A radiochemical neutron activation analysis procedure was applied to the analysis of foods for As, Cr, Mo, Sb and Se. The elements are retained on an inorganic chromatographic resin of hydrated managanese dioxide while interfering elements are removed. Activities from Br, K, Na and P interferences are reduced by up to six orders of magnitude, and detection limits for food analysis are reduced by factors of 100–2000, compared with those normally found for instrumental neutron activation analysis. Detection limits for the foods analyzed are 0.1–0.3 ng/g for As and Sb and 1–10 ng/g for Cr, Mo and Se. Results are presented for various foods and several National Bureau of Standards Standard Reference Materials.
Compton suppression spectrometry was used to analyze foods for elements with short-lived neutron activation products (half-lives
of about 2 minutes to 1.5 days). Analysis conditions were optimized to provide quality assurance analyses for iodine in FDA’s
Total Diet Study. Iodine mass fractions (0.075 to 2.03 mg/kg) were measured in 19 of 42 foods analyzed, with limits of detection
(LODs) ranging from 0.03 to 1.4 mg/kg, mostly depending on NaCl content. LODs were lowered by up to a factor of 2 for 16 elements.
Suppression factors ranged from about 2 to 8 over the energy range 400 to 3200 keV.
Foods collected for radionuclide analysis under the Food and Drug Administration's (FDA's) Total Diet Study (TDS) Program were analyzed by the Center for Food Safety and Applied Nutrition (CFSAN) as quality assurance (QA) for analyses performed at FDA's Winchester Engineering and Analytical Center (WEAC). 200-ml QA portions were analyzed for gamma-ray emitting fission products and naturally occurring radionuclides. Efficiency, pileup correction, absorption effects, and accuracy were determined by analyzing a variety of certified reference materials and KNO3 and KCl solutions. 40K results agreed well with those from WEAC and with total K results from other techniques. Count times as low as 2 minutes were sufficient to confirm that radioactivity concentrations were below regulatory limits.
Fifteen maple syrups were analyzed for137Cs and K (via40K) by using a low-background -ray counting system, and for B and K by using neutron capture prompt -ray activation analysis (PGAA). For low-background -ray counting, 3 limits of detection (24-hour counts) were 0.03 Bq137Cs/kg and 10 mg K/kg for 3.5-L portions and 0.08 Bq137Cs/kg and 20 mg K/kg for 1.0-L portions. K concentrations determined by the two methods (using 2-g portions for PGAA) were in excellent agreement. The products were obtained in 1991, with one produced in Maryland, three in New York, four in Pennsylvania, two in New Hampshire, and five in Canada. The average activity concentration for Canadian syrups (2.8 Bq137Cs/kg) was nearly a factor of 20 greater than the average (0.15 Bq137Cs/kg) for the other syrups, but all137Cs activity concentrations were at least 100 times lower than those for which controls would be recommended according to Federal Radiation Council guidance. The data exhibited distinct groupings related to the sources of the products when the ratios of137Cs activity to K content (BqCs/mgK) were plotted vs. B concentrations.
Epithermal-neutron activation analysis (ENAA) was applied to the analysis of foods for iodine. The procedure involves irradiation of wet foods in a boron nitride, vessel, followed by direct counting of the 442.9 keV gamma ray of128I without any processing of the sample. Three research reactors were evaluated for use in determining iodine by ENAA. The University of Virginia reactor at Charlottesville was chosen for this study because the reactor facilities minimized thermal heating of the boron nitride vessel, enabling irradiation of larger, more representative analytical portions. Iodine concentrations ranging from <0.003 to 0.74 g/g are reported for 17 different food matrices.
Authors:D. Anderson, W. Cunningham, and G. Alvarez
A method is described for the determination of H, B, Cl, K, Na, S, Ca, and Cd in foods using in-beam neutron capture prompt -ray activation analysis. Special calibration procedures were necessary because of matrix-related thermal neutron scattering-induced sensitivity and background enhancements. Detection limits and sensitivities are presented for best-case and worst-case irradiation conditions. The method was applied to multielement analysis of 41 foods and to B, Cl, and K analysis of 13 orange juice produts in conjunction with analysis by inductively coupled plasma atomic emission spectrometry. The purpose of the latter application was to study B losses during acid digestion.
Authors:W. Cunningham, D. Anderson, W. Lamont, P. South, M. Rury, G. Beachley, and J. Ondov
Transportable radioanalytical systems were assembled and tested for quantitative determination of γ-emitting radionuclides
and screening of β-emitting radionuclides. Standard operating procedures (SOPs), including instructions for assembly, disassembly,
operation, sample collection and analysis, and all other procedures needed, were developed. Foods, as well as National Institute
of Standards and Technology, International Atomic Energy Agency, and in-house Reference Materials were analyzed. An SOP for
γ-emitting radionuclides was successfully tested at 3 locations.