Chromatography Forum

The saga continues!

I have been trying to post for a while but i think the server was down

anyway,

I tried making a new dilution of our standard to rule out the instrument and it came out fine, so I went back to trying a few different things in prep. Eventually tried an extraction without acetone (just straight DCM) and it came back fine! Looks like we have both arrived at the same conclusion. We switched to a new batch and i have been getting improved results but still low. i will try and get hold of some acetone from a different supplier.

I'm still not sure that acetone is solely to blame though. We also have a prep method that does'nt concentrate the extracts, and that shows a much better recovery of 2,4DMP (though still less than other phenols). May be the boiling during concentrating is driving a reaction with something in the acetone?

We screen all our solvents but we only look for analytes that are in our suite of target compounds, so something may be missed.

I have been watching and chewing on this one for a while. Has anyone tried acidifying the glassware? Take the extraction beaker, and maybe even the KD reservoir and rinse it with dilute sulfuric or HCl and then DI wash and try an extraction. Just a thought experiment on my part since I don't support any of these toys any more.

Best regards.

Would that be to remove residues that may be interacting with the phenols?

I will give it a try but we get good recovery for the rest of the phenols in our suite.

tangaloo,

Ask your vendor if the acetone is preserved in some manner to prevent epoxide formation or whatever....

The idea behind acid rinse was originally to deactivate the glass surface, make it acidic which would keep phenol neutral. However, your point about cleaning is valid. Ammonia columns are often base washed for the same reason so I thought it might be worth a try.

2,4 dintro with the two nitro groups is probably one of the most reactive. At ppm levels it would not take much of a preservative to attack it and probably one of the first to be attacked because of the nitro groups.


Keep us posted.

Hello,

I know it has been a long time since this post was updated but I am seeing a similar issue in my lab where we are trying to perform an MDL study for very low levels. As with the original poster the issue is exclusive to 2,4-dimethylphenol and pentachlorophenol, while a more reactive 2,4-dinitrophenol yields acceptable recoveries. Is there any update on how you were able to overcome this issue?

We have done some studies to identify the concentration step as the main culprit, but it has been challenging figuring out how to fix the issue. We use glass concentrator vessels that are cleaned with soap and kilned before each use, which should get them pretty clean. I am considering rinsing the tubes with a low acid wash (2% HNO3) before use to see if that generates better recoveries, as one other user suggested, but the lab is very high throughput, and this would not be a great solution for production.

If any one has any thoughts or ideas I am open to suggestions since I am pretty stuck at the moment.

Tough compound... I have a bunch of questions

You're extracting from sand or sodium sulfate or what? (I agree with the person who said before to ditch the sand.)

What kind of extraction? Microwave/ultrasonic?

What solvent are you using? What kind of soap? I always rinsed my glassware with solvent after use, let them dry in the hood, washed with citranox and air-dried, then rinsed again with solvent before using.

What MDL do you need? How low are you able to calibrate and still get a linear response?

Is it possible that water is getting into the concentration tubes while you're blowing them down?

If you just spike solvent and concentrate it down do you use more of these compounds than similar ones? (There are trade offs at each flow rate / temperature, in my experience. Some cpds do better than others).

Regardless of the above, I have a suggestion. Buy a standard of just 2,4-dimethylphenol. Do the LCS at a few different concentrations and check the chromatogram for any breakdown products. I don't know what could be going on but if for some reason you saw cresols or something appear, that would be a clue.