Examples of validated immunoassay methods

The following methods serve as typical examples of immunoassay-based analytical methods applied to biomonitoring, environmental, and crop tissue analyses. Each method utilized a commercially available immunoassay kit that was combined with sample extraction and cleanup steps as part of an overall residue method. These methods can serve as models for resolution of similar problems. 

The only published immunoassay method submitted to date to EPA OPPTS as an enforcement method for a range of substrates (water, sediment, crops, processed crop fractions, and animal tissues) is the spinosad method, developed by Young et al. This method uses the spinosad RaPID Assay (Strategic Diagnostics) for determination of total spinosad residues (TSR). This discussion will be limited to crop and animal tissues, because the water and soil analyses are analogous to the triasulfuron method. The extraction, cleanup, and method parameters are summarized in Table 2. 

These authors noted the potential for the assay to underestimate the concentration of TSR due to decreased binding of metabolites relative to parent spinosad. However, the major residue found was parent spinosad, so underestimation of residues is not likely to be problematic. Overall, this method was validated in 34 matrices and showed excellent agreement with results obtained with a high-performance liquid chromatography/ultraviolet detection (HPLC/UV) method.  

Substrate Sub-sample (g) Solvent Technique Cleanup (pgmL- )  

Beef tissue 20 ACN-H2O (4 1) Homogenization Reflux Filtration Evaporation Dilution 0.003 0.01 

---