gc agilent 7890a

[mido23]

I have aproblem with gc conditioning , when I make oven temperature at 200 c , and raise flow of columns to 4 ml/min , the column (2) flow reach to 4 ml/min but column (1) flow not reach to 4 ml/min , it remains at (2.279 ml/min ) &not increase .

Column (1) for Ecd detector : 30m×0.320mm×0.5micron
Column (2) for Npd detector: 50m×0.320mm×1 micron
So plz help me , why flow of column (1) not increase to (4ml/min)??

[Jesse Robinson]

Are the columns connected to the same inlet via a union?

[mido23]

no each column connected to spararted inlet , there are two inlets (front & back)

[Jesse Robinson]

It could be something simple as a leak on the first column. The majority of the time leaks occur at the inlet, so that would be a good starting point. I would replace your septa, inlet seal, o-ring, and ferrule on the inlet side and see if this fixes it.

[Peter Apps]

Does the pressure of inlet 1 rise to the set point ? - if not you will get a pressure error. Check for leaks with a leak seeker before you start blindly swapping components. If the inlet does not reach the required pressure to give the set flow it usually means that too little gas is being supplied to the inlet. This is most likely due to a leak. What happens if you increase the split ratio ? - which supplies more gas to the inlet. Are you getting flow out of the split ? Check that you have the column dimensions entered correctly.

Peter

[Bigbear]

Make sure both columns are configured both in the instrument and software.

[Yama001]

I recall the 7890 can configure up to 6 columns at the instrument control panel. This can lead to scenarios where additional columns (numbers 3 to 6) may be configured, but not actually in use. The apparently goofy electronic control will try to split flows across uninstalled columns, giving unpredictable results and possibly damaged columns!. It is best to be sure that, if addition columns are configured, get rid of them (if possible), or be sure to configure them as not connected to a real inlet or detector.

This is a crazy system, though there may be sense to it in some applications.