Fig. 2

Mass defect as a function of m/z for all endogenous and food-derived compounds between 50 and 750 m/z in the human metabolome database (hmdb, n = 16,321) compared to features detected experimentally in plasma (n = 2227). The red line depicts the theoretical mass defect maxima for compounds containing only C, H, N and/or O (y = 0.00112x + 0.01953). Features above this line which are present only in the experimental dataset are likely to be salt clusters or multiply charged as indicated by the arrows. Hmdb masses are shown as theoretical [M + H]. Experimental data was acquired by positive ESI, and contains a variety of adducts including but not limited to [M + H], [M + Na], [M + K] and [M + NH₄], as well as isotopic peaks