Development and application of a comprehensive measurement equation for the direct comparator standardization method of Instrumental Neutron Activation Analysis

A comprehensive model equation for the measurement of elemental mass fractions in solid materials using the direct standardization method of Instrumental Neutron Activation Analysis was developed. The extensive modelling established for the single comparator standardization was revised and changed for the direct standardization to obtain a complete mathematical description of the measurand by physical and chemical quantities having dimensions in SI units. The model equation is presented both in case measurement and standard samples are measured in the same γ-counting position and in different γ-counting positions. The first was successfully applied for the quantitative determination of As mass fraction in a seafood matrix with a percent level relative uncertainty. The SI traceability of the result is established by a traceable standard via the measurement equation and the uncertainty budget compiled to highlight the input quantities that contribute most to the combined uncertainty.