Fig. 4

Problematic cases which can arise when ranking lipids by the sum of fragment intensities. The first panel (a) represents a case were lipids are accurately ranked (far right) based on the areas under the peak (far left). It also show that even in this case, the precursor intensity doesn’t reflect a single intensity, but a sum of the intensity of all precursor isomers (middle). In panel (b) two lipids (blue and light green) share a high intensity fragment with the same m/z (middle), inflating their intensity values leading to false ranking (far right). In panel (c) the MS/MS scan misses the apex of the lipid with a blue trace, and hence the summed intensity for the blue trace is reduced