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Evaluation of immunoassay kits for determination of ochratoxin A in cereals4.1.3 Equipment and materials4.1.3.1 Read-outFor the read-out of the ELISA kits a microplate reader model 550 of BIO-RAD (Hercules, US) was used. The readoutof Charms LFD was done with the proprietary LFD reader of Charm.4.1.3.2 Matrix effectMatrix interferences were checked with 3 blank samples of wheat, winter barley and oats (OTA content < 0.6 ppb 68OTA as checked by HPLC-IAC-FLD). Variability in the matrix (solid matrices can be very inhomogeneous) wasminimized by pooling three different extracts.4.1.3.3 AccuracyContaminated matrices, all barley, at levels of 4.13 ng/g, 13.25 ng/g and 35.40 ng/g (as by HPLC-IAC-FLD) wereused to assess the accuracy.We used samples that were characterised in our laboratory using our HPLC-IAC-FLD. Unfortunately there was notenough of each sample to do all kits on the same one. So different kits might be characterised using different CRMs.4.1.3.4 RecoveryTo assess the recovery a certified reference solution at approximately 10 mg/ml OTA in acetonitril from Biopurewas diluted with 50% MeOH/H 20 to obtain a working solution of ± 500 ng/ml that was stored until use at 4°C.Whole wheat flour (used in the recovery experiments for our accredited HPLC-IAC method and having a OTAcontent of about 0.8 ng/ml) is spiked with an appropriate volume of working solution to obtain the desired spikinglevel in ng OTA per g flour. The wheat is left overnight in an open container in the dark at room temperature toallow the solution to evaporate.4.1.3.5 Standard solutionsVerification of standard concentration was performed on a UPLC linked to a Quattro Premier XE system, bothby Waters (Milford, MA, USA).4.1.4 Work packages4.1.4.1 Work package I: Concentration accuracy of standards4.1.4.1.1 Study designA calibration curve with at least 6 points of OTA in 50% MeOH/water prepared from a commercially purchasedreference standard (BIOPURE) will be measured on the UPLC-MS. From each kit all the calibrator solutions will bemeasured to determine the accuracy in OTA content of the calibrators.68G. M. Wood, S. Patel b, A. C. Entwisle; A. C. Williams; A. Boenke; P. J. Farnel, Food Additives & Contaminants: Part A, Volume 14, Issue 3April 1997 , pages 237-2484-40 Experimental evaluation | CODA-CERVA