IMMUNOAFFINITY COLUMN COUPLED WITH SOLUTION FLUOROMETRY OR LIQUID-CHROMATOGRAPHY POSTCOLUMN DERIVATIZATION FOR DETERMINATION OF AFLATOXINS IN CORN, PEANUTS, AND PEANUT BUTTER - COLLABORATIVE STUDY

An AOAC/IUPAC (International Union of Pure and Applied Chemistry) collaborative study was conducted to evaluate the effectiveness of an immunoaffinity column for the determination of aflatoxin. The test portion is extracted with methanol-water (7 + 3), filtered, diluted to < 30% methanol with water, and applied to the affinity column. The column is washed with water and the concentrated aflatoxins are eluted with methanol. Total aflatoxins are determined by solution fluorometry with bromine (SFB), and individual toxins are determined by reverse-phase liquid chromatography with postcolumn derivatization with iodine (PCD). Corn naturally contaminated with aflatoxins, and peanuts, peanut butter, and corn containing added aflatoxins (B1:B2:G1:G2 = 7:1:3:1) were sent to 24 collaborators in the United States, France, Canada, and the Republic of South Africa. Twelve collaborators used the SFB method, 9 used the PCD method, and 3 used both SFB and PCD methods. Twenty collaborators completed the study (10 used the SFB method, 7 used the PCD method, and 3 used both SFB and PCD methods). Test portions were spiked at 10, 20, and 30 ng/g. For SFB analyses, recoveries of total aflatoxins were 123, 105, and 107%, respectively; the relative standard deviation for repeatability (RSD(r)) ranged from 11.75 to 16.57%, and the relative standard deviation for reproducibility (RSD(R)) ranged from 10.97 to 33.09%. For PCD analyses, recoveries were 81, 81, and 83%, respectively; the RSD(r) ranged from 5.20 to 17.22%, and the RSD(R) ranged from 4.68 to 50.77%. The RSD(r) for aflatoxins B1 and G1 for spiked test portions ranged from 5.45 to 23.55%, and the RSD(R) ranged from 4.21 to 57.28%. The RSD(r) and RSD(R) for aflatoxins B2 and G2 were higher because of small amounts added. Analyses by both SFB and PCD methods showed acceptable within-laboratory and between-laboratories precision. The method has been adopted official first action by AOAC as an AOAC-IUPAC method.