The solvent LOD of endogenous metabolites ranged from 0.001 µM (0.2 ng/mL) to 6.6 µM (1068 ng/mL) with a median of 0.04 µM (8 ng/mL) (Table , Figure ). The LOD values were estimated for 134 analytes, including several jointly evaluated isomers. Due to their high natural abundance, the LOD of several endogenous metabolites was not estimated in the human matrices. About one third of all compounds showed LODs < 0.01 µM (approximately 1.9 ng/mL) and about two thirds < 0.1 µM (approximately 19 ng/mL) allowing for the straight-forward (semi-) quantitative assessment of the metabolome in most biological systems. The reference standards spanned five orders of magnitude, from 0.001 µM to 10 µM. However, most metabolites were not detectable at the lower calibration level (0.001 µM -0.01 µM), limiting the linear dynamic range to four (45%), three (29%) or even less (8%) orders of magnitude (Table ).