A process system adapted for processing of or with a material therein. The process system includes: a sampling region for the material; an infrared photometric monitor constructed and arranged to transmit infrared radiation through the sampling region and to responsively generate an output signal correlative of the material in the sampling region, based on its interaction with the infrared radiation; and process control means arranged to receive the output of the infrared photometric monitor and to responsively control one or more process conditions in and/or affecting the process system.