Reference Material Needs for Regulatory Nutrient Analysis

Matrix Components The term matrix component refers to the constituents in the material aside from those being determined, which are denoted as analyte. Clearly, what is a matrix component to one analyst may be an analyte to another. Thus, in one hand for the case of analyses for elemental content, components such as dietary fibre, ash, protein, fat, and carbohydrate are classified as matrix components and are used to define the nature of the material. On the other hand, reference values are required to monitor the quality of determinations of these nutritionally significant matrix components. Hence, there is a challenging immediate need for certified values for dietary fibre, ash, protein, fat, and carbohydrate. Concomitantly, these values must be accompanied by scientifically sound definitions (e.g. total soluble dietary fibre, total sulpha-ted ash, total unsaturated fat, polyunsaturated fat, individual lipids, simple sugars, and complex carbohydrates). 

Reference Material Needs for Regulatory Nutrient Analysis 

For regulatory purposes, food-based RMs play an important role in validating accuracy of analytical data from use of routine methodology. For example, the quality of data obtained by analytical measurements serves an important function with regard to ensuring nutritional label claims. Unfortunately, and historically in some cases, assay data for the same analyte can vary greatly from laboratory to laboratory. Evalua- 

Currently, nutrient analytical methods development often utilizes the method of standard additions as an intrinsic aspect of the development process. Essentially, the analyte to be measured exists in the matrix to which an identical known pure standard is added. The spiked and non-spiked matrix is extracted and analysed for the nutrient of interest. By spiking at increasing levels the researcher can establish, to some degree of certainty, the recovery and linearity of the standard additions. One can also evaluate data to determine reproducibility, precision, and accuracy. Unfortunately, the method of standard additions does not allow the evaluation of the method at nutrient concentrations less than 100 % of the endogenous level. 

Chase and Long (1997) propose that this conundrum can be eliminated by the use of Zero Reference Materials (ZRMs) in analytical methods development to fully evaluate the method. A ZRM is a product matrix that lacks those nutrient components that are to be assayed, i.e. a blank matrix. The use of a ZRM in method development can and will give a true indication as to how the method will perform as the spiked nutrient levels approach zero. For example, two products. Corn Starch (NIST RM 8432) and Microcrystalline Cellulose (NIST RM 8416), contain very low elemental concentrations and could conceivably serve as real sample blanks or ZRMs in some analytical procedures. 

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