Uncertainty of standard addition experiments: a novel approach to include the uncertainty associated with the standard in the model equation

A new model equation for determining the measurement result in standard addition experiments was derived and successfully applied to the quantitative determination of rhodium in automotive catalysts. Existing equations for standard addition experiments with gravimetric preparation were changed in order to integrate the novel idea of including the uncertainty associated with the standard into the model equation. Using this novel equation combined with the ordinary least squares algorithm for the regression line also yielded a new formula for the associated measurement uncertainty. This uncertainty accounts for the first time for the uncertainty associated with the standard. The derivation for the model equation and the resulting associated measurement uncertainty is shown for gravimetric standard addition experiments both with and without an internal standard.