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Communication Dans Un Congrès Année : 2013

NMR Diffusion and chemometric methods to analyze complex mixtures of surfactants

Résumé

Study of complex mixture is an analytical challenge. Here, we used NMR spectroscopy which combines many advantages: structural and quantitative information of simple mixtures, minimum sample preparation and no degradation of sample. Our method is developed on surfactant mixtures. A sample database has been created composed of anionic, non ionic and amphoteric surfactants. 1D1H NMR spectra of each sample have been recorded. NMR spectra were divided into 0.04 ppm buckets over a range of 11 ppm (Amix, Bruker). No scaling was used for buckets. Combined to Principal Components Analysis, NMR spectroscopy enables the discrimination of the different family and to distinguish the different sub-structures inside a same family. In the case of complex mixtures, peaks superposition is the most important problem. To check the efficiency of NMR for resolving such problem, we prepared test complex mixtures. NMR diffusion experiment was chosen. In particular, DOSY experiment using pulsed field gradient allows solving peaks superposition . Using inverse Laplace transform (ILT), all chemical shifts in the direct dimension are dispersed along the second dimension in function of diffusion coefficient. This approach does not make any assumption about the number of exponential components. Diffusion coefficients are correlated to molecular mass through the Flory's law : D = KM-α, α> 0. However, this relation between molecular mass and diffusion coefficient is dependent of the family of samples and solvent. Samples were prepared in DMSO-d6 to limit the formation of micelles. A calibration curve has been fitted for pure surfactant samples and we extracted K = 0.76 and α=-0.50. Our fitted equation was then tested on a complex mixture composed of three compounds (TAM12002 + TAN12007 + TNI12018). Four diffusion coefficients were discriminated: D DMSO= 886 ± 89 μm².s-1, D TAM12002= 497 ± 50 μm².s-1, DTAN12007= 269 ± 27 μm².s-1 and DTNI12018= 145 ± 15 μm².s-1. Those results lead to: MTAM12002 = 143 ± 25 g.mol-1, MTAN12007= 488 ± 90 g.mol-1 and MTNI12018 = 1680 ± 350 g.mol-1. We can confirm the efficiency of NMR of resolving peaks superposition in case of surfactants mixtures
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Dates et versions

hal-00870945 , version 1 (08-10-2013)

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  • HAL Id : hal-00870945 , version 1

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Maggy Hologne, Corinne Sanglar, Alexandra Gaubert, Claire Bordes, Hervé Casabianca. NMR Diffusion and chemometric methods to analyze complex mixtures of surfactants. Small Molecule NMR Conference (SMASH 2013), Sep 2013, Saint Jacques de Compostelle, Spain. ⟨hal-00870945⟩
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