Here D1 and D2 refer to the diffusion coefficients of solute and solvent (or standard), while ri are the van der Waals radii of these two molecules and mi are the corresponding molar masses. It should be noted in the original paper which established the correlation in eqn. 2 that the masses of the solutes and solvents were the same order of magnitude.26 This is generally not true for MAO solutions. The combination of these correlations and widespread availability of NMR spectrometers with pulse gradient capability suggest an accessible and powerful approach to MAO or ionpair speciation, 28 particularly if the results can also be related to mass spectrometric or other absolute mass characterization of MAO or the MAO-based ions in question. Mass spectrometric characterization of MAO dates back to early methods of its synthesis, but only volatile, lower molecular weight components were detected using EI-MS. Much more recently, MMAO 12 (Sigma Aldrich), a 95:5 copolymer of methyl-and n-octylaluminoxane, was analyzed by low-and high-resolution MS using an inert atmosphere sampling technique. Families of ions with m/z ratios < 1000 Da were detected and which featured hydrolysis, possible pyrolysis, and no evidence for incorporation of n-octyl groups.