Does kinked tubing cause dipping baselines?

[EmpowersBane]

I run a complex method on Waters binary UPLC which requires me to insert a small C18 column between the Aqueous line and the mixer inlet, to trap ghost peaks before they reach the column. Now this obviously needs I have to bend and kink the tubes a bit so they can all fit and I can close the door on the BSM, which is particularly bent for the "mixer outlet to column inlet" tubing which runs up the length of the instrument to the 6 port loop and column valve.

I have noticed the last few runs have odd dips in the baseline or at the start of the gradient run the basline jumps up then 2 mins later back to normal, which Empower sees as a series of peaks. Could the tubing be causing this? I use high quality solvents.

[Consumer Products Guy]

I can't see a kink in tubing causing an intermittent issue. If pressure and flow are unchanged, doubt that would be an issue.

[mattmullaney]

Hi EmpowersBane,

I'm with Consumer Products guy. What you're doing with the small C18 "trap" column is fairly commonplace, at least in places where I've worked previously. The only effect I'm aware of in using kinked tubing (after the analytical colum and before the detector) is that the laminar flow profile of the peaks can be improved a bit, Peaks Can be Narrower, less bandspread.

With the UHPLCs, the only thing I can think of from my own experience, especially with these "extra" connections, is the possibility of tiny microleaks--if present, these may cause baseline artifacts such as those you're experiencing. Sometimes these are hard to ID from the pressure trace and you have to hold Kimwipe at each connection to ID a microleak source.

Something to try...Best Wishes! Kinked tubing should not be a problem--unless the connections aren't quite up to snuff.