Critical Point Drier

EMS 850 Critical Point Drier

What is CRITICAL POINT DRYING?

Critical Point Drying is so named as it includes, as part of its process, the occurrence known as the continuity of state for which there is no apparent difference between the liquid and gas state of a medium, the surface tension between this interface reducing to zero. This occurs at a specific temperature and pressure with resulting density, and is known as the Critical Point. This condition of zero surface tension can be used to dry Biological Specimens, avoiding the damaging effects of surface tension.

Critical Point Drier cross section In biological specimens we are mainly concerned with the removal of water. Unfortunately, the critical point for water of +374°C and 3212 p.s.i. is inconvenient, and would cause heat damage to the specimen. The most common and convenient transitional medium for critical point drying is Carbon Dioxide (CO₂), which has a critical point at 31°C and 1072 p.s.i. However, it is not miscible with water, and therefore, we have to involve a third medium, commonly Acetone, which is termed the intermediate fluid. We can now convert our transitional fluid, typically CO₂, from liquid to gas without surface tension at the critical point.

The EMS 850 Critical Point Drier is designed for use with CO₂, having first replaced any water in the specimen by a series of dehydration, often in the same fluid such as Acetone, which will also be the intermediate fluid.

(Wet Specimen)WaterAcetone30%100%CO₂ C.P.D.(Dry Specimen)

Critical Point Drier phase changes The specimens for critical point drying are located in the pressure chamber of the EMS 850. The chamber is pre-cooled to allow it to be readily filled with liquid CO2 from a gas cylinder. The chamber is then heated to just above the critical temperature with subsequent critical pressure being achieved. The CO₂ gas is vented through a needle valve, to avoid specimen distortion.

The EMS 850 is fitted with thermoelectronic Heating and Cooling and Temperature control of +5°C on Cooling, and +35°C on Heating. This ensures the critical point is accurately obtained, avoiding excess pressures or temperatures, or the need to rely on pressure relief valves to control pressure during the heating cycle. The chamber is vertical, with top loading, to ensure specimens do not become uncovered during the drying process, with a side viewing port to locate the miniscus for the correct level when initially filling the chamber.

Note: The EMS 850 is now fitted with a fine let down needle as standard and flow gauge is not required.

Features

Vertical chamber with top filling and bottom draining
Normal operating temperature 35°C pressure 1500 psi
Thermoelectric Peltier cooling and heating
Fine control needle valve pressure letdown
Illuminated chamber with side viewing port and protective 'Lexan' shield
Stirrer system for enhanced solvent exchange
Temperature monitoring and control with thermal cut-out protection
Pressure monitoring with pressure relief valve and rupture disc protection
Polycarbonate safety shield

Specifications

Instrument Case	450mm(W)x350mm(D)x175mm(H)
Weight	12Kg
Specimen Chamber	30mm(Dia.)x40mm(H)(Tested to 3000 psi)
Temperature Gauge	0-120°C
Thermal Cut-Out	40°C
Pressure Gauge	0-3000 psi
Pressure Relief	At 1500 psi
Rupture Disc	At 1900 psi
Peltier Cooling/Heating	+5°C to +35°C
Two On/Off Valves	Inlet/Outlet/Cool/Vent Needle Valve Letdown
Supply	115 volts 60Hz (6 amp Max incl pump) 230 volts 50Hz (3 amp Max incl pump)
Services	Requires CO₂ gas cylinder direct connection by high pressure hose. (High pressure hose included with instrument)