To generate the EMD probability distributions for the classification model, both true positive (TP) and true negative (TN) mono-iso pairs were required (Figure ). The mono-iso pairs in the training set were used as the true positive cases and true negative cases were generated based on the mono-iso pairs from the training set with a randomly added mass error between 0.01 to 1 Da to the isotopologue mass. For all mono-iso pairs in the TP and TN training set, the dEMDs were calculated for the selected elemental ratios (Equation ). These dEMD values were used to construct the TP and TN probability distributions for each of the six elemental ratios. To build these probability distributions, the generated dEMD values were binned, using a range between -1 and 1 Da with a 0.002 Da step size.