Fig. 3. Illustration of some common nominal mass m/z ions between analytes with the same retention time: ferulic acid 2TMS and tyramine 2TMS, both at c . 12.09 min (a,b) and malic acid 3TMS and threitol 4TMS, both at c . 8.85 min (c,d). Comparisons of overall spectra (a,c) with nearly common masses distinguishable with exact mass (insets, in red), and origin of fragments (b,d). In (c), ions ”other” refer to C7H18O2Si2+(190.083983 Da) and its protonated (+1.007825 Da) species (191.091808 Da). Note that tyramine yields a much higher signal (order of magnitude 109) then ferulic acid (107) despite the use of identical concentration in samples (500 ng mL-1). m +1 and m +2 refer to +1 a.m.u. (mostly 13C, and 29Si) isotopologues and +2 a.m.u. (mostly 13C2,30Si, and13C-29Si) isotopologues, respectively.