Abstract: A system for detecting the presence of contaminants in a flowing stream of supercritical fluid. A sample stream is removed from a flowing stream of supercritical fluid and subjected to reduced pressure in a contaminant measurement zone. The supercritical fluid turns into gas at the reduced pressure with the contaminants remaining in a non-gaseous form. An attenuated total reflectance plate is used to spectrophotometrically detect the presence of the non-gaseous contaminants which deposit on the surface of the plate within the contaminant measurement zone. The system is useful for spectrophotometrically detecting the presence and identity of contaminants in supercritical fluids and is useful in monitoring both cleaning processes and extraction processes.