Laboratory Proficiency Testing of Aflatoxins in Corn and Peanuts—A Cooperative Project between Thailand and the United States

Abstract

The objective of this project was to conduct an aflatoxin proficiency test program in government, academia, and industry laboratories in Thailand. Aflatoxin-free corn and peanuts and corn and peanuts naturally contaminated with aflatoxins diluted to approximately 25 micrograms/kg were analyzed. Homogeneity of prepared, naturally contaminated test samples was checked on multiple replicates. The test was conducted according to the ISO/IUPAC/AOAC INTERNATIONAL Harmonized Protocol with z scores indicating laboratory performance. The participants used 3 methods: enzyme-linked immunosorbent assay, thin-layer chromatography, and the minicolumn. Of 19 laboratories that reported results for aflatoxins in naturally contaminated corn, 13 (68%) performed satisfactorily, on the basis of the mean obtained by an expert laboratory, a calculated target value for standard deviation, and the z score. Of 21 laboratories that reported results for aflatoxins in naturally contaminated peanuts, 10 (48%) performed satisfactorily. For aflatoxin-free corn, 6 laboratories reported finding aflatoxins at > or = 10 ng/g, chiefly by the minicolumn method; for aflatoxin-free peanuts, 1 laboratory reported finding aflatoxins at > 10 ng/g. Subsequently, a workshop of lectures and laboratory sessions was conducted to improve performance. A new and simple successive outlier removal procedure applied to the same data removed the same laboratories as did the use of z scores.