Inorganic sorbents

Eor a long time there have been discussions about which type of sorbent is the best for SEC separations in various mobile phases. In principle, organic (copolymer) and inorganic packings can be used. Each type of packing has its benefits and drawbacks. Table 9.3 summarizes major sorbent properties and reveals some interesting aspects of SEC separations and its requirements on packings. 

The inorganic sorbents act as catalysts in all this [3,4]. Hie pH also probaUy plays a role. Reactions that do not otherwise occur are observed on add silka gd [3] or basic aluminium oxide layers. Reactions of this type have also been obsoved for amino [6-8] and RP phases [9]. The products of reaction are usually fluorescent and can normally be used for quantitative analysis since the reactions are reprodudble. 

Both inorganic and organic sorbent materials are suitable for apphcation in partition PLC. The relevant material in this connection is cellulose. Celluloses are natural products with the universal chemical formula (CgHioOj),. These native celluloses have a fibrous structure and they need to be groimd and purified before use in PLC. Besides native cellulose, microcrystalline cellulose can also be used in partition PLC. In this case the cellulose has been recrystaUized and is rod-shaped. The specific surface area of celluloses is in the range of about 2 m /g. 

Magnetite deserves further investigation as robust inorganic sorbent material. 

The effect that hydrophobic organic substances can become sorbed to organic coatings can be used to make sorbents by coating inorganic colloids such as ferri-hydrite with surfactants. Such surfactant-coated surfaces contain films of hemicelles (see 4.5) which are able to remove hydrophobic solutes, such as toluene or chloro-hydrocarbons, from solution (Holsen, et al., 1991). 

Dousova et al. [142] found that calcined Mg/Al LDHs were effective in removal of As (V) compounds from aqueous solutions at 293 K and neutral pH utilizing the memory effect . More than 70 % of As (V) compoimds were removed from aqueous solution at low sorbent-solution ratios. Parida et al. also studied the affinity of Mg/Fe LDHs toward the removal of inorganic selenite (SeOs ) from aqueous media [143]. The results indicated that the efficacy of SeOs removal increases with a decrease in either pH or temperature. 

For the extraction of Tc from molybdemun irradiated by neutrons or separated from uranium fission products, inorganic sorbents, especially aliuninum oxide have widely been applied. In preparing a Tc generator from irradiated molybdenum , MoOj is dissolved in cone, nitric acid, the solution is diluted and passed through an aluminum oxide column. The column is then eluted by 0.2 N H2SO4 to extract Tc. If molybdenum is adsorbed by AljOj as molybdatophos-phate instead of molybdate, the exchange capacity of molybdenum increases from... 

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