Analyte Loss EPA 525.2

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

75 posts Page 1 of 5
I am experiencing loss of Anthracene and Benzo(a)pyrene during the extraction/drying/concentration steps of EPA 525.2.

I have noted the formation of the quinone from anthracene so assume I am loosing both to oxidation.

Does anyone have any ideas on where this maybe happening?????

We use an automated system setup of Horizon 4790 extractors (atlantic C18 disks) and a Horizon Dry Vap for drying and concentration.

Please, ANY ideas are welcome.

Thanks,

J

:cry:
jkubeika wrote:
I am experiencing loss of Anthracene and Benzo(a)pyrene during the extraction/drying/concentration steps of EPA 525.2.

I have noted the formation of the quinone from anthracene so assume I am loosing both to oxidation.

Does anyone have any ideas on where this maybe happening?????

We use an automated system setup of Horizon 4790 extractors (atlantic C18 disks) and a Horizon Dry Vap for drying and concentration.

Please, ANY ideas are welcome.

Thanks,

J

:cry:



PAHs are light sensitive and are degraded easily by bacteria. I would think that if you are only losing 2 from the list, it's not during sample prep (even though Horizon is my competitor :cry: )

Try spiking extraction solvent, pass through sodium sulfate as normal, concentrate as normal, and analyze. Let us know if you get good recoveries.

Don
Don Shelly
LGC Standards
We actually don't use sodium sulfate to dry. We use a hydrophobic membrane on the dry vap to dry the sample. I have tried bypassing the dry vap as well as spiking before the dry vap and get similar results. This is why I think it's in the extraction. All of the PAHs are a little low, how light sensitive are they? Are they also picky to humidity?

THANKS!
:cry:[/quote]


I would think that if you are only losing 2 from the list, it's not during sample prep (even though Horizon is my competitor :cry: )

Don[/quote]

:oops:

I work for the Commonwealth of PA. All of our equipment purchases go through the bidding process. If you weren't the lowest bid, we don't get to play with your eqiupment.

:cry:
jkubeika wrote:
:cry:



I would think that if you are only losing 2 from the list, it's not during sample prep (even though Horizon is my competitor :cry: )

Don[/quote]

:oops:

I work for the Commonwealth of PA. All of our equipment purchases go through the bidding process. If you weren't the lowest bid, we don't get to play with your eqiupment.

:cry:[/quote]

Actually, we don't sell automated equipment, just the SPE products. :) If you need me, I am 1 hour away.

Don
Don Shelly
LGC Standards
How long have your PAH recoveries been low? Are the recoveries of the other compounds low too?

Don
Don Shelly
LGC Standards
A few months ago after moving to a new lab we noticed that 2 of the 16 EPA PAK disappeared after soxhlett extraction. It turned out to be the lights.
Especially in blanc (colorless samples) the recovery rate of D10-Athrancene and D14-Benzo(a)pyrene was only 10-30%.
So we installed less intensive lights and tried to do the extraction in the dark as much as possible which solved our problem.
Don't forget that some PAHs are also sensitive to acid / low pH.
Steve Reimer wrote:
Don't forget that some PAHs are also sensitive to acid / low pH.



These compounds should be stable down to pH 1. It would be difficult to take it much lower using method 525. pH 2 is required in this method for some of the other compounds that require protonation.
Don Shelly
LGC Standards
pH could be the culprit. Since the method states "less than a pH of 2" most of our collectors overkill on the HCl. We adjust the QC to match the samples which are always more like 0-1 than 2. That could be the problem. I'll also try to keep the lights out a bit and see if that helps too.

I am having a little less recovery with the other PAHs, but Anthracene is definately being oxidized because I can see the anthraquinone on the MS. My d12-perylene along with the benzo(a)pyrene is also a major problem.

Please add to the discussion any other ideas you may have.
jkubeika wrote:
pH could be the culprit. Since the method states "less than a pH of 2" most of our collectors overkill on the HCl. We adjust the QC to match the samples which are always more like 0-1 than 2. That could be the problem. I'll also try to keep the lights out a bit and see if that helps too.

I am having a little less recovery with the other PAHs, but Anthracene is definately being oxidized because I can see the anthraquinone on the MS. My d12-perylene along with the benzo(a)pyrene is also a major problem.

