LabAdviser/314/Preparation 314-307

Critical point dryer

Leica EM CPD300. The Critical Point Drier (CPD) is used for drying samples for the SEM. The machine uses the fact that at the critical point the solvent can be converted from liquid to gas without crossing the interfaces between liquid and gas (no surface tension) and hence no sample drying artefacts. CO2 is the solvent of choice as its triple point is suitable for biological samples (31°C and 74 bars). The CO2 is not miscible with water; therefore the sample should be dissolved in acetone or ethanol.