QC for 8260 - soil MS/MSD

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

3 posts Page 1 of 1
Hello,

I'm taking a second look at my lab's QC for 8260... we have a 6890/5973 with a purge & trap, which we use mostly for soil samples. Our P&T stir motor is broken so rather than just placing the soil into a vial with a stir bar, we extract 5g of soil into 5ml of methanol and spike a 40 ml voa of DI water with the extract.

Currently, to do an MS and MSD we add the spiking solution to the water in the 40 ml voa after the sample extract. This seems weird to me... I'm not sure what it tells us that a CCV doesn't. Would it make more sense to spike the soil itself?
That would give you the most information about interferences. Ideally the spike mixture would be in contact with the soil long enough to reach equilibrium. I have a TPH-G method that has this for a spiking protocol, where the diluted extract is spiked, to avoid having to deal with large spiking amounts.
For 50ng purged and 1 mL of extract diluted to 50 mL, 5 mL purged you would need 2500 ng for each spiked sample so it is possible but will require a concentrated solution.
MichaelVW wrote:
Hello,

I'm taking a second look at my lab's QC for 8260... we have a 6890/5973 with a purge & trap, which we use mostly for soil samples. Our P&T stir motor is broken so rather than just placing the soil into a vial with a stir bar, we extract 5g of soil into 5ml of methanol and spike a 40 ml voa of DI water with the extract.

Currently, to do an MS and MSD we add the spiking solution to the water in the 40 ml voa after the sample extract. This seems weird to me... I'm not sure what it tells us that a CCV doesn't. Would it make more sense to spike the soil itself?


That is the process we use for soils with high concentrations since it dilutes the sample.

When we had no stir bars or the stir motor is on the fritz what I would do is weigh the 5g sample into the vial and add 5ml water then shake the vial to break up the sample, it works as good as or sometimes better than the stir bar does. Then place it on the autosampler and let it run like a normal sample would. You end up with 10ml water since the sampler adds another 5ml with the internal standard, but as long as you calibrate the same way you are ok.
The past is there to guide us into the future, not to dwell in.
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