SPE procedures

[A.DeGraw.Yunker]

I know that when performing solid phase extractions, it is critical to dry the cartridge prior to elution of your analyte(s). Does anyone know if letting the cartidge dry during the washing steps is problematic? I tend to err on the side of caution and keep the cartridge wet through the whole procedure until the elution, but it would be nice if I didn't have too. And I have not had time to compare procedures to see if it matters.

Thanks!

[Don Shelly]

By washing steps, I assume you mean after the sample has been loaded onto the sorbent, you are washing the sorbent to remove impurities.

Drying the sorbent can actually be beneficial if the solvents you are using are not miscible with water or each other.

After the sample has been loaded on the sorbent; allowing the sorbent to dry out is not an issue. The sorbent really should be as dry as possible prior to elution.

Don

[A.DeGraw.Yunker]

Thanks Don.
Yes, I did mean the washing steps after loading the sample. The solvents I am using are miscible, but it gets difficult when using a manifold to run multiple cartridges simultaneously and not let them go dry.
Does anyone else deal with this?

[Don Shelly]

Yes. Using stopcocks to control flow rate helps. The only time that you don't want it to go dry is between the time that you condition the sorbent and when you add the sample. This doesn't mean that the sorbent must be under water. Unless you are in a desert, or some place with very low humidity, it is very hard to actually dry a sorbent completely.

Don

[Cotton Hawes]

Also dealed with this issue.
Unfortunately the solvents pass through cartridges with different speed, but you can stop the flow on the "fastest" ones when liquid surface reaches top of the sorbent and wait until all cartridges come to this. Then start next step. Thus, as Don has already mentioned, the stopcocks can help.
But another thing is the number of cartridges used simultaneously. I managed with 12-manifold, breaking the flow with stopcocks when necessary. But if there was 24-manifold, I'd never succeed (hard to keep eye and hand on each of 24), I'd better go learn playing organ

So, if you have few samples, you can just use stopcocks.
If your batch is large, then maybe you should't care much, cause the sorbent anyway won't dry in a second. Just make sure that you won't digress from the SPE process - I hope you gonna fulfil your experiments before EURO-2012

[zheyin]

I know that when performing solid phase extractions, it is critical to dry the cartridge prior to elution of your analyte(s). Does anyone know if letting the cartidge dry during the washing steps is problematic? I tend to err on the side of caution and keep the cartridge wet through the whole procedure until the elution, but it would be nice if I didn't have too. And I have not had time to compare procedures to see if it matters.

Thanks!

Dewetting does not happen on polymeric sorbents (for example: Waters mixed-mode SPE)
and happens on silica-based sorbents.

[Don Shelly]

De-wetting is an old wives tale. Silica based sorbents will not de-wet. That's only a problem with HPLC, not SPE.

Don

[zheyin]

De-wetting is an old wives tale. Silica based sorbents will not de-wet. That's only a problem with HPLC, not SPE.

Don

Have you tried to leave your silica-based SPE dry for a while and do the next step of elution?
I never dared to do it.
Are you defining everyone talking about dewetting as old wife?

[Don Shelly]

LOL - No, but they are listening to old wives.

it is always best to dry your sorbent completely prior to elution. Yes, I have thrown loaded SPE cartridges (silica based) in the drawer and eluted months later. Though, it depends on the stability of the analyte. A freezer might be better.

Don

[zheyin]

LOL - No, but they are listening to old wives.

it is always best to dry your sorbent completely prior to elution. Yes, I have thrown loaded SPE cartridges (silica based) in the drawer and eluted months later. Though, it depends on the stability of the analyte. A freezer might be better.

Don

I admire your spirit of challenging authorities.
And you have the time to do the research.

[Don Shelly]

In all honesty, I am one of the authorities. The company that I work for manufacturers SPE products. I am part of the technical support team.

Don