New validation of molecular mass measurements by means of 2D DOSY H-1 NMR experiments: application to surfactants
Résumé
This study proposes a new correlation equation between surfactant diffusion coefficients and molecular mass using 2D DOSY H-1 NMR experiment. Indeed, DOSY is a suitable NMR technique to discriminate the different components in a mixture. Using Inverse Laplace Transform (ILT), all chemical shifts in the direct dimension are dispersed along the second dimension in relation to the diffusion coefficient. This approach does not make any assumption about the number of exponential components. The empiric equation was determined for anionic and non-ionic surfactants dissolved in dimethylsulfoxide (DMSO). The parameters, K= C-r = 5.18 +/- 0.70 and a shape factor alpha= 0.45 +/- 0.02 that is related to the molecular family fractal dimension constant delta(F) = 2.21 +/- 0.11, have been extracted from the data. The equation validity was checked for simple commercial raw material and a simple mixture composed of three surfactants classically used in detergent formulations. This equation, which describes quite satisfactorily the diffusion phenomenon of surfactants, could be used for deformulation purpose to check commercial products in case of quality control or adulteration assessment.