Laboratory proficiency testing of aflatoxins in corn and peanuts - A cooperative project between Thailand and the United States

The objective of this project was to conduct an aflatoxin proficiency test program in government, academia, and industry laboratories in Thailand. Afl atoxin-free corn and peanuts and corn and peanuts naturally contaminated wi th aflatoxins diluted to approximately 25 mu g/kg were analyzed. Homogeneit y of prepared, naturally contaminated test samples was checked on multiple replicates. The test was conducted according to the ISO/IUPAC/AOAC INTERNAT IONAL Harmonized Protocol with z scores indicating laboratory performance. The participants used 3 methods: enzyme-linked immunosorbent assay, thin-la yer chromatography, and the minicolumn, Of 19 laboratories that reported re sults for aflatoxins in naturally contaminated corn, 13(68%) performed sati sfactorily, on the basis of the mean obtained by an expert laboratory, a ca lculated target value for standard deviation, and the z score, Of 21 labora tories that reported results for aflatoxins in naturally contaminated peanu ts, 10(48%) performed satisfactorily For aflatoxin-free corn, 6 laboratorie s reported finding aflatoxins at greater than or equal to 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 l aboratory sessions was conducted to improve performance. A new and simple s uccessive outlier removal procedure applied to the same data removed the sa me laboratories as did the use of z scores.