Chromatography Forum

Can someone explain to me the theory behind parallel column chromatography? The GC that I'm using has a Varian capillary column “Molsieve 5A/Porabond Q Tandem."

Thank you for your help.

Tandem means to me 'one after the other'. Are there two columns connected in series or are they in parallel, as mentioned in your subject line?

Gasman

Could be one from each inlet, going to each side of a TCD. You use one column for analysis, the other for the TCD reference.

We run a system with moly sieve and ppq in parrallel but on one injector.

After inj. none retained peaks pass though the first column onto the second.
The columns are then switch out of series.
The peaks from the first column are eluted to the injector.
At a defined time the second column is swithch back into the carrier flow and its peaks eluted.


Set up uses a pair of columns as above. Two valco valves, 1 inj the 2nd for column switching.

This is for CO, CO2, N2 and CH4 in H2

If you are running a dual column ( one injection with2 results, one per colum) it's for confirmation. To be a hit the compound must be found from botth columns.

Most of the time, for gas analysis, dual column configurations are series configuration, not parallel. Series means that you inject on something like a Q to retain CO2 and heavier long enough that they do not pass to your sieve. Once the "light" components are on the sieve you either backflush to vent or backflush to detector from the Q while you allow the sieve to continue eluting and, eventually, elute the sieve to detector.

It is unusual but entirely possible to run Q and sieve in true parallel (both columns side by side with one injector) but this puts whatever CO2 you have in your sample on the sieve which is not an ideal situation. It does, however, make for a very simple set-up.

Best regards,

AICMM

It's a reasonably common application for CO, CO2, O2, N2, H2. Maybe that's what you're doing? Can't do them all on one column. The Poraplot Q won't separate the H2, O2, N2, CO and the mol sieve won't elute the CO2.

Pass the H2, O2, N2, CO through a Poraplot Q unseparated. "Park" these on the mol sieve while allowing the CO2 to elute from the Q. Then get the flow through the mol sieve and elute the now separated H2, O2, N2, CO.

It can be plumbed/valved other ways, but the basic challenge is the same. Keep everything but CO2 on the mol sieve and keep the CO2 off the mol sieve.

Somewhat off topic and I dont want to start a firestorm, but CO2 WILL elute from a MS5A column if the packing is prepared and packed properly, but not in a timely or an isothermal manner. I have a chromatogram showing the elution following the temperature programing of the GC oven.

Email me if you wish to receive a copy of it.

best wishes,

Rod

I have a customer who occasionally shoots CO2 on a sieve to measure O2 and N2. She then bumps the temperature up and goes home for the day.

Best regards,

AICMM

What a waste of time. It should take only about 20 minutes, 30 minutes on the outside. Of course it only takes a 1 ft column to separate O2 and N2, Matthew.

best wishes,

Rod

ps
Your link to your web site is no longer functioning. Matthew, do you have an email I can use?

Rod,

I have updated my web address in my profile to my current web site.

Also, aicmm at flash dot net.

Best regards,

AICMM

It's a reasonably common application for CO, CO2, O2, N2, H2. Maybe that's what you're doing? Can't do them all on one column. The Poraplot Q won't separate the H2, O2, N2, CO and the mol sieve won't elute the CO2.

Pass the H2, O2, N2, CO through a Poraplot Q unseparated. "Park" these on the mol sieve while allowing the CO2 to elute from the Q. Then get the flow through the mol sieve and elute the now separated H2, O2, N2, CO.

It can be plumbed/valved other ways, but the basic challenge is the same. Keep everything but CO2 on the mol sieve and keep the CO2 off the mol sieve.

In case I want to analyse air eluted from a reactor, can I use instead of the above configuration (1 inlet, 2 columns, 1 valve, 1 TCD) a single packed column? I want to separate oxygen, methane and carbon dioxide, in a 6890N GC equipped with a TCD.

I have in mind to use HayeSep D 100/120, Nickel 200, 20ft x 1/8".

Is it possible, by ONE air sample injection to separate the 3 above-mentioned substances using the HayeSep D column?

Thanks in advance.

Sorry for the OT on this thread, but I have been wondering where Rod has been? Anyone have news?