Chromatography Forum

How often people develop LC method with flow rate change during the run? Is it common for complex method development or rare cases?

I developed and validated HPLC methods for over 35 years.

Rarely did I have a procedure where the flow rate increased at a certain timepoint to help a later-eluting analyte to elute. Most often I increased the flow rate after the analyte eluted if the pressure was low enough, and I had later-eluting stuff to get off the column. This could be faster to re-equilibrate than initiating a gradient.

And of course a gradient could not be used when we had a single pre-mixed mobile phase.

Flow programming is very 'rare' (it is an indication of a poor method). It is more advantageous to increase the composition of the organic phase slowly during a gradient method (shorter too) in order to 'boot' the target molecule off the column.

When I first started working with EPA Method 1694 I noticed they used flow rate changes (0.150ml/min then 0.250 ml/min then 0.300 ml/min then back to 0.150ml/min). That was the first time I ever saw it, and even though I am running the method I don't use the flow program I use a different column and gradient elution.

It seems to be something Waters likes to do with their "UPLC" instrument methods.

Hi KhareM,

Another older Waters method that employed a flow rate change was the AccQ.Tag kit method for amino acid analysis, in the middle of a gradient program.

I agree with these other folks above--it is less usual to vary flow rate during an elution program in HPLC than not.

Agree with the other posts here. The only time I use a change in flow-rate in a method is to hasten column washing/re-equilibration if possible. Never for analytes - suggests a poor method.