Chromatography Forum

Hi all, hoping someone can help me out with this.

I'm working on a way to lower the amount of separate sample extractions we do in our organic prep department to increase throughput and turn around time.

Currently we do 1 extraction that produces an extract that is split between 8270 and TPH, which works fine after picking common surrogate compounds. The limiting factor has been ETPH samples that require a silica gel cleanup prior to concentrating. We've just done a test by treating LCS's with silica gel to see if the 8270 compound list was affected, and most notably a few of the phenols (2,4-dinitrophenol, pentachlorophenol, 4,6-dinitro-2-methylphenol) and hexachlorocyclopentadiene are showing very low recovery when compared to a normal LCS without silica gel.

I'm not sure where to start to troubleshoot this one, maybe try a different pore/mesh size of silica gel? We are currently using 60-200 mesh grade 62

Any help is appreciated!

Those phenolics disappear if you just look at them wrong, but I'm guessing other stuff is being effected by the silica gel too.

Can you just split your extract prior to the silica gel cleanup and concentration steps? And maybe double the amount of material you extract if you want your RLs unaffected.

How is the silica gel prepared?

In the silica gel cleanup method in SW846 I think there are different preps for different classes of analytes.

Long ago I used to do a quick and dirty cleanup of extracts by packing a disposable pipette with some silica gel and pass the 1ml of extract through it before injecting. When I did that using a standard I was getting pretty much complete recovery of all analytes, but I was leaving a little of the extract behind, not flushing with solvent, since the internal standard had already been added I didn't need to bring it back to volume or flush any extra through the column.

A while ago, 25 years or so, we worked to get fish tissue (and maybe marine sediment?) cleaned up enough to get most of our 8270 list to perform. The bases were gone but we could get the phenolics to come through silica gel by adding an organic acid. I believe we had ~10% acetic acid in DCM for elution solvent, but I may misremember that. In general the phenols and more polar compounds will require a much stronger elution solvent than if you are just trying for PAHs and neutrals.

Those phenolics disappear if you just look at them wrong, but I'm guessing other stuff is being effected by the silica gel too.

Can you just split your extract prior to the silica gel cleanup and concentration steps? And maybe double the amount of material you extract if you want your RLs unaffected.

It seems that way! We can't use double the soil to extract only because we are limited by the size of our microwave tubes and glassware, but that would've definitely been an easy enough step. And water won't allow for double matrix unfortunately.

As for splitting prior to cleanup, I'll have to play around with that idea and test it out to maximize recovery. Thanks!

How is the silica gel prepared?

In the silica gel cleanup method in SW846 I think there are different preps for different classes of analytes.

Long ago I used to do a quick and dirty cleanup of extracts by packing a disposable pipette with some silica gel and pass the 1ml of extract through it before injecting. When I did that using a standard I was getting pretty much complete recovery of all analytes, but I was leaving a little of the extract behind, not flushing with solvent, since the internal standard had already been added I didn't need to bring it back to volume or flush any extra through the column.

We currently don't bake our silica or prep it in anyway after receiving it from the manufacturer, since it's clean enough to use straight out of the jar. To filter samples through it, we set up a glass funnel with a filter paper, put a small amount (less than dime size) of silica gel, and a small amount of sodium sulfate on top to dry the sample simultaneously. The same is done for soil and water extraction, just at different steps in the process.

I have done your quick and dirty method before but unfortunately not with 8270s.

A while ago, 25 years or so, we worked to get fish tissue (and maybe marine sediment?) cleaned up enough to get most of our 8270 list to perform. The bases were gone but we could get the phenolics to come through silica gel by adding an organic acid. I believe we had ~10% acetic acid in DCM for elution solvent, but I may misremember that. In general the phenols and more polar compounds will require a much stronger elution solvent than if you are just trying for PAHs and neutrals.

interesting point.. I'll have to see what we can get away with for that type of approach