Vitamins specific adsorption

Adsorptive purihcation, in its most general sense, involves the use of adsorbents to remove undesirable constiments and contaminants from fats and oils by adsorptive mechanisms. It must be noted, however, that although different adsorbents do exhibit some degree of selectivity for certain adsorbates (see Section 4.3), none exhibit specific selectivity for a single compound or chemical. Some trace constituents that are desirable (e.g., tocopherols) will also be removed. According to Boki et al. (106), 20-40% of the tocopherols present in most alkali-refined oils are removed by bleaching with acid-activated bleaching clay the exception is soybean oil, which only loses 3-5% (71, 105). Buxton has reported (107) that activated carbon removes antioxidants from fish hver oils and renders the vitamin A in the oil unstable. 

Bioselective adsorption is the process where the affinity is based on biologically relevant binding. It includes group-specific ligands, eg, lectins and nucleotide cofactors (NAD, AMP), and specific ligands, eg, certain less common cofactors (vitamin B12), receptor proteins, and antibodies as used in immunosorbents. 

A radioisotope dilution assay and an assay based on animal growth are the most reliable methods for the determination of vitamin B12 activity. The tracer technique is highly specific for cyanocobalamin or analogs which are convertible to cyanocobalamin. The assay is specific for cyanocobalamin if cyanide treatment of the sample is avoided total cobalamins convertible to cyanocobalamin are determined if a given sample is first treated with cyanide. The method consists in the addition of a known amount of pure [ Co]-cyanocobalamin. A series of selective extractions and adsorptions to remove interfering substances is completed and the radioactivity and color of the purified sample are measured. From these data, it is possible to calculate the amount of cobalamin present in the original sample. The isotope dilution method is accurate and precise and can be used for both relatively pure samples and for crude extracts of low potency. 

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