The Federal Bureau of Mines has derived a mathematical expression for the emulsion calibration curve used in optical emission spectroscopy. Employing a two-step preliminary curve method, an approximation of the first derivative of the calibration curve is formed and integrated. The final equation is <i>I</i> = (1 + β<i>S</i>)<sup>−α</sup> where <i>I</i> is the line intensity, <i>S</i> is the transform that linearizes the preliminary curve, and α and β are constants.
Jack R. Woodyard, B. C. Piper, and K. R. Stever, "The Functional Form of the Emulsion Calibration Curve," Appl. Spectrosc. 33, 25-28 (1979)