Chromatography Forum

We have a varian GC450 model. we are currently using argon as carrier gas. do we need to change any settings to change the carrier gas to helium.
Thanks

I don't know this particular model GC. But if you are using electronic flow controllers, they need to be set for the partcular gas you are using. Your optimium flow rate on the column will change from one gas to another as well.

There is a GC method translation software (you can download it free from Agilent website) for carrier gas change. You just enter your GC parameters for Argon, and then the software will give you all the new parameters for helium depending on your creterion: translate only, best efficiency,fast analysis or none.

On the GC front panel go into setup (the crossed spanner and screwdriver), then select setup on the touch screen, then sample delivery, then helium from the drop down list of carrier gas, then OK, OK.

If you have constant flow selected in the method you will need to increase the flow rate. If you have constatn pressure selcted, or a pressure programme it might not need changes.

Peter

hi peter,
thanks for the reply. I did change the gas to He. But I am getting an error message. In the GC software, at the COLOUMN PNEUMATICS flow is not constant. Can you suggest what can be done for this
Thanks

First thing to check is that you have a hogh enough pressure in your gas supply.

Then check for leaks everywhere, using an electronic leak seeker.

Is the problem thatthe flow is fluctuating, or that it cannot reach the setpoint ?

What are your gas control settings, column dimensions, and oven temperature ?

Peter

Dear Peter,
The colum pressure is at 23 psi. and the total flow is fluctuating. The cylinder is at 50 psi. Is that enough??
We have two colums molecular seive and porous polymer column. Column temperature is 70oC
Thanks
Jhansi

Have you checked for leaks ? There is no point trying to troubleshoot a leaky system.

If the 50 psi is in the gas supply line it should be enough, if it is in the cylinder the cylinder is empty.

You probably need to recalibrate the septum purge (if you have one).

Also, some of the EPCs had firmware problems, there is a downloadable fix available from Varian.

Measure at the detector with a flow meter to check whether the flow really is fluctuating, or is it just the flow readout. What flow do you expect, and what do you actually have ?

From your columns I suspect that you are doing gas analysis, how are you injecting samples ?

Is the flow readout fluctuating while the pressure remains stable, or is the pressure also fluctuating.

Are you running constant flow or constant pressure ? What happens if you switch between them ?

Peter

hi peter,
thanks for the reply. I did change the gas to He. But I am getting an error message. In the GC software, at the COLOUMN PNEUMATICS flow is not constant. Can you suggest what can be done for this
Thanks

If your GC has electronic pneumatic control, you have to tell the software what kind of gas you are using. From Ar to He, there a big change in viscosity.

Hi Peter,
I changed the flow rates and it worked well.
Thanks

Thanks for the feedback - I'm glad it worked out.

Peter

Hi everyone,

I'm having the same problem with a Bruker 450-GC (before was Varian), trying to change Ar to He.

When I change Ar to He, using the same inlet pressure to the GC (5 bar), the GC is not able to reach the head pressure of 45.7 psi (set point) and for this reason the screen shows equilibrating all the time avoiding the injections. The head pressure reached is around 30 psi and fluctuating
If I decrease the head pressure to 30 psi (set point), then the pressure is around 23 psi, leading to the same problem. The flow is constant (60 ml/min).
I didn't find any leak, and if I put Ar again it works perfectly.
I also didn't find nothing in the control program (galaxy) in the computer to change the carrier gas, as I know that this GC has electronic controllers of flow and pressure.

Jlkishore or someone, could you tell me how did you solve the problem? because I thing that I have exactly the same problem.

I would appreciate it so much,

Thanks,

Follow the instructions in post number 4.

Peter