Determination of O2 and CO2 in N2

[emsman]

Hello,

For permeation tests on polymer materials of my colleagues in ADC I need to establish the analytical equipment for separation and determination of carbon dioxide and oxygen in nitrogen matrix. As I have several Agilent GCs 6890 at my disposal I want to equip one of this instruments with an additional channel for the new analysis. However, I haven't got any experience in permanent gas analysis. Can anybody give me hints on the following questions?
- which inlet, column and detector would You recommend?
- can I use helium as carrier gas? (at the moment all our GCs use helium)
- can I leave the new column built in when using the GC for "normal" analysis on capillary columns and oven temperatures up to 280°C?
- sample introduction: gas-tight syringe or some way of purging the sample?

Thanks in advance for Your answers
Florian

[chromatographer1]

Florian,

I would recommend either a Carboxen 1010 PLOT capillary column or a micropacked 80/100 MS13X column using fused silica coated SS tubing.

Extended times at 280°C for the C-1010 PLOT will require reconditioning of the column with air before oxygen analysis is performed but the analysis will be accurate if this is done. The MS13X will tolerate this temperature without problems for many hours. Ideally one would use a porous polymer PLOT for CO2 and a MS5A PLOT for O2 in nitrogen, but 280°C is a bit too high for optimal results.

Helium carrier is fine for discharge detectors or for TCD. Argon is also a possibility if preferred.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rodney.george@sial.com

[tigerk2001]

Dear sir,
If you are interested, we have analyser configured to do such kind of application.
We use our K4000ng platform configured with a packed column porapak Q 1/8''OD for CO2 and a Mol Sieve 5A 60/80 1/8'' for O2 in pure N2.
We have system that works from ppb to % for such kind of analysis.

Please contact me if you have any question.

We also have demo unit available.

Dany Gagne
Production Manager and Technical Support
Contrôle Analytique
1076 Johnson
Thetford Mines
Quebec, G6G 5W6
Canada
phone : 418 334-0990
web site : www.cai-ca.com

[AICMM]

You don't say what levels you are interested in. If very high levels you might be able to use an Agilent TCD and it will pop right in. If lower levels, low percent to ppm, you could use a helium ionization detector, Valco or AIC Corporation and still use helium as the carrier and reaction gas. I am biased on which one you should use (see earlier thread) but both of these are plug and play and will look like just another FID since they use Agilent FID electrometers. Frankly, both HIDs are probably cheaper than the Agilent TCD but I am not sure so don't quote me.

You can also probably use a ShinCarbon column but it is probably not rated to the 280 C mark so that may be an issue. Finally, I would strongly recommend against a gas tight syringe because in my experience, no matter how hard you try, you are going to get a bit of air and since you are looking for O2.... I would recommend a 6 port valve injector.

[chromatographer1]

AICMM is correct in his comments. I agree that using a valve for injection is preferred. Agilent 6890 GCs should be capable of adding a sampling valve and loop internally as a standard part or externally as an add-on. The hardware is Valco based for both solutions.

A micropacked or packed MS13X column is preferred over any PLOT column due to the ability to measure % levels down to ppb with a HID detector (AIC or Valco) by changing the sample loop. With an Agilent µTCD you should be able to measure % levels down to ppm levels. Using a PLOT column like the Supelco 1010 you should be able to measure below 1000 ppm without difficulty.

A valve injection will give you the flexibility to use both split/splitless injectors when you don't wish to use the valve, a positive asset to have.

Accuracy and reproducibility will be vastly improved if you avoid a gas tight syringe.

best wishes,

Rod

[chromatographer1]

AICMM is correct in his comments. I agree that using a valve for injection is preferred. Agilent 6890 GCs should be capable of adding a sampling valve and loop internally as a standard part or externally as an add-on. The hardware is Valco based for both solutions.

A micropacked or packed MS13X column is preferred over any PLOT column due to the ability to measure % levels down to ppb with a HID detector (AIC or Valco) by changing the sample loop. With an Agilent µTCD you should be able to measure % levels down to ppm levels. Using a PLOT column like the Supelco 1010 you should be able to measure below 1000 ppm without difficulty.

A valve injection will give you the flexibility to use both split/splitless injectors when you don't wish to use the valve, a positive asset to have.

Accuracy and reproducibility will be vastly improved if you avoid a gas tight syringe.

best wishes,

Rod

[chromatographer1]

If I may add a commercial comment about a packed column solution, a stock 4.5 meter 60/80 mesh Carboxen 1000 column will separate O2 from N2 and will measure CO2 as well. Water contamination will not affect this separation.

This is important if you don't wish to spend the time to recondition a sieve column before use.

It will require reconditioning with air if exposed to temperatures above 200°C or so, as I suspect a Shin Carbon column would require also.

I have chromatograms if anyone would like to review them.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rodney.george@sial.com

[emsman]

Thanks all for the helpful comments.

