Shocking a Column

[Schmutz9]

I have heard about column shock but cannot find much on it. My sample is soluble in methanol. Is it ok to inject that methanol solvent on a column that is starting in 0.1% TFA in water or will this hurt the column?

[Kostas Petritis]

No it won't hurt the column at all, but the mismatch between the mobile phase and the injection solvent will affect negatively your chromatography (i.e. split peaks, peaks eluted in the void volume while they should have been retained etc.). How negative the impact will be depends on your injection volume, the nature (hydrophobicity etc) of your analytes etc. You always want your injection solvent to be of equal or lower elution strength than your mobile phase A (i.e. initial conditions).

[sassman]

Also, be sure that your column can handle 100% aqueous mobile phase (ie. 0.1% TFA). Most modern columns can handle 100% aqueous conditions, but with cheap and older columns it can cause the stationary phase to collapse on itself.

[lmh]

To enlarge on Kostas' accurate reply: the problem with injecting a sample in MeOH is that you are injecting in a solvent that is itself eluting. As a result, rather than sticking to the top of the column as it should, your sample will elute into the column in the solvent. How far it gets depends on how far it takes for the solvent to be diluted out by the water in the column. If it gets a long way, this will broaden peaks. In the worst case, it may get all the way to the other end of the column.

Generally the worst affected peaks will be those at the beginning of the run (because they are the easiest to elute). If you have no early peaks, you may get away with it. But if you have no early peaks, perhaps you could start your gradient later! Similarly, you may get away with it if your column volume is big compared to your injection volume.

You can largely forget column shock with modern C18 columns. They're nearly indestructible (except by gross pH abuse, contamination with particulates or very hydrophobic things, or by putting immiscible solvents down them).