GC Column Seletion

[SJ.LI]

My lab is using the Agilent GC-6890N for VOC (methane and Carbon dioxide) analysis.
The columns used are HP-PLOT U (for carbon dioxide) and HP-MOLSIV (for methane).

I am going to develop new methods for the following five parameters:
-Nitrogen
-Ethane
-Propane
-n-Butane
-Carbon monoxide

I am just few experienced on using GC so i want to know if the two columns can be used for analysing the five parameters or not ?

If not, what types of column should i buy ?


Thank you!!
SJ

[GasMan]

SJ,

You need to give a bit more information. If you are presently using two valves on the GC, one to inject the sample and the other to isolate the molecular sieve column, then you can use the same columns for the compounds in your message. You may have to change the valve switching times. If there are other compounds in your sample that you are not interested in measuring, then there could be problems.

Gasman

[chromatographer1]

What you describe is an application of multidimensional chromatography. I suspect that this might be above your technical experience.

One could use a reverse column step single 10 port valve configuration but you would have to customize the column lengths and perhaps buy a third short column or use a piece of your HP-PLOT U column.

A three valve, backflush trap configuration could be used effectively with three columns.

Using a MOLSIV column with higher carbon alkanes C2+ will be short lived as the pores would become blocked and the analysis ruined in short time. This is what Gasman is referring to as 'problems'.

best wishes,

Rod

[jdezeeuw]

If your target analytes are the ones you listed, you have a few options.

I only can give information on the characteristics of the columns I know. Different vendor materials may act differently. We have used Molsieve 5A capillary by itself and this column will separate nicely N2, CO and also C1-C6 hydrocarbons but you have to heat it up to 300 C.
You can choose between fused silica or metal (MXT) capillaries, both with give good separation. Higher alkanes will also elute as sharp peaks, they do not harm the 5A.
I can sent a C'gram if you want.
You need relative short columns, I would not use > 15 meters for this. You may even consider to use a 1m 0.53mm MXT micropacked. Best is to use a splitted injection. Only use direct injection if you need very low detection limits. In thsi case also make sure you use an "uniliner" for best possible sdample transfer.

You have to get the U-PLOT out as this will be killed if you heat > 190C.

jaap de zeeuw, restek corporation

[SJ.LI]

SJ,

You need to give a bit more information. If you are presently using two valves on the GC, one to inject the sample and the other to isolate the molecular sieve column, then you can use the same columns for the compounds in your message. You may have to change the valve switching times. If there are other compounds in your sample that you are not interested in measuring, then there could be problems.

Gasman

Gasman,

I am sorry for the insuffient information i given.

Actually, my lab is using the GC-TCD system (Agilent 6890N) for the Methane and CO2 analysis.
There is individual injector, column and detector for each channel.

Channel "A"
Parameters: Methane and O2
Column: HP-MOLSIV (30m 0.32 25)
Detector: TCD

Channel "B:
Parameters: CO2
Column: HP-PLOT U (30m 0.32 10)
Detector: TCD

Both of the two channels are using Helium as the carrier gas.

If i want to develop a new method for N2, Ethane, Propane, n-butane and CO, are the presently columns suitable for the parameters? or should i use another carrier gas ?

SJ

[chromatographer1]

The propane and butane will take some time to elute from the PLOT U column, but what you have will work well for your analyses.

best wishes,

Rod