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()Evaluation of immunoassay kits for determination of ochratoxin A in cereals4.2 ROSA OCHRATOXIN GRAIN by CHARM4.2.1 Concentration accuracy of standardsUnlike the well-type ELISA kits further discussed the LFD doesn‟t rely on an end users defined calibration curve.The reader uses a proprietary internal calibration.4.2.2 Cross-reactivity4.2.2.1 SolventThe external OTA concentration in the extraction solvent (equivalent from 0 to 8 ng/g in cereal) was used asreference value for the other compounds. Standard concentrations used are equidistant, this might seem unusual foran immunoassay but Charm‟s kit doesn‟t generate results as a logistic regression dose-response curve. UsingEquation 8, the relative cross-reactivity was calculated (Table 44). The calibration curve (Figure 8) clearly shows thatthe kit is not able to differentiate between OTA and OTB (the dechloro analog of OTA, Table 2). The CR% basedon the slope difference is marginal and Lin‟s concordance coefficient (ρ c) clearly indicates that there is no statisticallysignificant difference in reaction of OTB and OTA.OTB can be produced by the same fungi as OTA. If it would interact with the anti-bodies in the same manner asOTA it could increase the signal (a translational bias indicated on recovery curves by an intercept statisticallydifferent from 0, non-proportional recovery will be manifested as a slope statistically different from zero) leading toan increased false positive rate. However, OTB is usually far less abundantly present in cereals than OTA 74 . As quicktests are intended for fast screening to detect possible screen positive samples a (slightly!) increased response shouldbe a manageable problem.12ObservedConcentration10864ng/g200 1 2 3 4 5 6 7 8 9Concentration (ng/g)OTA OTB Otα CIT ZEA AFLA B1 Cou 4-HC PheFigure 8: Standard curve of OTA, OTB, OTα, Citrinin, Zearalenone, AFLA B1, Coumarin, 4-HydroxyCoumarin and L-phenylalanine(n=1)74A, Visconti and A. Bottalico, J. Agric. Food Chem, 31, 1122-1123 (1983)4-46 Experimental evaluation | CODA-CERVA