Efficient and reliable fraction collection is obviously of paramount importance in preparative chromatography. In SFC, the separation of CO2 gas from the liquid droplets of co-solvent (which contains the products) is best carried out using a cyclone separator. In systems with CO2 recycle, the cyclones are operated at 50 bar and are periodically emptied into bottles at atmospheric pressure. The slide show opposite shows the details. For other systems, a small cyclone fitted to the collection bottle allows flexible operation together with high collection efficiency (typically 95 to 98% recovery).
Collection with CO2 Recycle
The video shows the version of PIC Solution's Open Bed collection system used in the SFC-PICLab Hybrid 10-100 HT/MS system. The collection head is mounted on a robot with a short, low volume tube leading to the top of the collection tubes. The gas-liquid separation is carried out close to the tube top, eliminating losses and the need for a solvent make-up flow. The head is optionally washed with a user-selected volume of 1 - 2 ml at the end of the collection before it is moved to the next tube.