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Low level Oxygen and CO by 490 Micro GC in plant's nitrogen supply

Question asked by eme091 on Jun 5, 2018
Latest reply on Jun 1, 2020 by vjpugal

Utilizing a 490 Micro GC with a TCD and MolSieve 5A 20 m column we are attempting to determine the purity of our plant's nitrogen as Airgas( run the nitrogen generation plant on site) can not provide chromatography or proof of the 99.99% purity of their nitrogen.  We were told by the sales rep that the 490 micro GC can see down to the 5ppm levels of CO and O2 in nitrogen, but we have yet to obtain even a peak at 10ppm of either in a nitrogen balance.  Below is the system parameters we are currently running:

    1. Channel 1:

  i.    Carrier gas: Helium

  ii.    Description: 20m MS5A Unheated Injector,Backflush

    1. Injector:

  i.    Injector Time: 40ms

ii.    Backflush time: 0s

    1. Detector:

  i.    Detector state: Checked

ii.    TCD temp limit check: Checked

iii.    Invert signal: unchecked

iv.    Sensitivity: Auto

    1. Column and pneumatic:

  i.    Column temperature: 40°C

ii.    Pressure mode: Static

  iii.    Initial Pressure: 200.0 kPa

    1. Signal Settings:

i.    Acquire Channel: Checked

ii.    Sampling Frequency: 100 Hz

iii.    Run Time: 500 s

iv.    Acquisition delay: 0 s

    1. Common:
  • Stabilizing Time: 5 s
  • Sample Time: 30 s
  • Continuous Flow: Off
  • Flush Cycles: 1 cycle
  • Injection Delay: 0 s


Any suggestions are much appreciated.