Chromatography Forum

Hi
I'm using a Varian CP-3800 GC with Saturn 2000 MS. The system says that a Mass calibration is required. So I have done an FC-43 mass calibration and it runs ok. However, when I click on the aquisition tab, an error message appear stating a mass calibration is required.
In manual control, I have checked the cal gas pressure, and it says it needs decreasing. I decrease the pressure by turning it the black nozzle on the front of the MS clockwise. But it still says it needs decreasing.
I'm unsure how to proceed. Can anyone help??
Aman

Just close the needle valve totally (don't overtight; be gentle) and allow the system to equilibrate for some minutes.

Alternatively the background noise is very high which confuses the data system.

@aman, I have a similar problem with my Varian Saturn 3 MS. When I tested it first, the calibration gas was even too low. So I opened the needle valve a bit and it adjusted.

A little later, I did another Calibration Run and it started complaining the calibration gas pressure was too high. I closed the needle valve completely, but the error remained. However, I could see the background noise in real time. I have too admit that I made a big mistake not providing properly cleaned Helium (long plastic tubes and no additional gas filter) so I'm quite sure I contaminated my system to some degree and this is causing the error - exactly as HbJ was pointing out. Next step for me is to replace the tubing with decontaminated copper tube and install a GC gas filter. Will see if this helps.

Stephan

The cal gas now reads ok.
However, it still says I need to run a mass calibration, which I run in autotune and it says mass calibration ok. But when I go back to the aquisition page, an error still occurs saying I need to do a mass calibration.
Has anybody else had this problem, if so how did yo remedy it?
Thanks Aman

Okay doesn't always mean okay

Please watch the mass calibration: It has to find all masses (464 comes to mind...) and watch for the shape of the masses. If they are severly distorted the data system can't acquire a correct mass calibration.

I'd recommend a complete autotune including getting the multiplier voltage right and properly setting the AGC target.

Hi,

I have had similar problem with the cal gas, the system was running ok for awhile then I noticed the baseline is bit noisier than normal, so I went to do the autotune and adjusting cal gas. However, the it seems to have problem with maintaining the cal gas pressure as the pressure kept decreasing, which caused the mass calibration to fail. Has anyone had any idea what the problems might be?

Thanks,

JT