All our columns are mixed-mode columns. That's mean that compounds are retained and separated by more than one mechanism. For reverse phase mixed-mode it is combination of reverse phase/cation-exchange or reverse phase/anion-exchange mechanisms. For HILIC mixed mode it is HILIC/cation-exchange/anion-exchange mechanism.
Retention time of analytes controlled based on their reverse phase and ionic properties or by polar and ion-exchange properties. Both mechanisms allow you to control retention time independently. Based on the fact that all compounds have different polarity/Hydrophobicity and ion-exchange properties you have at least 3 parameters to control selectivity and elution order of your separation. Amount of organic (ACN) will affect elution of hydrophobic compounds, buffer concentration will affect elution of ionic compounds, Buffer pH will affect ionization state of compounds and stationary phase and thus affect elution of ionizable compounds and some times even neutral (change of polarity and conformation of stationary phase at different pH).
Here is a graph which shows how powerful mixed-mode can be. You are basically using 2D approach on one column:
http://www.sielc.com/Technology_2D_Properties.html
For reverse phase cation-exchange separations we have the following columns:
Primesep A - has C12 carbon chain and carboxylic acid (pKa below 0) attached to the surface
Primesep 100 has C12 carbon chain and carboxylic acid with pKa of 1
Primesep 200 C12+ carboxylic acid with pKa of 2
Primesep C C12+ carboxylic acid with pKa of 3
Primesep P phenyl + carboxylic acid with pKa of 1
Obelisc R C12 plus basic and acidic groups attached to the silica
For reverse phase anion-exchange separations:
Primesep D C12 basic group pKa of 10
Primesep B2 C12 plus zwittre-ionic fragment (both basic and acidic groups)
Primesep SB C18 pus basic group pKa 14
For HILIC Mixed-mode:
Obelisc N has hydrophilic chain and both basic and acidic groups on the surface. This is different than SeQuant because both charges are separated by long chain and they both can participate in ion-exchange interactions vs. very tide pair on the surface of SeQuant. Separation of charges allows using less ACN (improves solubility in HILIC mode) and alos use ion-exchange to achieve extra resolution.
All columns have close to 100K/meter efficiency, but by using double or triple gradient (ACN, buffer concentration and buffer pH) you can have way over 1 million plates (even this is not an accurate statement about plate count in gradient mode). You can learn much more from our web site. Check applications and brochures. You usually don't need to know exact structure of the compounds - just general properties (hydrophobic or hydrophilic, ionic or neutral, single charge or multiple charges) Once you learn how retention time is controlled your method development will be extremely efficient (we never spent more than a day on any screening method development, unless it is complicated sample with 5-10 compounds and a complex sample matrix)
