Abstract
Concentrations of P, S, Cl, K, Ca, Mn, Fe, Zn, Br, Rb, and Sr were measured in quadruplicate analyses of 239 fast-food samples representing 40 kinds of breakfast foods, sandwiches, Mexican foods, pizzas, deep-fried foods, salads, desserts, and beverages. Samples were randomly collected from franchised chains in Utah and were analyzed by the CEMAS multielement X-ray fluorescence (XRF) method. Variations among franchise chains (23%) and outlet locations (10.7%) were significant in about half of the determinations when compared to sample and analytical variations. Duplicate sample aliquots exhibited homogeneity variations averaging 6.3%, and duplicate analyses exhibited analytical variations averaging 3.3%. Each element was validated by measurements on 7-13 NIST standard reference materials. Analyses of standards averaged within 7% of reference values, with an average bias of -2.8%. Comparisons with reference atomic absorption determinations of Mn, Fe, and Zn in the fast-food samples indicated a mean bias of +1.3% for the XRF data. Long-term analytical variations monitored from zinc in tomato leaves in 75 batches over a 7-month period averaged 2.1%, and aU were within 3sigma control chart limits.
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