Principle and characteristics of critical point dryer

The critical point dryer refers to the surface tension of the medium when the drying medium is converted between liquid and gas. The surface tension of the medium is zero (this point has a specific pressure and temperature, called the critical point), and the damage of the zero surface stress on the biological sample is greatly reduced. A dryer made using this principle is a critical point dryer.

We often dehydrate biological samples, but it is inconvenient and easy to damage the sample at the critical point of water (+374 ° C and 3212 psi). The critical point of CO ₂ is +31 ° C and 1072 psi, which is very easy to operate. However, CO ₂ is not easily mixed with water, and acetone is usually used as an intermediate medium. When CO _{2 is} converted from a liquid to a gas, the surface tension at the critical point is zero.

The EMS850 Critical Point Dryer uses CO ₂ to replace all of the water in the sample through a series of operations. We often use an intermediate medium such as acetone. Such as: (wet sample) water - acetone - 30% - 100% - CO ₂ - CPD - (dry sample). The biological sample to be dried at the critical point is placed in the EMS850 pressure chamber, and the chamber is pre-cooled so that the cylinder is easily filled with liquid CO ₂ . The pressure reaches a critical point and the chamber is heated just above the critical point temperature. At this point, the CO ₂ gas is released through the needle valve to avoid sample damage.

The EMS850 uses semiconductor heating and air-cooling to control the temperature of the drying chamber. The temperature is controlled between 5 °C and 35 °C. This ensures that the critical point is accurately obtained and that excessive pressure or temperature is avoided. The pressure is controlled by a pressure reducing valve during the heating cycle. The vertical cavity and top loading ensure that the sample is not covered during the drying process and has a surveying window.