A switchable reagent ion high resolution time-of-flight chemical ionization mass spectrometer for real-time measurement of gas phase oxidized species: characterization from the 2013 southern oxidant and aerosol study

摘要

A novel configuration of the Aerodyne high resolution time-of-flight chemicalionization mass spectrometer (HR-TOF-CIMS) as a switchable reagent ion (SRI)HR-TOF-CIMS is presented and described along with data collected at theSouthern Oxidant and Aerosol Study (SOAS) during the summer of 2013. Thecalibration system and reduced pressure gas phase inlet arecharacterized. The average limit of detection and limit of quantification forformic acid during SOAS are 82 and 863 ppt, respectively, corresponding toan average sensitivity of 13 ± 5 Hz ppt?1. Hourly backgrounddeterminations and calibrations are shown to be essential for trackinginstrument performance and accurately quantifying formic acid. Maximumdaytime formic acid concentrations of 10 ppb are reported during SOAS, and astrong diel cycle is observed leading to nighttime concentrations below thelimit of quantification. Other species presented exhibit diel behaviorsimilar to formic acid. The concept of the mass defect enhancement plot andthe use of signal-to-noise are described in detail as a method forinvestigating HR-TOF-CIMS spectra in an effort to reduce data complexity.