Gas standard

[Grace2007]

Hello everybody,

I have developed methods for analysis of permanent toxic gases likeSO2, NH3, Ethylene oxide etc.

How can I quantify the concentrations of these gases? do I have to buy a couple of standard gases for every gas?

How do EPA methods quantitively analysize permanent gases?

thanks,

Grace

[danicrd]

Grace
you can buy a mix of your gases (if stable together) or two at high concentration and dilute it.
Normally quantification is by %mol/mol or more simple %V/V.
So you can dilute your mix and create curve for quantitation.
Good luck

[Grace2007]

Grace
you can buy a mix of your gases (if stable together) or two at high concentration and dilute it.
Normally quantification is by %mol/mol or more simple %V/V.
So you can dilute your mix and create curve for quantitation.
Good luck

Thank you Daniele!

[oscarBAL]

Dear Grace, I think you can go to www.chemservice.com and find gas standard.

You can Use Gas Chromatografi for this , but depending on the Concentration level you will need one or another detector, a very good one for this kind of aplication is the....
ho, yes I remember already, it took me amoment to remember it.

The PID dtector, Photo Ionization Detector.

[Grace2007]

Dear Grace, I think you can go to www.chemservice.com and find gas standard.

You can Use Gas Chromatografi for this , but depending on the Concentration level you will need one or another detector, a very good one for this kind of aplication is the....
ho, yes I remember already, it took me amoment to remember it.

The PID dtector, Photo Ionization Detector.

Thank you very much oscarBAL! It is a very good useful website


Grace

[AICMM]

grace_2007,

Your other option is to look at permeation tubes, especially for the more reactive species. There are advantages and disadvantages to perm tubes over cylinder gases but propably the biggest factor is whether you are working at percent or ppm levels. If percent, perm tubes are out, if ppm perm tubes could offer you a lot of flexibility. You would have to have a standards generator (because you have to control temperature and flow) but this can be made in the lab relatively easily, espeically if you have an oven or used GC laying around. Look at VICI or Kin-Tek for more information.

You cannot use a PID for SO2 since it has too high an ionization potential (12.3 eV) but you can use a PID or argon ionization detector for NH3 and EtO. So, how are you doing SO2?

Best regards.

[Grace2007]

grace_2007,

Your other option is to look at permeation tubes, especially for the more reactive species. There are advantages and disadvantages to perm tubes over cylinder gases but propably the biggest factor is whether you are working at percent or ppm levels. If percent, perm tubes are out, if ppm perm tubes could offer you a lot of flexibility. You would have to have a standards generator (because you have to control temperature and flow) but this can be made in the lab relatively easily, espeically if you have an oven or used GC laying around. Look at VICI or Kin-Tek for more information.

You cannot use a PID for SO2 since it has too high an ionization potential (12.3 eV) but you can use a PID or argon ionization detector for NH3 and EtO. So, how are you doing SO2?

Best regards.

Hi AICMM,

Thank you very much for your excellent permeation tube suggestion!
I have visited VICI website and want to try it.

The gases are all at ppm level (PEL), I analyze SO2 using GC/FPD or GCMS

Grace

[Suresh Seethapathy]

Grace_2007,

Like AICMM suggested, permeation tubes are a nice Idea. I make permeation tubes myself, but have made them for only those compounds which are liquids at room temperature. I use a GC oven (which was lying around without being used) to control the temperature and use a mass flow controller for controlling the flow rate of sweep gas. To make the permeation tubes, all you will need is to have a teflon tube and teflon plugs (appropriate dimension) and a simple trick to seal the liquid inside the tube properly.

Suresh Seethapathy.

[Grace2007]

Grace_2007,

Like AICMM suggested, permeation tubes are a nice Idea. I make permeation tubes myself, but have made them for only those compounds which are liquids at room temperature. I use a GC oven (which was lying around without being used) to control the temperature and use a mass flow controller for controlling the flow rate of sweep gas. To make the permeation tubes, all you will need is to have a teflon tube and teflon plugs (appropriate dimension) and a simple trick to seal the liquid inside the tube properly.

Suresh Seethapathy.

Hi Suresh,

Thank you very much!

We have experimental conditions (ovens ,mass flow controllers, teflon tubes etc. ) to make permeation tubes. If we can make them ourselfs, that's great, we can save some money.

The liquid has very high boiling point (200C), how can I prevent it to condensate after it becomes to gas phase? we have 6 port valve from VICI for gas injection. that means we have to heat the valve to 200C. can I use a gastight syringe to inject this standard gas?


Grace

[AICMM]

Grace2007,

If you put the liquid in the teflon tube, it slowly bleeds out into the gas phase at very low concentrations. Gas phase concentration is a function of membrane, pressure, and temperature (http://www.kin-tek.com/how_permeat.html). Once in the gas phase, I generally don't worry about re-condensation but I have dealt mostly with light components so I can get away with more.

You can use a gas tight syringe to inject but if you have flow through the perm tube device (which is how they work) why not just hook that up the Valco valve and inject from there?

Best regards.

[Suresh Seethapathy]

Hello Grace,

Sorry i was away for a couple of days. Please email me and i will email you back a MS Word attachment on how to make the permeation tube.

The compound with the highest boiling point i work with is butylbenzene (183 C). I don't have any specific problem with condensatino like AICMM mentioned. The amount of material permeating out of the tube is very very low.

Suresh.

[Grace2007]

Grace2007,

If you put the liquid in the teflon tube, it slowly bleeds out into the gas phase at very low concentrations. Gas phase concentration is a function of membrane, pressure, and temperature (http://www.kin-tek.com/how_permeat.html). Once in the gas phase, I generally don't worry about re-condensation but I have dealt mostly with light components so I can get away with more.

You can use a gas tight syringe to inject but if you have flow through the perm tube device (which is how they work) why not just hook that up the Valco valve and inject from there?

Best regards.

Hi AICMM,

Thanks for your reply again!

I injected 1ml, 1ppm some gas samples, by valco valve ( no leak), I didn't get a peak, but by a syringe, I got a peak. so I suspected condensation or reaction with the wall of the valve ( or thansfer line).

Grace

[Grace2007]

Hello Grace,

Sorry i was away for a couple of days. Please email me and i will email you back a MS Word attachment on how to make the permeation tube.

The compound with the highest boiling point i work with is butylbenzene (183 C). I don't have any specific problem with condensatino like AICMM mentioned. The amount of material permeating out of the tube is very very low.

Suresh.

Hello Suresh,

Thank you very much !

Although I don't think I can try it recently, I eagerly want to know how to do it.

Please email me :grace2007.gc@gmail.com

Thanks for sharing your experience!

Grace

[Suresh Seethapathy]

Email sent. I use the permeation tubes for a different reason. I work on passive sampling and generate standard gas mixture for exposing my passive samplers. It works just fine for me. If its possible to heat your valve, i guess its worth trying it as well?

Goodluck!
Suresh

[Grace2007]

Hello Suresh,

I got your email, Thank you very much !

It is very helpful.

Grace