Matrix‐assisted diffusion‐ordered spectroscopy: mixture resolution by NMR using SDS micelles

Abstract

Diffusion-ordered spectroscopy (DOSY) is a powerful technique for mixture analysis, but in its basic form it cannot separate the component spectra for species with very similar diffusion coefficients. It has been recently demonstrated that the component spectra of a mixture of isomers with nearly identical diffusion coefficients (the three dihydroxybenzenes) can be resolved using matrix-assisted DOSY (MAD), in which diffusion is perturbed by the addition of a co-solute such as a surfactant [R. Evans, S. Haiber, M. Nilsson, G. A. Morris, Anal. Chem. 2009, 81, 4548-4550]. However, little is known about the conditions required for such a separation, for example, the concentrations and concentration ratios of surfactant and solutes. The aim of this study was to explore the concentration range over which matrix-assisted DOSY using the surfactant SDS can achieve diffusion resolution of a simple model set of isomers, the monomethoxyphenols. The results show that the separation is remarkably robust with respect to both the concentrations and the concentration ratios of surfactant and solutes, supporting the idea that MAD may become a valuable tool for mixture analysis.

Natural product mixture analysis by matrix-assisted DOSY using Brij surfactants in mixed solvents

“…SDS and AOT (micelles and reverse micellar aggregates, respectively) have been shown to be useful tools in the separation of signals of dihydroxybenzenes, monomethoxyphenols 8,9 (in both cases positional isomers), and medium chained alcohols 9 in MAD experiments. SDS micelles have also been used with a mixed solvent system, allowing complete identication of each component in avonoid mixtures.…”

“…Various surfactants, including SDS, AOT and CTAB, have already been used in MAD analysis, 6,8,9 but not the Brij family of nonionic surfactants. These consist of a hydrophilic head containing a variable number of polyoxyethylene groups, and a hydrophobic polymethylene tail.…”

NMR Chromatography: Molecular Diffusion in the Presence of Pulsed Field Gradients in Analytical Chemistry Applications

“…First, towards optimization of spectral resolution of increasingly similar mixtures [51,52] and second, as a powerful probe of micelle aggregation and behavior. Tormena et al, looked at the concentration dependence of SDS and three methoxyphenol isomers [53]. In the presence of all three methoxyphenols (14 mM each), the critical micelle concentration (CMC) for SDS was reduced (to 3 mM) from the literature reported, 7 mM and with 35 mM of each methoxyphenol the CMC was 2 mM as seen in Figure 6.…”

Matrix-assisted diffusion-ordered spectroscopy

“…The ordering of apparent diffusion coefficient in the micellar solution matched the trend in partition coefficient between oil and water (log P) 57 . The analogous set of methoxyphenols was also separated using this approach 58 .…”