[NYCWhite]

Hi all.  Let me just say up front, I have been doing this kinda thing for 26 years and have never seen this stuff before.  I ran two columns in the last couple of weeks which, upon evaporation of the appropriate fractions, have shown a non-volatile residue - both physically in the flask, and clearly in the NMR.  Particularly infuriating as I trying to clean up trace products for identification-characterization-publication purposes.   

The first I traced to our hexanes - I think it's longer chain alkanes [>= decane etc] as it eventually is removed at the pump.  Easily (!) solved by distilling ~20 L of hexanes and crossing the supplier off my Christmas card list. 

Thinking my problem would be solved, I moved onto my second column.  4:1 hexanes/ether eluant.  Now I have a residue in the CH-X region - 3 broad peaks [almost polymeric?] at 3.8 to 3.4 plus a terminal methyl triplet around 1.2.  Sorry I'm doing this from memory right now so this may not be entirely accurate.  There may be other peaks but they would be under my product signals.  That are otherwise beautiful I might add.

So far I've only checked my CDCl3, CHCl3, hexanes but am working through everything else. I'm guessing this one is from my ether - it varies from sample to sample but has always been turning up in every one.  Right now I'm vaccing solvents and NMRing to isolate the source but I just wondered if anyone else has experienced similar?  My guess is some kind of glyme or maybe a PEG, given the chem shifts, hence my gut feeling its the ether to blame.  Given the earlier hexane problem, I also think this is coming from the supplier, not a lab contaminant. 

Finally, and this is a gripe, I am an academic at a chiefly UG institution so my time in lab is very precious - this has really eaten up my winter break.  Any help would be most appreciated.  I'm getting really tired vaccing down solvents. 

[BobfromNC]

We have found a common impurity we kept finding to be mold release agents from plastics.   Nearly anything in the lab molded from polypropylene or similar plastics is molded and the mold is sprayed with a release agent, similar to PAM or butter.   They tend to be mono or diglyceride type compounds, often with more pola head groups, similar to soap or lecithin, but often man made derivitives.   We found that rinsing plastic ware (wash bottles, funnels, anything made of plastics) as well as glassware with methanol before use was a big help.   We had been using some plastic 96 deep well plates for LC/MS samples, and kept finding peaks for these type items.   And glassware can get them as well, but much less common, we likely contaminated it from wash bottles or other plastics. 

Also, manyu solvents like chloroform, DCM, and more come with stabilizers, like alkenes, ethanol, tBuphenols, etc, which can get concentrated in your products.   That is another common source of impurities in products.   Good luck.