EPA 522 Confirmatory Ion interference.

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

7 posts Page 1 of 1
Running EPA 522 (1,4-dioxane) splitless SIM-mode on an Agilent GC-MSD (5977B) nearly exactly as described in the original method.

We are having trouble with an unresolved, fairly large leading interference peak on the M+ 58 (confirmation ion) SIM that tails over the top of the smaller confirmatory ion peak at the LOQ. I am fairly sure it is a hydrocarbon of some sort. The solvents are clean, but the signal is still there for every injection. (Note that this is a peak and not a continuous background interference). I believe it is hydrocarbon-based because it also has the co-eluting M+ 43 signal.

We have tried new He cylinder, a new "large" He hydrocarbon/O2 scrubber. cleaning the injector, a new inlet liner, new septum, new column (all have been conditioned) and a new injector syringe. Also baked out the MSD and source.

Has anyone encountered this with EPA 522 or similar method? Anyone have suggestions?
Is your methanol P&T grade? Have you tried a different lot#? I know it is expensive but it is necessary.
Steve Reimer wrote:
Is your methanol P&T grade? Have you tried a different lot#? I know it is expensive but it is necessary.


Thanks for the suggestion. Yes, we have confirmed it is not the methanol or the dichloromethane used in the method. This M+ 58 peak is occurring with all injections of any GC solvents at roughly the same raw count intensity. Since it is a peak (albeit broad and tailing) and not baseline noise, I believe it is likely prior to the MSD.
How bad are we talking? I've seen a fronting peak in samples but I usually just ignore it. I don't see it in our unextracted curve and it's barely there in our blanks.

We run a really janky method based off 522 that's missing some preservatives and the surrogate became the IS, same column though.

Image
70 eV wrote:
How bad are we talking? I've seen a fronting peak in samples but I usually just ignore it. I don't see it in our unextracted curve and it's barely there in our blanks.

We run a really janky method based off 522 that's missing some preservatives and the surrogate became the IS, same column though.

Image


This is exactly what we see! On the M+ 58 SIM (blue trace) at 7.95X min. (can't make out the last digit), the large preceding peak is unresolved and prevents the accurate integration of the confirmatory ion to determine the ion ratio as required in the method, unless we are reading the method incorrectly. We have been unable to reduce or resolve this interference peak.
Doesn't look like 522 says anything about letting analyst judgement overrule ion ratios. You could try finding a particularly bad offender and injecting a large volume in scan with an increased multiplier voltage and see what you pick up.
Are you using sodium sulfate in the extraction process?

That is notorious for having hydrocarbon impurities in it, and would be a cause for it to be in samples but not in unextracted standards.

The method suggestions of baking sodium sulfate at 400c helps but we have had some in the past that required putting it in a Soxhlet with DCM overnight to remove all the hydrocarbon interferences.
The past is there to guide us into the future, not to dwell in.
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