GC- Calibration for Nitrous-Oxide- diluting gas

[ashrestha]

Hi friends,
I really need help to calibrate this new GC that we have in our lab. I want to measure Nitrous Oxide.

I have a nitrous oxide of 100 ppm concentration. How do I dilute the gas to lower concentration so that I could inject it to the GC to calibrate ?

Please help.

thanks

[ashrestha]

so many views and no reply. common guys help me out here !

[chromatographer1]

Easiest way is to have a pressure gauge on an empty vessel. Evacuate the vessel to full vacuum filling with an inert gas to atmospheric pressure a few times.

=-14.7 psi, then fill to 15 psia ( one of the following: N2, Ar, He, H2, etc), then bleed off to atmospheric pressure. Repeat as many times as you wish to fully purge vessel.

After the last evacuation fill with your standard to 14.7 psia then fill to any pressure multiple of 14.7 psia: for example 58.8 psia would be a 4x dilution so the new blend would be 25 ppm.

Repeat using new vessels until you get the levels you desire.

In the future if you want a quick answer, try to include more information, details like what balance of gas do you wish to use, what levels do you see to prepare. This information increases someone will try to help you and give you a decent answer rather than trying to write a manual on all the possible variations one could imagine.

best wishes,

Rod

[AICMM]

ashrestha,

Depends a lot on how low you want to go. Rod's way is a great way to do it and it will get you way down in concentration. The other way, which won't go nearly as low, is to take a flow of your standard (say 5 mL/min) and add it into a T with another flow (say 500 ml/min) of diluent gas and you get a 1 ppm standard. Requires a good flow meter and controllers and does not give you a huge dynamic range but it does work for some applications.

Best regards,

AICMM

[ashrestha]

Thanks a lot Rod and AICMM.

The information was indeed informative. However, our lab does not have any pressure gauge right now. Could tell me what kind of pressure gauge will I need to buy ? how much do u think it will cost ?

I want to make my standards for Nitrous Oxide and I will be using nitrogen as a balance gas. I will be getting most of my concentration in between 0 to 100 ppm so I need to dilute 100 ppm ( which I have) for my standards which I am thinking of 0.5 ppm, 1 ppm, 25 ppm, 50ppm and 75 ppm.

I will appreciate your suggestions.

Thanks
Anil

[chromatographer1]

Gauges are like cars. You buy what you need after you determine the specs available and the specs you need. They range from tens of dollars to several hundreds of dollars.

Do a search from gas suppliers or scientific equipment suppliers and review what is available in your area. It does no one any good to suggest a gauge that you cannot afford or cannot purchase.

best wishes,

Rod

[JI2002]

What will be the injection volume?

[AICMM]

anil,

You want to stay in the ppm range with your standards. Therefore, a dual flow dilution scheme will work for you. Standard on one leg with a good needle valve for flow control AND good pressure control; diluent flow on the other leg, set the flow for both according to the concentration you want at the end. This scheme is not going to work if you are using a 14L type standard since it will consume quite a bit of standard setting up the flows. To do this you have to have a large standard cylinder to work with.

Best regards,

AICMM

[chromatographer1]

MM is correct.

If you are sample limited in your stds then using the dilution procedure I gave you may be the only way. Minimize the sample line volume to your sample valve or syringe sampler and don't waste any gas.

best wishes,

Rod

[ashrestha]

Thanks for the suggestions. I have one more question .

so I have the following settings for my GC.

Detector ECD: Helium as carrier gas. flow rate is 10 ml/ min. Using to measure CO2.

Detector TCD: Helium as carrier gas. Flow rate is 10 ml/min. Nitrogen is the carrier gas. Using to measure Nitrous Oxide.

It is set up in a way so the carrier gas first goes to TCD and then to ECD.

What should be the balance gas for Nitrous oxide when I will dilute it ?

I will appreciate your suggestions.

thanks
Anil

[chromatographer1]

What is your NO std gas balance? N2 or He? or Other?

You listed two carrier gases for the TCD. Which is it? He or N2? A mixture?????

Can- do - you separate NO from N2?

If you don't then you cannot use N2 to dilute the NO std gas. (you won't see NO)

best wishes,

Rod

[ashrestha]

Hi Rod,
Sorry about earlier wrong post on carrier gas. My carrier gas is Helium and make up gas is Nitrogen for ECD.

I want to be able to see N20 (nitrous Oxide) on ECD.

I want to know which balance gas should I have for Nitrous Oxide to be able to detect on ECD ?

Right now I have 100 % pure Nitrous Oxide and
100 ppm Nitrous Oxide balanced on N2.

I wish to know the right balance gas for N2O to detect on ECD ?

Thanks
Anil

[chromatographer1]

Doesn't N2 detect on an ECD?

Rod

[ashrestha]

Hi Rod,

N2 is not detected on ECD.

[chromatographer1]

Thanks, ashrestha.

It has been so long since I did ECD, I could not remember. Seem to remember we used Argon/methane or helium but there was some problem with helium.

Since your present diluted std is in nitrogen I would suggest to avoid issues due to the gas used for balance, stay with nitrogen. NO should elute just after CO peak on a porous polymer and prior to methane. (RT IN MIN)
Q QS
CO 0.153 0.176
NO 0.187 0.213
C1 0.231 0.273

Good luck,

Rod