Coupling method selection

To do so, however, a tandem of several columns would be needed. In the case of a two-component polymer system, the molar mass effect can be suppressed selectively for one component and the molar mass of the second component can be assessed by means of one single SEC measurement. A more general approach is represented by the two- and multidimensional procedures in polymer HPLC (Section 16.7), in which the coupled methods of polymer HPLC are included as an important (usually the first) separation steps. 

In any 2D HPLC, it is important to attain certain degree of both the complementarity and the orthogonality between the two separation dimensions [255-257]. The so far most universal approach to 2D polymer HPLC assumes the partial or possibly full suppression of the molar mass effect in the first dimension of the separation so that the complex polymer is separated mainly or even exclusively according to its chemical structure. Selected coupled methods of polymer HPLC are to be applied to this purpose. In the second dimension of separation—it is usually SEC—the fractions from the first dimension are further discriminated according to their molecular size. Exceptionally, SEC can be used as the first dimension to separate complex polymer system according to the molecular size. This approach is applicable when the size of polymer species does not depend or only little depends on their second molecular characteristic, as it is the case of the stereoregular polymers... 

Selective alkylation of the enamidic nitrogen in 159 with 2-iodo-4,5-methylenedioxybenzyl bromide afforded the enamino-enamide 160 (Scheme 23). Application of Heck s oxidative coupling method to 160, generated by 6-endo addition, the tetracydic enamide... 

A strong preference in speciation analysis is to use a separation step that can be combined with a detection step in an on-line system [45]. In such coupling, analytical selectivity relies on the application of different chromatographic or electrophoretic methods, while the use of atomic spectrometric techniques assures high sensitivity and f>t-for-purpose limits of detection (LoDs). However, hyphenated techniques with element-specif>c detection do not provide structural information on the species. If appropriate standards are available, the assignation of chromatographic peaks can be accomplished by spiking experiments. On the... 

Different methods are used to tackle these problems [10-13], Some of these coupling methods, such as moving-belt coupling or the particle beam (PB) interface, are based on the selective vaporization of the elution solvent before it enters the spectrometer source. Other methods such as direct liquid introduction (DLI) [14] or continuous flow FAB (CF-FAB) rely on reducing the flow of the liquid that is introduced into the interface in order to obtain a flow that can be directly pumped into the source. In order to achieve this it must be reduced to one-twentieth of the value calculated above, that is 5 pi min. These flows are obtained from HPLC capillary columns or from a flow split at the outlet of classical HPLC columns. Finally, a series of HPLC/MS coupling methods such as thermospray (TSP), electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) can tolerate flow rates of about 1 ml min 1 without requiring a flow split. Introducing the eluent entirely into the interface increases the detection sensitivity of these methods. ESI can accept flow rates from 10 nl min-1 levels to... 

Prior to the advent of 2D methods, selective spin decoupling was used extensively in both proton NMR and in heteronuclear (especially 13C) NMR to ascertain which sets of nuclei contribute to observed spin coupling. Such information is critical to assignment of resonances and to the elucidation of the structure of an unknown molecule. 2D methods now largely supply this information much more efficiently, by correlations that depend on the existence of spin coupling. The homonuclear version of one such experiment is called COSY (correlation spectroscopy), and the heteronuclear version is known by several acronyms, most commonly HETCOR (lieferonuclear correlation). 

Another problem in model applications is the adsorption on a nonuniform adsorbent. The immobilization of polyclonal antibodies will lead to different populations of binding sites, and the measurements will only give an apparent adsorption rate constant [22], The properties of the adsorbent surface are also greatly affected by the procedure used for protein immobilization. It may be important to select coupling methods that orient the covalently attached protein... 

The increased sensitivity of the sialic acid glycerol moiety to periodate oxidation as compared with other sugars has been used as a coupling method to label gangliosides selectively (141). 

Labeling of Antigens and Antibodies with Enzyme. Many methods exist for coupling haptens, proteins, and carbohydrates to proteins. Some of the most commonly used are summarized in the table together with some selected references. An extensive review on protein-protein coupling reactions has recently appeared and could be used as a source of additional chemical details on the coupling methods. 

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