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Antonia Gilligan said on 01 August 2008

"Supercritical grade CO2 is a high purity product that should be cleaner than the typical CP grade used by many clinics. It is marketted to anaytical chemists for extraction of pesticides, etc. The next question is: Is it worth the cost? Maybe not...


Here are soem factors to consider:

Consider using the CP grade with an activated carbon filter

Even CP grade CO2 is very clean, when it first starts to be used and contiues to be clean as long as there is liquid CO2 in the cylinder. At this stage the presure doesn't chage as you withdraw the CO2. As use contiues it eventually can't maintain the crital presure to keep the CO2 in the liquid phase. It is at this point that any impurity that was disolved in the liquid CO2 will now be relases as a gas impurity. It is at this point the presure drops very quickly. In our lab we change out the CO2 tank once we seek the presure drop precipitiously.

Alternately, the typical J size cylinder contains 50 lbs of CO2. Some labs place the CO2 cylinder on a bathroom scale and when it has lost 45 lbs, they change out the tank...They don't ever see the bottom of the tank when the impurirites are disolved in the remaining liquid CO2.

Recall that CO2 is a great solvent, that is why it is used in super fluid extraction. Most CP grade CO2 comes from the petroleum or fertilizer industries.

Prices for CO2 vary widely depending on purity, you may want to consider a CO2 carbon filter on you CP grade metaerial

Finally, some labs (2) did use elctronic grade CO2 and while they didn't puplish the data, they didn't see any improvement in outcomes."

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