A uniform nonlinearity criterion for rational functions applied to calibration curve and standard addition methods

• Rational functions of the Padé type are applied for modeling purposes.
• The integral criterion of nonlinearity in normalized coordinates is suggested.
• This criterion is common for standard addition and calibration curve methods.
• This criterion is applied for results of three methods of spectrometric analyses.

Rational functions of the Padé type are used for the calibration curve (CCM), and standard addition (SAM) methods purposes. In this paper, the related functions were applied to results obtained from the analyses of (a) nickel with use of FAAS method, (b) potassium according to FAES method, and (c) salicylic acid according to HPLC-MS/MS method. A uniform, integral criterion of nonlinearity of the curves, obtained according to CCM and SAM, is suggested. This uniformity is based on normalization of the approximating functions within the frames of a unit area.

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