I'm not quite sure yet about the kind of apparatus used in ADC for the permeation test itself and so I don't know how to connect it to a sampling valve and loop.

But another question arises on chromatographer1's answer: Do You mean, that I can use the existing split/splitless inlet both with the sampling valve/loop configuration and the normal liquid injector?

Then I wouldn't built up a second channel in the GC but only use it alternatively in the two configurations. Probably it's more troublesome than useful to have both channels, not only regarding the column temperature. GC capacity in my lab is enough and it would also be cheaper without a second inlet.....

thank You again for the comments
Florian

[chromatographer1]

I have three GCs that have dual split/splitless injectors as well as a 6port valve with sample loop. This can be ordered from the factory in this configuration.

If you have a single injector you can also add a valve without changing anything but a pneumatic switch valve and a 6 port valve for sampling.

Contact Valco if you have any specific questions to the GC model you have, or your local representative of your GC manufacturer.

best wishes,

Rod

[AICMM]

Rodney,

Just curious. Why do you need to expose the Carboxen to air if it has been above 200C? How would you recommend doing that, large volume injection, small air injection, ??

[AICMM]

Emsman,

You can plumb the 6 port valve in front of the split/splitless injector and the loop would inject into the injector. Or you can also plumb the valve into the system after the split/splitless injector but you face a potential valve temperature limitation. I am not sure why you would want to do that though. If you are already going to go buy the valve, you don't need to plumb it into the split/splitless injector unless this is being driven by a desire to not buy another EPC channel. If you do go this route, you will probably be changing columns per application.

Best regards.

[chromatographer1]

AICMM

I would be glad to discuss rather than type answers to your questions as I talk faster than I type.

Agilent's hardware configuration is to plumb the valve in parallel to the injector and switch between them as needed. Thus, your EPC can control by pressure or flow for the injector and can control by flow using the valve. Alternatively, you can have a separate pneumatics system for the valve independent of the GC pneumatics entirely.

Since this valve flow can be turned off you can remove any packed or capillary column attached to the valve IF YOU WISH. If one is using a Carboxen or MS13X/MS5A packed column it will not be a cause for concern to leave the columns installed as air will not damage the packings.

best wishes,

Rod
814-359-5737 voice
800-359-3041 voice

[GasMan]

Let me explain to all concerned the valving on the Agilent 6890, as this is the area of my expertise.

The gas sample valve is plumbed in SERIES to the capillary inlet. If it is plumbed upstream, the carrier inlet line to the capillary inlet is diverted to the valve, and then returned to the capillary inlet. To use the capillary inlet as a normal inlet, you do not actvate the valve.

If the valve is plumbed downstream, the column outlet of the capillary injection port is connected to the valve using 1/16 tubing with 0.01 inch I.D. A special column nut and 'gold' seal need to be used to accomodate the larger diameter tubing.

You would connect the valve upstream if you have concentrated samples and there is a danger of overloading the column. You can then set a split ratio to prevent this. If you have low concentrations you may loose sensitivity by splitting the sample, so then you would install the valve downstream so that all of the sample is injected onto the column.

However, I think that much of this is irrelevant for Florian as there is ( to my knowledge) no capillary column that will separate the compounds of interest, so we should not be discussing the use of the capillary column.

He does not need an inlet as the flow source, he can use one of the auxillary flow/pressure controllers that can be built into the 6890.

If Florian would post what options the 6890 has already installed on it, I would be happy to advise suitable hardware to upgrade the 6890.

Gasman

[emsman]

Gasman,

I found many applications with PLOT columns, from J&W as well as from Supelco, chromatographer mentioned them already. Am I right, that these columns are installed and handled more or less like capillary columns? At least they look similar and have dimensions like 30m x 0.53 I.D. x 25um film, ok ID and film differ from our normal capillaries, but isn't this only a question of the right ferrules?

Regarding my 6890: I got a SSL inlet and a FID detector installed and am using the ALS for automation. Do You need further informations on the instrument or can You recommend me a upgrade based on this informations? The flows are EPC-controlled.

If it is difficult to determine O2 in N2 as Matrix, I could also determine CO2 permeation in N2-matrix and O2 permeation in CO2-matrix. The permeation tests itself can be adjusted in this way.

[chromatographer1]

It is much easier to measure CO2 in nitrogen and O2 in CO2 than O2 in N2. The proper column would be a PLOT porous polymer capillary column.

BUT, You can not have any CO or N2 present when you measure O2 as they will coelute. There are no coelutions with CO2. Temperature settings should be between 40 to 80°C and isothermal.

Supel-Q would be a good column (split injection with higher LODs, or you can use a micropacked column (direct injection with much lower LODs), or a packed column (valve loop injection) for extremely low LODs.

Pick whatever suits you.

By The Way: you cannot use a FID. You need a helium ionization detector or a TCD. See Valco, AIC (http://www.detectorsbyaic.com), or Agilent for details.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rodney.george@sial.com