GC Calibration with Partial Pressures
Posted: Fri Feb 29, 2008 3:54 am
I am trying to calibrate my GC with a single Calibration Cylinder (2%H2, 98%N2). I am measuring H2 with a TCD. The sample goes through a 6 port switching valve through a sample loop to vent, and then gets injected through a split/splitless inlet onto the column and then to the TCD.
Has anyone ever calibrated a GC by partial pressure? Using the 2% H2 cylinder and changing the pressure in the sample loop to change the partial pressure of H2 (mole fraction of H2 times the total sample loop pressure). I get a good linear curve with low errors for H2 from 20ppm to 20% but when I try to calibrate with a H2 mass fow controller and N2 mass flow controller at a constant sample loop pressure the calibration curve is also very linear and has low errors but the slope is different to the partial pressure calibration.
Thanks,
Michael
Has anyone ever calibrated a GC by partial pressure? Using the 2% H2 cylinder and changing the pressure in the sample loop to change the partial pressure of H2 (mole fraction of H2 times the total sample loop pressure). I get a good linear curve with low errors for H2 from 20ppm to 20% but when I try to calibrate with a H2 mass fow controller and N2 mass flow controller at a constant sample loop pressure the calibration curve is also very linear and has low errors but the slope is different to the partial pressure calibration.
Thanks,
Michael