Chromatography Forum

Dear Sirs,

Our lab has to analyse Ethanol, IPA and Water content in Ethanol and IPA samples. Water contents of sample are between 0.01- 40%.

In the present we do have GC (7890A) - TCD and columns are DB624 and HP-5. I've searched from internet and got information that alcohol/water can be analyse by DB624 (TCD) but a GC specialist told me that filament of TCD will be destroyed by oxygen from water. So it makes me confuse if TCD can be used to this kind of samples.

We tried to optimise condition of Ethanol sample by using column DB624. Both peaks separate well but less sensitivity.

I would like to asked if TCD and columns which we have (DB624 or HP-5) can be safely used to our target samples. And it would much appreciate if someone can guide us the GC operating conditon.

Best Regards,

Hi Luckync,

Im not sure about Oxygen burning the TCD filament if inject at small quantity. What i know is Oxygen can destroy a column if it is kept in contact to air too long in certain type of column. And for the TCD you need to keep flow of carrier gas when it is hot ( > 100 degrees) otherwise the filament can burn. Thats probably what the GC specialist meant by what he told you.

What i know is if you have an FID detector that would be easier for Ethanol and Isopropanol testing if you take either of your column you mentionned but i prefer the DB-WAX because i already test these solvent (too many times...lol) with that column. Few things i could recommend:

1. Water tested by Karl Fischer because its the best technique for water content.
2. Water tested by GC-TCD using a glass packed column. (you could ask column provider for the type to use- i dont remember the type of column i was using for the water test - thing i know we never use capillary column to test water)
3. For ethanol and IPA , GC-FID with DB-Wax, on-column. injection 0,5uL 80 degree celcius isothermal(around 5 minutes ), injector temp: 150 degrees, detector 200 degrees. This way you get very high sharp peak....

What i told is only my experience.....With all you have under hand i cant help you that much. Hope this will help a bit.

Willy the GC

Dear Willy,

Thank you very much for sharing your experience. It's very useful for us.

Best Regards,

Luckync,

Putting water as a liquid on a capillary column will be harmful to the column. The 624 phase separates IPA and EtOH nicely but most likely at temperatures where water will condense onto the column surface and possibly damage it. I would try to keep my column temperature above 80°C if possible to minimize this problem. The Wax column will have both alcohols eluting at almost the same retention time although peak shape should be excellent.

I would recommend a porous polymer packed column such as Porapak or Hayesep R in glass or fused silica lined SS. Be certain that you have adequate evaporative injector volume so you do not create a backflash of water vapor in your injection port. You should be able to inject small amounts of sample and still have adequate sensitivity to measure water at very low levels using TCD.

Ethanol and IPA also separate very well on this packed column.

best wishes,

Rod

Dear Rod,

Many thanks!

I also got info from internet that someone use Porapak Q for alcohol&water analysis and it works well. We may try this way for safe the capillary column.

Once again, thank you for the knowledge.

^__^

Best Regards,

You will find that water will tail more on the Q polymer than on the R polymer. The R polymer is the industry standard choice for water analysis in many applications and certainly is the better choice if accurate trace measurements are required.

best wishes,

Rod

Rod,

Thanks a lot!

So I got useful information for talking to our GC supplier on tomorrow morning.

Best Wishes,

Dear Sirs,

If someone has experience or comments on DB-WAXETR (30m, 0.25mm, 0.25 um) or HP-INNOWax (30m, 0.25 mm, 0.25 um) with TCD.

Please share the knowledge.

Best Regards,

They are bonded carbowax phase columns made by Agilent.

They are different but similar to Supelcowax or Omegawax made by Supelco.

They can have slight selectivity differences due to the nature of the chemical bonding mechanism used to bond polyethyleneglycol to the fused silica surface and the surface deactivation procedures used.

What else do you want to know?

The world is a big place.

best wishes,

Rod

Dear Rod,

Would it be OK if these both columns will be used to analyse Ethanol/IPA/Water instead of packed column?

Is it suitable work? Is packed column (Porapak R) better?

Many thanks!

Best Wishes,

I would try Willy the GC's method and see if you are satisfied with it.

I agree that Karl Fischer titration might be the best method for water determination instead of GC.

100 ppm to 40% is a very broad range.

I would not prefer to use capillary columns for this analysis. There are many packed column that might be a better choice.

Use what you have. If you are happy then go with it.

best wishes,

Rod