Chromatography Forum

I have been noticing lower pressures, and retention times shifting to the right. Today I did a flow rate test and noticed that the flow rate was about 3/5 of what it should be for both pump A and B.

I had a similar problem about 4 months ago and changing the pump inlets seemed to greatly help the problem. The flow rates improved dramatically but were still slightly low. Also the retention times went back to normal.

I looked closely for any leaks today and did not see any. Any ideas on what could be causing the problem?

My research suggested to check the siphon flow rate, but I could not find detailed instructions for that. The article also suggests a faulty check valve could cause the symptoms but I am unsure how to determine if it is faulty.

If you introduce an air bubble into the solvent line at the bottle and watch it flow through the system at normal flow rate you can see leaks in the inlet check valve. The bubble should only flow in one direction, towards the pump. If it flows back between piston strokes then the inlet valve is probably not sealing completely. If the inlet valve is sealing, and you see a ripple in the pressure which drops on the rearward stroke of the piston, then it could be the outlet check valve is leaking and allowing solvent to flow back into the pump on the suction stroke.

Another thing that can cause similar problems is a clogged inlet frit on the end of the solvent line in the solvent bottle. If you remove it and the problem goes away, then it is definitely time to change that filter frit.

The previous flow rate test was post column. This morning I did a flow rate test pre column and the flow rate is 4.6 mL out of an expected 5 mL.

I plan to sonicate the check valves when I get some time and will troubleshoot farther.