Chromatography Forum

WK makes an excellent point. Perhaps a question that should have been asked early on. The inlet will catch all kinds of nonvolitle gunk out of your injections. And that gunk makes a film that can cause degredation of various compounds in the inlet. Change the inlet liner often when you are injecting solvent extracts of plant materials.

If you don't have a furaneol standard, you should be able to purchase some. Looking at prices in the US, it is not very expensive. Or if you have a contact in the flavor/fragrance world, perhaps you can even get a small sample from them.

This stuff on "gunk" reminds me of some work with fatty acids in the 1980´s. We had the methyl esters start disappearing beginning with the highest weight FAME. It was a honey like gunk in the inlet liner, mostly consisting of Triglycerides, phospholipids wre also in there. This stuff caused the discrimination at about 280°! So, if you have some switching mechanism, like we did (Dean´s heart cut method which included a flow reversal of the first column, thus a timed injection without split), you can loose material without degrading it.

I believe furaneol is reasonably unstable.

https://online.tu-graz.ac.at/tug_online ... rrPk=37502

WK

Oh yah...
while searching for such info, I also have found a following paper...
http://www3.interscience.wiley.com/jour ... 1&SRETRY=0
Thanx
Ram

Hi Ram,
What was the gist of the abstract - I can't seem to open the link.
Furaneol is reasonably stable in propylene glycol.
Regards
WK

Hey WK, sorry for the dealy...
Yah now even I cannot open the link which I had posted
can you give your mail ID so that I can send you the PDF?
Anyway..They have compared 5 different columns and found that on 1. stainless steel, 2. the BaC03-treated borosilicate 3. the commercial glass
WCOT columns furaneol was not detected. Whereas sample run on borosilicate column which had been pretreated by HF etching or on the fused silica column gave furaneols peak..
(Williams and Mottram, 1981, Gas chromatographic analysis of furaneol, Journal of High Resolution Chromatography, 4, 421-422)

Since you have a fused silica column which is way more inert than any of the steel and glass columns considered in the reference I do not think that you need to worry unduly about furaneol having disappeared on-column.

The evidence that you had furaneol there in the first place is weak to say the least - an MS library spectrum match from a mixed peak. Unless you can show that the peak was at furaneol's retention time (which would need an injection of the standard that you do not have) the most logical conclusion is that the peak was partly due to an unknown compound which cannot be reproducibly extracted from the sample and which is unstable in extracts. Anything else is based on your wish to find furaneol.

Peter

Thanks for the comment Peter.
We don't have std furaneol yet. But we have determined Kovat's index by parallely running a mixture of straight-chain alkanes and found that it's same as the reported one.

Ram,

Any luck with a changed out inlet liner? Be sure, by the way, that the glass wool is deactivated after insertion into the liner. (If you try to repack a liner with deactivated glass wool, strands will break in the glass wool - and freshy broken glas is very active.)

Ram,

Any luck with a changed out inlet liner? Be sure, by the way, that the glass wool is deactivated after insertion into the liner. (If you try to repack a liner with deactivated glass wool, strands will break in the glass wool - and freshy broken glas is very active.)

Yah... We have tried changing the liner as well as glass wool but that didn't help..
What do you mean by glass wool is deactivated? How to be sure about it? I didn't understand. Thanks

Glass is chemically active and will bind or react with some kinds of molecules. Glass has lots of hydroxyl groups on the surface. Therefore, we use deactivated liners and glass wool in the GC - and we can purchase them this way. The glass is chemically treated (typically sililanized) to eliminate the chemical activity of the glass.

When you purchase commercially made liners, they are treated by the vendor. And, liners with glass wool inserts are treated after the glass wool is inserted. (I ran into a vendor, years ago who was deactivating glass wool and then placing it in the liner. This was corrected -- and I would assume that deactivation after assembly is standard practice. But, you can check with your vendor to be sure.)

So, to be sure about the deactivation of your liners: Purchase them as deactivated. When you remove a liner from the GC, discard it so that it dos not get back in collection of clean liners. (I know the practice of keeping an old liner "just in case." But, once it is suspect, it is always suspect.)

--

From what I've seen, it looks like the next best step, once you are sure the GC is in good condition, is to spike a an extract with furaneol at about the level you thought you first saw it. If the peak shows up - the problem is unlikely to be chromatography. If the peak vanishes in the GC, you get to check that out...

Thanks for the info. Every time after cleaning the liner, I fill it manually with the glass wool and directly use...

If I carry out the GC injection of the fruit samples prepared solely by SPME, then is it fine if I DO NOT fill the injector liner with glass wool?

If I carry out the GC injection of the fruit samples prepared solely by SPME, then is it fine if I DO NOT fill the injector liner with glass wool?

If you're doing "SPME fiber" injection of the extracted fruit analytes you don't suppose to fill the injector liner with any wool. Remember that you'll have to use narrow (SPME) liner with 0.75mm i.d, in order to avoid peak broadening in the chromatogram.

Regards

You can also get the SPME fiber caught in the glass wool - and lost in the inlet. I won't tell you how I know! (And it can be reproduced, which proves that it was done by a scientist...)

Even if you do not lose the fiber, you can rub the coating off the fiber if the fiber contacts the glass wool. The narrow diameter liner that zokitano mentions is a really good idea. It helps to make the chromatographic peaks sharper. And sharper peas give stronger signals and better resolution.