Chromatography Forum

I have experimented that two C18 columns (same length and ID) may produce different retention to the same sample. I know this behaviour is due to different parameters like: base material, particle shape, particle size, carbon load, pore size, surface area, endcapping,...
My questions are: How can these parameters affect? And how can I choose one column taking into account these parameters?

Thank you.

All of the above factors you mention are part of what defines a column's selectivity. Selectivity is the portion of the resolution equation that has nothing to do with column length, particle size etc. The best thing is to shoose the column whose selectivity works well for you, then verify that it will work well using different lots of that same stationary phase.

In the event that you have poor reproducibility from identical columns, you have to examine the use histories of each of the columns. Chances are that one of them has been exposed to some MP modifier that has altered the column's selectivity (TEA, for example).

There have been many scholarly articles on this subject, but I think that Lloyd Snyder's series on the PQRI method is one of the best. See J. Chromatography A 1057, (2004) pp.49-57 and references therein. Then look at http://www.usp.org/USPNF/columns.html for an implementation of that approach and one other.

Hi atram

I often refer to a C18 column comparison guide published by ACE column manufacturers. you may want to have a look at it.
http://www.ace-hplc.com/assets/download ... e_2006.pdf