Extended Data Fig. 1: Quality control for mass-spectrometry analysis of succinate in thermogenic adipose tissue.

a, Because of its unusual abundance in BAT, special consideration is required to determine the linearity of the relationship between LC–MS succinate peak intensity and succinate concentration for quantitative analysis. Succinate abundance is measured in extraction solution as described in the methods section. Absolute determination of succinate concentration is compared between succinate extracted from BAT (red) and the same samples following 100-fold dilution (green). Samples are analysed in parallel with defined amounts of [¹³C]succinate (black) used at concentrations that are within the established linear range of the mass spectrometer. Following 100-fold dilution of BAT extracts, succinate signals are within the linear range of detection. However, undiluted extracts are at concentrations that result in a nonlinear relationship and are therefore not appropriate for quantitative analysis. b, Calculation of the apparent dilution factor reveals the effect of nonlinearity with apparent dilutions ranging from ~11–28-fold that are in fact 100-fold.