis of liquid and gaseous media. One larger field, for which results are reported, is chemical reactor monitoring. Other applications are concerned with bio-reactor monitoring, or quasi-continuous measurements for the food industry. Infrared spectroscopic cosmetic assays for determining the chemical composition of skin-care formulations are a further promising field of application, for which an example is given.
