Physicochemical Studies of Separation

Physicochemical Studies of Separation of Isomers by Supramolecular Systems... 

Nassimbeni, Luigi R., Physicochemical Studies of Separation of Isomers by Supramolecular Systems, 8, 123... 

Figure 13.8 shows the first separation of small molecules by FFF. Ascorbic acid was separated from toluene through a secondary chemical equilibrium with field-retained microemulsiom droplets. Once again, the exchange between the aqueous phase and the swollen micelles is low, i. e., the efficiency is low and broad peaks are obtained (Figure 13.8). There are so many powerful techniques for small molecule separation that micellar FFF was not used for this purpose. Its interest could be in the physicochemical study of the micellar or microemulsion structure. For example, in the case of the Figure 13.8 experiment, the separation allowed the estimation of the average mass of the mobile phase microemulsion droplets (1.4x 10 %) and consequently, its radius (35 nm) [38], These values can be obtained by heavy methods such as small angle neutron scattering or high resolution NMR [38]. Micellar FFF can be an easy alternative in such studies.

Because of their simplicity, easy-to-carry-out, low requirement of prepurification, and rapidity, TLC methods have been frequently applied in the analysis of synthetic dyes. However, the majority of invetigations were performed in model systems to establish the optimal separation conditions, and to determine various physicochemical parameters of dyes. The number of studies dealing with the analysis of dyes in complicated natural accompanying matrices is relatively low. 

Among various physicochemical methods, IR spectroscopy and NMR are most appropriate tools for the study of dihydrogen bonds in solution. However, it is worth mentioning that these methods are basically different. First, they measure physical properties that change upon complexation bond vibrations and magnetic behavior. Second, equilibrium (4.1) is usually slow on the IR spectroscopy time scale and very fast on the NMR time scale. In other words, proton donors, proton acceptor, and their complexes are detected separately in IR spectra, whereas the NMR parameters of these moieties are usually averaged. 

Finally, when RPC methods are used in preparative studies with peptides, the opportunity routinely exists for subsequent analysis of the recovered fractions by a variety of analytical methods including high-speed RP-HPLC, HP-IEX, HP-HILIC, or HP-IMAC, zonal or micellar electrokinetic high-performance capillary electrophoresis (HP-CZE and MECK-CZE), capillary electrochromatography (CEC), or capillary isotachophoresis. The combination of the RPC information, drawn from the In k versus i > plots, with the data derived from on-line spectroscopic detection thus readily provides a comprehensive opportunity to assess the purity of an isolated peptide, many of the physicochemical features of the interaction, as well as a means to optimize the resolution in the RPC separation. 

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