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2.3 Freeze-Pump-Thaw cycle
Using this system it is possible to operate freeze-pump-thaw cycles on sample liquids
held in any of the three vessels. Procedures appropriate to each vessel are outlined
below.
2.3.1 Sample in Vessel 1
• All taps and valves should be closed.
• Open valve V2 and tap A on Vessel 1, and freeze the sample liquid by slowly
raising a dewar of liquid nitrogen around it.
• When it has been determined that the liquid has completely frozen switch the
pump to roughing mode and open valve V1.
• Switch the pump to turbo mode and leave for several minutes. The pressure
within the system can be read from the baratron gauge on the pump.
• When sufficient pumping has been done and the sample is ready to thaw, close
valve V1 and remove the dewar of liquid nitrogen from around Vessel 1.
• The system must be ‘let-up’ to atmospheric pressure using helium gas by
opening valves V3 and V9. The pressure of gas in the system can be read
from the baratron gauge.
• Tap B should be closed to prevent suck-back of the liquid as the solid thaws.
• The sample can be warmed gently to aid the thawing process and when
complete close tap A.
2.3.2 Sample in Vessel 2
• All taps and valves should be closed.
• Open valve V2 and tap E on Vessel 2 and freeze the sample liquid by slowly
raising a dewar of liquid nitrogen around it.
• When it has been determined that the liquid has completely frozen switch the
pump to roughing mode and open valve V1.
• Switch the pump to turbo mode and leave for several minutes. The pressure
within the system can be read from the baratron gauge on the pump.
• When sufficient pumping has been done and the sample is ready to thaw, close
valve V1 and remove the dewar of liquid nitrogen from around Vessel 2.
• The system must be ‘let-up’ to atmospheric pressure using helium gas by
opening valves V3 and V9. The pressure of gas in the system can be read
from the baratron gauge.
• Valve V7 should be closed to prevent suck-back of the liquid as the solid
thaws.
• The sample can be warmed gently to aid the thawing process and when
complete close tap E.
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