Generally, older HPLC methods used higher molarity buffers than present methods and thus required lengthy equilibration times(eg, 5mins back to original composition and either 10-15 column volumes.
Do people believe this should still be the case for lower molarity buffers? For example, I've looked at changing over 2min from 30:70 0.05M NH4H2PO4:CH3CN to 65:35 and then a further 5 min equilibration at 1.5mls on a 20cm Octyl column(approx 4 column volumes). Do people think this is suffient or should the longer time still apply? Ie, I know it'll depend on a case by case basis, but should the minimum column volumes required for re-equilibration still be 10-15?
I have tried these conditions and it doesn't appear to affect the chromatogrpahy.

Appreciate any thoughts.

Regards.

A good rule of thumb is to re-equilibrate for 3 times the system volume plus 5 times the column volume. This is usually enough for most situations.

I agree with the previous reply. The large "reequilibration volume" used with older methods is largely due to the gradient delay volume of dinosaur HPLC systems.