Bad pump that passes diagnostic tests?

Hello,

I am not sure what gradient test you are running.  You said that all channels have the same mobile phase in them.  Normally, a gradient test is run with two channels one of which has solvent and the second has the same solvent with a small amount of tracer.  For example:  Channel A is water and Channel B is water with 0.5% Acetone.

If you are using a tracer and cannot resolve your gradient issue, you may want to have onsite service.

In order to check your new MCGV valve is functioning correctly, I would also suggest running this quick t-shooting test on Agilent quaternary pumps, the bubble test.

Lift the bottle filter above the line of solvent in each bottle currently in use in the LC bottle tray and pump for 30 secs to introduce a bubble into each solvent line. Then place the bottle filter back into the solvent in each bottle and manually pump each solvent line separately in turn via Chemstation pump control (so 100% A, then 100% B, then 100% C, then 100% D).  While pumping from one channel only (e.g 100% A) look for movement of bubbles in the other three lines. If there is significant movement of the bubbles in the other three lines this shows you have a leak across your solvent selection valve, which would mean that your LC gradient is not being produced correctly

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