GC/ECD for cannabis pesticide analysis rather than GC/MS

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

14 posts Page 1 of 1
I know quite a few labs are using a GC/MS for the pesticide analysis for cannabis testing but I was wondering if anybody is using a GC with Electron Capture Detection for the GC pesticides. Looking at the action limits for the pesticides, I think an ECD should be able to see those limits no problem.
Hi,
I haven't seen much research into using the ECD but it is possible to use an NPD instead of MS.
Hi I would like to ask if anyone has used HPLC for the analysis of residual pesticides in the water with what procedure, you have also used standards to understand the type of pesticide
pacerlaser wrote:
I know quite a few labs are using a GC/MS for the pesticide analysis for cannabis testing but I was wondering if anybody is using a GC with Electron Capture Detection for the GC pesticides. Looking at the action limits for the pesticides, I think an ECD should be able to see those limits no problem.
Back in the mid 90's I was using ECD for pesticides and PCB's. You need dual columns for confirmation. I was using a DB-1701 and I think the other column was a DB-5. You would need to be sure the list for cannibis analysis are all chlorinated.

Many labs are using HPLC by preference for cannibis pesticides. But I don't know any specifics.
While not specifically for cannabis, EPA method 8081b uses GC/ECD for organohalide pesticides.
I think the only real concern is potential terpene/hydrocarbon interference with the ECD. I asked a sales rep about using the ECD and they (of course) said I needed to use a GC/MS system to achieve the action levels. I think it is funny though that the EPA methods (SW8081B and SW8082A) use ECDs but apparently a GC/MS is needed when it comes to cannabis.
A lot of difference when looking for pesticides in water or soil versus the Quechers method for plant materials. It is difficult to resolve the pesticides from the background noise at the levels needed. Most are using GCMS SIM or LCMSMS to be able to see the levels and eliminate the interferences. Also using GC you would probably need both ECD and NPD to get all the compounds and dual column for confirmation.

For the full list you usually need both GCMS and LCMS since some of the pesticides are more water soluble and some are more soluble in organic solvents.
The past is there to guide us into the future, not to dwell in.
Hello,

I’ve tried multiple methods and instruments. Everything under the top of the line GC-QQQs are cant defect under 0.1ppm.

When it comes to LC it’s almost the same effect. In case of Agilent the 6470 and 6495 are the once to go.

All instruments need a very time intense cleanup step and dilution, dilution, dilution.

Also if you can’t see a see a peak that you spiked and extracted out of a plant sample, your method is not 100% validated. I hear constantly that people are still calibrating neat standards.
adler_LAB wrote:
Hello,

I’ve tried multiple methods and instruments. Everything under the top of the line GC-QQQs are cant defect under 0.1ppm.

When it comes to LC it’s almost the same effect. In case of Agilent the 6470 and 6495 are the once to go.

All instruments need a very time intense cleanup step and dilution, dilution, dilution.

Also if you can’t see a see a peak that you spiked and extracted out of a plant sample, your method is not 100% validated. I hear constantly that people are still calibrating neat standards.


I agree. I am starting on the Oregon list for Hemp Pesticides and am finding most on the list are not good by GC, especially since many are Carbamates. All but a few are working well on LCMSMS as far as detecting in clean standards, but have not began testing with matrix yet. I haven't been able to see MGK-264 on LCMSMS but it works on GCMSMS also Prallethrin and Pyrethrins don't seem to work on the LC. Detection limits for 20ppb by Quechers I think will work for several even on our ABI3200, but for some it may not be possible to go that low.
The past is there to guide us into the future, not to dwell in.
ECD will work just fine if you go to sufficient lengths to clean up the sample appropriately. "Appropriately" does NOT mean QuEChERS; that is a screening method that relies heavily on the ability of the MS to separate out interferences. See the FDA Pesticide Analytical Method for appropriate cleanup methods for selective detectors.

QuEChERS was never intended for complex matrices like cannabis. It works quite well for foods where the hydrocarbon loadings are low; it does not work nearly as well for high-hydrocarbon (fatty acid) foods like avocado. Cannabis is a really complex, hydrocarbon-rich matrix. It is a quite difficult matrix and to analyze for pesticides properly in that matrix you need to use more vigorous extraction and cleanup techniques than QuEChERS. Because it is fast and easy (and cheap, thus the Ch) everyone (including me!) wants to apply QuEChERS to the entire world, but it just is not appropriate for some matrices.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
mckrause wrote:
ECD will work just fine if you go to sufficient lengths to clean up the sample appropriately. "Appropriately" does NOT mean QuEChERS; that is a screening method that relies heavily on the ability of the MS to separate out interferences. See the FDA Pesticide Analytical Method for appropriate cleanup methods for selective detectors.

QuEChERS was never intended for complex matrices like cannabis. It works quite well for foods where the hydrocarbon loadings are low; it does not work nearly as well for high-hydrocarbon (fatty acid) foods like avocado. Cannabis is a really complex, hydrocarbon-rich matrix. It is a quite difficult matrix and to analyze for pesticides properly in that matrix you need to use more vigorous extraction and cleanup techniques than QuEChERS. Because it is fast and easy (and cheap, thus the Ch) everyone (including me!) wants to apply QuEChERS to the entire world, but it just is not appropriate for some matrices.


I am beginning work on this and found an application from Restek that uses a cartridge cleanup instead of the dispersive cleanup step, I am going to try that and see if it works better.

I tried last year to do a method for pesticides in turkey fat, that normally would use GPC, but since management wanted to reduce solvent usage we tried cartridge cleanup. I never found one that would remove enough lipids to be able to inject more than one or two samples before needing to do inlet maintenance. Glad we never got actual samples for that one.
The past is there to guide us into the future, not to dwell in.
The real problem that we've had with high fat matrices isn't so much the fat; it's that a lot of the pesticides are lipophilic and hard to get out of the matrix. Cannabis is even worse, since it's not only high fat but high terpene. Kind of like dealing with oily wastes; it ain't purty!

Been working with a couple of Oregon labs and so far I haven't found anything short of mini-Luke that will come close to dealing with that matrix. Of course all the Oregon folk want to do this for $40 a sample; yeah, sure, not a problem! LOL!

In that matrix I think that you are pretty much forced to go to MS/MS, both on the GC side as well as the LC side. Single quad data just will not get around the interferences, and even with MS/MS you need to use known addition.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
I'm trying matrix matched standards on the GC/MS/MS now and yes, it looks terrible. The terpenes and the cannabinoids both still show up as high background peaks even when doing MS/MS. Definitely will have to try to increase sensitivity and use higher dilutions after Quechers extraction and cartridge cleanup.

Haven't tried LC/MS/MS except for solvent standards, but the detection limit is going to be fairly high since I am using the ABI3200.
The past is there to guide us into the future, not to dwell in.
I can't agree that the GC-MSD is appropriate for pesticide testing on cannabis. We had multiple B-Samples that other labs failed for bifenthrin because certain strains have ingredients that can't be distinguished from this pesticides. You also can't apply a high enough dilution to have matrix matched standards and still have no variation in between results. Neat standards in general recover completely different on a GC-inlet due to active spots than matrix standards, not even considering ion suppression in the source later on. A calibration with matrix matched standard 30% THC results in a way different recovery than a 50% THC matched standard if not diluted enough and cleaned up.
There is no way somebody can accurately see 0,05 ppm in flower with a device lower than 6470 and 6490 for concentrate LC-MSMS
When i comes to GC even with a 2 column setup an a 500 fold dilution its quite difficult to get the Pyrethroids to 0,05ppm in flower and 0.1ppm in concentrate on the top of the line 7010B HES.
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