Problem with GCMS 4000 Varian

[mabrouk mahmoud]

Hi everyone
I have a problem with GC ms varian, the report/ratio 19/18 is between 20-30% after bekout but after one day it believes at 47% and it is established at 60-67 % although I do not have any external leak.
The conditions of the instrument are:
external source, damping gaz: 1 ml/mn, T gater: 425°C, T source 200, T trappe: 200, T tranfert line: 300, T manifold: 40, T colonne: 200, T inj: 230,
split 1/10, pump foreline: 35 mtorr, pump turbo: 16,1 µtorr, current: 241 mA,
pump speed 100%.
when i test the air water check, i obtain the result:
base peak: 28, amount: 200
32 is the 1/4 of 28
the width of 28 is 0,8
I used the He "N 60" (purity:99,99999)
I worked with another bottle of He, i changed the filter but I board obtained the same results.
when i make the autotune, the result is: test autotune passed. the ration of 19/18 believe down 50%, but after a few hours it believe at 60-67%.
when I make the test of HMN, the base amount is 5.
Note: in the software, the report 19/18 is acceptable when the value is down the 50%
Please can you help me.

[ChromatographyDude]

I would not worry about the 18/19 ratio too much, certainly don't let it hold you back from moving forward with your analyses. In your daily checks method, under segment 1, if your 100% or base amount is less than 500, you should be good to go. Sounds like you are at 200, so I wouldn't worry. How do you enjoy the system? I operate a Varian 2000 MS and I think it's incredible.

[mabrouk mahmoud]

Thank you for your help, my question why the report 19/18 got down after bekout, but after a few hours it still to 60-70%.
about the system 4000 varian, it's very well, but the air water check is the most difficulty in my opinion.
what's the value of report 19/18 who you stopped your analysis.
if i haven't any external leak, who do the elevate report of 19/18.

[kerri]

What type of column are you experiencing this with? Every column you have or is this just recent to one...

It sounds like the system is nice and sensitive..

[mabrouk mahmoud]

the column is Vf-1 ms: 30 m; 0,32 mm; 0,25 µm,

[ChromatographyDude]

I guess if you need to better understand what's going on with your 18/19 ratio, remove the column from the injector and seal it off with a septum. What happens to your ratio? Then, reinstall the column back in the injector. Monitor the 18/19 ratio with your split closed, then monitor it at two different split values, say 10:1 and 100:1. Sometimes I've noticed changes in my 18/28/32 ratios simply by varying the injector split.

Good luck on figuring it out. The system is so incredibly sensitive that, in my opinion, I wouldn't worry too much about 18/19 giving slight variation, given that your overall level of air/water is quite acceptable.

[mabrouk mahmoud]

Hi Dud;
thank you for your help, the leak became very fatale because
The all pick became overload and will appears the 32 and it's the base pick, The report of 19/18 became over then 150%; the pressure of foreline pump became 40 mTorr. I 'm going to repeat all diagnostic; first I isolate the masse to the GC and I would fixed the location ok leak (in the mass or in the GC).
I realized the test of split ratio but i don't observed any change,