Over a 6.5-year period a total of 2554 values were reported by nine laboratories for 259 certified or reference nutrient concentrations in 26 certified reference materials (CRM) submitted to contract laboratories, blinded, as part of the qualifying process for analytical contracts and in the routine sample stream as part of the National Food and Nutrient Analysis Program. Each value was converted to a Z′-score, reflecting the difference from the assigned value related to the combined expected analytical uncertainty plus the uncertainty in the CRM value. Z′-scores >|3.0| were considered unacceptable. For some nutrients (Na, folate, dietary fiber, pantothenic acid, thiamin, tocopherols, carotenoids, monounsaturated, and polyunsaturated fatty acids), >20% of Z′-scores were >|3.0|. For total fat, vitamin C, and niacin >25% of Z′-scores were >|2.0|. Components for which CRM data were best (more than 90% of Z′-scores <|2.0|) were Mg, P, Mn, Se, and vitamin B12. In some cases deviations from assigned values were not uniform across laboratories and materials. For Na almost all high Z′-scores were for low-Na matrices, suggesting analytical problems related to concentration.
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The statistics advice and assistance on statistics by David Duewer, of the NIST in developing Eq. 1 for Z′-scores used in this study is acknowledged. This study was conducted as part of specific cooperative agreement #Y1-HV-8116-11 between the United States Department of Agriculture (USDA) Nutrient Data Laboratory and Virginia Polytechnic Institute and State University, with support from the National Heart, Lung, and Blood Institute, National Cancer Institute, the National Institute for Dental and Craniofacial Research, the Office of Dietary Supplements, and numerous other Offices and Institutes through the interagency agreement #Y1-HV-8116 between the National Institutes of Health and the USDA.
Disclaimer: Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, or the United States Department of Agriculture, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.
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Phillips, K.M., Wolf, W.R., Patterson, K.Y. et al. Reference materials to evaluate measurement systems for the nutrient composition of foods: results from USDA’s National Food and Nutrient Analysis Program (NFNAP). Anal Bioanal Chem 389, 219–229 (2007). https://doi.org/10.1007/s00216-007-1366-0
- Reference materials
- Food composition data