Mass Spectrometry. All experiments were performed using a Thermo Scientific linear quadrupole ion trap mass spectrometer (LQIT) equipped with an atmospheric chemical ionization (APCI) source and operated in positive ion mode. Sample solutions were prepared at concentrations ranging from 0.01 to 1 mg/mL with methanol as the solvent. The solutions were injected into the APCI source through a syringe pump at a rate of 15 µL/min by using a 500 μL Hamilton syringe. In the APCI source, typical flow rates for sheath and auxiliary gases (N2) were 30 and 10 (arbitrary units), respectively. The vaporizer and capillary temperatures were set to 300 and 275 °C, respectively. The ions generated upon APCI were transferred into the ion trap. The voltages applied to the ion optics were optimized for each protonated analyte via the tune feature of the LTQ Tune Plus interface. The neutral reagent, MOP, was introduced into helium buffer gas line of an external mixing manifold via a syringe pump operating at a rate of 5 µL/h. The surrounding areas of the syringe port were heated to about 120 °C to ensure that MOP (boiling point: 34-36°C<add reference) evaporated completely. MOP was then diluted and directed into the ion trap by a constant flow of helium gas, controlled by a leak valve. Protonated analytes were isolated using an isolation width of 2 m/z units and a q value of 0.25, and then allowed to react with the neutral reagent in the ion trap for up to 10,000 ms. After this, all ions were detected. The MS/MS results for the test set used in this paper are given in Figures .