Application of Statistics to Evaluate Iranian Analytical Laboratories Proficiency: Case of Aflatoxins in Pistachio

The aim of this study was to evaluate the utility of a proficiency testing program among limited number of local laboratories as an alternative to the IUPAC/CITAC guide on proficiency testing with a limited number of participants, specially where international schemes are not accessible. As a sample scheme we planned to determine aflatoxins (B1, G1, B2, G2, total) in Iranian pistachio matrix. A part of naturally contaminated pistachio sample was tested for sufficient homogeneity by a competent laboratory and then homogenized sub-samples were distributed among participants all across the country. The median of participants’ results was selected as assigned value. Student t-test was applied to show there is no significant difference between assigned and mean values of homogeneity test results obtained by the competent laboratory. Calculated z-scores showed that 6 out of 8 results in aflatoxin B1, 7 out of 8 results in aflatoxin B2, 5 out of 8 results in aflatoxin G1, 7 out of 8 results in aflatoxin G2 and 6 out of 9 results in aflatoxin total were in satisfactory range. Together our studies indicate that the approach described here is highly cost efficient and applicable for quality assurance of test results when there is no access to international proficiency testing providers.