title: Sampling almonds for aflatoxin, part I: estimation of uncertainty associated with sampling, sample preparation, and analysis.
abstract: Domestic and international regulatory limits have been established for aflatoxin in almonds and other tree nuts. It is difficult to obtain an accurate and precise estimate of the true aflatoxin concentration in a bulk lot because of the uncertainty associated with the sampling, sample preparation, and analytical steps of the aflatoxin test procedure. To evaluate the performance of aflatoxin sampling plans, the uncertainty associated with sampling lots of shelled almonds for aflatoxin was investigated. Twenty lots of shelled almonds were sampled for aflatoxin contamination. The total variance associated with measuring B1 and total aflatoxins in bulk almond lots was estimated and partitioned into sampling, sample preparation, and analytical variance components. All variances were found to increase with an increase in aflatoxin concentration (both B1 and total). By using regression analysis, mathematical expressions were developed to predict the relationship between each variance component (total, sampling, sample preparation, and analysis variances) and aflatoxin concentration. Variance estimates were the same for B1 and total aflatoxins. The mathematical relationships can be used to estimate each variance for a given sample size, subsample size, and number of analyses other than that measured in the study. When a lot with total aflatoxins at 15 ng/g was tested by using a 10 kg sample, a vertical cutter mixer type of mill, a 100 g subsample, and high-performance liquid chromatography analysis, the sampling, sample preparation, analytical, and total variances (coefficient of variation, CV) were 394.7 (CV, 132.4%), 14.7 (CV, 25.5%), 0.8 (CV, 6.1%), and 410.2 (CV, 135.0%), respectively. The percentages of the total variance associated with sampling, sample preparation, and analytical steps were 96.2, 3.6, and 0.2, respectively.
authors.affiliation: Agricultural Research Service, Department of Agriculture, Box 7625, North Carolina State University, Raleigh, NC 27695-7625, USA. Tom_Whitaker@ncsu.edu
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Whitaker
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Slate
authors.forename: Merle
authors.initials: M
authors.lastname: Jacobs
authors.forename: J Michael
authors.initials: JM
authors.lastname: Hurley
authors.forename: Julie G
authors.initials: JG
authors.lastname: Adams
authors.forename: Francis G
authors.initials: FG
authors.lastname: Giesbrecht
mesh_terms: D016604:Aflatoxin B1 / Q000032:analysis*; D000348:Aflatoxins / Q000032:analysis*; D000704:Analysis of Variance; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005069:Evaluation Studies as Topic; D005504:Food Analysis / Q000379:methods*; D027861:Prunus / Q000378:metabolism*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012107:Research Design; D018401:Sample Size
chemical_list: D000348:Aflatoxins; D016604:Aflatoxin B1