What Dichloromethane do you use for extractions?

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

13 posts Page 1 of 1
Recently we have been seeing interferences in our samples run on GC/FID and GC/ECD.

Looking at the solvents, it appears we currently have HPLC grade DCM being used for extracting DRO, PCB, Pesticide and Semivolatile samples using Continuous Liguid/Liquid Extraction EPA3520C. I am concerned that this could be the wrong grade of solvent.

For anyone doing this extraction and analysis, what grade and supplier are you using for DCM? If I can get some part numbers to purchase small amounts for testing I can clear up if this is the cause or if it is in some other part of the process.

Thanks
The past is there to guide us into the future, not to dwell in.
We use EMD (Milliapore/Sigma) #DX0831, no issues. I don't think they offer it with amylene stabilizer anymore. Also check this:

"Due to the popularity of dichloromethane as a solvent in environmental labs, it should be noted that over time, alkene stabilizers produce chlorinated byproducts that may interfere with some GC analyses. This is particularly true in the case of cyclohexene since these byproducts are relatively higher boiling and will elute further away from the solvent front and may interfere with target analytes."
Thanks, that is one I will look in to.

I believe we need better than just HPLC grade, since it isn't tested for any residues that respond to ECD or FID.
The past is there to guide us into the future, not to dwell in.
Hi James

It's not really a question of "better", more of suitability for purpose. Residue grade solvents are tested for interferences in residue analyses - so maximum allowable responses in GC-ECD and GC-MS are specified. HPLC solvents are tested for UV absorption, fluorescence etc. A chlorinated impurity that messes up a GC-ECD analysis is no bother for HPLC, and a low MW aromatic that gives a high basleine in HPLC elutes with the solvent peak in GC.

Peter
Peter Apps
We use Pestinorm grade, VWR, #83665.320.
Thanks everyone!

In the past we would purchase entire lots of solvent to be delivered over time and we would test it in each analysis to ensure it was suitable for use. Management has gotten away from this practice and trying to reduce cost as much as possible, which is good but if you have analysis failures it ends up costing more.

We currently have HPLC grade which is being used for everything and we have been seeing what looks almost like gasoline in the background of the MS and FID analysis. Also there is a major peak near the middle of the NPD analysis. I am going to try some of the other grades that have been mentioned to see if it is the solvent causing the problems.

Convincing people that spec sheets are not always good indicators of suitability is not easy :)
The past is there to guide us into the future, not to dwell in.
We now use Sigma Aldrich # 650463 for EPA 525.2. We have also used EMD Millipore and Fisher Optima.
We do something similar to James in that we request samples from a supplier for testing before we get a new lot.
Hi James

we have been seeing what looks almost like gasoline in the background of the MS and FID analysis.


Do you mean hydrocarbons and aromatics consistent with gasoline/diesel?

Probably not helpful but when analysing a beer taint I found that it came from the silica used in filtering the beer.

It eventually transpired that the taint came from vehicle exhaust fumes adsorbed onto the silica from the local air environment during manufacture

I appreciate that it doesn't answer your query but if you are seeing and identifying background peaks consistent with vehicle exhaust then you may be on to something with the source of your impurities

Regards

Ralph
Regards

Ralph
GOM wrote:
Hi James

we have been seeing what looks almost like gasoline in the background of the MS and FID analysis.


Do you mean hydrocarbons and aromatics consistent with gasoline/diesel?

Probably not helpful but when analysing a beer taint I found that it came from the silica used in filtering the beer.

It eventually transpired that the taint came from vehicle exhaust fumes adsorbed onto the silica from the local air environment during manufacture

I appreciate that it doesn't answer your query but if you are seeing and identifying background peaks consistent with vehicle exhaust then you may be on to something with the source of your impurities

Regards

Ralph


Just doing a blow down of 300ml to 1ml, we saw toluene, xylenes, trimethylbenzenes and other aromatic and aliphatic compounds present in the chromatogram. One other thing we found was about the time the problem began on the DRO samples we switch from using tanks of nitrogen in the turbovaps to using a nitrogen generator supplied by a large scroll compressor.

I would have thought that if the nitrogen generator could filter oxygen from the air it should be removing hydrocarbons also. There is also one peak showing up in the NPD run that when we run it on the MS shows up to be a possible flame retardant, not sure if this could come from the compressor or not.
The past is there to guide us into the future, not to dwell in.
Nitrogen generators use selective adsorbents, not filters, to take out the oxygen and they need their feed air to be oil-free. It sounds as if you have identified the source of the problem. Big activated charcoal traps in the nitrogen lines will probably solve it.

Peter
Peter Apps
Activated Carbon filters cured the beer taint problem

My predictive text tried to suggest beer tent
:lol:
Regards

Ralph
Peter Apps wrote:
Nitrogen generators use selective adsorbents, not filters, to take out the oxygen and they need their feed air to be oil-free. It sounds as if you have identified the source of the problem. Big activated charcoal traps in the nitrogen lines will probably solve it.

Peter


This one is the high output permeable membrane type, but I believe it has the same principle. I know the pressure swing adsorption unit we us for ultra pure in the lab has a hydrocarbon reactor on the inlet that breaks hydrocarbons down to CO2 so it can be removed. I wasn't sure if the membrane types would filter out the hydrocarbons or not.

The compressor is oil free, but they store the Gator and generator used for well sampling in the same room :roll:
The past is there to guide us into the future, not to dwell in.
twranger wrote:
We use EMD (Milliapore/Sigma) #DX0831, no issues. I don't think they offer it with amylene stabilizer anymore. Also check this:

"Due to the popularity of dichloromethane as a solvent in environmental labs, it should be noted that over time, alkene stabilizers produce chlorinated byproducts that may interfere with some GC analyses. This is particularly true in the case of cyclohexene since these byproducts are relatively higher boiling and will elute further away from the solvent front and may interfere with target analytes."


Could you expand on this?

I use DCM and have noticed persistent contaminants in it for some time. Apart from the amylene (stabiliser), 2-Chloro-2-methylbutane and trans-3-Penten-2-ol and also present. Both of these elute after the DCM. I would love to be able to confirm how they got there.
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