# Using collision-induced dissociation to constrain sensitivity of ammonia chemical ionization mass spectrometry (NH 4+ CIMS) to oxygenated volatile organic compounds

Chemical ionization mass spectrometry (CIMS) instruments routinely detect hundreds of oxidized organic compounds in the atmosphere. A major limitation of these instruments is the uncertainty in their sensitivity to many of the detected ions. We describe the development of a new high-resolution time-of-flight chemical ionization mass spectrometer that operates in one of two ionization modes: using either ammonium ion ligand-switching reactions such as for inline-formula $M2inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimg607f7ebf9a4fde3320a23a055c7bd38e amt-12-1861-2019-ie00003.svg24pt15ptamt-12-1861-2019-ie00003.png CIMS or proton transfer reactions such as for proton-transfer-reaction mass spectrometer (PTR-MS). Switching between the modes can be done within 2 min. The inline-formula $M3inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimgf83a9f1907f38a5589c34b239e10518b amt-12-1861-2019-ie00004.svg24pt15ptamt-12-1861-2019-ie00004.png CIMS mode of the new instrument has sensitivities of up to 67 000 dcps ppbvinline-formula−1 (duty-cycle-corrected ion counts per second per part per billion by volume) and detection limits between 1 and 60 pptv at 2inline-formulaσ for a 1 s integration time for numerous oxygenated volatile organic compounds. We present a mass spectrometric voltage scanning procedure based on collision-induced dissociation that allows us to determine the stability of ammonium-organic ions detected by the inline-formula $M6inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimg6ca56caa63735c5009fe6b299c1a126b amt-12-1861-2019-ie00005.svg24pt15ptamt-12-1861-2019-ie00005.png CIMS instrument. Using this procedure, we can effectively constrain the sensitivity of the ammonia chemical ionization mass spectrometer to a wide range of detected oxidized volatile organic compounds for which no calibration standards exist. We demonstrate the application of this procedure by quantifying the composition of secondary organic aerosols in a series of laboratory experiments.

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Zaytsev, Alexander / Breitenlechner, Martin / Koss, Abigail R. / et al: Using collision-induced dissociation to constrain sensitivity of ammonia chemical ionization mass spectrometry (NH4+ CIMS) to oxygenated volatile organic compounds. 2019. Copernicus Publications.

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