Ochratoxin A in wheat: An intercomparison of procedures

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Abstract
The Commission of the European Communities’ Community Bureau of Reference (BCR) has undertaken a project to improve methodology and to prepare suitable certified reference materials in order to provide a basis for analytical quality control for the determination of ochratoxin A. The first phase of the project, an intercomparison of procedures for the determination of ochratoxin A in wheat at a level of approximately 13 μg/kg, is described. The study involved 24 European laboratories which analysed a naturally contaminated wheat and a ‘blank’ wheat sample (ochratoxin A content < 1 μg/kg). The participants used a variety of procedures, including chloroform, methanol, toluene and ethyl acetate for extraction, and silica‐, reversed phase‐ and immunoaffinity columns for clean‐up. HPLC (one laboratory used TLC) was applied as the determinative step. Several performance characteristics were checked and the ochratoxin A content was determined. Recoveries were found to range from 25 to 100%. The coefficient of variation from all the results calculated on the basis of peak height was 23%. The study showed that the variation of results was influenced more by the clean‐up step than by the extraction solvent. Some laboratories suffered significant day‐to‐day effects while others found difficulties with interfering peaks in the ‘blank’ material. It is planned for the next study to improve the recovery range, the clean‐up step and the reproducibility (within‐laboratory, between‐days) and to check the influence of co‐extractives from the matrix.