Chromatography Forum

I'm working the development of 525.2 method including a short list of semivolatiles (PAHs, phthalates and a few others) and wonder if anyone has any advice regarding the following:

1.) Hexachlorocyclopentadiene, 2,4-DNT and 2,6-DNT are only recovered at 25 - 40% of TV. They need to be 70% - 130%.
2.) ISTD recoveries based on use of fortification standard are around 50%. They need to be 70% - 130%.

I've followed the EPA method as its written. If anyone has any sample prep wisdom regarding the use of C18 solid phase extraction disks for the 525.2 method, please help.

Make sure you dry the cartridge/disk enough.
Elute with EtOAc/MeCl2, then with rinsed solvent from the sample bottle.

Be careful during extract concentration. Too rapid of a concentration can result in loss of the lighter compounds. Also, use a SPE product that is Teflon or has Teflon frits. Some compounds can become hung up in polyethylene. Avoid extracting in bright light. Light can cause some of the analytes on the list to degrade. Hope this helps.

Very interesting, I have seen recent losses of hexachlorocyclopentadiene as well. I have had my autoextractor rebuilt with no gain . I have always used a polyethylene cartdidge and frits ( same manufacturer) with the losses getting very bad only in the last 18 months or so.
In my testing I tested my extract drying ( poly tube and 1 frit + sulfate) by running about 15 mls of solvent through the tube and drying=== no loss.
Could the loss be due to the water at pH <2 and the 2 poly frits in the cartridge?

We do run on the ragged edge for exa.. at 70% recovery.
Anyone know of anyone selling 6ml cartridges with 1g C18 and made of teflon?

At the risk of sounding commercial. UCT sells just the product that you are looking for. EC525006. It is an unendcapped C18 blended for 525 in a 6 ml cartridge with Teflon frits.

Don

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chromabond offers a glass cartridge...6mL/1000.$$$$$ i had to go there to get my phthalates under control...the next step would be to clean your inlet...a dirty inlet with lots of active sites will eat hexcpd like candy. just went through this problem...the light trick actually works and so does the concentrator suggestion... sometimes fast isnt the best.

I may have spoken too soon. Our hexachlorocyclopentadiene results baffle me. As of late our recoveries of LFB and LFM @ 2 ppb are at the ragged edge on the low side. We did a MDL study @ 0.2 ppb and our average recovery was 115% with a SD of 0.01!!!! What am I missing?

Bigbear,

Keep your sample, sample prep and extract in the dark. Pass the sample through the C18 slower. 10 ml/minute is optimum for that "bad actor".

Don

I'm always in the dark! G

I flow through my bed @ 30 ml/min ( and have with no problem except for the last 18 or so months). The strange thing is @ 2 ppb the recovery is marginal, but @ 0.2 it's great. This is what I'm having trouble wrapping my head arround!

I can only come up with the theory that the lower the concentration, the less chance for breakthrough.