Novell in GC-ECD

[zango]

Hello all,

I never used a GC but I have been put in front of a HP5890A GC-ECD to analyze CFCs and I am trying to learn how to use it.

I have read some works where they explain they tune up their machines at MAKE UP gas N2 at 40mL/min, CARRIER He at 1mL/min and PURGE gas at 60mL/min.

I think I have get to measure the flows for the He: (not sure but...)
Carrier is the TOTAL Flow in the HP5890A
Purge is SEPTUM purge in the HP5890A

On the other hand I cannot find anywhere to measure the N2 flow. I think N2 (Make Up gas) controls are in the left side panel of the machine where I can modify its pressure, but I dont see how to measure them.
The upper two gauges are marked as AUX A and AUX B (the GC has 2 ECDs) The lowest button says CARRIER.

There are also ECD-Anode Purge and ECD-Aux Gas buttons which I don't know how to use.

This question explains what I think I have "discovered" about the HP5890A, so please any suggestion is welcome and let me know if something stated above is wrong.

Very grateful,
Zango.

[Schmitty]

The anode purge should only be 5-6 mL/min. What size column are you using? The size of the column will determine the approximate flow you should use (1-15mL/min). The makeup should be adjusted to deliver a total of ~60mL/min of all three of these gas flows.

You can measure the anode purge from the detector outlet with the column flow off or disconnected and the detector capped and temperature off.

Measure the column flow by reconnecting the column and getting the flow from the detector outlet and subtracting the anode purge. (Personally, I never turn off the anode purge).

Leave the column flow and anode purge on. Turn on the makeup gas flow, and increase the pressure until a flow of ~60mL/min at the detector outlet is seen.

The "buttons" you refer to are needle valves. On my instruments these are typically on/off, with the flow being adjusted on the inside left of the instrument by increasing/reducing the pressure on the supply gauges.

The total flow is the total gas going into the injection port. The septum purge passes over/around the injection port liner. The Split vent goes through the liner but not onto the column. So, you must add the column flow, septum flow and split flow to get the total flow.

On an instrument that is this old, you may not want to trust the electronic flow controls.

There is more, let us know if you need more help. Do you have a manual?

[zango]

First of all, thank you very much. It was a good starting point to look for the different flows. I'm not experienced with the GCs and had no idea how to start with it. I have the manual of the GC, so I will try to follow your instructions.

One of the columns is a HP-5 Crosslinked 5% PH ME Siloxane, (30m*0.32mm*0.25microm Film Thickness). The other column is a RESTEK RTX-5ms.
I think these both columns are not designed for CFCs but compounds of larger masses. They are what I have available so I will try to tune up the GC-ECD to do the analysis with them.

As I read more, I realize that most of the people has built a CFC pre-concetration line before the machine injection ports. The GC also has "cryo" function, which I assume must be fed by a LN2 dewar. I will try to find where is the inlet-outlet for the cryo function and see if I can use it to avoid the pre-concentration line.

Thanks a lot,
Zango.

[pi3832]

The GC also has "cryo" function, which I assume must be fed by a LN2 dewar. I will try to find where is the inlet-outlet for the cryo function and see if I can use it to avoid the pre-concentration line.

In college I ran some sub-ambient analyses on an HP5890 that used carbon dioxide to cool the oven, not liquid nitrogen.

Double check the manual for the instrument, or see if you can find a part-number on the valve that controls the flow of the cooling gas (probably installed on the left side of the instrument, with a nozzle that extends into the oven) and check with HP (N.K.A. Agilent) as to what that valve is intended for.

If it is for CO2, then make sure your vendor gives you a CO2 cylinder with a "dip tube" (a.k.a. "syphon tube"). Without a dip tube you'll never get liquid CO2 out of the cylinder, which is what you need to efficient cooling.