Polymer-Based Cation Exchangers

1 Polymer-Based Cation Exchangers Styrene/divinylbenzene copolymers 

Separator column Manufac- turer Dimensions [length X I.D.] [mm] Max. flow rate [mL/min] Max. Solvent operating stability pressure [%] [MPa] Capacity [mequiv/g] Particle diameter [pm] 

Polymethacrylate and polyvinyl resins play only a secondary role in the manufacture of cation exchangers. Presently, the only polymethacrylate-based cation exchanger is offered by Sykam (Gauting, Germany) under the trade name LCA K02. This column differs from its PS/DVB analogue (see Table 3-24) only in the particle size (5 pm) and exchange capacity (0.4 mequiv/g). With a tartaric acid eluent, this phase is preferred for the analysis of heavy and transition metals. 

As a representative for all separator columns of this type. Fig. 4-2 shows a chromatogram with a separation of alkali metals suppressed conductivity detection was used. 

Mineral acids such as hydrochloric add or nitric add are employed as eluants, regardless of whether the background conductivity is chemically suppressed or electronically compensated. While alkali metals are eluted within 10 minutes 

The big advantage of this eluant is that the net charge of 2,3-diaminopropionic acid and, thus, the elution strength, is solely determined by the HCl concentration. In the early days of cation exchange chromatography, m-phenylenedi-amine was recommended as an eluant for alkaline-earth metals, but it isn t used anymore because it is not available in the required ptirity. Moreover, m-phenyl-enediamine tends to undergo polymerization at the stationary phase, which leads to a significant and irreparable loss of separation power. 

A quality feature of all cation exchangers suitable for simultaneous analysis of mono- and di-valent cations is the maximal concentration ratio between sodium and ammonium that allows a separation of both components. Under isocratic conditions with 10 mmol/L methanesulfonic acid at 2 mL/min, the lonPac CS12 separates ammonium in the presence of a 250-fold to 500-fold amount of sodium. Higher concentration differences are only applicable when using a step gradient or a continuous concentration gradient (see Section 4.7). 

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Reactions catalysed by organic polymer-based cation exchangers... 

Like anion exchangers, cation exchangers are divided into polymer-based cation exchangers (PS-DVB, EVB-DVB, polymethacrylate, and polyvinyl copolymers), latex-agglomerated cation exchangers, silica-based, and other (e.g., crown ether, aluminia materials).Modern cation exchangers contain sulfonic, carboxylic, car-boxylic-phosphonic, and carboxylic-phosphonic-crown ether functional groups. 

The last two examples show that, in a number of cases, cation-exchange chromatography can be regarded as an alternative to reversed-phase chromatography on chemically bonded silica phases, especially because the characteristic interactions between the basic compounds and the free silanol groups of silica are not observed with polymer-based cation exchangers. 

In this equation, Res denotes resin or polymer. Silica-based cation exchangers are generally prepared by reacting silica particles with an appropriate chlorosilane or methoxysilane. A common type of silica catex has the structure ... 

If the analytes are ionic or ionizable, they can be separated by ion-exchange, ion-pairing, or reversed-phase chromatography. Both polymeric and silica-based ion exchangers are available. Silica-based ion exchangers exhibit better efficiency than polymer-based ion exchangers, but can not be used at basic pH values. Silica itself is a cation exchanger of excellent efficiency and can be used for the analysis of basic sample compounds. For a detailed discussion, see Chapter 12. 

Poly(vinyl alcohol)-based cation exchangers are currentiy offered by Metrohm (Herisau, Switzerland) and Showa Denko (Tokyo, Japan). The respective product from Metrohm is the carboxylate-based Metrosep C3, which belongs to the group of chemically derivatized polymers [17]. Metrosep C3 is offered in three... 

Before polyacrylamides are sold, the amount of residual acrylamide is determined. In one method, the monomer is extracted from the polymer and the acrylamide content is determined by hplc (153). A second method is based on analysis by cationic exchange chromatography (154). For dry products the particle si2e distribution can be quickly determined by use of a shaker and a series of test sieves. Batches with small particles can present a dust ha2ard. The percentage of insoluble material is determined in both dry and emulsion products. 

Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

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