Ultra high performance liquid chromatography–mass spectrometry method for metabolomics
In the discovery set, the collected sputum supernatant samples were thawed on ice, and metabolites were extracted with acetonitrile and methanol using previously described method22, 23. Sputum supernatant samples were analyzed through using an UHPLC system (1290, Agilent Technologies) with a UPLC BEH Amide (2.1 mm × 100 mm, 1.7 μm) coupled to TripleTOF 6550+6600 (Q-TOF, AB Sciex) via a previously described method with modifications24. The detailed sputum preparation, spectrometry method and metabolite identification were described in the Online Data Supplement.