Calibration in quantitative analysis Part 1. General considerations

Abstract

Mathematical procedures for calibration require assumptions to be made, e.g. the homogeneity of variances and the mathematical relationship between the analyte content x and the signal y. Little is known about the magnitude of errors arising from incorrect assumptions. The variation of the standard deviation of the analytical procedure with the content of the analyte, the selection of the type of mathematical relationship between x and y, and the types of errors made in testing hypotheses are discussed. In certain practical situations, the standard deviation (s.d.) is nearly independent ofx if x < 22p (p = detection limit) and the relative standard deviation (r.s.d.) is nearly independent of x if x> 50p. If the s.d. is constant, calibration relations of the typey = a + bx are frequently to be preferred; with a constant r.s.d.. relations of the type log y = a + b logx have advantages.