Derivatized products - Real and philosophical questions

[kostas]

I have a philosophical question and two real questions:

Philosophical:
What happens to the Si when analytes that contain Si are run through a capillary column with a FID in the back end? Will Si be oxidized to SiO2? Is this not a problem for the FID?

Real question 1:
Will there be any problems if I inject dimethyldichlorosilane in a HP-1 column followed by a FID?

Real question 2:
It seems that glass liners need to be deactivated and that dimethyldichlorosilane is the reactant of choice for this. Can this be done while the liner (or any other part that needs to be deactivated) is still connected to the GC?

Many thanks!

Kostas

[chromatographer1]

There are products for the deactivation of glass that are to be directly injected onto a column in an active GC. Most chromatography houses sell them.

The Si does become SiO2 and is found as a white deposit inside a FID flame tip. Heavy use of such reagents require frequent cleaning of FIDs.

The best solution is to buy new parts from quality suppliers. The cost of wasted time for labor and machine is almost always several times more expensive.

Rod

[kostas]

Many thanks for your answer, Rod! I have bought Supelco's Sylon CT (5% DMDCS in toluene) for this purpose. I want to inject it in the running GC to titrate the siloxane groups in the liner and the column. However, I am worried of the damage the HCl ensuing from this reaction could potentially cause. Is there any easy answer to that or should I just treat everything offline?

Thanks again,

Kostas

[chromatographer1]

"......should I just treat everything offline"

That would be better, Kostas.

HCl can speed up the FID components corrosion and can damage capillary columns.

For packed columns in glass, the reagent can help the column along through a difficult day, but it is no long term cure.

If it were my decision and my hardware I would perform any corrective deactivation of components of the GC in a lad hood, outside an active GC.

I would soak any glass inlet liners in anhydrous H2SO4, then carefully heat the bath to remove any deposits. Follow that with a triple (distilled water) rinse (soak), and drying in a oven, and then using the Sylon CT (5% DMDCS in toluene) to treat the glassware.

Rodney George

[krickos]

Hi Kostas

As for real question 1:

Have you considered other column brands? The HP-1 column is or at least was not the most inert column in the tool box when using thin films some years ago. So examining alternatives brands might save you from any tideous deactivation procedure.

Below you have an example of this concerning BDE-209.



Journal of Chromatography A, 1041 (2004) 201-210.

http://www.sciencedirect.com/science/ar ... 8c93801e8d

[kostas]

Thank you both for your suggestions! I will proceed to deactivate everything offline, per Rod's suggestion. We thought about using alternative stationary phases, but the versatility of Polydimethylsiloxane keeps us from changing. However, the article is quite an interesting read.

[krickos]

Well just to avoid any potential misunderstanding.

I did not suggest changing the stationary phase, if you read the appriopiate section of the article you will find a few comparsions of "identical phases" and dimensions from different column brands. Although that case is a bit extreme it makes a point.