Monolith technique

Most MIP materials described to date have been prepared by the so-called monolith technique. However, it is possible to produce MIPs by different approaches, each with its advantages, shortcomings, and applications. Figure 4 summarizes a typical synthetic procedure to obtain the polymerization... 

Particles in the submicrometer scale (typically 0.3-10 pm) can be obtained through this method. The synthesis is similar to the monolithic technique, but an excess of porogenic solvent is used. As particles grow, they become more insoluble in the organic solvent, and precipitation of nano- and microparticles is finally produced to form a polymer monolith. The main drawback is the larger amounts of template needed because of the dilution factor, but the particles work better than those obtained by grinding and sieving procedures. This method has been... 

In the latter twentieth century, spent automotive catalysts have emerged as a significant potential source of secondary Pt, Pd, and Rh. In North America, it has been estimated that 15.5 metric tons per year of PGM from automotive catalysts are available for recycling (22). However, the low PGM loading on such catalysts and the nature of the ceramic monoliths used have required the development of specialized recovery techniques as well as the estabhshment of an infrastmcture of collection centers. These factors have slowed the development of an automotive catalyst recycling iadustry. 

Much effort has been devoted to the development of a multi-step swelling polymerization technique using water as suspension medium [98]. This has resulted in polymers showing similar selectivities but slightly improved mass transfer characteristics compared with the corresponding monolithic polymers. Of particular rele-... 

Unlike other thin film techniques such as sputtering CVD can also be used to produce fibers, monoliths, foams and powders. 

Hydrocortisone microspheres (108,109) and films (110) based on poly(lactic acid) have been investigated. A cage implant technique was used to study the performance of monolithic poly (DL-lactide) films loaded with hydrocortisone acetate (110). Films 1.5 x 0.6 cm were inserted into titanium wire-mesh cages 3.5 x 1.0 cm. The cages were implanted in the backs of rats and the inflammatory exudate was sampled periodically. The white cell concentration in the samples was lower than that of controls at all times during the 21-day test. 

Scientists from Politecnico di Milano and Ineos Vinyls UK developed a tubular fixed-bed reactor comprising a metallic monolith [30]. The walls were coated with catalytically active material and the monolith pieces were loaded lengthwise. Corning, the world leader in ceramic structured supports, developed metallic supports with straight channels, zig-zag channels, and wall-flow channels. They were produced by extrusion of metal powders, for example, copper, fin, zinc, aluminum, iron, silver, nickel, and mixtures and alloys [31]. An alternative method is extrusion of softened bulk metal feed, for example, aluminum, copper, and their alloys. The metal surface can be covered with carbon, carbides, and alumina, using a CVD technique [32]. For metal monoliths, it is to be expected that the main resistance lies at the interface between reactor wall and monolith. Corning... 

The latest innovation is the introduction of ultra-thin silica layers. These layers are only 10 xm thick (compared to 200-250 pm in conventional plates) and are not based on granular adsorbents but consist of monolithic silica. Ultra-thin layer chromatography (UTLC) plates offer a unique combination of short migration distances, fast development times and extremely low solvent consumption. The absence of silica particles allows UTLC silica gel layers to be manufactured without any sort of binders, that are normally needed to stabilise silica particles at the glass support surface. UTLC plates will significantly reduce analysis time, solvent consumption and increase sensitivity in both qualitative and quantitative applications (Table 4.35). Miniaturised planar chromatography will rival other microanalytical techniques. 

The achievements in optical detection techniques and the interest in the sol-gel process for creation of new materials, are leading to developing of various sensors. The majority of reported sensors developments have concentrated on the use of thin films. There are many reasons for this. The important one is the susceptibility of monoliths to cracking due to internal stresses, particularly when exposed to liquid penetration. More attractive are... 

HPLC has high-throughput capability when it can simultaneously determine multiple drugs and their metabolites or when coupled with a unique monolithic column or sample preparation technique. Some examples are summarized below. 

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