title: Testing shelled corn for aflatoxin, Part I: estimation of variance components.
abstract: The variability associated with testing lots of shelled corn for aflatoxin was investigated. Eighteen lots of shelled corn were tested for aflatoxin contamination. The total variance associated with testing shelled corn was estimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased as aflatoxin concentration increased. With the use of regression analysis, mathematical expressions were developed to model the relationship between aflatoxin concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific aflatoxin concentration. 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 analysis showed that the total, sampling, sample preparation, and analytical variances 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 sampling, sample preparation, and analytical was 77.8, 20.5, and 1.7, respectively.
authors.affiliation: US Department of Agriculture, Agricultural Research Service, North Carolina State University, Raleigh 27695-7625, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Johansson
authors.forename: T B
authors.initials: TB
authors.lastname: Whitaker
authors.forename: W M
authors.initials: WM
authors.lastname: Hagler
authors.forename: F G
authors.initials: FG
authors.lastname: Giesbrecht
authors.forename: J H
authors.initials: JH
authors.lastname: Young
authors.forename: D T
authors.initials: DT
authors.lastname: Bowman
mesh_terms: D000348:Aflatoxins / Q000032:analysis*; D000465:Algorithms; D003625:Data Collection; D012107:Research Design; D012494:Sampling Studies; D003313:Zea mays / Q000737:chemistry*
chemical_list: D000348:Aflatoxins