Allure™ Acidix HPLC Column - Chromtech.com.au

Restek -- Ultra IBD Intrinsically Base Deactivated HPLC Column
as do most C18 chains under high aqueous mobile phase conditions (see Figure 1). Chain folding on C18
phases results in complete or partial loss of retention and resolution. Fourth, the Ultra IBD phase shows
excellent peak shape for acids, bases, and zwitterions. The polar group plays an active role in
deactivating undesirable silanol interactions with the analyte. As a result, samples containing mixtures of
widely different pKa's can be run simultaneously. Finally, the Ultra IBD phase is often a good choice for
LC-MS applications. Simple, MS-compatible mobile phases can be used with IBD columns while
maintaining good peak shape and selectivity. IBD columns are an excellent alternative to ion pair
methods on conventional C18 phases.
II. Applications
Figure 1A depicts the chain collapsing phenomenon associated with most C18 and some C8 phases under
high aqueous mobile phase conditions. With insufficient organic content in the mobile phase, the
hydrophobic chains of the phase fold down on themselves to obtain an energetically more favorable
position, to avoid the outer aqueous, hydrophilic environment. The chains are no longer in a position to
interact with the analytes, resulting in partial or complete loss of retention, depending on the degree of
chain folding. In contrast, under the same high aqueous mobile phase conditions, the Ultra IBD phase
provides essentially no net gain in energy from chain folding, because the polar group within the chain is
hydrophilic. Therefore, the chains remain extended and can continue to interact with the analytes (Figure
1B). Typically, this scenario is chromatographically manifested in reversed-phase mode as plotted in
Figure 1C, where retention continues on an upward swing (no loss of retention) even at 100% aqueous
mobile phase composition.
Peak shape of basic compounds on silica bonded phases can be improved by lowering the pH to
protonate active silanols. However, there are times when more neutral conditions are required, such as
with samples that are labile at acidic pH's. The Ultra IBD phase performs well even at neutral pH (see
Figure 2), which makes it a particularly valuable packing in this instance.
Figures 3 and 4 serve as examples of how the Ultra IBD phase performs well for acid/base mixtures.
Many C18 packings show good peak shape for acids (in the case of active phases) or bases (in the case of
deactivated phases), but not for both. The Ultra IBD phase exhibits good peak shape for a wide variety of
solute types, at both acidic (Figure 3) and neutral (Figure 4) pH.
It is noteworthy that the Ultra IBD phase is similar to conventional C18 phases in one aspect. That is,
acidic mobile phases decrease retention for basic analytes and increase retention for acidic analytes. To
increase retention for bases and/or increase retention for acids, use a neutral pH mobile phase.
Retention of polar compounds that are difficult to obtain on C18 phases can often be retained on the
Ultra IBD phase. The famotidine/ranitidine chromatogram in Figure 5 is indicative of this increased
retention of polar compounds.
III. Summary
Ultra IBD columns are intrinsically base deactivated phases for reversed-phase separations of acids,
bases, zwitterions and polar compounds. They demonstrate strength in areas weakly serviced by
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