Submitted to: Fresenius Journal of Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 17, 1997
Publication Date: N/A
Interpretive Summary: Estimations of the sampling constant for niacin in SRM 1846 Infant Formula by both the AOAC microbiological method and a newly developed ion exchange separation HPLC method, give a value of about 2-3 grams. Use of subsample sizes lower than this amount of material can introduce significant inhomogeneity variation (greater than 1%) into determinations using this SRM to validate analytical methodology. Extending the sampling constant approach to organic components in foods will significantly aid food analysts to obtain more reliable data on these components required for food labeling and research.
Technical Abstract: Modern measurement systems for food components often require use of smaller and smaller sample sizes down to mg sample sizes for some new micro techniques. This puts a stronger demand on development of reference materials with defined homogeneity for subsampling at these lower levels. One approach to evaluate the homogeneity of materials is the characterization of sampling constants, defined as that amount of material that gives a 1% error for subsampling. This approach was developed for geological sampling and has been applied in a limited way for inorganic components in food/biological materials. We have extended this approach to the determination of the sampling constants for an organic component, niacin, in the SRM 1846 Infant Formula material. This material was produced by blending of a dry vitamin mix (5% weight) into the bulk freeze dried powder, for long term stability purposes. By analyzing similar aliquot of a reconstituted homogeneous fluid solution of a large sample size, in comparison to smaller portions of dry powder, an estimate of the variation due to sampling can be separated from estimates of variation due to analysis. Using either the AOAC microbiological method or a newly developed HPLC method of analysis, sampling constants for the niacin content of SRM 1846 are in the range of 1-3 grams. Use of subsamples lower than this amount can introduce significant variation into determinations using this SRM.