Water suppression enhanced through

WET (water suppression enhanced through Ti effects) presaturation. 

A common drawback to LC-NMR analysis derives from the interference of the resonances of the mobile phase, usually much higher than those of the analyte itself. To overcome this problem, the mobile phase coming from the liquid chromatograph is efficiently suppressed with techniques such as water-suppression enhanced-through Ti effects (WET). This allows the separation of analytes in typical RP-HPLC conditions using common solvents such as MeOH or acetonitrile, yet usually replacing water by D2O to achieve better quality spectra however, in the case of analyte signals coincident with the suppressed solvent resonances, those of the analytes will also be suppressed. On the other hand, in spite of the usefulness of LC-NMR for stmcmral elucidation of flavonoids, this is not a sensitive LC detection technique. Therefore, to improve sensitivity, transients can be accumulated by operation in two different modes the on-flow and stop-flow modes. In both cases, the analytes from an LC column pass into an NMR microflow probe that typically has an active volume of 60-120 p.L, comparable with the conventional NMR sample size of 500-600 p,L. 

Finally, it is important to notice the effect of the support in the pervaporation flux, analyzed by de Bruijn et al. [164] who proposed a model and evaluated the contribution of the support layer to the overall resistance for mass transfer in the selected literature data. They found that in many cases, the support is limiting the flux the permeation mechanism through the support corresponds to a Knudsen diffusion mechanism, which makes improvements in the porosity, tortuosity, pore diameter, and thickness necessary for an increase in the pervaporation flux. In fact, the researchers of Bussan Nanotech Research Institute Inc. (BNR), Sato et al. [165], designed and patented an appropriate asymmetric ceramic porous support to suppress pressure drop, and in this case, the water flux increased dramatically compared to previous reported results. Wang et al. [166] have clearly shown that the flux of the membranes increased with the porosity of the hollow fiber supports. In spite of the thin 1 pm zeolite layer, prepared by Zhou et al. [167], the flux enhancement compared to layers 10 times thicker [168] was not significant. 

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