BS EN ISO 14675 pdf download Milk and milk products — Guidelines for a standardized description of competitive enzyme immunoassays — Determination of aflatoxin M 1 content
This International Standard give guidelines on the use of screening methods used for the determination of aflatoxMicontent in milk and milk products, based upon competitive enzyme immunoassays.
For legal purposes, positive enzyme immunoassay results require confirmation by an accepted reference methoHowever, depending on whether the test complies with the specifications given hereafter, enzyme immunoassaycan be used for routine quality control, especially when the absence of aflatoxin My above the regulatory linneeds to be documented.
lmmunochemical methods are based on the ability of antibodies to bind to specific substances. Thereversible association between antibodies and their corresponding antigens is called the immunological reaction.Thebinding forces involved are weak molecular interactions, such as Coulomb and van der Waals forces, as well ashydrogen bonds and hydrophobic binding.
The antigen-antibody reaction is based on the law of mass action and the amount of antigen or antibody presentin the reaction mixture can be inferred from the extent of the reaction.
The “quality” of any immunoassay is a function of the immunochemical principle of the method, the properties ofthe reagents，the assay design and the experimental errors. These basic principles determine thesensitivity, specificity,precision and accuracy of the assay.
Concerning the principle of the method, a distinction exists between competitive methods and non-competitive methods.
For practical reasons, these methods need either labelled antigen or labelled antibody to permit observation of the antigen-antibody reaction.
Competitive methods are based on the competition of free(A ) and labelled (A ) antigen for a limited numberof antibody-combining sites (AB).
Schematically, this immunochemical principle may be presented according to the following formula:
In most cases, the assay response represents the bound-labelled antigen, but any measure of the distribution of the labelled antigen is, in principle, possible. For the detection of low molecular weight compounds like mycotoxins, which possess only one antibody binding site (epitope), the competitive assay format is mandatory. To provide a distinction between unreacted and complexed reactants, most assays use either antibody (direct competitive assay) or antigen (indirect competitive assay) bound to a solid-phase as immunosorbent. So all the reagents that are not bound by the antibody can be easily removed by “washing” the solid phase.