SAMPLING CONSTANTS FOR NIACIN CONTENT IN STANDARD REFERENCE MATERIAL 1846 INFANT FORMULA

Modem measurement systems for food components often require use of eve r smaller sample sizes, down to mg for some new microtechniques, which puts a stronger demand on development of reference materials with def ined homogeneity for subsampling. One approach to evaluate the homogen eity of materials is the characterization of sampling constants, defin ed as that amount of material that gives a 1% error for subsampling. T his approach was developed for geological sampling and has been applie d in a limited way for inorganic components in food/biological materia ls. We have extended this approach to the determination of the samplin g constants for an organic component, niacin, in the SRM 1846 Infant F ormula material. This material was produced by blending of a dry vitam in mix (5% weight) into the bulk spray dried powder, for long term sta bility purposes. By analyzing similar aliquots of a reconstituted homo geneous fluid solution of a large sample size, in comparison to smalle r portions of dry powder, an estimate of the variation due to sampling can be separated from estimates of variation due to analysis. Using e ither the AOAC microbiological method or a newly developed HPLC method , sampling constants for the niacin content of SRM 1846 are in the ran ge of 1-3 g; use of smaller sub-samples can introduce significant vari ation into determinations using this SRM.