Please add to the discussion any other ideas you may have.


Probably there's free chlorine in your samples that oxidized the 2 PAHs, try dechlorinate before acidifying the samples.
X wrote:
jkubeika wrote:
pH could be the culprit. Since the method states "less than a pH of 2" most of our collectors overkill on the HCl. We adjust the QC to match the samples which are always more like 0-1 than 2. That could be the problem. I'll also try to keep the lights out a bit and see if that helps too.

I am having a little less recovery with the other PAHs, but Anthracene is definately being oxidized because I can see the anthraquinone on the MS. My d12-perylene along with the benzo(a)pyrene is also a major problem.

Please add to the discussion any other ideas you may have.


Probably there's free chlorine in your samples that oxidized the 2 PAHs, try dechlorinate before acidifying the samples.


EPA 525.2 requires dechlorination at time of sampling with sodium sulfite, but it is always a good idea to double check before you extract.

One thing you may notice if the pH is too low is that you can lose your Deuterated surrogates. I have seen instances where one would be low and when you look at the spectra you see ions for the d12, d11, d10, d9 ect analogs all coming off together in a broad peak. Very low pH causes a D/H exchange to take place.


A few months ago after moving to a new lab we noticed that 2 of the 16 EPA PAK disappeared after soxhlett extraction. It turned out to be the lights.
Especially in blanc (colorless samples) the recovery rate of D10-Athrancene and D14-Benzo(a)pyrene was only 10-30%.
So we installed less intensive lights and tried to do the extraction in the dark as much as possible which solved our problem.


We have had some problems with recoveries when doing PAH by EPA 550 so I may look into having less exposure to light and see if that helps ours, thanks.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
X wrote:
jkubeika wrote:
pH could be the culprit. Since the method states "less than a pH of 2" most of our collectors overkill on the HCl. We adjust the QC to match the samples which are always more like 0-1 than 2. That could be the problem. I'll also try to keep the lights out a bit and see if that helps too.

I am having a little less recovery with the other PAHs, but Anthracene is definately being oxidized because I can see the anthraquinone on the MS. My d12-perylene along with the benzo(a)pyrene is also a major problem.

Please add to the discussion any other ideas you may have.


Probably there's free chlorine in your samples that oxidized the 2 PAHs, try dechlorinate before acidifying the samples.


EPA 525.2 requires dechlorination at time of sampling with sodium sulfite, but it is always a good idea to double check before you extract.

One thing you may notice if the pH is too low is that you can lose your Deuterated surrogates. I have seen instances where one would be low and when you look at the spectra you see ions for the d12, d11, d10, d9 ect analogs all coming off together in a broad peak. Very low pH causes a D/H exchange to take place.


A few months ago after moving to a new lab we noticed that 2 of the 16 EPA PAK disappeared after soxhlett extraction. It turned out to be the lights.
Especially in blanc (colorless samples) the recovery rate of D10-Athrancene and D14-Benzo(a)pyrene was only 10-30%.
So we installed less intensive lights and tried to do the extraction in the dark as much as possible which solved our problem.


We have had some problems with recoveries when doing PAH by EPA 550 so I may look into having less exposure to light and see if that helps ours, thanks.


It's been my experience that polyethylene with retain PAHs, especially those that are deuterated. Avoid sample contact with PE.

Don
Don Shelly
LGC Standards
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.
wmbigham wrote:
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.


Wow! After 26 years of analyzing PAHs I thought I'd seen everything.
You have eliminated chlorine and pH. We can also rule out microbial activity.
That leaves: light, ozone, temperature (as a catalyst) and possibly particulates in the final extract. Since you run 550, which uses DCM, it would be hard to believe that PAHs would have a greater affinity for particulates than for the solvent. That leaves light, ozone and temperature. If there is any other way to breakdown PAHs, I suggest publishing.
I believe anthracene is the most susceptible to photo-oxidation.
If you can provide any other details it would be helpful.

Don
Don Shelly
LGC Standards
75 posts Page 1 of 5

Who is online

In total there are 3 users online :: 0 registered, 0 hidden and 3 guests (based on users active over the past 5 minutes)
Most users ever online was 599 on Tue Sep 18, 2018 9:27 am

Users browsing this forum: No registered users and 3 guests

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry