Chromatography Forum

Helium pressure of my gc-ms system decreases by about 1 bar a day when the whole system is off. is this consider to be a normal or should i worry about a leak in the plumbing system?

syshanika wrote:
Helium pressure of my gc-ms system decreases by about 1 bar a day when the whole system is off. is this consider to be a normal or should i worry about a leak in the plumbing system?

Is that 1bar at the cylinder or in the injection port?

If you turn off the power to the GC and it has electronic pressure controls some of them stop regulating the flow but do not close it off completely, best to leave the instrument on and set the temperatures and flow to a low setting. The MS should always have the vacuum on even if not using it for a long time.

Thanks a lot.
The 1 bar pressure reduction is at the pressure cylinder.
i got agilent 7890b GC with 5977 MS. i will check again with flow on.
Will a flow rate of about 10 ml/min would work?
With that kind of flow rate how much of a pressure reduction can be expected if the system has no leak.

syshanika wrote:
Thanks a lot.
The 1 bar pressure reduction is at the pressure cylinder.
i got agilent 7890b GC with 5977 MS. i will check again with flow on.
Will a flow rate of about 10 ml/min would work?
With that kind of flow rate how much of a pressure reduction can be expected if the system has no leak.

I have a system here with two columns that run about 30ml/minute split flow in standby, 0.5ml/min column flow. That system has been on a single cylinder of Helium for almost two months and only used about 1/3 of pressure in the cylinder. A single inlet with standby split flow of 10ml/min will last at least 6 months per cylinder.

A typical gas cylinder will contain about 7,503,740 ml of gas at atmospheric pressure so at a flow of 10ml/minute that would be a flow time of 750,374 minutes which is 12,506 hours which is 512 days. So a cylinder should last between 6 and 12 months at such a flow rate.