Background: Sulfobetaine zwitterionic stationary phases are offering various retention
modes, but the influence of the capacity has never been investigated systematically.
Objective: The capacity dependence of the retention and selectivity in zwitterionic ion chromatography
mode has been investigated for common UV absorbing anions.
Methods: Stationary phases with variable distances between the charged groups (one to four methylen
groups) were prepared with capacities from 296 to 790 (one and two methylene groups as charge separator)
or from 212 to 298 µeq g-1 (three and four methylene groups) by grafting polymerization on highly porous divinylbenzene
polymers. The different spacer lengths and capacities are used as an investigative tool for the retention behavior
of the anions nitrate, nitrite, bromide, iodide and thiocyanate. The separation mechanism is explored by varying eluent
ionic strength and pH.
Results: Remarkably, an increasing capacity leads depending on the charge distance to an increase for two and three
methylen groups, decrease for four or no significant change in the retention times of inorganic anions for one methylene
group charge distance. No significant change of selectivity occurred in investigated range of capacities. It should be noted
that the higher capacity of the exchanger with two methylene groups between the oppositely charged groups exhibit a different
separation behavior for inorganic anions in comparison to a previous study.
Conclusions: The capacity plays in zwitterionic ion chromatography an important role for the retention behavior. The
changes in retention behavior are depending on the spacer length between the charged groups.