Chromatography Forum

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.

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.

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.

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..

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

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.

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,