Chromatography Forum

Posted: **Wed Aug 03, 2005 7:52 am**

Hi,

I excuse me for the message I sent in july 26, because I was in a hurry and I didn't explain properly the phenomenon.
I try now:

More and more time I observed that semivolatile compounds (anilines, phenols, PAHs, erbicides, ...) extracted from water with an organic solvent (methylene chloride, n-hexane), then concentrated and injected in splitless mode in GC (DB-5ms or DB-5) showed a norrow peak, while the same compound in a reference solution (the same solvent used before) showed a wide (and tailing, in the case of phenols, anilines and erbicides) peak. I observed the phenomenon with both "young" and "old" GC column.

I supposed that the difference could depend on the presence of water in the solvent, so I tried to saturate the reference solution with water, but no improvement was shown.
At the moment I think that it could be a problem of different solvatation of the compounds
- in organic solvent, after being solvated in water, and
- directly in organic solvent

May you show me your opinion about this, please?

Thanks

Posted: **Wed Aug 03, 2005 12:44 pm**

I think your reference solution has degraded or is contaminated.

Get fresh stds. You have something very polar in the reference solution you don't know about.

Posted: **Wed Aug 03, 2005 3:15 pm**

I don't think so,
because I spiked a blank water sample with the same reference solution (the one which gave bad peaks), I extracted the sample, I injected and I found narrow peaks.
It is a strange behaviour, but I couldn't find an explanation!

Posted: **Wed Aug 03, 2005 4:05 pm**

Can you give more detail about your extraction procedure? What's the solvent for the STD? Is it also MECL2?

Posted: **Wed Aug 03, 2005 5:19 pm**

Yuri,

You wrote:

"I spiked a blank water sample with the same reference solution (the one which gave bad peaks), I extracted the sample, I injected and I found narrow peaks. "

What you did was to clean up your std solution. See? What was polar in the reference solution was removed by your extraction from spiking into a water blank.

best wishes

Rod

Posted: **Fri Aug 05, 2005 7:02 am**

First, I reply to JI2002.

There are two different situations.
I extracted water samples with Methylene chloride three times then I concentrated to small volume and I injected in methylene chloride (Phenols and anilines), or exchanged solvent to n-hexane (PAHs and erbicides) and I injected.

Reply to Rod.

I can't exclude your explanation, it is quite convincing.
My only doubt is that I observed the phenomenon more and more time, also when I prepared a new fresh reference solution (this was for erbicides) just before the extraction of a spiked water sample and it seems to me a strange thing that I could have contamined every solution with polar substances.
Anyway I will try in the future with a new fresh reference solution.

Thanks

Posted: **Fri Aug 05, 2005 12:22 pm**

Your "polar substance" may be in the original chemicals you use to make your reference std.

Herbicides, phenols, and anilines (fresh out of the bottle so to speak) can have impurities that may be removed by the water extraction.

I hope your problem gets resolved.

best wishes,

Rod

Chromatography Forum

Different peak shape in GC - 2

Different peak shape in GC - 2

problems?

extraction

one more thing