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- Posts: 1859
- Joined: Fri Aug 08, 2008 11:54 am
Scenario: I'm developing a method with a methanol/water gradient. I can enter the percentages and flow rates as normal. I'd like the method to be fast, so I'm trying to use a high flow-rate, and it looks fine at the start, but the pressure hits a hideous maximum somewhere in the middle, the pump goes over-pressure, and it stops. So I have to go back and fiddle with the flow rates. The aim is to generate a method that reduces the flow-rate in the middle of the gradient, to balance the increased viscosity of MeOH/water mixtures, so that I run the whole gradient at the highest flow-rate I can get away with.
What I want: a system that will run my gradient at constant pressure, but remember the actual flow-rates, and will subsequently generate a method that runs at the measured flow-rate profile, whatever the pressure (because for stable retention times I want defined volumes of solvent passing through the column per unit time, even if the column starts to develop a bit of excess back-pressure).
I suppose Ideally I'd like to be able to choose whether to run my gradient during method development at known rate of change of percentage with time, or known rate of change of percentage with volume of solvent pumped.
This shouldn't be immensely complicated, but I haven't come across it. It'd be so practical: with a 400-bar column, you could set up your method with a target pressure of 330 bar or something, and have a happy safety margin for deterioration of the column, while keeping a good fast method.