# GC-MS TQ 7010 inlet and column pressure low

Hello,

I am running a GC-MS TQ 7890A/7010B coupled with a HS 7697A. The column installed is 30 m x .320 m x 1.80 um.

At a flow rate (constant flow) of 1.2 ml/min, the column/inlet pressure is only around 2.2 psi. Looking at my other GC-MS instruments, at this flow rate the pressure should be around 8-10 psi. I reinstalled the column and still experiencing the same pressure. What should be the typical operating inlet/column pressure?

I am having issues with Air/Water check and I believe it's related to the low pressure, if that is an issue at all.

Parents
• Are the other columns 0.250 mm id?

Using the Pressure-Flow calculator -  PSI units, outlet to vacuum, 100°C oven - 2.5 psi is the head pressure.

with a 0.250mm id column:

You are correct, it's always best to have 5psi or greater inlet pressure.

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• Are the other columns 0.250 mm id?

Using the Pressure-Flow calculator -  PSI units, outlet to vacuum, 100°C oven - 2.5 psi is the head pressure.

with a 0.250mm id column:

You are correct, it's always best to have 5psi or greater inlet pressure.

.

.

.

.

Children
• Thanks! Yes, those other columns are 0.250 mm ID which makes a lot of sense now.

Besides changing the column ID, is there anything I can do to increase the inlet pressure to greater then 5 PSI?

• narrower I.D. column - I'm a big fan of 0.18mm ID columns

Longer column, but there are diminishing returns as double the length does not mean double the column RT resolution

A restrictor at the end, but that has its own set of things to deal with, too.

Higher flow into the MS is not optimum, especially on the 5977B HES and the 7010x. The HES does NOT like flows higher than 1.3 to maybe 1.4 ml/min.  It's an interesting issue. If you turn up the helium flow to 2 ml/min it might look OK but you'll think there is an air leak even though the air is the exact same as it was at 1.2 ml/min.  The higher flow in the HES skews the spectral tilt.   That might work for your application running in MRM mode but someone someday will think there's an air leak and all that it needs is to turn down the column flow to 1.0 to 1.2 ml/min.   Many hours have been wasted because of that.   The HES is best from 0.8 to 1.2 ml/min Helium and 0.4 to 0.75 ml/min Hydrogen.

You have the Agilent Pressure-Flow Calculator installed on your system.