Abstract
An interlaboratory study of a solvent-efficient thin-layer chromatographic (TLC) method for the determination of aflatoxins B1, B2, G1, and G2 was conducted in laboratories located in the United States, France, Tunisia, and Denmark. Eighteen artificially contaminated samples plus blanks of raw peanuts and peanut butter and corn containing varying amounts of aflatoxins B1, B2, G1, and G2 were distributed to participating laboratories. The method consists of elements of the U.S. Food and Drug Administration (FDA), Contaminants Branch (CB) (AOAC Method 968.22) and FDA, Best Foods (BF) (AOAC Method 970.45) methods with reduced requirements for solvents. Participating laboratories used either visual or densitometric techniques during the final determinative step. Statistical analysis of the data was performed to determine or confirm outliers and to compute repeatability and reproducibility of the method using either visual or densitometric techniques for the determinative step. Reported results from laboratories using a densitometer showed that, for corn, the relative standard deviation for repeatability (RSDr) for aflatoxin Bi ranged from 56.6 to 41.7% for contamination levels ranging from 5 to 50 ng/g. For raw peanuts and peanut butter, the RSDr values for aflatoxin Bi ranged from 21.3 to 37.3% and 65.9 to 42.1%, respectively, for the contamination levels ranging from 5 to 25 ng/g. RSDr ranges for anatoxins B2, Gi, and G2 were similar. For reproducibility (R), the RSDr ranges for aflatoxin Bi were 41.7-56.6%, 56.6-84.8%, and 26.4-37.3% for corn, peanut butter, and raw peanuts, respectively. Average re-coveries for all aflatoxins at all levels were 95.3, 139.0, and 95.6% for corn, peanut butter, and raw peanuts, respectively. When analysts determined af latoxin concentrations in corn by visual comparison to standards, the RSDr values for aflatoxin Bi were 47.8-11.4% for contamination levels ranging from 5 to 50 ng/g. For raw peanuts and peanut butter, the RSDr values for aflatoxin Bi were 76.3-12.6% and 33.4-8.8%, respectively, for the contamination levels ranging from 5 to 25 ng/g. RSDr values for aflatoxins B2, G1, and G2 were similar. The RSDr values for aflatoxin Bi were 34.6-90.2%, 45.5-59.3%, and 31.8-78.3% for corn, peanut butter, and raw peanuts, respectively. Average recoveries for all anatoxins at all levels were 111.0,157.6, and 92.3% for corn, peanut butter, and raw peanuts, respectively. High recoveries were noted for anatoxins in peanut butter determined by either a densitometer or comparison to standards. Generally, increased precision was observed with the method at higher contamination levels. On the basis of the results obtained in this AOAC/IUPAC collaborative study, the solvent-efficient TLC method using densitometry for the quantitative step was adopted first action by AOAC for the determination of aflatoxins B1, B2, G1, and G2 in corn at levels within the range of 5-50 ng/g, 3-15 ng/g, 10-50 ng/g, and 3- 15 ng/g, respectively, by densitometry; for anatoxins B1 and B2 in raw peanuts at levels ranging from 5 to 25 ng/g and from 1.5 to 7.5 ng/g, respectively, by densitometry; and for aflatoxins B1 and G1 in corn at 10-50 and 50 ng/g, respectively, and aflatoxins B1, B2, and G1 in raw peanuts at 10-25 ng/g, 7.5 ng/g, and 10-25 ng/g, respectively. Because of high recovery values, additional study is recommended for peanut butter. The solvent-efficient TLC method for determination of aflatoxins B1, B2, G1, and G2 in corn and peanuts has been adopted first action by AOAC INTERNATIONAL.
A rapid method for the determination of asphaltene content in crude oils and bitumens using thin layer chromatography
