A Low-cost In-situ Imaging Sensor for Crystallization Monitoring: Stroboscopy Assisted Endoscopy

Since the 2004 FDA initiative the investigation and evaluation of in-situ process analytical methods (PAT) has been significantly intensified. In the class of PAT tools relevant for the monitoring of crystallization processes belong the spectroscopy based methods which monitor the liquid concentration; an exception is the FT-Raman spectroscopy which is also capable to deliver information related to the crystal structure of the solids, thus to the polymorphic forms. The second class of PAT sensors is represented by those which allow the monitoring of the solid phase. From complexity point of view the entry level representative is the turbidity probe, gives a reflective property related solid concentration. More complex sensors are the laser reflectance based ones, which provide rather indirect information about the crystal properties in slurry. The in-situ imaging based sensors have received significant attention during the last decade. Sensor development activities have been reported by companies such as Du Pont, Lasentec/Mettler Toledo, MTS-Düsseldorf and Perdix BV, which propose probe based sensors. Recently also universities have been involved in the design of such probes. Other options are the flow-through cell imaging devices such as the XPT from Prozesstechnik and Qicpic from Sympatec. While the embracement of this technology is remarkable, both at universities and companies, the relatively high acquisition price is certainly a bottleneck for the diffusion of this process monitoring concept in several universities and companies. Therefore, the development of alternative imaging solutions which maintain or improve the information/price ratio is certainly justified and also necessary.