Issues with 525.2 surrogates

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

8 posts Page 1 of 1
I've been doing 525.2 for close to 16 years, and lately been having issues with perylene d 12, and triphenyl phosphate failing the +/- 30% of targeted concentration. I don't think the issue is due to my sample concentration step, as the nitro xylene recovers very well. The triphenyl phosphate sometimes recover over 130% and the perylene d 12< 70%.

With what I see it may be due to the way I handle my surrogate mix. The mix is a commercial 3 component mix @ 500ppm in acetone.Manufacturer's storage requirements are ambient temp. I store it in a freezer that is usually about -15C. Prior to use I warm it and then vortex.

My theory is that the perylene d12 falls out of solution in the freezer and warming and mixing is not enough. the other week I prepared a continung calibration std. using the mix of compounds used to spike my LFM/Bs. I combined this mix, the IS and surrogates and brought to volume. When I ran it against the initial calibration everything was very much in range with the exception of the perylene d12, which recovered in the mid 70%. I see similar results using the con cal prepared with the initial calibration.

The implication is that I am not completely reconstituting the perylene d12.

Any thoughts?
Bigbear wrote:
I've been doing 525.2 for close to 16 years, and lately been having issues with perylene d 12, and triphenyl phosphate failing the +/- 30% of targeted concentration. I don't think the issue is due to my sample concentration step, as the nitro xylene recovers very well. The triphenyl phosphate sometimes recover over 130% and the perylene d 12< 70%.

With what I see it may be due to the way I handle my surrogate mix. The mix is a commercial 3 component mix @ 500ppm in acetone.Manufacturer's storage requirements are ambient temp. I store it in a freezer that is usually about -15C. Prior to use I warm it and then vortex.

My theory is that the perylene d12 falls out of solution in the freezer and warming and mixing is not enough. the other week I prepared a continung calibration std. using the mix of compounds used to spike my LFM/Bs. I combined this mix, the IS and surrogates and brought to volume. When I ran it against the initial calibration everything was very much in range with the exception of the perylene d12, which recovered in the mid 70%. I see similar results using the con cal prepared with the initial calibration.

The implication is that I am not completely reconstituting the perylene d12.

Any thoughts?


It is definitely possible they are falling out of solution, maybe try storing more in the 4c range if you worry about losing the early surrogate.

TPP may be going high if the PAH internal standard is also falling out of solution if it is stored the same way. You may just have slightly low recovery of the nitro xylene that is hidden by a low internal standard area which also boosts the apparent recovery of the TPP. Also light can degrade the PAH compounds which could be causing a similar effect as them falling out due to cold storage.
The past is there to guide us into the future, not to dwell in.
The surrogate I have trouble is the last one to come out.
The point about the internals is well taken as they do lower over time while stored in the freezer.
Areas of the internals and surrogates except for the perylene track roughly the same when compared to the area average of the initial calibration. Perylene being 10-15% lower.
I can resolve this issue by running an initial calibration for every set of sampled, but feel this is unnecessary.
Dreaming up some experiments to run next week.
Thanks
Bigbear wrote:
The surrogate I have trouble is the last one to come out.
The point about the internals is well taken as they do lower over time while stored in the freezer.
Areas of the internals and surrogates except for the perylene track roughly the same when compared to the area average of the initial calibration. Perylene being 10-15% lower.
I can resolve this issue by running an initial calibration for every set of sampled, but feel this is unnecessary.
Dreaming up some experiments to run next week.
Thanks


I am running 525.3 now for the UCMR project and it seems I have to run a calibration every time if it goes more than a day or too between sets. I think for the 525.3 it is the buffer in the samples as sometimes I have to inject the later CCVs two or three times to get them to pass, initial injection is high then it drifts back down to passing, internal standard areas though hold steady.

525.2 doesn't have so much matrix to cause problems and the extracted internal standards should help, but if the freezer is causing them to fall out of solution that would cause plenty of problems.

What I think is odd is the method states to store the sample extracts in the freezer, but never mentions sonicating or shaking to reconstitute before injection yet many of the stock standards you purchase come with storage recommended at room temperature and tell you to sonicate before using.
The past is there to guide us into the future, not to dwell in.
Thanks James.
That's true.
Yesterday I took a 2 ppb calibrator that was stored in a -15C freezer out and thawed it. I then sonicated it for about 5 min. I ran it and compared the std and surrogate area to the time it was run for calibration. The interesting point is, the areas were very comparable, 96-114% of that of the first time the standard was run.
This may be the issue as I have calibrated a few times with this set of standards, the ares compared to the latest calibration were mostly in the 80 percentile, with the exception of the perylene d12 which was 59%.
The next step is to prepare a new set of calibrators, and tp sonicate them prior to using.
BTW, what do you store your calibrators in? I use crimped amber autosampler vials.
Bigbear wrote:
Thanks James.
That's true.
Yesterday I took a 2 ppb calibrator that was stored in a -15C freezer out and thawed it. I then sonicated it for about 5 min. I ran it and compared the std and surrogate area to the time it was run for calibration. The interesting point is, the areas were very comparable, 96-114% of that of the first time the standard was run.
This may be the issue as I have calibrated a few times with this set of standards, the ares compared to the latest calibration were mostly in the 80 percentile, with the exception of the perylene d12 which was 59%.
The next step is to prepare a new set of calibrators, and tp sonicate them prior to using.
BTW, what do you store your calibrators in? I use crimped amber autosampler vials.


We are using screw cap amber autosampler vials for our standards. Being in Ethyl Acetate they don't evaporate much overnight so we recap any in the morning that did not run before going home in the evening. Over the weekend though they will evaporate some, but not terribly bad.
The past is there to guide us into the future, not to dwell in.
Thanks James
I was not clear in my question. We prepare calibrators from 0.1-10ppm and store them in amber crimped autosampler vials in a -15C freezer. We aliquot from the 2 ml vials into a 300ul vial for injections. Recap the 2 ml vials and return to the freezer. We use the 2.0 std as a con cal, and continue to use the calibration until it has signs of failure. Usually we re calibrate when the is and surrogate areas get into the 70% range when compared to the average of the initial calibration.
We most times use the calibrators that were stored in the freezer.
For how long do you use your calibrators?
We use the 2ml vials to store the standards and to inject them, recapping and returning to the freezer. As you do, we use them until we see signs of degradation when comparing to a second source standard, or until 6 months as listed in the method. Currently we only are using 525.2 to analyze for bis-2-ethylhexyl phthalate and bis-2-ethylhexyl adiapate. We use method 550 to analyze for benzo[a]pyrene and method 508 or 507 for the pesticides and 515 for herbicides.

We are currently working to move the 550 and 507 method analytes into 525.3 to reduce the number of extractions and analytical runs. Eventually I would like to move the pest and pcb analytes over to 525.3 also which would leave only 515 herbicides, and 548 endothal as the extra GC methods.
The past is there to guide us into the future, not to dwell in.
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