Critical Point Drying Care, Maintenance and Other Useful Information

Please note: critical point dryers use a pressure vessel. If you have any doubts about maintenance procedures or required spare parts please contact our service team before proceeding. Always refer to the equipment operating manual for details of specific safety points for the Quorum critical point drying product concerned.

Carbon dioxide (CO2) grades required for critical point drying

Generally speaking, the grade we recommend is ‘normal’ grade - that is the one most commonly offered by industrial gas suppliers.

In most parts of the world, ‘normal’ grade of CO2, from the suppliers is specified as ‘N4.5’ or 99.995% minimum purity with a maximum level of 50 ppm of impurities.

There are, however, two other grades available by special order from most gas suppliers. One is ‘N4.0’ or 99.99% (less pure than ‘normal’ grade). The other is ‘N5.5’ or 99.9995% minimum purity. The N5.5 purity is easier to find in those parts of the world where there is high level of activity in electronics, since these customers often demand gases with higher purities.

We are not aware of anyone who has ever reported either superior results using N5.5 purity vs N4.5, or inferior results using N4.5 vs N5.5. However, we do want our customers to have the benefit of such detail about liquid carbon CO2 procurement in the event they should ever find reason to believe that their particular specimens might benefit from the higher purity product.

Remember, the requirement is for LIQUID carbon dioxide and NOT gaseous carbon dioxide. For this reason a cylinder with an internal ‘siphon’ must be specified. A siphon cylinder is normally denoted by a white stripe painted along its length. No pressure regular is needed.

General background information

Critical point drying method - summary (PDF)

Critical point drying technical brief (PDF)


If in doubt, or you need further assistance, please contact our UK-based service team:

E3000/E3100: bonded seal durability (PDF)

E3000/E3100: critical point dryer rupture discs (PDF)

E3000/E3100: replacing safety bursting disc (PDF)

E3000/E3100: securing the bonded door seal into door (PDF)

E3000/E3100: viewing window maintenance (PDF)

E3000/E3100: viewing window maintenance diagram (PDF)