TMS derivatization on PEG SPME fiber

[rafanugo]

Dear All
I know silylation reagents could react with polyetilenglicol GC columns as they have active hydrogens. So, by the same reason, I wonder wether I could derivatice post extracction using the same reagents when using PEG fibers. My compound, benzenetriol, it is well extracted with PEG fiber but I need to derivatice to get good peak shape on GC. Any advices
Thanks
Rafael

[chromatographer1]

I would throw away the fiber if you subject it to reagents. It will no longer behave in the same manner as before.

One fiber per injection seems expensive to me. But what do you think?

best wishes,

Rod

After extraction by SPME why not do LC instead?

[rafanugo]

Dear chromatographer1
Thanks for the answer
First, I have no the device to connect fiber to the LC-MS. Second, what do you think about the performance of Poliacrylate fiber, I guess wouldn´t have any problems using on fiber TMS postderivatization, would I?

[chromatographer1]

A better choice, but I would expect some changes in behavior.

Hey, that is why we call it research.

Rod

[Don_Hilton]

I recall seeing someone describe derivitization on a fiber before GC analysis. The impression that I have was that it was on an autosampler with multiple samples and the derivitization was with vapors of the derivitizing agent. With the warning that I could have jumbled a couple of things together over time, I will encourage you to do some looking in the literature.

But even without looking in the literature - if you are to reuse the fiber, try exposing the fiber to derivatizing agent and then your sample. See if it works. Polyethylene glycol does not have many active hydrogens, so, even slightly modified with derivitization, the fiber may work well for you. And keep in mind that on performing derivitization, you do not want to extract your compound from the fiber. My memory of the work from years ago was that this was the point of derivitization with vapors rather than liquid. And as I am trying to remember back, those vapors may have been before exposing the fiber in the inlet - or may have been introduced in the GC inlet as the fiber was exposed.

[chromatographer1]

And the fiber itself was a PDMS fiber which has been exposed to reagent in its manufacture.

Your memory is correct the reagent was exposed as a vapor.

b est wishes,

Rod

[rafanugo]

Dear Hilton
You are right, I have been working in the process of on-fiber derivatization for time and I know that it has to be on head space before injection and after extraction. I know also the theoretical posibility of doing the way back, firt expose the fiber to derivatization agent and later go to the extraction (in my case "DI or Direct Inmersion") but I have not try it jet. Using PEG fiber with TMS on fiber derivatization I got some time good results and some time not. So, that is the reason of my question about wether PEG fiber could be damaged by the reactive. It seems Rod consider it could be useless after one exposure to the TMS reactive, but you don´t. Well, now I have a problem
Any other answer, please

[Don_Hilton]

Go with Rod on this one. Rod noted that the work was done by the vendor of the fiber. If I recall correctly, Rod knows that vendor - and their work - much better than I do.

SPME may not be the best approach for this analysis. A solvent extraction or ion exchange separation (with a reducing agent present) may be something to consider.

[rafanugo]

Dear Hilton
Well, I don´t want go very deep in the research the people are doing (I am only the GCMS guy you know...) but seems samples have problems with oxidation if air exposed and are difficult for doing other type of extraction as liquid-liquid and so on. Today I am getting good results with an adsortion fiber that I hope is not afected by derivatization reagent...
Thanks
Rafa

[Don_Hilton]

Benzene triols are very easily oxidized. (Notoriously easily oxidized.) Just moving solutions about in unclosed containers will change the results. And putting in an oxygen scavenger -- well the best that comes to my mind for protecting organic analytes is galic acid, which is a trihydroxy benzene with a carboxylate group hanging off the side... I know this is not easy. Preparation steps in a glove bag or glove box are a pain - but...

Another option would be to see if you can desorb these compunds into a solvent in a GC vial, then add a derivatizing agent and inject. If you use a large volume injection, you can use one or two hundered microliters of solvent to desorb the compounds and still get most of the sample onto the column. Just remember that the solvent has to boil considerably lower than the derivatized analyte.

[rafanugo]

Interesting .... I will take in mind. Thanks a lot

[Don_Hilton]

As I walked down to the kitchen something in the back of my brain said "No, it was pyrogallic acid." And with a quick look, yes that is what I had used and it is benzene 1,2,3-triol. pH is important - oxidation is more rapid at high pH.

And it has been years ago. I have used ascorbic acid more reciently to protect easily oxidized compunds. And depending, an excess of ascorbic acid may be sufficient to help protect pyrogallic acid.

[rafanugo]

Dear Hilton
The researcher thinks the compound is 1,2,4-benzene triol althought I identified as other isomer because is not in my NIST database... It cames of a microbial degradation and it seems degrade (oxidized?) to other compounds. So they want me to know what is desapearing and what is appearing... By the way, do you know what would be the oxidized product?

[Don_Hilton]

My impression is that the oxidation product is a bit messy. I would take a look in the literature. It seems to me that trihydroxy benzene type compounds are found in lignans and that might be a good resouce to see how people are handling those types of compounds.