Use of various clean-up procedures for the analysis of ochratoxin A in cereals

A rapid and reliable procedure has been developed for the determination of ochratoxin A in wheat and oats. The method consists of extraction of the sample with acidic chloroform, followed by defatting with n-hexane and finally, HPLC determination with fluorometric detection. Mean recoveries for wheat and oats spiked at levels between 1 and 100 micrograms/kg ranged from 80 to 104%. The limit of determination (field blank +6 sigma) was 0.8 micrograms/kg and the precision (within-laboratory relative standard deviation) ranged from 3 to 7%. The method was tested on 34 wheat and 34 oats samples. Ochratoxin A was confirmed in some positive samples by methyl ester formation and/or by clean-up of the extracts with immunoaffinity columns. The method was not appropriate for the analysis of barley (45 tested samples), rye (69 samples) or trout feed (13 samples). A false positive was recorded within the four positive barley samples and 18 false positives were recorded within the 21 positive rye samples whereas trout feed samples could not be analysed due to insufficient clean-up. The use of immunoaffinity columns made the analysis of trout feed and rye samples possible, providing excellent clean-up of the extracts with no false positive results and a good limit of determination (0.2 micrograms/kg).