CO2 Gas Analysis - 7890A GC - TCD

[brainz]

Hey,

So i want to be able to detect CO2 gas in my analysis but really confused about a whole bunch of things.

I decide to run my CO2 sample with the following configuration
Inlet Temperature at 270 deg C
Oven temperature starting from 50 deg C to a max temp of 270 deg C
TCD - 300 deg C
... but i really couldnt get a signal.


I have read in several papers that to analysis a permanent gas sample (e.g CO2), more than one column should is used and valves should be switched which I still don't fully understand.

My GC, as far as I know has or can only have one column installed at a time, (It is either a HP PLOT 5 - which i have at the moment or a HP PLOT Q.

Cheers,

Ajay.

[GasMan]

We need a lot more information.

What else is in your sample besides CO2, and at what concentrations?
What are the concentration levels of CO2 that you need to measure?
Are there any other compounds in your sample that you need to MEASURE?
How are you injecting the sample?
What carrier gas are you using?
What carrier gas flow and what TCD reference flow
If you are using PLOT columns I presume you are also using a capillary inlet.
Are you running splitless of in split mode. If split mode, what is the split ratio?

I presume that the 'HP PLOT 5' column is a HP PLOT molecular sieve 5A column. This column will absorb CO2.

The HP PLOT Q column would be better for CO2 measurement, but this depends on what else is in your sample.

Gasman

[brainz]

We need a lot more information.

What else is in your sample besides CO2, and at what concentrations?
What are the concentration levels of CO2 that you need to measure?
Are there any other compounds in your sample that you need to MEASURE?
How are you injecting the sample?
What carrier gas are you using?
What carrier gas flow and what TCD reference flow
If you are using PLOT columns I presume you are also using a capillary inlet.
Are you running splitless of in split mode. If split mode, what is the split ratio?

I presume that the 'HP PLOT 5' column is a HP PLOT molecular sieve 5A column. This column will absorb CO2.

The HP PLOT Q column would be better for CO2 measurement, but this depends on what else is in your sample.

Gasman

Hi Gasman,

We are running a CO2 flooding experiment. So we expect to produce some amount of CO2 as effluents which will be collected in 2ml vials. It is our intention to run these samples to determine the % composition of CO2 in it. That will give us a sense of how much CO2 has been produced by measuring the weight of vials before and after sample collection. Ideally nothing else is meant to be in the CO2 sample maybe just air.The concentrations therefore are unknown or so I think.

CO2 is injected using the ALS - Automatic Liquid Sampler
The GC settings is as follows:
Inlet temperature: 35 deg C, split-less – 50mL/min
Carrier gas: Helium, Flowrate: 8mL/min, TCD reference flow: 28.6 mL/min
Oven temperature: 35 deg C, max 100 deg C
Detector Temperature: 120 35 deg C
Column configuration – HP PLOT Q ( 30m x 530um x 40um)

Cheers,
Ajay.

[GasMan]

You say that you are using 2ml vials and an autosampler. How much are you injecting?

Gasman

[brainz]

You say that you are using 2ml vials and an autosampler. How much are you injecting?

Gasman

0.5mL

Ajay

[AICMM]

1) You are pulling 1/2 mL out of 2 mL vial? You are creating quite a vacuum on your vial/syringe. You have a 1/2 mL syringe mounted?
2) You say splitless at 50 mL/min but column flow 8 mL/min? where is all the other flow going? Out some port unless something is missing in the details.

Try the following. i) manually inject a high concentration of CO2 using a hand syringe. This establishes retention time. Even though the TCD is not very sensitive, it will see high percentage even with a split injection. ii) reduce your total flow (50 mL/min) to something more like 20 and repeat the hand injection.

A Q should separate CO2 from air at that starting temp so it tells me that you are not getting material on column.

BTW, raise your TCD temp. At 125 with an Agilent TCD you risk condensing water.

BTW (2) why not do this with a gas valve and do it in real time?

Best regards,

AICMM