Chromatography Forum

hi every body
am new to lc & am thinking of some qs:
* what if i used a c18 hplc column as guard column for pfp propyl column? will RT will differ? how much?
* f i have an article which used same column to mine but differ size, how can i correct the gradient n the flow rate?
* could be a way to regenerate pfp propyl column?

* what if i used a c18 hplc column as guard column for pfp propyl column? will RT will differ? how much?

Probably very little, but it depends on two things:
- the retention (k' values) of your compounds on the two different packings
- the relative volume of the guard and analytical columns.
Because most guard cartridges are small (typically something like 5 mm long by 4.6 mm id) compared to the analytical column, there usually isn't much of an issue unless you have compounds that are *much* more strongly retained on the C18.

* if i have an article which used same column to mine but differ size, how can i correct the gradient n the flow rate?

If you keep the flow constant, scale the gradient time to the column volume. If the new column has half the volume of the old, then double the gradient time. To be more general, you want to keep the product (tG x F / Vm) constant
tG is gradient time
F is flow rate
Vm is column volume.

* could be a way to regenerate pfp propyl column?

The general answer for *any* column is "it depends". If you have cleaved off bonded phase or dissolved away silica (generally either of those occurs at extreme pH values), then it's a lost cause. If the column is contaminated, then you need to back-flush the column with something that will solubilize the contamination. That means you have to make an educated guess as to what kind of CRUD is on the column and pick an appropriate solvent.

"CRUD" = "Chromatographically Retained Undesirable Debris"

Also, be sure to consult your column manufacturer regarding column cleaning/regeneration practices.

I have used C18 guard cartridges from Phenomenex with a Luna PFP(2) columnm and have not seen a retention time issue with that setup. Like Tom said, if the dimensions of the guard are small in relation to the dimensions of the column, and your compound is not excessively retained by a C18 phase, you probably won't see a difference. However, you *should* use a guard of the same phase as your column, because what will foul your column will foul your guard first.