Ion-exchange and hydrophobic interactions affecting selectivity for neutral and charged solutes on three structurally similar agglomerated ion-exchange and mixed-mode stationary phases.
The nature and extent of mixed-mode retention mechanisms evident for three structurally related, agglomerated, particle-based stationary phases were evaluated. These three agglomerated phases were Thermo Fisher ScientificIon PacAS11-HC - strong anion exchange, Thermo Fisher Scientific IonPac CS10--strong cation-exchange PS-DVB, and the Thermo Fisher Scientific Acclaim Trinity P1silica-based substrate, which is commercially marketed as a mixed-mode stationary phase. All studied phases can exhibit zwitterionic and hydrophobic properties, which contribute to the retention of charged organic analytes. A systematic approach was devised to investigate the relative ion-exchange capacities and hydrophobicities for each of the three phases, together with the effect of eluent pH upon selectivity, using a specifically selected range of anionic, cationic and neutral aromatic compounds. Investigation of the strong anion-exchange column and the Trinity P1 mixed-mode substrate, in relation to ion-exchange capacity and pH effects, demonstrated similar retention behaviour for both the anionic and ampholytic solutes, as expected from the structurally related phases. Further evaluation revealed that the ion-exchange selectivity of the mixed-mode phase exhibited properties similar to that of the strong anion-exchange column, with secondary cation-exchange selectivity, albeit with medium to high anion-exchange and cation-exchange capacities, allowing selective retention for each of the anionic, cationic and ampholytic solutes. Observed mixed-mode retention upon the examined phases was found to be a sum of anion- and cation-exchange interactions, secondary ion-exchange and hydrophobic interactions, with possible additional hydrogen bonding. Hydrophobic evaluation of the three phases revealed logP values of 0.38-0.48, suggesting low to medium hydrophobicity. These stationary phases were also benchmarked against traditional reversed-phase substrates namely, octadecylsilica YMC-Pac Pro C18 and neutral μPS-DVB resin IonPac NS1-5u, yielding logP values of 0.57 and 0.52, respectively.
Pfizer Analytical Research Centre, Australian Centre for Research on Separation Science, School of Chemistry, University of Tasmania, Private Bag 75, Hobart, Tasmania 7001, Australia.
Artaches A
AA
Kazarian
Mark R
MR
Taylor
Paul R
PR
Haddad
Pavel N
PN
Nesterenko
Brett
B
Paull
D002852:Chromatography, Ion Exchange / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007474:Ion Exchange; D007475:Ion Exchange Resins / Q000737:chemistry*; D008958:Models, Molecular; D012822:Silicon Dioxide / Q000737:chemistry
D007475:Ion Exchange Resins; C026679:octadecylsilica; D012822:Silicon Dioxide
Charged/neutral solutes; Hydrophobicity; Ion-exchange; Mixed-mode chromatography; Retention mechanism