Chromatography Forum

hi all

i have tried all kinds of different things and i am not getting any closer.

however. what i have noticed is that channel B and C are the problematic channels. but the issue is not reproducible.

if i switch off my pump/degasser module (all 4 channels of the MCGV close) no leaks. switch it on and off again, sometimes it leaks sometimes not.
running isocratically, just 1 injection, 95/5 A/B or C, turn off the pump, leaks.

no leaking issue with A or D.

Hi

have you done the gradient step test, like described in the troubleshooting wizard here: http://www.lcresources.com/resources/TSWiz/hs450.htm, with different combinations of line (A+B, and A+C, B+C maybe even combinatinos with D)?
Also, as you're mixing low percentages, you may reduce the step heights at the low and high end, e.g. 0/5/10/20/30/40/45/50/55/60/70/80/90/95/100% of a channel. keep the step length long enough to get an even baseline for each step (e.g. 5-10? min or ml, whatever is appropriate), otherwise the evaluation of the steps will be difficult/incorrect.
Maybe repeat it several times (e.g. 3x with each combination), to see if it is reproducible.

I guess otherwise you won't get a real idea of what is happening to your gradient mixing system.
Pressure and "leaking" checks aren't sensitive enough.