Chromatography Forum

We have been having problems with the performance evaluation of our size exclusion columns after they have been packed. The asymmetry values have been greater than 1.4 (usually arouund 1.5) using 0.24M NaCl solution. Our product peaks have had an asymmetry of 0.9-1.1 so fortuanately our salt test has not been representative of our product peaks. We used to routinely pass this salt test but something has changed. I've looked at all of the obvious things such as the column not being packed tight enough, clogged screens or frits at top or bottom of the column, small void at top of column, air pockets in column hardware, void spaces, minimizing tubing lenghts, but I've been unable to solve the problem. Anyone have any suggestions?

I know lots of people who would kill for As values of only 1.5!

Seriously, though, if you're seeing the tailing on some peaks but others are OK, that pretty much eliminates physical problems (which you've already eliminated anyway) and points toward some chemical interaction with the packing. Ion exchange is the obvious suspect.

Either a new batch of packing or a higher ionic strength in your mobile phase might help.