Chromatography Forum

Helo All,
I would really appreciate your help with my GC problem for my PhD research. I am realy running out of time for my defence.
I have dehydrogenation (oxidative dehydrogenation) experiments with product gasses as ( H2,N2,O2,CO,CO2,CH4,C2H6,C2H4,C3H8,C3H6,H2O).
I have my Shimadzu-2010 GC with TCD and FID connected in series (TCD-FID) with Argon as Carrier gas (for H2 detection).
I have Carboxen-1000 column only that separates well the ( H2,N2,O2,CO,CO2,CH4) gasses but not the (C2H6,C2H4,C3H8,C3H6,H2O) gases.
The only option I have is to buy a Porapak Q column and connect in serise with the Carboxen-1000 column to get the desired separation in one GC.
Please advice me about this possibility and the series connection of columns

thank you all

You really should replace your 6 port sample valve with a 10 port two column sampling valve and perform two dimensional analysis of your gas sample for most effective and timely analysis. You might replace the Q with a A or N polymer and you could use a mole sieve 5A instead of a Carboxen 1000, but that isn't a necessity. You could also use a short coated Carbopak B as a pre-column to reverse the C1+ or CO2+ peak through a Q or A porous polymer through the buffer column before the detector. As long as you don't pass CO2+ peaks through the mole sieve you should separate the C2s-C3s and CO2 on a polymer column, but other columns might separate them more quickly and even better.

Single dimensional analysis of these light gases is not a recommended practice. But good luck with it.

Look at Valco or Agilent's web sites for assistance. If cost is an issue you could manually inject and switch the valve instead of doing it automatically.

best wishes,

Rod

salgham2,

Rod is dead on on this one. You don't want series, you want parallel. Even if you hook the Q to an injection port and FID, make it its own channel. If you make the FID its own channel, then you could use a syringe for that side (not my recommendation but still do-able.) That's because any air inclusion by syringe will be mitigated by the FID not measuring the air. This route still leaves hydrocarbons on the Carboxen but at least you will get decent chromatography off the Q. Better still is the backflush for the Carboxen to limit the heavies.

Water is a separate issue.... Best column I have seen for this is a thick film DB-5 but I don't think that is an option for you. Therefore, maybe some other instrument (like humidity meter) would be a good choice.

Best regards,

AICMM

If you reverse column step the heavies and water then you will not send the CO2+ peaks onto the sieve, be it carbon or mole. That includes the water.

Parallel analysis on two columns will not harm the porous polymer column but will 'clog' up the Carbosieve eventually and degrade your analysis results. That is why two-dimensional or three dimensional analysis is better and faster. Plus you won't have so many problems with measurement.

A ionization detector like AICMM sells (or Valco or Gow-Mac) is a better solution if you can get adequate separation of the components and you can almost normalize the results due to the similarity of response on these detector for the gases and hydrocarbons.

There are better columns for C2s, and for C3s separations than the porous polymers. But you can determine that.

best wishes,

Rod