Chromatography Forum

We use a empty plastic 6ml cartridge ( supelco) to hold the Na2SO4 to dry the extracts. We have been using a lot for quite a while. Lately we get a very large peak in every extract that has 59m/z as the most abundant ion.

How do you folks dry your extracts prior to concentration?

Thanks
Bear

Most of the time, I'm extracting using SPE (ENVI-18 from Supelco). After extracting the sample, I get rid of as much water as possible by pulling air through the tube via vacuum. I add a couple of scoops of anhydrous Na2SO4 in a 4 mL autosampler vial and elute the analytes from the C18 with methylene chloride (usually 2 mL total but in 3 shots of 0.6:1.0:0.4 mL) over the Na2SO4 in the vial. Then, I decant the dry methylene chloride to another vial for injection or further concentration.

You've probably already tried it but have you checked to see if it's coming from the empty 6 mL tube/frit?

We normally use a glass funnel with a plug of glass wool with the sodium sulfate on top of it and pass the extract through before blowing it down with nitrogen.

I have been experimenting with 525.3 for the UCMR project and found as listed it transfers quite a bit of water since using full vacuum for 10 minutes just doesn't remove the water. I did however start using the positive pressure manifold from Supelco (Visidry setup, go to with the VisiPrep extraction manifold) and flow dry nitrogen through the cartridges. You can watch the water line move down as they dry. Afterwards I rinse the extraction mainfold valves with a little methanol to remove any residual water trapped in them before eluting. With this you get extracts that only take a pinch of sodium sulfate to make sure they are dry. This greatly improved the recovery of the 1,3-dimethyl-2 nitrobenzene surrogate. I went from about 50% recovery on the wet extracts to 85% on the dry extracts. Seems the wet sodium sulfate can hold on to some of that one.

It was from the empty poly tubes/frits. I tried some fresh ones from another manufacturer and the peak was almost non existent.
the strange thing is that when the Supelco lot was opened the peak was so small we ignored it. Over the last few months it's now ~4X taller than our internal standards.
I've been wondering if phase separation filter paper would work for 525.2?

Yes James, N2 drying is better. We started with a manual vacuum method and now use an Autotrace extractor. It drys the cartridges with N2, and we get lots less water in the extracts than when using the vacuum extractor.

These drying SPE-tubes are available in glass as well. This might be a solution?