Biochemical or biological rapid screening assays

Validations for classical instrumental chemical analysis methods are relatively straightforward, but the introduction of (multiplex) biochemical or biological rapid screening assays requires a new fit-for-purpose approach. Typically the data output is generating qualitative or semi-quantitative results, while the scope of bioactive analytes covered might be rather diverse in terms of physicochemical parameters. As a pragmatic solution we applied the following validation procedure to the validation of a whole-cell estrogen bioassay: first, five different bioactive estrogen representatives were selected ranging from polar to apolar chemistries assuming that both known and unknown estrogens would have physicochemical characteristics within that range. Then, representative sample matrices, in this case calf urine and three different types of feed matrix, and acceptable spiking levels were defined based on current legislation and/or expected sensitivity of the bioassay for that particular compound. For each sample matrix both unspiked and samples spiked with the representative individual estrogen were analysed. By doing so the unspiked samples were always screened compliant while the spiked samples were always screened suspect non-compliant at the levels chosen, allowing validation as a qualitative screening method and assessment of CCa and CCb values according to 2002/657/EC; even ISO 17025 accreditations could be obtained [75,76]. Moreover,

^chem + 1 ng/ml 17bE2 -•-urine + 1 ng/ml 17bE2 -•- blank chem -*- blank urine

May 2005

# control samples

Figure 7 Long-term performance of a validated estrogen bioassay for blank and estradiol-containing control samples [22].

^chem + 1 ng/ml 17bE2 -•-urine + 1 ng/ml 17bE2 -•- blank chem -*- blank urine

May 2005

# control samples

Figure 7 Long-term performance of a validated estrogen bioassay for blank and estradiol-containing control samples [22].

as shown in Figure 7 routine operation of the validated bioassay showed that the non-compliant control sample was always screened above the CCa decision limit and declared non-compliant while the compliant blank was only screened two times false non-compliant over a two-year period, despite the inherent signal variability of such a bioassay [22]. In other words, even a biological assay can provide consistent results as an on/off screening tool in residue and contaminant control.

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