This interlaboratory study was uniquely designed to determine the effects of material granularity and sample processing techniques on the measurement variability (i.e. precision) of nutritional elements in various cereal materials. Participants were asked to determine in triplicate the levels of iron, calcium and zinc in six breakfast cereals (three wheat-based, two rice-based and one wheat/rice mixture). Processing of the three ground materials (ground and homogenized wheat, ground wheat and ground rice) was anticipated to be relatively straightforward, whereas the two flake materials (wheat flake and rice flake) were expected to require appropriate processing prior to subsampling to limit measurement variability. The final material (wheat/rice mixture with a hand- crushed granularity) was anticipated to be a challenge material due to its inherent heterogeneity both in content and in granularity. In general, approximately 25% of the laboratories processed and analyzed the suite of six cereal materials with adequate to exemplary measurement precision. Another 60% of the laboratories experienced measurement issues related only to a specific type of cereal matrix (e.g., wheat vs. rice or the challenge wheat/rice sample), or for only a select element (e.g., Fe vs. Ca or Zn). A small number ( 15%) of laboratories experienced significant sample processing and/or measurement problems. It should be noted that this study is a precursor to possible future exercises that will assess method precision using commercially available nutritional products that will contain more varied ingredients and thus exhibit significant heterogeneity.
Citation: NIST Interagency/Internal Report (NISTIR) - 7927
NIST Pub Series: NIST Interagency/Internal Report (NISTIR)
Pub Type: NIST Pubs