Ionic function/groups

In the case of functional polymers such as nylon, the molecular size can increase because ionic functional groups contained in the molecule repel each other. To decrease ionic repulsion, sodium trifluoroacetate should be added to HFIP. 

T3 1 solvent modifier. with ionic functional groups. (See also Section 19.6.2). peptides, nucleic acids, proteins. Saccharides. 

The ion-exchangers used in LC consist either of an organic polymer with ionic functional groups, or silica coated with an organic polymer with ionic functional groups. The types of functional groups used are the same as described in Chapter 18. Since IEC can be carried out with an aqueous mobile phase near physiological conditions, it is an important technique in the purification of sensitive biomolecules such as proteins. 

The uptake of electrolyte by many hydrophobic polymer separators can be enhanced either by wetting agents or ionic-functional groups (e.g. ion-exchange membranes). 

Rohm and Flaas Company has developed Amberlite polymeric adsorbent resins that can be used to remove organic compounds from contaminated groundwater, aqueous wastes, and vapor-phase wastes. Amberlite XAD-4 is a crosslinked polystyrene-type polymer. It is hydrophobic and has no ionic functional groups incorporated into its resin structure. The material is most useful in removing low-molecular-weight organic substances from aqueous systems. Amberlite XAD-4 has been commercially available since the 1970s. 

Polymeric Materials with Ionic Functional Groups and Their Protein Adsorptive Behavior... 

Ion-exchange packing materials are traditionally formed from the emulsion copolymerisation of styrene and divinylbenzene, the latter polymer is used to provide cross linking and thus increase the rigidity of the beads. Ionic functional groups are chemically bonded to this backbone. Pellicular silica-based packing materials may also be used which are then coated with a synthetic ion-exchange resin but these tend to have comparatively less sample capacity. 

Later the same research group claimed that, in the first step of the in situ synthesis scheme, ionic functional groups as such are not necessary for the introduction of ferrous ions into a cellulose matrix [161,162], This suggestion was made based on a comparative study of ferrite synthesis between a case with anionically modified cellulose materials and the other case with non-ionic cellulose gels, which included a never-dried bacterial cellulose (BC) membrane and a never-dried cellulose wet-spun filament or cast film (Lyocell) using N-methylmorpholin-N-oxide as the solvent. SPM proper-... 

It has been suggested that the low molecular weight protective substances for freeze-drying have a common characteristic whereby each molecule contains a total of more than three hydrogen-bonding function (—OH, —NHj, =NH, =0) or ionic function groups (either acidic or basic) in a specifically organized structure. 

Ion-exchange packing materials are chemically modified silica or styrene-divinylbenzene copolymers, modified with ionic functional groups, e.g., n-propylamine, diethylaminopropyl, alkyl-N" (CH3)3, carboxylic acid, or benzenesulfonic acid. The retention is primarily influenced by the type of counter-ion, the ionic strength, the pH and modifier content of the mobile phase, and the temperature. 

Carbohydrate supports such as dextran or agarose are very hydrophilic and easily derivatized with ionic functional groups. They have been very popular for analysis and purification of biological molecules like proteins. One major drawback to these supports is that their volume changes with mobile-phase composition. This has been alleviated in part by higher cross-Unking. 

Polyelectrolyte. A macromolecule containing multiple ionic functional groups (either cationic or anionic). 

Another concept to consider in reversed-phase elution is selective elution. Selective elution consists of using sequential elution solvents to selectively remove several classes of solutes, or using wash solvents to remove impurities that will interfere with the analysis. An example of selective elution is the separation and isolation of herbicides and their metabolites by a reversed-phase C-18 mechanism. Figure 3.5 shows the separation of alachlor, a herbicide, and its sulfonic-acid metabolite. In this method, both compounds are sorbed to the C-18 resin by a reversed-phase mechanism. Even the ionic sulfonic acid is bound to the C-18 bonded phase. The metabolite, whose structure is shown in Figure 3.5, is a surface-active compound and is bound by reversed phase with its ionic functional group solvated by the aqueous phase. The parent compound is eluted with ethyl acetate while the ionic metabolite stays bound to the C-18 resin. Apparently the solubility of the ionic metabolite in ethyl acetate is too low for dissolution. When methanol is applied to the column, the sulfonic acid metabolite elutes from the column. Thus, a fractionation is obtained by selective elution (Aga et al., 1994). 

The first considerations in determining the most appropriate SPE methodology are the structure and polarity of the analytes of interest. Table 7.1 shows a selection of environmentally important compounds as examples for SPE methods development from aqueous solution. The polarity range of environmentally important analytes is broad and stretches from nonpolar compounds, such as polychlorinated biphenyls (PCBs), dioxin, and l,l,l-trichloro-2-2-bis(4-chlorophenyl)ethane (DDT), to moderately nonpolar compounds, such as polynuclear aromatic hydrocarbons (PAHs), to polar compounds such as the herbicides. The most polar compounds are those containing multiple polar functional groups or an ionic functional group, either anionic or cationic. The type of SPE cartridge and elution solvent that are used depends on the polarity of the compound. 

---