Chromatography Forum

Hello!

I've been assigned to a new GC this month, and the front EFC 21 shows 0,0 mL/min flow on the Compass CDS software. It also shows less than 1,0 cm/sec linear velocity. Even though it shows no flow, the system accepts changes in the column pressures and actually spends some time getting the system to the set pressure, marking the 0,0 flow as 'Ok' afterwards, as if the set pressure had been achieved.

I asked around, and it seems the previous technician switched the septum, liner and trimmed the column recently, and that before all that had been done, the EFC showed flow and velocity normally.

I hope you guys can help me with that

Dear Lucas,

1. Start from the end , Make sure that the septa is there on the place. It could be that septa was fallen down because of the back pressure from the column and technician carelessly tightened thinking septa would be there.
2. Check the injector nut is tight enough.
3. Check the column ferrule is inserted properly and the right ferrule has been used.
4. Make sure the EFC is enabled in the method.
5. Column length and Id setting is also important however not doing it also will show some pressure.
If you find the fault let us know what was the problem.

regards,
Jihad
Kuwait

Hi Lucas

Welcome to the forum.

Review the settings that have been programmed into the GC and make sure that the previous operator did not leave it set to zero flow after doing the inlet maintenance. If indeed the method parameters are correctly entered and have sensible values for flow and pressure then you need to do the checks that Jihad suggested, and also check for leaks using a leak seeker. Make sure also that you have pressure in the carrier gas supply line.

You might also consider looking in the instrument log to see what the previous operator did, and asking for some training on the instrument - which you should also log.

Peter

Thanks for the answers!

I've asked around a little more and it seems that the problem started when the previous technician replaced the column by one with a smaller OD. I cheked the ferrules and column nuts, and they are bigger than the curent column. I'm gonna try changing them to appropriate sized ones and let you guys know the result!

So, I changed the ferrules and column nuts to appropriate-sized ones, bue the problem still continues. I took a photo of the problem. The EFC shows correct flow and pressure, but the pneumatics still show no flow and low linear velocity. Any ideas?

EFC is nice, BUT;

1. Did you check the valve on the main tank is open.
2. Is the pressure of the regulator set properly.

The 1st thing the service technician/engineer does is put them in the off position.

Thanks for replying, but the valves are on and the regulator is set properly

Check that the column dimensions are correctly entered - and that your predecessor did not confuse microns with millimetres or something similar.

Measure the flow at the split outlet and the septum purge with and independent flow meter - they should add up to 29.5 ml/min.

Peter

We've just bought an flowmeter, but it's still in the mail.

I've ran methanol through my bonded phase column to try to estimate the linear velocity. It went through the column at a 23,48 cm/sec velocity, and the column pneumatics system says the carrier gas has a 0,6 cm/sec velocity, which would mean there's some sort of problem with the pneumatics system, right?

As the system does not seem to have leaks and the linear velocity is being displayed wrong, I may be able to estimate the velocity by using unretained compounds until we get it fixed. Every article I find suggests the use of methane or ethane as unretained compounds, but would they be unretained in a apolar stationary phase as bonded phase (poly(50%n-octyl/50%methylsiloxane)?

We've just bought an flowmeter, but it's still in the mail.

I've ran methanol through my bonded phase column to try to estimate the linear velocity. It went through the column at a 23,48 cm/sec velocity, and the column pneumatics system says the carrier gas has a 0,6 cm/sec velocity, which would mean there's some sort of problem with the pneumatics system, right?

As the system does not seem to have leaks and the linear velocity is being displayed wrong, I may be able to estimate the velocity by using unretained compounds until we get it fixed. Every article I find suggests the use of methane or ethane as unretained compounds, but would they be unretained in a apolar stationary phase as bonded phase (poly(50%n-octyl/50%methylsiloxane)?

The problem was solved! It seems the previous technician inputted the column settings completely wrong, and the calculations the EFC was doing were wrong as well, thus showing those unreal values of Flow and Linear Velocity. When I corrected the column parameters, the correct values of flow and linear velocity were shown.

Thank you for all the help!