Document - FAVV

Evaluation of immunoassay kits for determination of ochratoxin A in cereals4.4.3 Matrix effectTo assess the matrix effect calibration curves were constructed for OTA in solvent and in extract for three matrices(wheat, winter barley and oats), for each matrix one 5 times diluted and one undiluted. The results of this exercise aresummarized in Table 59 and Table 60. From these results it can be clearly seen that the amount of OTA necessary toobtain a 50% signal reduction is higher in the matrix than in the solvent, the result of a matrix suppression effect.Table 59: Matrix-effect calculated as relative (IC50) extinctionControlOTAWheatUndilutedWheatDilutedWinter BarleyUndilutedWinter BarleyDilutedOatsUndilutedOatsDilutedSlope -0.928 -0.764 -1.265 -0.545 -0.665 -0.660 -0.586Intercept 1.539 1.485 2.234 1.228 1.386 1.494 1.011R 2 0.919 0.968 0.934 0.881 0.978 0.962 0.921SE Intercept 0.215 0.108 0.262 0.156 0.077 0.102 0.133SE Slope 0.195 0.098 0.238 0.142 0.070 0.092 0.121IC50 (ng/g) 45.545 87.590 58.347 179.355 121.502 184.277 53.175RelativeCrossreactivity100% 192% 128% 394% 267% 405% 117%Table 60: Matrix-effect calculated as percentage color reduction to the control (%CCR)ControlOTAWheatUndilutedWheatDilutedWinter BarleyUndilutedWinter BarleyDilutedOatsUndilutedOatsDiluted% Control ColorReduction100% 101% 108% 85% 93% 100% 81%CV / 13% 9% 12% 8% 11% 12%4.4.4 AccuracyAccuracy was assessed on two reference materials, one from FAPAS (barley, 4.13 ng/g OTA) and one from BIPEA(also barley, 13.25 ng/g OTA) The results in Table 61 indicate a slight underestimation of the true value.Table 61: Accuracy on two reference materialsFAPAS BIPEATRUE VAL (ng/g) 4.13 13.25N 9 9Degrees of freedom 8 8t (95) 2.31 2.31SD (ng/g) 1.60 3.03Q1 (ng/g) 1.53 4.90Q3 (ng/g) 2.73 8.76Mean (ppb) 2.18 7.01xe-xt (ng/g) -1.95 -4.19Criterium (ng/g) 1.23 2.33CODA-CERVA | Experimental evaluation 4-57