Nonlinear calibration by the standard addition method

The possibility of using the standard addition method (SAM) for calibration in the case of nonlinear relationship between the analytical signal and the analyte concentration is investigated. Analysis of both the precision and the accuracy of SAM has been theoretically carried out assuming that the measurement data are produced with constant random error and then fitted by parabolic function. Several empirical parameters were considered, including, e.g., the number and size of additions, and the curvature degree. Theoretical examinations have been verified by experimental results of some determinations performed by flame atomic absorption and emission spectrometry. Criteria for the selection of linear and nonlinear approximations were discussed. Consequently, the experimental conditions have been suggested allowing the nonlinear calibration by SAM to be applied in practice.