hplc problem

[WS]

> channel 8 had the largest peaks, 1 had the smallest

Hm. A bad / loose cable, shielding, grounding comes into my mind?
Interference from a machine like realtime PCR, mass spec, warp
generator etc (with high periodic currents / magnetic fields) in the
lab on the other side of the wall or connected to the same circuit in
your building? Trapped airbubbles? A worn out piston or pulsation
damper?

If the frequency of your sine waves is related to the flow rate, then
the problem rather might be in your machine, if not rather somewhere
in outer space :)

Just some thoughts.

Wo