Fig. 4 ∣. Confirmation of [¹³C] peaks in HRMS.

a,b, The extracted ion chromatograms (XICs) of lactate and [U-¹³C] lactate (m + 0 and m + 3, respectively) (a), and glucose and [U-¹³C]glucose (m + 0 and m + 6, respectively) (b), are overlaid. Comparison of the glucose XIC with a chemically purified standard confirms the correct peak is identified. To calculate fractional enrichment, only the overlapping peaks in each XIC are integrated. In the case of glucose, we resolve two structural isomers of the sugar in our HILIC chromatography (confirmed with chemical standards), so both peaks in the bimodal distribution between 7 and 7.5 min are integrated to calculate fractional enrichment.