Chromatographic NMR Spectroscopy with Hollow Silica Spheres

Abstract

The use of micrometric hollow silica spheres is described as a strategy to reduce magnetic field inhomogeneities in the context of NMR chromatography. When employed as a stationary phase, hollow silica microspheres allow the use of common solution-state NMR instruments to measure the diffusion coefficient perturbation induced by the interaction of the analytes with the silica surface.

Resolving DOSY spectra of isomers by methanol‐d4 solvent effects

“…The approach is called chromatographic NMR or more often matrix‐assisted DOSY and involves the addition of chromatographic medium‐like macrocyclic compounds (i.e. cyclodextrins), metal complexes, micelles, (soluble) polymers or silica gel to the sample. General guidelines for the choice of matrix have been developed, and the technology has found applications, for instance, in the analysis of a flavonoids mixture .…”

Matrix-assisted diffusion-ordered spectroscopy

“…Using hollow silica spheres reduces the magnetic dipole of the silica, and large reductions in the magnetic dipoles of silica particles are achieved when the shell thickness is 5 % of the sphere radius. Successful separation of a benzoic acid/benzyl alcohol/benzaldehyde sample was demonstrated with hollow silica spheres with shell thickness of 13 % of the sphere radius 44 . Chromatographic supports are not limited to silica-based materials.…”

Size‐exclusion chromatographic NMR under HR‐MAS

“…The idea of adding a sample modifier has been proposed and utilised by a number of groups and is known as chromatographic NMR or matrix‐assisted DOSY . Typical sample modifiers include bare and functionalised silica, polymers, nanoparticles, surfactant micelles and chiral shift reagents …”

“…[11,12] The idea of adding a sample modifier has been proposed and utilised by a number of groups and is known as chromatographic NMR [9] or matrix-assisted DOSY. [13,14] Typical sample modifiers include bare and functionalised silica, [8][9][10]15,16] polymers, [17][18][19] nanoparticles, [20,21] surfactant micelles [13,22,23] and chiral shift reagents. [14] Recently, we have extended the concept of chromatographic NMR to the use of size-exclusion stationary phases.…”