EPA 524.2 Chlorofluorocarbons

Discussions about GC and other "gas phase" separation techniques.

6 posts Page 1 of 1
I run EPA 524.2, purge and trap concentrator connected to GCMS. I've noticed lately that I have been having a problem with the chlorofluorocarbons. Whenever I calibrate, my curves for dichlorodifluoromethane and trichlorofluoromethane come out great (<20% RSD) However, when I run a CCV the concentrations for these analytes come out much higher and I fail the 30% acceptance criteria. Any ideas?
Is the ccv made from the same stock/daily as the cal? If gasses come out high the cal standards were low. How was your 2nd source check?
DOn't forget to check the fluorobenzene, if it's low.....
I use the MiniInert caps on 5ml reaction vials to store my volatiles standards to prevent loss of the lighter analytes such as these. If your standard is a few days old and you have to open the cap each time you make a dilution you will lose the gasses very quickly, within a couple days. I also use the standard still cold, I don't allow it to warm completely to room temperature. The reasoning behind this is that the small volume of methanol you pull up into a gastight syringe will equilibrate to the temperature of the syringe barrel within a couple seconds, so just pull up the amount you need, wait a few seconds for equilibration and you have an accurate amount. Plus keeping the standard cold reduces loss of analytes over time.

https://www.sigmaaldrich.com/analytical ... alves.html
The past is there to guide us into the future, not to dwell in.
Steve Reimer wrote:
Is the ccv made from the same stock/daily as the cal? If gasses come out high the cal standards were low. How was your 2nd source check?

The CCV is made from the same stock as the cal. I make my cal standards from brand new stock. The 2nd source check (QCS) comes out high as well.
James_Ball wrote:
I use the MiniInert caps on 5ml reaction vials to store my volatiles standards to prevent loss of the lighter analytes such as these. If your standard is a few days old and you have to open the cap each time you make a dilution you will lose the gasses very quickly, within a couple days. I also use the standard still cold, I don't allow it to warm completely to room temperature. The reasoning behind this is that the small volume of methanol you pull up into a gastight syringe will equilibrate to the temperature of the syringe barrel within a couple seconds, so just pull up the amount you need, wait a few seconds for equilibration and you have an accurate amount. Plus keeping the standard cold reduces loss of analytes over time.

https://www.sigmaaldrich.com/analytical ... alves.html

But wouldn't you expect to see the concentrations coming out lower if that were the case? The concentrations are increasing over time.
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