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Conformational temperature dependence of a poly(ethylene‐ co ‐acrylic acid) stationary phase investigated by nuclear magnetic resonance spectroscopy and liquid chromatography
Author(s) -
Meyer Christoph,
Pascui Ovidiu,
Reichert Detlef,
Sander Lane C.,
Wise Stephen A.,
Albert Klaus
Publication year - 2006
Publication title -
journal of separation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.72
H-Index - 102
eISSN - 1615-9314
pISSN - 1615-9306
DOI - 10.1002/jssc.200500376
Subject(s) - chemistry , magic angle spinning , alkyl , nuclear magnetic resonance spectroscopy , acrylic acid , polymer , sorbent , analytical chemistry (journal) , spectroscopy , monomer , phase (matter) , chromatography , organic chemistry , adsorption , physics , quantum mechanics
A polymer‐based RP sorbent was prepared by immobilizing a poly(ethylene‐ co ‐acrylic acid) copolymer with an acid mass fraction of 5% on silica by using a 3‐glycidoxypropyl linkage. 13 C cross‐polarization/magic angle spinning NMR spectroscopy of the sorbent, either in the dry state or suspended in the mobile phase, showed an increase in mobility at elevated temperatures. Alkyl chain segments with gauche conformations were more mobile than chain segments with trans conformations. The strength of the 13 C‐ 1 H dipolar couplings in the alkyl chains was measured using the constant time dipolar and chemical shift pulse sequence, revealing less molecular motion for the trans conformation. Non‐linear van't Hoff plots were observed for separations of shape‐constrained solutes (such as geometric β‐carotene isomers and polycyclic aromatic hydrocarbons). At higher temperatures, the retention behavior was similar to that of monomeric C 18 sorbents, whereas at ambient and lower temperatures, enhanced shape‐selective properties were exhibited similar to those of polymeric C 30 sorbents.