Immunoassay precipitation reagents

The assay described below in more detail uses the principle of a competitive immunoassay with a double antibody precipitation (Chard 1990). The antibody (from guinea pig) bound tracer is separated from the free tracer by the second antibody present in the precipitating reagent (goat anti guinea pig antibody). After... 

Precipitation techniques can be categorized into two general classes, non-specific and specific. The nonspecific separations involve the addition of a salt or solvent that decreases the solubility of the antigen-antibody complex under conditions that do not affect the free-labeled antigen. After addition, the immune complexes can be precipitated by centrifugation and the radioactivity in either the supernatant solution or the precipitate can be measured. Examples of precipitation reagents used in immunoassays include alcohol, ammonium sulfate, polyethylene, and dioxane. Care must be taken to avoid coprecipitation of the unbound label. 

When extracting with superheated water, soil samples do not require predrying. Water is the ideal solvent when performing immunoassay detection because it does not denature the reagents. However, a small amount of methanol can be added to prevent precipitation of the analytes on to container walls. 

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