Analyte Loss EPA 525.2

[wmbigham]

I was able to get dichloromethane and methanol from another source but my ethyl acetate is stuck in the weather somewhere. I extracted a test LFB yesterday and analyzed it as soon as it came out of the concentrator. I got good recoveries for the compounds that I was having trouble with and thought I might be on to something. I reran the sample this morning and the compounds have almost disappeared.

Perylene-d12 96% yesterday to 16% recovery today
Anthracene 97% to 9%
Benzo(a)pyrene 76% to 8%
Acenaphthylene and benzo(a)anthracene dropped off also but to a lesser extent.

jkubeika, were you able to figure anything out?

[Don Shelly]

I wonder if the ethyl acetate being used for sample prep has a high carboxylic acid content? Take a CCV standard that you know is good and add 10 uL COOH to 1000 uL and see if the breakdown occurs. 1% should not be a major problem to your instrument, (disclaimer) but I don't know your instrument.

[James_Ball]

I was able to get dichloromethane and methanol from another source but my ethyl acetate is stuck in the weather somewhere. I extracted a test LFB yesterday and analyzed it as soon as it came out of the concentrator. I got good recoveries for the compounds that I was having trouble with and thought I might be on to something. I reran the sample this morning and the compounds have almost disappeared.

Perylene-d12 96% yesterday to 16% recovery today
Anthracene 97% to 9%
Benzo(a)pyrene 76% to 8%
Acenaphthylene and benzo(a)anthracene dropped off also but to a lesser extent.

jkubeika, were you able to figure anything out?

Are you storing these at room temperature or in a freezer? If in a freezer I wonder if the compounds could be dropping out of solution.

[wmbigham]

They were stored at room temp on this test.

[Don Shelly]

When ethyl acetate is exposed to moisture, acetic acid starts forming. I highly suggest checking this out.

[wmbigham]

I'll give it a try.

[wmbigham]

Didn't seem to make much of a difference. I prepped two standards and added acetic acid to one. I ran them both yesterday afternoon and again this morning. Not much if any difference between any of the four reps. If anything, the biggest change was in the standard that did not have acetic acid added to it. Benzo(a)pyrene and perylene-d12 had slightly reduced response after sitting over night.

[Don Shelly]

Didn't seem to make much of a difference. I prepped two standards and added acetic acid to one. I ran them both yesterday afternoon and again this morning. Not much if any difference between any of the four reps. If anything, the biggest change was in the standard that did not have acetic acid added to it. Benzo(a)pyrene and perylene-d12 had slightly reduced response after sitting over night.

I find that fascinating. Although I'm sure that you find it very irritating! If the acetic acid is "preserving" the samples (which would require more testing), and the PAHs are actually degrading, then the only possible explanation that I can come up with would be enzymatic digestion. I ran this past an organic chemistry guru and he concurs. The fascinating part is how there could be bacteria living in your ethyl acetate.

One more thing to check. Add tap or reagent (not DI) water to your vials and check pH. If the pH is 9 or higher, let me know.

Don

[Don Shelly]

Didn't seem to make much of a difference. I prepped two standards and added acetic acid to one. I ran them both yesterday afternoon and again this morning. Not much if any difference between any of the four reps. If anything, the biggest change was in the standard that did not have acetic acid added to it. Benzo(a)pyrene and perylene-d12 had slightly reduced response after sitting over night.

I find that fascinating. Although I'm sure that you find it very irritating! If the acetic acid is "preserving" the samples (which would require more testing), and the PAHs are actually degrading, then the only possible explanation that I can come up with would be enzymatic digestion. I ran this past an organic chemistry guru and he concurs. The fascinating part is how there could be bacteria living in your ethyl acetate.

One more thing to check. Add tap or reagent (not DI) water to your vials and check pH. If the pH is 9 or higher, let me know.

Don

I just found this in Wikipedia.

Acetobacter are of particular importance commercially, because they are used in the production of vinegar (intentionally converting the ethanol in the wine to acetic acid), and they can destroy wine which they infect by producing excessive amounts of acetic acid or ethyl acetate, both of which can render the wine unpalatable. Acetobacter are also used to intentionally acidify beer during long maturation periods in the production of traditional Flemish Sour Ales.

[wmbigham]

The one with acetic acid was about pH 3 and the other was at pH 7.

[Don Shelly]

The one with acetic acid was about pH 3 and the other was at pH 7.

Okay, thanks. pH 3 will inhibit any microbial activity. I recommend trying a higher quality ethyl acetate.

Don

[jkubeika]

I haven't managed to get anywhere with this problem yet. I am at the PA state lab and am waiting for my purchase request for different solvents to get through the red tape (at this time of year with budget pending it is a LONG wait). I have done a study and confirmed that it is only extracted analytes that are degrading. I have tested prepared standards (same exact vials I use to spike) over time in only ethyl acetate and they do degrade, but not nearly at the same rate. It takes 7-10 days of sitting out to drop under 40% recoveries.

I have had our micro lab test the equipment and they have been unable to grow or detect anything that may be eating the analytes.

[Don Shelly]

I haven't managed to get anywhere with this problem yet. I am at the PA state lab and am waiting for my purchase request for different solvents to get through the red tape (at this time of year with budget pending it is a LONG wait). I have done a study and confirmed that it is only extracted analytes that are degrading. I have tested prepared standards (same exact vials I use to spike) over time in only ethyl acetate and they do degrade, but not nearly at the same rate. It takes 7-10 days of sitting out to drop under 40% recoveries.

I have had our micro lab test the equipment and they have been unable to grow or detect anything that may be eating the analytes.

If a company is using bacteria to produce acetic acid and ethyl acetate from ethanol, any residual enzymes would cause PAH degradation.

A team of volunteers/members of AOAC International were developing a method using PAH incurred seafood to test Gulf seafood for PAHs. We discovered that the PAHs in the seafood were subject to bacterial degradation down to a temperature of -70 degrees. Tough little buggers.

Bottom line, if PAHs are degrading in a sealed container of ethyl acetate it's either UV light or enzymes.

[Bigbear]

I had a problem with Fisher Optima ethyl acetate having enough phthalates to "activate" my injection port after 5-8 injections.
Now I try to request a sample of any solvent we purchase and then concentrate 10-15ml to 1 ml and shoot it. If it has any significant peaks it is not purchased.
Don't overlook your methanol. In the past I found what seemed to be an early eluting hydrocarbon in Fisher Optima, we have switched to VOC grade MEOH.

I now use EMD omni solv with good luck. Still have no problems with Fisher Optima MeCL though.

[Don Shelly]

I had a problem with Fisher Optima ethyl acetate having enough phthalates to "activate" my injection port after 5-8 injections.
Now I try to request a sample of any solvent we purchase and then concentrate 10-15ml to 1 ml and shoot it. If it has any significant peaks it is not purchased.
Don't overlook your methanol. In the past I found what seemed to be an early eluting hydrocarbon in Fisher Optima, we have switched to VOC grade MEOH.

I now use EMD omni solv with good luck. Still have no problems with Fisher Optima MeCL though.

Thanks!