Analyte Loss EPA 525.2

[jkubeika]

I have eliminated chorine; pH; light and bacterial or algea growth. I am currently suspecting the DCM because that's the only other thing I can think of. If anyone has any ideas at all I am all ears!

[jkubeika]

We are having the same issue. Major loss of Anthracene, Benzo(a)pyrene and Perylene-d12. Driving me crazy. I have tried adding preservative (sodium sulfite) and altering the amount of 1:1 HCl to see if that makes a difference. It hasn't. Also, if I run the extract as soon as they are ready we get low recoveries but if we wait to run them the compounds disappear completely. If I rerun the extract several days in a row I can watch the recovery get lower each day for these compounds. I haven't tried to avoid light although our sample bottles and chromatography vials are all amber glass. We didn't used to have this problem and are now starting to see this happening in our 550.1 extracts too. I'm not sure what changed.

Let's compare - I am using Fisher Optima Solvents; Accustandard and Ultra mixes for standards and Atlantic C18 or Speedisks. I have seen the problem in both disks as well as trying the Restek Resprep Disks. Also same problem with Accustandard/Ultra or Restek Standards!!!! I have also seen them disappear over time. I have seen this problem since the summer (when I suspected the hot and humid conditions) and still see it now (It's 3 F here today and a balmy 63 in the lab). Please let me know what you are using.

[wmbigham]

jkubeika, we are also using Fisher Optima Ethyl Acetate and Fisher HPLC grade DCM. Ultra Scientific 525.2 mixes and using an Autotrace SPE with UCT 525 cartridges (1.5g/6 mL) and concentrating using Turbovaps. We use sodium sulfate for water removal from extracts.

[jkubeika]

Does the Turbovap use heat as well as nitrogen? I use a dryvap that uses a submerged heater til 5 mL then N2 and vacuum to 0.8mL.

[wmbigham]

Turbovap uses heated water to heat the tubes and nitrogen blowdown.

[Don Shelly]

So that I understand correctly, both of you are having the same problem?

[Don Shelly]

So that you folks know where I am coming from, here is my background in a nutshell.

After 16 years working in environmental testing labs, I went to work for my SPE vendor UCT. My job was to develop products for environmental testing laboratories that would make your jobs easier. One of the first products developed was the special C18 sorbent being used by wmbigham for 525 analysis. That C18 was designed specifically for 525 and works well. My current position is to offer tech support to environmental testing labs.

I prefer Baker solvents and Restek standards. I prefer the TurboVap for concentration. DryDisks work better than sodium sulfate, but sodium sulfate should not affect PAHs.

TurboVaps - used minimum nitrogen flow. Nitrogen flow and vacuum will quickly purge PAHs from solvent. If you need more speed, turn up the heat. I learned this the hard way.

Here are some long shots that will enhance photo-degradation of PAHs.
peroxides
humic acid
hydroxyl radicals
manganese peroxidase enzyme
sonication in DCM

Suggestions:
try different solvents
if there is an ozone source in the prep area, remove it
if the final extracts are near sonicators, move them

[jkubeika]

I believe it is the same problem.
I am going to try to bypass the heat and vacuum next week and use a simple NEVAP and will let you know.
I have also ordered some Baker solvents to see if it's something in the Fisher Solvents.

[Don Shelly]

I believe it is the same problem.
I am going to try to bypass the heat and vacuum next week and use a simple NEVAP and will let you know.
I have also ordered some Baker solvents to see if it's something in the Fisher Solvents.

Be vary careful with a n-evap. It tends to be too harsh. Adjust the flow so that you barely see a divot in the water. If you can reprogram your evaporator to keep the heat on until it reaches the final volume and minimize everything else it does, it should work for you.

Don

[wmbigham]

We use a 45C temp for the Turbovaps with as low a flow as possible.

I reran my latest 525.2 LFB as a test. This was originally analyzed Tuesday afternoon at about 5 pm on the GCMS. Benzo(a)pyrene dropped from 50% recovery two days ago to 15% today. Anthracene and Perylene-d12 fell from 75% recovery to 38% today. The internal areas were in the 91-94% range and other compounds and surrogates were comparable to the original analysis. These extracts were run through the Autotrace at the end of last week and concentrated on Tuesday.

We use Ultra Scientific 525 mixes as our calibration and extraction spike mixes and have not had a problem with the stability of our calibration standards. These are made in Ethyl Acetate only. The stock mixes are in a mix on DCM, Acetone and Methanol. We use Spex and Restek standards as our second source check standards.

[Don Shelly]

We use a 45C temp for the Turbovaps with as low a flow as possible.

I reran my latest 525.2 LFB as a test. This was originally analyzed Tuesday afternoon at about 5 pm on the GCMS. Benzo(a)pyrene dropped from 50% recovery two days ago to 15% today. Anthracene and Perylene-d12 fell from 75% recovery to 38% today. The internal areas were in the 91-94% range and other compounds and surrogates were comparable to the original analysis. These extracts were run through the Autotrace at the end of last week and concentrated on Tuesday.

We use Ultra Scientific 525 mixes as our calibration and extraction spike mixes and have not had a problem with the stability of our calibration standards. These are made in Ethyl Acetate only. The stock mixes are in a mix on DCM, Acetone and Methanol. We use Spex and Restek standards as our second source check standards.

First:
Try some more LFBs using different DCM

If that doesn't work:
Keep everything covered and in the dark

As a last resort:
- Vial your extracts in an area without electronics or any other possible source of ozone

A long shot:
No ultrasonics around the vialed extracts

Don

[Don Shelly]

X, if you are out there? Do you have any ideas?

[X]

X, if you are out there? Do you have any ideas?

Not much I can think of, not sure if acetone in the stock solution matters, I remember someone mentioned that acetone is somehow oxidative.

[Don Shelly]

X, if you are out there? Do you have any ideas?

Not much I can think of, not sure if acetone in the stock solution matters, I remember someone mentioned that acetone is somehow oxidative.

That was probably me. I've never seen it oxidize PAHs.

[James_Ball]

You may want to check your Fisher solvents for preservatives, especially the DCM. We had a problem several years back and what we found that caused the problems was Fisher had given us solvents with a different preservative. I can't remember what the different one was, but it wreaked havoc with our 8270 extractions and recoveries. Once we got a different lot# of solvent the problems went away.