Ether separation from mineral spirits

Discussions about GC and other "gas phase" separation techniques.

15 posts Page 1 of 1
I have an analyte I am trying to characterize but I'm not getting good separation from the background solvent. I have tried a few capillary columns without luck.

This is GC-FID. Background solvent is LVP-100 - a low VOC mineral spirits, aliphatic, BP range from 212-245°C. Analyte in question is di-n-hexyl ether, CAS 112-58-3. BP 228°C. I have tried different temperature parameters on a DB-1 and DB-WAX columns but I am getting no analyte separation from the broad solvent range.

Any other ideas or better columns that would retain longer chain ethers and let aliphatics pass?
Ethers/hydrocarbons can be tough because neither is very polar relative to the other. I have seen where you can get some interesting retention behavior with 50:50 methyl:phenyl columns. You might give that a shot. Does the retention of the dihexyl ether change a lot when you go from the nonpolar phase to the wax?

I will also give you the suggestion that I offer to others when they come to us with these sorts of problems. A GC with heartcutting ability will likely solve your problem. I haven't had too many instances (only one that I can remember) where a precolumn separation on a nonpolar phase followed by a heartcut to a polar phase has resulted in coelution on both.

Here's a description of my system and an example of how it worked on the menthol/camphor problem (similar to yours).

viewtopic.php?f=3&t=38411&p=184011&hilit=menthol#p184011

I wish I had some dihexyl ether. I'd give a shot for you. You can retrofit existing GC's with the heartcutting kits - if the GC's are not too old I suppose. Electronic pressure control makes getting the system balanced easier but you can do it with analog pressure/flow control.
I fully agree with rb6banjo

Ethers/hydrocarbons can be tough because neither is very polar relative to the other. I have seen where you can get some interesting retention behavior with 50:50 methyl:phenyl columns. You might give that a shot. Does the retention of the dihexyl ether change a lot when you go from the nonpolar phase to the wax?


Do you have any example chromatograms from your non polar DB1 and polar Wax phase, both spiked and unspiked?

Also any other analytical conditions or detection levels or background for the analysis
Regards

Ralph
Initial method parameters (which were based on the previous replacement for this ether compound):

CHP @ 15 PSI (He)
Inlet temp at 250C - split 12:1
Typical FID settings (300C, 30/30/300 for gases, He as makeup gas)

Oven temp at 150, ramp to 250 at 10/C minute, hold 3 minutes

For both DB-1 and DB-Wax I tried dropping initial oven temp to 100C, and reducing ramp to 2.5C/min instead of 10. No luck.

I have spiked chromatograms using both DB-1 and DB-WAX columns which are at:
https://imgur.com/a/OMaTl

Note: the ramp parameters are slightly different. I ran unspiked chromatograms as well but did not attach those.
What are your column dimensions (DB1 and wax)?
I doubt that there is a way to get the ether completely out of the retention range of the hydrocarbons and so you need to focus (pun!) on getting it as a repeatably separated peak in the middle of the bunch.

You peak shapes on the DB1 column are dreadful, if you can get all the peaks sharp and symmetrical you might have an ether peak that can be integrated - I suspect that you have a very dirty inlet or a deteriorated column, maybe both.

Simply decreasing the initial temperature of the column programme might help with the wax column, and on the DB1 once you get the peak shapes sorted out.

Peter
Peter Apps
Thank you for posting the chromatograms - very useful

Your non- polar LVP-100 appears to be a very narrow range mineral oil

Hmmm

di-n-hexyl ether, CAS 112-58-3. is fully miscible in water.
https://www.alfa.com/en/catalog/L07076/

Your mineral oil is not miscible in water

Perhaps it is worth experimenting with dispersing your sample in hexane and extracting with water and/or methanol?
Regards

Ralph
Column dimensions:

DB-1 30m x 0.320mm x 0.25 um

DB-Wax 30m x 0.25mm x 1.0 um

The DB-1 column is several years old so I am not surprised I am getting brutal peak shapes.

Thanks everyone for your suggestions so far.
Wow! Doesn't that have to be a misprint? Diethyl ether isn't terribly soluble in water. I'd be very surprised if you added 8 more carbons to diethyl ether and the result would be a material that is water soluble.
@rb6banjo

I fully agree, it sounds unlikely and defies logic but appears on more than one site as to be fully miscible in water
Also http://www.chemicalbook.com/ChemicalPro ... 360873.htm

Unless they are copying a misprint from each other
(always possible)

Perhaps they have a definition of miscibility in water that differs from solubility in water?

From yet another site
http://www.sasoltechdata.com/MSDS/NACOL_ETHER_6.pdf

Water solubility 0.39 mg/l @ 25 °C

Easy to test in 2 minutes :-)

If I was still working in the lab and had this as an analytical challenge using only GC FID I would be all over it and would give liquid extraction with water or methanol a try ( nothing to lose but a few hours and possibly some pride :lol: ) and see if I could get enough out free of oil to form the basis of a method :-)
Regards

Ralph
Definitely not miscible with water, just tried. Methanol might be a legitimate extraction option. Working through that now.
If it's soluble in methanol and you get too many interfering hydrocarbons from your oil, perhaps you could play a game where you pass some volume of your oil onto a C8 SPE cartridge. Then, use the methanol to elute the ether from the packing - hopefully leaving the hydrocarbon interferences behind.

You might dilute the ether some but it doesn't look like your detection limit is a problem for you.
If you have a continuous liquid-liquid extractor that works with heavier than water solvents you could use water as the heavier than sample solvent. I can't find a number for the solubility of mineral oil in water, but it must surely be less than an ether's.

Peter
Peter Apps
So, I tried a few things -

A brand new DB-1 column - same characteristics, definitely better resolution of peaks but not sufficient separation from co-eluters.

Liquid-liquid extraction with diethyl ether - too miscible with the mineral spirits.

Liquid liquid extraction with methanol - this worked great with the Wax column. 10 mL sample and 10 mL methanol, agitate and centrifuge to separate layers. Take methanol layer and analyze. I dropped the initial temperature and the ramp speed as well. This gave me sufficient separation the hydrocarbon background.

I had a colleague make up a small blend at a unknown concentration to me, and I got pretty close to actual. Just need to prep a blank and make sure we don't have any hidden co-eluters.

Thanks everyone. This is an industrial blend so I won't go crazy with method validation but I have something I can work with.

https://www.docdroid.net/eTLkSqT/myster ... alysis.pdf
Result !

Thanks for the feedback.

Peter
Peter Apps
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