A laboratory ring trial was performed in four laboratories for determination of Cry1Ab toxin in leaf material of MON 810 maize using a standardised enzymelinked immunoassay protocol. Statistical analysis was carried out by the ISO 5725-2 guidelines, sample standard deviation and standard error, withinlaboratory and inter-laboratory SD and SE were calculated. Measured interlaboratory average values were 12.594.0, 15.394.6 and 72.6917.8 mg/g for three lyophilised samples, and 27.894.3 mg/g for a frozen sample, yet, Cry1Ab concentrations ranged 66.5Á160.1% of the corresponding IA. Determined concentrations by in-house protocols were statistically not different in one laboratory and different in two laboratories from the corresponding values by the joint protocol. Results emphasise the importance of a standardised protocol among laboratories for comparable quantitative Cry1Ab toxin determination. However, even when using a standardised protocol, significant differences still occur among toxin concentrations detected in different laboratories, although with a smaller range of variation.

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