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- Posts: 1
- Joined: Wed Sep 20, 2017 9:00 am
Hi guys,
Got some problem with high N2 % in GCMS. Wondering if somebody can help. Here comes a short summary.
After summer break, I found the gas tube was empty and the copper tube was damaged. I cut the damaged part and connected with a new tube, charged column and restarted the instrument. The instrument was running over the weekend, I ran air water test and found that N2 level was close to 10% (vs m/z69) that indicates a leak (although I cant see N2/O2 in a ratio of 80/20). I checked the whole gas supply line, baked the system on 110 °C for couple of hours and ran air water test, again same (actually this time N2 was higher than 10%).
I removed the column, plugged a blank nut on MS and let it run overnight, again high N2. I checked the vacuum gauge that states a value 10^-6 that showed no vacuum problems. I connected the column again, ran another cycle of bake out (at 150°C) but still high N2 (the values fluctuate a bit without an apparent trend but always higher then optimum). I also checked if the split vent was open and air entered through it (on low split ratios), quality of gas (compared to another GCMS connected to same gas cylinder), sealing of MS door (without dust spray).
A summary of different value is given below.
Blank nut on MS (after running overnight)
18/69 = 1.83 Water%
28/69 = 8.59 Nitrogen%
32/69 = 2.10 Oxygen%
44/69 = 0.30 Carbon Dioxide%
28/18 = 469.19 Nitrogen/Water%
with GC column
18/69 = 3.84 Water% (recommended<1%)
28/69 = 17.29 Nitrogen% (recommended<5%)
32/69 = 4.32 Oxygen%
44/69 = 0.53 Carbon Dioxide%
28/18 = 450.33 Nitrogen/Water%
Now I am running out of options and we have no idea what could go wrong. Wondering if it rings a bell and you guys can help.
Got some problem with high N2 % in GCMS. Wondering if somebody can help. Here comes a short summary.
After summer break, I found the gas tube was empty and the copper tube was damaged. I cut the damaged part and connected with a new tube, charged column and restarted the instrument. The instrument was running over the weekend, I ran air water test and found that N2 level was close to 10% (vs m/z69) that indicates a leak (although I cant see N2/O2 in a ratio of 80/20). I checked the whole gas supply line, baked the system on 110 °C for couple of hours and ran air water test, again same (actually this time N2 was higher than 10%).
I removed the column, plugged a blank nut on MS and let it run overnight, again high N2. I checked the vacuum gauge that states a value 10^-6 that showed no vacuum problems. I connected the column again, ran another cycle of bake out (at 150°C) but still high N2 (the values fluctuate a bit without an apparent trend but always higher then optimum). I also checked if the split vent was open and air entered through it (on low split ratios), quality of gas (compared to another GCMS connected to same gas cylinder), sealing of MS door (without dust spray).
A summary of different value is given below.
Blank nut on MS (after running overnight)
18/69 = 1.83 Water%
28/69 = 8.59 Nitrogen%
32/69 = 2.10 Oxygen%
44/69 = 0.30 Carbon Dioxide%
28/18 = 469.19 Nitrogen/Water%
with GC column
18/69 = 3.84 Water% (recommended<1%)
28/69 = 17.29 Nitrogen% (recommended<5%)
32/69 = 4.32 Oxygen%
44/69 = 0.53 Carbon Dioxide%
28/18 = 450.33 Nitrogen/Water%
Now I am running out of options and we have no idea what could go wrong. Wondering if it rings a bell and you guys can help.
