calibrating pressure vs flow rate on 5890 Series II

[UBC Forestry SIF]

Hi everyone,

I have adopted a stand-alone HP 5890 Series II GC (dual FID and ECD; packed column) which we use for manual gas injections for CO2 and/or N2O determinations. Based on notes from a long-gone previous user, I have figured out how to set up a run for CO2 analysis (gas flows, pressure, igniting FID, etc.). However, setting up the GC for N2O is still a mystery, and the user's manual hasn't helped.

I have the P5 (Ar-CH4 mix), air and He gases set-up and the system is leak tight. However the only instructions I have are:
"If you are to analyze N2O as well, you need to adjust P5 flow at both Valve 1 on and off positions. Disconnct the venting tube of the ECD from the tubing going to the exhaust hood and connect the flow meter. Should get ~14mL/min. Adjust the flow with 3-point pressure vs flow rate calibrations with Valve 1 off. Then adjust the flow by an 'ECD' knob on the left side of GC with Valve 1 off."

I have figured out how to open and close Valve 1 (purge valve on/off), but am not sure how to do the 3-point pressure vs. flow. I know how to do this on ChemStation for CO2 via the FID (e.g., change the pressure on the GC and record what flow rate responds though the unlit FID and calculate; column flow set to 35 mL/min), but changing the pressure on the GC doesn't change the 14 mL/min flow when I have the meter hooked up to the ECD. I believe the "ECD" knob is for manually changing the pressure of the P5 gas coming into the GC, and the flow rate does change when the ECD knob is turned. What's more confusing, the user's manual says I need a total flow rate of 60 mL/min (total = P5 plus He flows?).

Anyhow, I am confused. If anyone out there has a similar system for similar applications, please let me know what a standard list of things to do would be.

Much appreciated. Thank you,
Alice

[AICMM]

Alice,

Does your GC have electronic pressure control for the ECD gases? I suspect not from your description. Is the knob you are turning have an inner screw inside the knob and an outer knob or is it just one knob? I suspect just one knob. If just one knob it is simply on-off and not flow control. If single knob, then the way you adjust the flow is you increase the pressure of the P5. Simple test, set up your flow meter on the ECD and then go turn the P5 regulator up by 10 psi and re-measure the flow. I suspect it will have gone up.

Good starting point I think...

Best regards,

AICMM

[UBC Forestry SIF]

AICMM,

Yes it looks like the knob on the GC for Aux gas (P5) has a little slit inside that I can use a screwdrive to adjust with. Thanks for the tip. I will give this a try.

Regards
Alice