Chromatography Forum

Hi ,

when working in HPLC isocratic mode, have you heard of any study comparing pre-mixed solutions work with solutions mixed in the pump?
If you have any advantages or disadvantages comparision, I´d appreciate.best regards.Julian

Preferably, manually prepare your mobile phase--that way you are 100% certain that it contains all the components are in proper ratios and is homogenous.

Preferably, manually prepare your mobile phase--that way you are 100% certain that it contains all the components are in proper ratios and is homogenous.

Thanks Jumpshooter. I was looking for an study comparing both situations. It is also true that most of the people do it with pumps, and I´m trying to find why.

I use the pump to mix for a number of reasons:

1. Consistency. If I suspect a problem with my proportioning valve, it's both easy to spot and easy to diagnose so why not? Determining the accuracy of a GPV isn't tough.
2. Waste minimization: I use my LC for many different methods and don't want to waste solvent.
3. It's more efficient: I don't have to spend time mixing a mobile phase.

I use the pump to mix for a number of reasons:

1. Consistency. If I suspect a problem with my proportioning valve, it's both easy to spot and easy to diagnose so why not? Determining the accuracy of a GPV isn't tough.
2. Waste minimization: I use my LC for many different methods and don't want to waste solvent.
3. It's more efficient: I don't have to spend time mixing a mobile phase.

4. One doesn't have to wonder or worry about selective evaporation of a more-volatile component from a solvent mixture when mixing at the pump. Obviously, such changing mobile phase means shifting retention times, possibly resolution, etc.

We pre-mix if doing a low-level assay with RI or conductivity, and then bypass the mixing valve.