Radioimmunoassay RIA

Although the RIA is not used routinely for mycotoxin analysis, it is currently used by some laboratories for research purposes. RIA has been used to detect aflatoxins (140), ni-valenol (141) deoxynivalenol (142), ochratoxin A (143), and T-2 toxin (144,145) in food.

In RIA, sufficient radiolabeled analyte (125I, 14C or 3H) is added to an antibody such that 50% of the label becomes antibody bound. A proportion of this label is then displaced when a known concentration of standard analyte or an unknown amount of sample analyte is added. Activated charcoal is then used to remove the antibody-free fraction. The amount of analyte can be calculated by comparing the concentration of isotope in either the supernant fluid or the residue to a standard curve (146). Detection limits for purified mycotoxin are 0.25 to 0.5 ng when tritiated mycotoxins are used as markers (131). The sensitivity of the method can be improved by using radioactive markers of high specific activity or using a simple cleanup step after extraction. RIA has several drawbacks, including the instability and expense of some radioisotopes as well as the hazards in handling isotopes (146).

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