Polymeric Monolithic Anion Exchangers

5 mmol/L from 0 to 2 min, 5-30 mmol/L from 2 to 8 min flow rate 1 mUmin detection  

A polymeric monolith is a continuous porous polymeric rod made from a mixture of an initiator, monomers (including a cross-linking monomer), and a porogen (pore-forming solvent) that are polymerized in situ in a column. Tuning of the porous properties is typically achieved with a mixture of solvents such as toluene, THF, or decanol. The rationale for choosing an initiator depends on the mode of initiation and on solubility aspects. A common initiator is 2,2-azo-bis-isobutyronitrile (AIBN). Most polymerizations are radical polymerizations, activating radical formation either thermally [54] or with UV radiation [55]. Common monomers used in the preparation of polymer monoliths are styrene, (meth)acrylate, and acrylamide-based materials. The formation of the monolith 

A higher content of divinyl monomer directly translates into more cross-linked polymers in the early stages of the polymerization process and, therefore, lead to an earlier phase separation. This approach is predominandy used for the preparation of monoliths with very large surface areas [54]. Typical cross-linking monomers used today are ethylene dimethacrylate for methacrylate-based monoliths and divinylbenzene with styrenic monomers. 

The breakthrough in the development of organic polymer monoliths for use in conventional anion-exchange chromatography of common inorganic anions and organic acids was made possible by several new advancements including as follows  

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Hutchinson, J.P. Zakaria, P. Bowie, A.R. Macka, M. Avdalovic, N. Haddad, P.R. Latex-coated polymeric monolithic ion-exchange stationary phases. 1. Anion-exchange capillary electrochromatography and in-line sample preconcentration in capillary electrophoresis. Anal. Chem. 2005, 77, 407 16. 

Figure 29 Separation of the nonsteroidal anti-inflammatory drugs ibuprofen (peak 1), naproxen (2), ketoprofen (3), and suprofen (4) in anion-exchange CEC mode using a strong anion-exchange monolithic column. Conditions on-column alkylated monolith prepared from mixtures consisting of 8% 2-dimethylaminoethyl methacrylate, 24% 2-hydroxyethyl methacrylate, 8% ethylene dimethacrylate, 20% cyclohexanol, 40% 1-dodecanol UV-initiated polymerization at room temperature for 16 h cfpmode= 1423 nm. Column dimensions inner diameter 0.1 mm, total length 335 mm, effective length 250 mm. Mobile phase 0.4 mol/L acetic acid and 4 mmol/L triethylamine in acetonitrile/methanol (60/40), voltage -25 kV, injection -5 kV for 5 s, temperature 50°C, UV detection at 250 nm. (Reprinted from Ref. 127, with permission.)...

The epoxide groups of a polyglycidyl methacrylate-co-ethylene dimethacrylate monolith readily react with diethylamine to create a weak anion exchange column. This monolithic column is characterized by fast mass transport kinetics leading to excellent resolution. The columns seem to be stable, and the specific capacity is 40-mg/g medium for ovalbumin [60,62]. More recently, graft polymerization within... 

SPE is an exhaustive and almost solvent-free sample preparation technique. Typically, a tube is filled with a sorbent, which can be porous particles or a polymerized monolith. Various interactions are used to extract analytes from complex samples. Many of the commercially available SPE systems are for single use, but some, like RAM (restricted access materials) and MIP (molecular imprinted polymers), are typically obtained as reusable extraction devices. As will be discussed in detail, the extraction sorbents mainly function as normal phase, reversed phase, cation exchange, anion exchange, or a combination of these. 

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