[vtnhuy]

 Hi, I'm so confusing how to calibrate the mixture gas ( NO,NO2,N2O,SO2,NH3) by using external standard. As I understand, external standard is the method in that the standard is injected after sample and we can know the quantitive by comparing ( for shame, I don't know exactly about external standard method).Can you tell me more in detail about this?
 Right now, I'm using standard mixture and I have 2 problem need to be solved :
- The GC places a little far from the standard cylinder and the sample line so what can I do to prevent the leak from air to the syringe. Can I use any rubber to fix the needle ? Will there any contaminate from the rubber ?( I intend to use the solsept, is it ok? )
- How can I withdraw the standard  from the cylinder? It is ridiculous question,isn't it ? but I can't solve this problem -___- last time I just connected the cylinder with the pressure gauge and put the rubber line and air easily leak into the sample
Anybody can help me ,pls 
Thanks in advance

[JGK]

I would stay away from rubber tubing, maybe using something more inert (silicon tubing if you have it)

Also, if you only want to temporarily seal the needle tip why not just use an old silicon GC injection septum embed the needle in that until you make the injection.

[vtnhuy]

Thankyou for your answer. This GC had been used before I came so I coudn't find any silicon embed to the syringe but I'll buy one.
I found one small pack name " syringe plunge " , can it be used for this purpose ?
About the mixture gas, how can I withdraw the standard gas without leaking air ?

[JGK]

Are you using a gas tight syringe (fitted with a teflon plunger tip) for this process?

If you are using a standard GC syringe, you will have problems and, as NO is highly reactive with air, you may not get consistent measurements at all.

You can get gas tight syringes fitted with valves to "seal" the barrel contents during transit.  If you sample excess volume from the cylinder you can seal the barrel of the syringe and use the excess to purge the needle, where the content may have been exposed to air, immediately prior to injection

[Gerard]

I would stay away from rubber tubing, maybe using something more inert (silicon tubing if you have it)

Also, if you only want to temporarily seal the needle tip why not just use an old silicon GC injection septum embed the needle in that until you make the injection.

i can relate to this,rubber tubings tend to make the operation lets say not so cooperative

[vtnhuy]

I do agree with JGK , air easily leak into the sample so I always find nitrogen peak although my mixture don't content any nitrogen. It's very difficult to prevent the air leak eventhough I already used the tedlar gas sampling bag. During the transfer from cylinder to tedlar gas sampling bag, there is still air in the connecting pipe  and right now I must buy the sample lock syringe also   

[JGK]

I do agree with JGK , air easily leak into the sample so I always find nitrogen peak although my mixture don't content any nitrogen. It's very difficult to prevent the air leak eventhough I already used the tedlar gas sampling bag. During the transfer from cylinder to tedlar gas sampling bag, there is still air in the connecting pipe  and right now I must buy the sample lock syringe also   

Turn the cylinder on and purge the tube with the gas before connecting the bag to the tube, this should remove the air from the tube (hopefully your cylinder can be located next to an extract cabinet to do this).

[vtnhuy]

I did like this but there is still one connection pipe of the bag so that why air could go inside