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White Paper
COMPARING HIGH PRESSURE FREEZING
PRINCIPLES
related instruments: EM ICE
2
COMPARING HIGH PRESSURE FREEZING
PRINCIPLES
The EM ICE is the only High Pressure Freezer on the market using a pneumatic freezing principle and no alcohol in the pressure chamber.
All other suppliers are using a hydraulic freezing principle and alcohol in the pressure chamber. This white paper offers a short comparison of
the two principles and shows the advantages of the pneumatic freezing principle of the EM ICE.
Hydraulic freezing principle
1. Unpressurized LN
2
is waiting in tube
2. Pressure chamber is lled with alcohol
3. For pressurization:
> The hydraulically driven piston pushes LN
2
towards the chamber to replace the alcohol
> The alcohol ow is blocked by the exit nozzle and the full pressure of 2100 bar builds up before pressurized LN2 comes in contact
with the sample
4. Cooling by LN
2
only after the alcohol has been pushed out
Advantages
> Small piston diameters
> Timing of pressure / temperature can be inuenced by alcohol volume
> Less abrupt pressurization
Disadvantages
> High system pressure (320 bar) with large pressurized gas volume for pressure stability imposes regular safety inspection
> Regular change of hydraulic uid necessary
> Cooling rate inuenced by the turbulence at the ethanol/LN
2
interface
> Sample may be exposed to ethanol before freezing
> Alcohol residues after freezing
Pneumatic freezing principle
1. LN
2
gets compressed by a pneumatically driven piston in front of a valve
2. Samples sits dry in pressure chamber
3. For pressurization:
4. By opening the valve, a pressure wave rushes into the chamber, compressing the air surrounding the sample. The air is warming up,
preventing the sample from cooling down while pressure is established
5. The pressure wave is stopped by the exit nozzle causing pressurization of the chamber
6. Cooling starts immediately in the wake of pressurization
7. Pressurized LN
2
volume is calculated to keep the pressure up to around 360 ms
Advantages
> Maximum 10 bar system pressure and no hydraulic oil
> Fastest pressure increases in pressure chamber
> Sample is cooled immediately after pressurization (minimum pressure induced artefacts)
> No effect of alcohol on sample
> No alcohol residues on sample and carriers
> No alcohol exhaust fumes
> Well dened light and electrical stimulation timing
Disadvantages
> Abrupt pressurization is a challenge for carrier stability
> Pressure and cooling synchronisation is a given no shift possible
LNT White Paper - COMPARING HIGH PRESSURE FREEZING PRINCIPLES 3
Illustration of pneumatic freezing principle of the EM ICE
1. Liquid nitrogen gets pressurized in front of needle valve
2. Sample inside cartridge moves into pressure chamber.
3. Sample sits in pressure chamber. Light or electrical stimulation happens now if programmed.
4. Needle valve opens. Pressurized LN2 hade in pressure chamber and freezes sample. LN
2
leaves pressure chamber via outlet nozzle.
5. Pressure chamber is empty.
6. Sample cartridge moves out of pressure chamber.
7. Sample cartridge is clipped. Sample arm removes. Sample cartridge is released and falls in LN
2
sample Dewar.
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© 2018 by Leica Microsystems GmbH.
Subject to modications. LEICA and the Leica Logo are registered trademarks of Leica Microsystems IR GmbH.
Leica Mikrosysteme GmbH | Vienna, Austria
T +43 1 486 8050-0 | F +43 1 486 8050-30
www.leica-microsystems.com
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