Hi all,

One of the SPE cartridge constructor recommends in its procedure (for C18 columns) to dry the cartridge after sample loading and washing even when there is no immiscibility problems between the wash and elution solvent. They claim that this allows better reproducibilities and recoveries.

This is the first time I see something like this. Is it a common procedure? Do other people allow their cartridges to dry before the elution step? Does chromatographically speaking makes any sense?

Thanks for you input!

makes no sense - voodoo!

Hi, anonymous #1
yes, in certain cases it's a correct practice to dry cartridge after sample loading and washing.
Consider, for example, extraction of pesticides residue from water with C18 or polymeric cartridge. After sample loading and washing (with distilled or milliQ water) elution step is usually performed wirh methanol.
If you do not dry the cartridge, methanol will interact with water present in sorbent material making elution less efficient (in the worst case analyte's elution do not take place).
To overcome the problem without drying the cartridge you must use a larger volume of methanol to complete elution of analytes and so further problems will arise: volume reduction became time-spending and the water content in your eluate make difficult to reduce the volume or changing solvent (e.g. toluene or hexane if a GC analysis is needed).
I hope this note is useful to explain the question.

While I would not call it voodoo, I do not see an advantage with this approach. In the alternative case, where one needs a somewhat larger elution volume of methanol, the evaporation of this liquid volume is no more complicated than drying the water out of the cartridge. Evaporation step one way or the other! I actually prefer the second approach, because now I can see when the sample is dry.

I can see an evaporation to dryness on the cartridge as a tool, if one wants to reextract with a water-immiscible solvent. But such cases are rather rare, I think.

Oh I should have said that I do not see the argument that there is an advantage in reproducibility and recovery...

Maybe the manufacturer meant to just push the liquid out with a small amount of air, not really drying. I often push through a few mL of air, between different steps, to decrease solvent mixing. Real drying would cancel your preparation steps of the cartridge (you might have seen the dewetting discussions above). This would mean you are throwing away a large portion of your function (separation capability....).

our SPE-procedure starts wit weting the cartdridge with 2 ml methanol. so if the pores do not get wetted after drying after loading the sample, then the pores do not get get wetted in the first place and SPE as we kno it would not work...

From Original Anonymous:

The manufacturer procedure advice to dry the cartridge (after the washing step) under full vacuum for 2 to 5 minutes or until dry. He makes the difference though between dry and overdrying so maybe HW Mueller is right.

But I agree also with Uwe that if the recovery was a problem some more of the elution solvent should do the job. Maybe we need to evaluate in our lab both approaches, while I am still sceptic about drying the cartridge.

Anyway, thank you for your inputs!

Looks like we have a language voodoo. Overdry? To me drying means there is NO liquid left. That would be ultimate dewetting.
You mean that up to 5 min of pulling air through was recommended? You can get a lot of evaporation that way, thus most likely various states of dewetting. This does not make sense. When you gently push a few mL of air through, you do not remove the liquid from the pores, or not even all the liquid between the particles (~ no evaporation).

Hi, HW Mueller,

I agree. I guess for them complete drying (overdrying) can happen after 5 min of pulling air through. Yes it is recomended to pull air through for 2-5 minutes.

I think that it is time to reveal where all these information comes from to avoid any assumptions like if these are my voodoo ;-).

You may find the information I provided in the "SPE Reference Manual & Users Guide" by Phenomenex in page 17.

In fact they say that the overdrying of the cartridge should be avoided, which makes sense.

Well, you will avoid overdrying, if you do not dry at all in between your sample preparation steps....