Monitoring Pharmaceutical Solvent Drying Processes Image Credit: Thermo Fisher Scientific – Environmental and Process Monitoring Instruments In a number of pharmaceutical processes, one of the key stages is the partial or complete removal of a solvent, or solvents, from an intermediate or product. The drying process needed can happen in a number of process vessels, including tray dryers, vacuum dryers, and rotary dryers. The success of the drying process was measured upon conclusion by simply taking a sample for laboratory analysis until now. Organic solvent concentrations in the active pharmaceutical ingredient (API), or intermediate, were measured by gas chromatography; residual water levels were usually investigated by carrying out a Karl Fischer titration.