Critical Point Dryer Standard Operating Procedure

Updated on 2/13/2018

Note:

• The critical point dryer can dry delicate samples without any damaging effect of surface tension, using the zero surface tension of carbon dioxide at the critical point at 31°C and 1072 psi (cf. the critical point of water = 374°C and 3212 psi).
• Biological specimens are NOT allowed on the critical point dryer in QNF.
• The sample must completely be dehydrated in a fluid without drying the sample before the critical point drying.  However, since water is not miscible with liquid carbon dioxide, it is necessary to use an intermediate fluid which is miscible with both water and liquid carbon dioxide.  Although the intermediate fluids commonly used are methanol, ethanol, isopropyl alcohol, amyl acetate, and acetone, only methanol is allowed on the critical point dryer in QNF.  The intermediate fluid is replaced by liquid carbon dioxide during the process. 
• You must follow QNF Critical Point Dryer Wet Chemical Procedure to perform the pre-dehydration process. See the link.

Contents

1 Check-in

2 Pre Dehydration Process

3 Cold Start

4 Load Sample

5 Auto Mode Run

6 Unload Sample

7 Shut Down

8 Check-out

9 Supplemental Docments

1. Check-in

1. Log-in on the ISIS scheduler

2. Pre Dehydration Process

Note:

• You must follow QNF Critical Point Dryer Wet Chemical Procedure to perform the pre-dehydration process. See the link.

1. Put the sample into the sample holder provided.

2. If you treat your sample with some chemicals, e.g. hydrofluoric acid, before critical point drying, you must remove the chemicals from the solution after the treatment.  This is done by immersing the sample in de-ionized water or some solvent miscible with alcohol, using three separate changes of water or the solvent.  

3. Immerse the sample in ultrapure anhydrous methanol, using three separate changes of methanol, to dehydrate the sample.

Note: Only ultrapure anhydrous methanol in a glass bottle, provided by QNF, is allowed on the critical point dryer.

4. Keep the sample in the alcohol until it is transferred to the process chamber.

Warning: You MUST NOT dry the sample!

3. Cold Start

2. Turn on the "Chiller Power" 30 min before the process run.

3. Turn on the "Condenser Power".

4. Turn on the "Chamber Power".

5. The following screen appears.

6. Press the "Enter User/Sample Information" button to enter user/sample information, if necessary.

7. You may also press the "Main Menu" button to start operation without entering user/sample information.

Note:

• If the process chamber is under pressure, the tool will display "Chamber Under Pressure". 
• Press the "VENT VALVE" to vent the chamber.

8. The "Main Menu" screen will be displayed.

4. Load Sample

1. Loosen the knurl nuts according to the numbering sequence, using the spanning wrench provided.

2. Remove the chamber lid carefully. 

Note: Make sure that the chamber lid is placed on a clean wipe.

3. Place the spacers into the process chamber to minimize the space other than the sample holder.

3. Pour sufficient alcohol into the process chamber to cover the sample.

4. Quickly transfer the sample holder containing the sample into the process chamber.

5. Carefully lower the chamber lid onto the chamber.

6. Use fingers to evenly tighten the nuts.

7. Tighten each nut uniformly according to the numbering sequence, using the spanning wrench.

Note: Do not tighten the nuts too much from the begining. 

8. Repeat this tightening until the nuts are unable to tighten further.

5. Auto Mode Run

• The Manual Mode: Each process mode is paused, and input the parameters for the process mode.  See User Manual,

1. Press the "Auto" button on the "Main Menu" screen.

2. The following screen appears.

Note: The factory default setting values are shown on the screen.

Each Process Mode:

• Slow Fill: Process chamber is slowly filled with liquid carbon dioxide to prevent damage by liquid carbon dioxide in-flow.  Liquid carbon dioxide will mix with ultrapure alcohol.

• Fill Time: Process chamber is filled with liquid carbon dioxide.  Liquid carbon dioxide will mix with ultrapure alcohol.

• Purge Time: Alcohol is replaced by liquid carbon dioxide during the PURGE mode.

• Post Purge: Process chamber will be filled only with liquid carbon dioxide upon completion of previous "PURGE Mode". Post Purge Fill ensures process chamber is 100 % full of liquid carbon dioxide. 

• Heat: Critical point passage.  Heat is now applied to process chamber elevating the transitional fluid (liquid carbon dioxide) to above its critical point temperature and pressure (31°C and 1072 psi).

• Critical Point: Process chamber will maintain critical temperature and pressure (31°C and 1072 psi) for 4 min.

• BLEED: Once the critical point has been achieved, and the system has remained in equilibrium, the carbon dioxide (now in the gaseous state) is exhaused slowly from the process chamber.

• VENT: Accelerates decomposition of exhaust carbon dioxide gas from the process chamber.

3. To modify the setting value, press the button of each process mode, and change the parameter.

• For example, in the "SLOW FILL" process mode, the time can be changed using the arrow buttons, and click the "SAVE" button, if necessary.
• If you click the "UNDO" button, the default value will be restored.

4. Press the "NEXT" button after changing the parameters.

5. The following screen appears.

6. Press the "COOL" button.

7. When the cooling process is completed, the following screen will appear.

8. Press the "SLOW FILL" button.

9. The following screen appears.

10. Press the "CONFIRM" button, and the critical point drying from the "SLOW FILL" to the "VENT" process mode will start automatically.

11. When the critical point drying is completed, the following screen will appear.

12. Press the "EXIT" button.

6. Unload Sample

1. Remove the knurl nuts using the spanning wrench provided.

2. Remove the chamber lid carefully.

3. Remove the sample holder from the process chamber.

4. Reseal the chamber with the lid to keep it clean and moisture free.

7. Shut down

1. Turn off the "Chiller Power".

2. Turn off the "Condenser Power".

3. Turn off the "Chamber Power".

4.  Write down the weight of the liquid CO2 cylinder on the CPD log sheet.

8. Check-out

1. Log-out on the ISIS scheduler

9. Supplemental Documents

• QNF Critical Point Dryer Wet Chemical Procedure

Revisions

9/14/2016, by Hiro, added Critical Point Failure Correction.

9/27/2016, by Meredith, added QNF Critical Point Dryer Wet Chemical Procedure

2/13/2018, by David, added CPD log sheet