Chromatography Forum

Hello,

Could anyone help?

I'm running EPA 525.2 for months without problem till about 3 weeks ago. My Aldrin recovery was found in LFM, LFB as low as 50%, sometimes other analytes like Hexachlorocyclopentadiene, Benzo(a)pyrene also low. I used amber glassware and avoid the lights. PH<2, no free chloride. Horizon altlantic C18 disk. Turbo-Vap II condenser.

I injected 2ppb standard to test my instrument and the result is good. So I think the instrument is OK. I changed a new batch of C18 disk but got the same result.

Thank you for the help!

Since you injected the 2ppb standard and didn't see loss, try reducing the nitrogen flow on the turbovap and also inspect the tubes to make sure there are no scratches in them. If there are scratches in the tips of the turbovap tubes you may try silanizing them to remove active sites.

Another thing that seems to affect recoveries is the preservative in the solvents. We started getting terrible recoveries once and found the supplier had changed the preservative in the methylene chloride, once we purchased a different lot with the correct preservative everything returned to normal.

Thanks James. I will try silanizing turbovap tubes. I did see some scratches. Do you have a protocol for silanizing these volumetric tubes? What is the N2 flow rate you suggested? and I used the same lot of DCM as before but I will try to see if I can find the other lot. Thanks again

I found there's one post in the forum about silanization by geget. Is this OK?
A procedure of silanization :
Prepare a solution of diméthyldichlorosilane (Sigma D-3879) at 5% in toluene
Introduce this solution in the glass container and shake 10 min
Rince with toluene
Rince with methanol
Rince with toluene
Rince with methanol
Dry 20 min at 80°C

Thank you

I found there's one post in the forum about silanization by geget. Is this OK?
A procedure of silanization :
Prepare a solution of diméthyldichlorosilane (Sigma D-3879) at 5% in toluene
Introduce this solution in the glass container and shake 10 min
Rince with toluene
Rince with methanol
Rince with toluene
Rince with methanol
Dry 20 min at 80°C

Thank you

I think our process is similar. We use the the Sylon CT solution which is basically the same thing. In the turbovap tubes you will probably just want to swirl it around a little instead of shaking it, but otherwise that should work.

Update:
lower Turbovap N2 flow to 10 psi, Aldrin still low. will try other steps and update. Thanks

Have you ruled out the extraction disks? Try spiking your LFB amount directly into the solvent in the turbovap tube, take it down to whatever volume you use and inject. This will tell you if it is the blowdown.

Thanks for all the suggestions.

I spiked LFB to turbovap solvent and found everything was good. This indicated the burbovap was good. Problem must before concentration.

Then I spiked LFB to the solvent (EtAC+MeCl2) and passed it through Na2SO4 to dry (pH was not adjusted) added same amount of MeCl2 I used. After blew down to 1mL, aldrin was good but some other analytes like simazine, metribuzin, butachlor, benzo(a)pyrene lower than before.

I will continue on Monday then update.

Thanks again everyone! Have a good weekend!

Tried new concentration tube and new batch of MeCl2. Both aldrin are still low.
Will maintain the extractor then test. Waiting new C18 disk.

After maintenance of the extractor and changed some parts of them by manufacturer, the recovery of these analytes getting better but not totally satisfied.
I must thank all the advises I received. These advises are very useful to find out where the problems are! Thank you!

James
I don't know if you remember this topic from a few years ago, but I see you mentioned preservative in the methylene chloride affecting your recoveries, but you didn't say which ones. Which preservative did or didn't get good recoveries and in what concentrations? I am working on a GC method from the USP where methylene chloride does not dissolve the sample, only the analytes, and my recoveries for 2 types of aminophenol are low. I am using methylene chloride with amylene (50-140 ppm) supplied by Sigma, but I am wondering if a different methylene chloride mixture would get better recoveries for my method as well.

Regards
Melissa

Since you injected the 2ppb standard and didn't see loss, try reducing the nitrogen flow on the turbovap and also inspect the tubes to make sure there are no scratches in them. If there are scratches in the tips of the turbovap tubes you may try silanizing them to remove active sites.

Another thing that seems to affect recoveries is the preservative in the solvents. We started getting terrible recoveries once and found the supplier had changed the preservative in the methylene chloride, once we purchased a different lot with the correct preservative everything returned to normal.

I can't remember exactly what the stabilizers were, but currently we are using methylene chloride with amylene. I looked and it seems the other stabilizers are normally cyclohexane and cyclohexene. Since these boil at about 80c while amylene boils at about 30c, I would think the amylene is probably the better one, where the cyclohexane could become more concentrated as you blow down the extracts and cause problems. I am pretty sure it was a high boiling compound that was causing us problems because it was becoming more concentrated in the extract and the analytes were less soluble in the mixture.