A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography
2011 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 38, 6630-6638 p.Article in journal (Refereed) Published
(2)H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between -80 and +4°C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the (2)H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase. A distinct difference was seen between the neat and modified silicas tested. For the neat silicas, the relationship between the freezing point depression and their pore size followed the expected Gibbs-Thomson relationship. The polymeric stationary phases were found to contain considerably higher amounts of non-freezable water compared to the neat silica, which is attributed to the structural effect that the sulfobetaine polymers have on the water layer close to the stationary phase surface. The sulfobetaine stationary phases were used alongside the 100Å silica to separate a number of polar compounds in hydrophilic interaction (HILIC) mode, and the retention characteristics could be explained in terms of the surface water structure, as well as by the porous properties of the stationary phases. This provides solid evidence supporting a partitioning mechanism, or at least of the existence of an immobilized layer of water into which partitioning could be occurring.
Place, publisher, year, edition, pages
Elsevier , 2011. Vol. 1218, no 38, 6630-6638 p.
HPLC, Hydrophilic interaction chromatography, Retention mechanisms
IdentifiersURN: urn:nbn:se:umu:diva-46064DOI: 10.1016/j.chroma.2011.04.056PubMedID: 21855078OAI: oai:DiVA.org:umu-46064DiVA: diva2:436904
Available online 29 April 2011