(Over-) critical point drying is a drying method to avoid artifacts that can occur during air drying of biological samples. In this process, the water present in the samples is exchanged for ethanol, for example, in the prefold. The samples are then placed in the drying system. The drying plant exchanges the liquid ethanol with liquid carbon dioxide (CO2), whose critical point is 31.0 °C and 73.8 bar. The sample chamber of the drying system then controls a temperature and pressure above the critical point of CO2. Finally, since the liquid-gas phase boundary no longer exists in the supercritical state, the CO2 can be drained from the sample chamber without artifact formation, since the surface forces that alter sensitive membranes and the like are avoided.
Different sample holders are available to dry powdery samples up to ordinary insects (approx. 1 cm³). The total volume of the sample chamber is 185 mL and can be used for several samples depending on the object shape and size.