November 30, 2020, 05:38:27 PM
Forum Rules: Read This Before Posting


Topic: Liquid-liquid Extraction  (Read 395 times)

0 Members and 1 Guest are viewing this topic.

Offline jhcoleman53

  • Regular Member
  • ***
  • Posts: 9
  • Mole Snacks: +1/-0
Liquid-liquid Extraction
« on: September 18, 2020, 04:18:28 PM »
Hi all,

Looking for some help.  I’m doing liquid-liquid extractions with natural water samples, using dichloromethane as my solvent, and am having some problems with emulsions.  I have tried the “salting out” technique, using 10% NaCL, or even as high as 20%, but this has not helped.  In fact, it seems to have made things worse, especially for one of the water types, if that’s possible.  One of the waters is from a freshwater creek in Pennsylvania, and the other one is from a tributary of the Chesapeake Bay in Maryland.  I have not done any measurements, but I suspect the one from Maryland may have some minor component of salinity to it, just because of its proximity to the bay and the influence of tidal fluctuations.  This is the one that the salting out appears to be making worse.  Could adding the salt be causing more harm than good?  Does anybody have any suggestions for when salting out just doesn’t work? 

Thanks.


Offline marquis

  • Full Member
  • ****
  • Posts: 336
  • Mole Snacks: +32/-3
Re: Liquid-liquid Extraction
« Reply #1 on: September 21, 2020, 11:49:34 AM »
What is the final test you will be doing?  What can you say about the rest of the method?

Regards,

Offline jhcoleman53

  • Regular Member
  • ***
  • Posts: 9
  • Mole Snacks: +1/-0
Re: Liquid-liquid Extraction
« Reply #2 on: September 21, 2020, 12:07:36 PM »
Marquis,

The next step would be to concentrate the extracts, i.e. evaporate off the DCM, then reconstitute in acetonitrile:water, and finally, analyze by HPLC.  But first I have to make sure I get all the analyte out of the aqueous phase, which I can't be sure of due to the aforementioned emulsions.

Thanks for any additional insight.

Offline marquis

  • Full Member
  • ****
  • Posts: 336
  • Mole Snacks: +32/-3
Re: Liquid-liquid Extraction
« Reply #3 on: September 21, 2020, 08:45:54 PM »
are you looking for nitrosamines, or something related?

Offline jhcoleman53

  • Regular Member
  • ***
  • Posts: 9
  • Mole Snacks: +1/-0
Re: Liquid-liquid Extraction
« Reply #4 on: September 22, 2020, 08:48:33 AM »
Marquis,

I really can't say anything about the analyte of interest due to confidentiality.  Suffice to say that the HPLC method has been verified and is reliable, given a clean DCM extraction.  I really just need some suggestions for clearing up these emulsions when salting out doesn't work.  Thanks.

Offline marquis

  • Full Member
  • ****
  • Posts: 336
  • Mole Snacks: +32/-3
Re: Liquid-liquid Extraction
« Reply #5 on: September 22, 2020, 10:27:32 AM »
Yes, the nitrosamine  method I used was validated also.  It gave many problems even though it had been validated.  And it also used a DCM extraction.

The start and stop point was a big issue. The method took several days.  We just had to find the right places to stop the procedure.

I hate to say it, but many times these methods will give choices in detectors.  In reality, there isn't one.  Only one detector will give good results.  Try using the detector specified by the original method. 

As a starting point, try finding the correct starting/stopping points and see where it gets you.

Sponsored Links