Chromatography Forum

SIELC_Tech,

My point wasn't related to the theory of how to control retention with mixed mode phases (I'm aware of how to control chromatographic retention using mixed mode phases as I've been working with them since the late 80s) but that there are two separate ways to control interaction of ions at an ionic site: control of type and concentration of electrolyte and control of the ionization of the ion exchange site and/or the analyte. Both of these control mechanisms might be considered to be ionic retention "switches" but the control parameters are different so if they are lumped together under a common terminology this confuses unnecessarily the prospective user of the technique. Since the topic at hand was control of ionization of the ion exchange site, it was obviously bringing in an unnecessary element confusion to add comments related to the other control mechanism in the midst of the discussion. Alternatively, if instead you say, for example, you adjusted the pH to minimize ionic retention or you adjusted the ionic strength to mask ionic retention, you have conveyed not only the fact that retention has been minimized but the mechanism by which you did this.

To Chris Pohl

Chris you are absolutely right about pH and ion strength. The only reason why we want to separate these two is the fact that in most cases we change ion-strength in linear fashion (10, 30, 50 mM), but we change H+ concentration in exponential fashion (from 10^-2 to 10^-7). Because of that, it is absolutely legitimate to use term switch. With such drastic change in H+ concentration within 2-7 pH range the retention is in most cases, specially with polar basic compounds, can be switch on and off when one uses Primesep C column.