Precision Parameters of Methods of Analysis Required for Nutrition Labeling. Part II. Macro Elements—Calcium, Magnesium, Phosphorus, Potassium, Sodium, and Sulfur

Abstract

A previous paper reviewed the precision of analyses for the major macronutrients—fat, protein, and carbohydrates— as well as moisture/solids, ash, and "fiber." A similar review is now presented for the macro inorganic nutrients—calcium, magnesium, phosphorus, potassium, sodium, and sulfur. The precision parameters among laboratories (standard deviations, S; relative standard deviations, RSD; and repeatability, r, and reproducibility, R, values) are not characterized by any conventional distribution. The typical precision of the methods of analysis for these elements In food can be expressed solely as a logarithmic function of concentration, Independent of analyte, matrix, and method. The average RSDR value from each collaborative assay found in the literature Is used as the numerator in a ratio containing, as the denominator, the value calculated from the logarithmic function: RSDR(%) = 2( 1 -0.5 log C) where C Is the concentration as a decimal fraction. If this ratio, designated as HORRAT, Is above 2, the method Is probably unacceptable with respect to precision. About 20% of the 465 interlaboratory data sets studied for this paper show an RSDR exceeding the acceptable limit, with an overall average HORRAT of 1.2 at C ranging from about 20 x 10-6(20 ppm) to about 10-1 (10%). The variability, although high, may be acceptable for the purpose of nutrition labeling.