Determination of aflatoxins in peanut butter, using two liquid chromatographic methods: collaborative study

Two methods for determining aflatoxins in peanut butter, one using normal phase and the other reverse phase liquid chromatography (LC), were studied by 8 and 10 collaborators, respectively. Fluorescence detection was used for the determinative step in both methods. For reverse phase LC, aflatoxins B1 and G1 were converted to B2a and G2a; for normal phase LC, a silica gel-packed flow cell was placed in the irradiating light path of the detector. The samples included spiked and naturally contaminated peanut butter with total aflatoxin levels from about 5 to 20 ng/g and controls in a balanced pair design. For the normal phase LC method, recoveries of B1, B2, G1, and G2 from spiked samples averaged 79, 92, 74, and 88%, respectively; for the reverse phase method, the recoveries were 103, 104, 89, and 163%. For the normal phase LC method, pooled repeatabilities were 20, 23, 28, and 17% for B1, B2, G1, and G2, respectively; for the reverse phase method, the repeatabilities were 19, 22, 38, and 31%. For the normal phase method, pooled reproducibilities were 34, 33, 39, and 34% for B1, B2, G1, and G2, respectively; for the reverse phase method, the reproducibilities were 32, 46, 51, and 52%. Both methods show an improved limit of detection and better within-laboratory precision over current AOAC methods; however, between-laboratory precision is no better, and the reverse phase method shows evidence of interferences being measured. For these reasons and because of no benefits of present value, neither method was submitted for adoption as official first action.