In our dataset, measured by 1 H-NMR, the concentration of hydroperoxides varied between 0 and 400 mmol/kg oil, while the concentration of aldehydes varied between 0 and 6 mmol/kg oil. To be equally weighted in the optimisation procedure, the datasets (𝑋 ̃) were thus normalized to be the same range of 0 and 1, following Equation 3 before calculating the sum of squared errors (Equation ). As each set of starting values returned different estimated values, the optimal estimated values were selected based on the least estimate of errors (Equation ).