Chromatography Forum

Hello

I'm having trouble resolving an issue with an ossicilating baseline that seems clearly to originate from the pump. When I double the flow rate the humps double in frequency, and they decrease in size by maybe a third. The noise is about 15mV and some of my smaller peaks are 150-200mV high.

The system has a crude pulse dampner, using a massive amount of side tubing to absorb the pulses, and I'm thinking of getting a off-the-shelf dampner to supplement/replace the manufacturer's.

Is my theory correct? Any ideas to flatten this down?

You are probably correct. You can get the "hockey-puck" style of damper from SSI. The kind based on flattened tubing do go bad from age and high pressure.

Your existing damper might also be contaminated, and throwing pulses of dirt; try cleaning it.

Also, if you don't have enough pressure, the pulse damper will not work. You need at least 70 bar (1000 psi).

Thanks, I figured that. I've been looking through catalogues at replacements and I'm familiar with what you describe. The pressure at which I'm running is borderline with your recommendation (I'm around 76 or so).

Are there any other causes at which I should be aware? Check valves, bubbles, stained cells, leaks: these I have considered but have ruled out or worked on.

Bad checkvalves usually cause pressure oscillations in excess of the manufacturer's specification. Often irregular too. If this describes your situation, replace them.

Sometimes I will bypass the heat exchanger on the UV detector cell to gain peak efficiency, but the price is more sensitivity to pump pulsation and other thermal effects. One other detector-related possibility is a tiny bubble stuck in the cell that expands and contracts with the flow.