Calibration and Detection of Phosphine Using a Corrosion-Resistant Ion Trap Mass Spectrometer

We present a corrosion-resistant quadrupole ion trap mass spectrometer (QIT-MS) designed for trace detection of volatiles in sulfuric acid aerosols, with a specific focus on phosphine (PH3). Here, we detail the gas calibration methodology using permeation tube technology for generating certified ppb-level PH3/H2S/CO2 mixtures, and report results from mass spectra with sufficient resolution to distinguish isotopic envelopes that validate the detection of PH3 at 62 ppb concentration. Fragmentation patterns for PH3 and H2S agree with NIST data, and signal-to-noise performance confirms ppb sensitivity over 2.6-hour acquisition periods. We further assess spectral interferences from oxygen isotopes and propose a detection scheme based on isolated phosphorus ions (P+ ) to enable specific and interference-resistant identification of PH₃ and other reduced phosphorus species of astrobiological interest in Venus-like environments. This work extends the capabilities of QIT-MS for trace gas analysis in chemically aggressive atmospheric conditions.