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. Copyright ?? 2010 John Wiley \& Sons, Ltd.