Starting tips for newbie with QuEChERS

[Mr.Brown]

Hello

We are starting with pesticide analysis in our lab and the way to go now days seems to be QuEChERS.
Off course i read a lot about it but experience is king and so i was wondering if some of you could give a fellow analyst some hint.

I have some questions about GC analysis of QuEChERS extracts.
Are you using LVI?
I am not quite happy to inject acetonitrile (ACN) to GC-MS how are you handling that
do you do a solvent exchange?

I apreciate any tips and hints you can give me.

Thanks a lot

[Don Shelly]

LVI is the way to go. I highly recommend solvent exchanging into toluene for GC analysis. Send me your email address and I will send you a copy of my QuEChERS Booklet which covers the basics of QuEChERS.

Don
dshelly@unitedchem.com

[Camisotro]

I don't handle the GCMS in my lab but we do indeed use solvent exchange. Our instrument is not set up for LVI.

[Winters]

In our lab we run all QUECHERS samples on our Agilent GCQQQ systems. We do not do any solvent exchange prior to analysis on GC. We use the MMI (multimode inlet) on the 7890 in a solvent vent configuration so as to vent off the ACN. This produces excellent results on the GCQQQ in MRM mode and allows us to hit LODs for most pesticides of 1ppb in the best matrices and 5ppb in the worst. The solvent vent mode does an excellent job of removing the ACN without much discrimination. It also does a decent job of keeping the thermally liable compounds relatively happy. Not sure what kind of inlets you have available but solvent vent is worth considering if you want to avoid solvent exchange.

We also have a few 6890s with specific detectors that we run in a pulsed spliteless mode and for the very limited screens that we do with them it works surprisingly well. Not sure how well this method would work for a large screen but for our purposes it works quite well.

Our columns on both systems last for over a year normally.

[Mr.Brown]

In our lab we run all QUECHERS samples on our Agilent GCQQQ systems. We do not do any solvent exchange prior to analysis on GC. We use the MMI (multimode inlet) on the 7890 in a solvent vent configuration so as to vent off the ACN. This produces excellent results on the GCQQQ in MRM mode and allows us to hit LODs for most pesticides of 1ppb in the best matrices and 5ppb in the worst. The solvent vent mode does an excellent job of removing the ACN without much discrimination. It also does a decent job of keeping the thermally liable compounds relatively happy. Not sure what kind of inlets you have available but solvent vent is worth considering if you want to avoid solvent exchange.

We also have a few 6890s with specific detectors that we run in a pulsed spliteless mode and for the very limited screens that we do with them it works surprisingly well. Not sure how well this method would work for a large screen but for our purposes it works quite well.

Our columns on both systems last for over a year normally.

Thank you for your response

We also want to go for LVI and solvent venting.
We have an OPTIC-4 (ATAS GL) on a shimadzu QP2010 system.

Any advice on the Solvent venting, time line, temparatur, heat up rate etc?

[Winters]

Sure thing. Listed below are the parameters that we run our Agilent MMIs at.

I am actually working on optimizing the inlet as we speak. The configuration listed below works great except it causes some degradation problems with a handful of thermally labile compounds (most noteworthy: Captan, Folpet, and Chlorothalonil). To help alleviate this problem I have begun experimenting with lower ramp temperatures on the inlet and a pulsed injection on the MMI. So far I have had good luck with this by lowering the inlet ramp from the 280C listed below to a value of 200C and bumping my column 1 flow up by 5x for 0.8min. This saves all of my thermally liable compounds and still provides good results with my late eluters.

I would recommend you start with something similar to the listed below and see what you get. You will most certainly want to tweak your parameters to find what runs best on your system though.

He Carrier Gas
20 minute run time
2 Columns - installed in a back-flushing configuration (kicks into backflush after last compound (deltamethrin) elutes ~16 minutes)
5m HP5MS from MMI into purged ultimate union
15m HP5MS from purged ultimate union into MS interface

Column 1 Flow
0.8mL/min for 16 minutes
-1.6mL/min for 0.5minutes
-6mL/min until end of run

Column 2 Flow
0.9mL/min for 17minutes
2.4mL/min until end of run

2uL injection volume from 10uL syringe
Start Inlet Temp at 60C hold for 0.35min
Ramp Inlet Temp to 280C @ 900C/min hold for 15min
Ramp inlet Temp to 300C @ 900C/min hold until end of run
Septum Purge 3mL/min
Vent flow 25mL/min until 0.3min
Purge flow to split 50mL/min at 1.5min

Start Oven Temp at 60C hold for 1.5min
Ramp to 160C @ 50C/min
Ramp to 240 @ 8C/min
Ramp to 280 @ 50C/min hold for 2.5min
Ramp to 290 @ 100C/min hold until end of run

[Camisotro]

In our lab we run all QUECHERS samples on our Agilent GCQQQ systems. We do not do any solvent exchange prior to analysis on GC. We use the MMI (multimode inlet) on the 7890 in a solvent vent configuration so as to vent off the ACN.

Noticing that you mention GC-QQQ. Presumably the MS/MS helps you get better sensitivity.

On a single quad, my colleague has some trouble getting the sensitivity we need without solvent exchange. It too is a 7890(A) but I don't think we are well-equipped for LVI and buying any new parts for the machine is unlikely to be on the horizon at the moment.

[Mr.Brown]

MS/MS for sure helps with sensitivity
unfortunately we "only" habe a single quad

How is your colleague managing de exchange?
And to which solvent?

[Don Shelly]

You can add 500 microliters to 1 mililiter of extract, evaporate to 500 uL, bring to 1 ml in toluene. With the right liner with glass wool you can achieve amazing linearity with a single quad system

[Mr.Brown]

@ Winters

Thanks for the detailed Information
Sounds like a good starting point

How many pesticides are you analyzing with a single Run?

I am planning injections in the range of 50 micro liter
So i habe to figure out the optimal times and conditions for injection

[Mr.Brown]

You can add 500 microliters to 1 mililiter of extract, evaporate to 500 uL, bring to 1 ml in toluene. With the right liner with glass wool you can achieve amazing linearity with a single quad system

Sounds simple enough

So i understand it correctly I ad 500 mictoliters of toluene evaporate to 500 and reconstitute to 1 mL
this should reduce ACN to a minimum and keep the pesticides from evaporation

[Don Shelly]

yes

[Camisotro]

In our lab it's 4 mL of QuEChERS exctract, add 1 mL toluene, evaporate under N2 to 0.3-0.5 mL, make up to 1 mL with toluene and add MgSO4. Mix, centrifuge, transfer for analysis.

It's also very slow evaporating that much ACN so we may see the method change further.

[Winters]

Yes, as mentioned above we are able to hit the lower limits of detection with this method thanks to the MS/MS.

We are generally screening for about 120 pesticides in our samples right now. We are hoping to add more as time progresses. The instruments seem to have no problems with cycle time right now so I am thinking we should be safe to possibly come close to doubling this number one day.

[Mr.Brown]

In our lab it's 4 mL of QuEChERS exctract, add 1 mL toluene, evaporate under N2 to 0.3-0.5 mL, make up to 1 mL with toluene and add MgSO4. Mix, centrifuge, transfer for analysis.

It's also very slow evaporating that much ACN so we may see the method change further.

yea I already recognized that ACN evaporation is a pain in the a....
4mL at 40°C and N2 stream takes up to 40 min

Now a very stupid question
How are you measuring the 1mL