Chromatography Forum

I am about to start doing extractions for the EPA 548 method. Our past analysts said she had problems with emulsions forming during the neutralization step of adding the Sodium Sulfate solution to the samples prior to shaking them out. she felt like this was giving her low recoveries. I was wondering if anyone else had encountered this problem and if there were any suggestions on things to try out before I begin on this method.

Thanks.

1. Treat the emulsion with 0.1 g of Anhydrous Sodium Carbonate (Mallinkrodt/other).
2. Shake for 30 seconds; then let settle (de-coalesce) on lab bench for 15 mins.
3. Put on centrifuge and spin (2500 rpm for 3 mins).
4. Recover the clarified supernatant.
5. Continue processing per your SOP.

This step Will help de-emulsify the sample (the emulsion is a mixture of water droplets and solvent and matrix constituents).

Regards,
Jumpshooter.

I have seen this problem. The emulsion was formed from the acidic methanol dissolving the stopcocks on the manifold. When the sodium sulfate solution is added it drives the dissolved material out of solution. I fixed the problem by repacing the PTFE stopcocks with Teflon, and haven't seen the problem now in over 5+ years.

Another option is to add extra methylene chloride to compensate for the emulsion. I am intrigued by the stopcock issue. That might explain why some labs have this issue and some don't. I have never been able to duplicate this problem.

Don

We are having issues with this off and on and the 125 mL sep. funnels we use during the sodium sulfate shaking step have glass stopcocks. When I did the extraction a couple years ago, it always seemed to happen alot when my EDTA solution was freshly prepared or when it was extremely humid out. I don't know if recovery was affected by it since I didn't perform the analysis at that time but the layer was always relatively minor. We do add 2 mL of methylene chloride, shake the funnel and remove the 2 mL layer an additional 2 more times after pulling the extract out so in theory, wouldn't that rinse the emulsion of any residual analyte anyway?

We are having another issue with recovery entirely but today was the first time that the person who extracted it said the emulsion was so bad that she couldn't distinguish between it and any methylene chloride layer at all. This is another developing problem we have that is waiting in the wings, but my sanity is thinly spread enough and it's just going to have to take a number until we get the current problem at hand under control.

I wish I could help you with that problem, but we have never seen an emulsion with 548 in our lab.

Jumpshooter's suggestion, below, will certainly help fix / resolve your emulsion problem; rem'ber to centrifuge the meth chlor layer recovered from the sep funnel action--this will maximize the mass transfer of the analyte for optimal measurement.


1. Treat the emulsion with 0.1 g of Anhydrous Sodium Carbonate (Mallinkrodt/other).
2. Shake for 30 seconds; then let settle (de-coalesce) on lab bench for 15 mins.
3. Put on centrifuge and spin (2500 rpm for 3 mins).
4. Recover the clarified supernatant.
5. Continue processing per your SOP.

This step Will help de-emulsify the sample (the emulsion is a mixture of water droplets and solvent and matrix constituents).