Sulfonium and phosphonium, new ion-pairing agents with unique selectivity towards polarizable anions.
Ion-pair chromatography (IPC) almost universally relies upon ammonium-based ion-pairing agents (IPAs) for anion separations. This work compares tetrabutylammonium (TBA) with tetrabutylphosphonium (TBP) and tributylsulfonium (TBS). To best understand the retention behavior analytes used for characterization of the IPAs spanned the Hofmeister series; from kosmotropic monoanions (iodate, chloride, nitrite) and intermediate anions (nitrate, bromide) to chaotropic ions (perchlorate, thiocyanate, iodide). The studies demonstrate that tetrabutylphosphonium is the most chaotropic IPA, followed by tetrabutylammonium and finally tributylsulfonium is the least chaotropic. In the case of the chaotropic anions, the retention of perchlorate was least with tributylsulfonium, and greatest for tetrabutylphosphonium, with tetrabutylammonium being intermediate. The multivalent kosmotropic anions (sulfate, chromate, thiosulfate) demonstrated unique selectivity changes depending on the kosmotropic/chaotropic nature of the IPA. Demonstrating increases in retention with increasing IPA concentration only with tributylsulfonium, whereas the more chaotropic IPAs universally decreased the retention of the multivalent anions.
Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alta., Canada T6G 2G2.
Christopher R
CR
Harrison
Jayden A
JA
Sader
Charles A
CA
Lucy
D000838:Anions; D007202:Indicators and Reagents; D009943:Organophosphorus Compounds / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013452:Sulfonium Compounds / Q000737:chemistry*
D000838:Anions; D007202:Indicators and Reagents; D009943:Organophosphorus Compounds; D013452:Sulfonium Compounds