The application of HPLC-NMR for the analysis of a mixture of fatty alcohol ethoxylates (FAEs) is described. The use of the new generation, cryogenically cooled probes is investigated in respect of the sensitivity advantage that they provide. The FAE mixture is separated using liquid chromatography at the critical point of adsorption. The ability of the method to differentiate between the different end groups and the degree of polymerization of the mixture constituents is investigated. Both on-flow and stop-flow HPLC-NMR techniques were used together with two-dimensional NMR spectroscopy. The results are compared with those obtained by using an evaporative light scattering detector for the HPLC.
Liquid chromatography of polymers is traditionally a slow technique with analysis times of typically 30 min per sample. For the application of liquid chromatographic techniques in combinatorial materials research the analysis time per sample must be reduced considerably. For fast high performance liquid chromatography (HPLC) small columns and new stationary phases with improved separation efficiencies can be used. HPLC separations of poly(ethylene oxide)s with different end groups can be conducted in less than 4 min. Accordingly, with new column technology and optimized separation methods time savings of more than 90% can be achieved as compared to conventional technology.
Liquid chromatography of polymers is traditionally a slow technique with analysis times of typically 30 min per sample. To adapt liquid chromatographic techniques to combinatorial materials research the sample throughput must be significantly increased. Preferably, the analysis time per sample is to be reduced to a few minutes. Short analysis times can be achieved using high resolution stationary phases, high flow rates, and fast gradients. The present work demonstrates that gradient HPLC of polymethacrylates can be accomplished in less than 2 min. The fast separation of poly(methyl methacrylate), poly(i-propyl methacrylate), poly(n-butyl methacrylate), poly(tbutyl methacrylate), and poly(n-decyl methacrylate) is conducted on a short monolithic stationary phase using a flow rate of up to 7 mL/min. The optimization of the gradient is conducted by running a number of linear gradients and by simulating an optimum step gradient. Further modification of the simulated gradient results in the desired short analysis times.
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