Testing shelled corn for aflatoxin, Part I: Estimation of variance components

The variability associated with testing lots of shelled corn for aflatoxin was investigated. Eighteen lots of shelled corn were tested for aflatoxin c ontamination. The total variance associated with testing shelled corn was e stimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased as aflatoxin concentration increased. Wi th the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sa mpling, sample preparation, and analytical variances. The expressions for t hese relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentrati on. Test results on a lot with 20 parts per billion aflatoxin using a 1.13 kg sample, a Romer mill, 50 g subsamples, and liquid chromatographic analys is showed that the total, sampling, sample preparation, and analytical vari ances were 274.9 (CV = 82.9%), 214.0 (CV = 73.1%), 56.3 (CV = 37.5%), and 4 .6 (CV = 10.7%), respectively. The percentage of the total variance for sam pling, sample preparation, and analytical was 77.8, 20.5, and 1.7, respecti vely.