Analytical methods for Challenge15 Sample: The compound has a neutral nominal mass of 464. MS analysis Instrument: Dionex U3000 and Exactive Orbitrap (Thermofisher Scientific) Resolution: 100,000 Ion source: ESI, negative ion mode CID conditions: 10 and 40 V for MSnegCE10_Challenge15 and MSnegCE40_Challenge15, respectively. MS/MS analysis Instrument: Acquity UPLC and a Xevo TQ (Waters) Ion source: ESI, negative ion mode CID conditions: 10 and 45 V for MSMSnegCE10_Challenge15 and MSMSnegCE45_Challenge15, respectively. LC column: L-column 2 ODS Solvents: methanol containing 2 mM formate (A)/water containing 2 mM formate (B) Gradient: 0 to 5 min, a linear increase from 10% to 100% B; 5 to 10 min, hold at 100% B; and 10 to 15 min, equilibration at 10% Flow rate: 0.2 mL/min Retention time: 7.3 min