A Chemical Ionization High-Resolution Time-of-Flight Mass Spectrometer Coupled to a Micro Orifice Volatilization Impactor (MOVI-HRToF-CIMS) for Analysis of Gas and Particle-Phase Organic Species

• Published in: Aerosol science and technology Vol. 46; no. 12; pp. 1313 - 1327
• Main Authors: Yatavelli, Reddy L. N., Lopez-Hilfiker, Felipe, Wargo, Julia D., Kimmel, Joel R., Cubison, Michael J., Bertram, Timothy H., Jimenez, Jose L., Gonin, Marc, Worsnop, Douglas R., Thornton, Joel A.
• Format: Journal Article
• Language: English
• Published: Colchester Taylor & Francis Group 01.12.2012; Taylor & Francis; Taylor & Francis Ltd
• Subjects: Aerosols; Chemical compounds; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Hydrocarbons; Ions; Mass spectrometry; Oxidation; Surface physical chemistry; Water; Resolving power; High resolution; Prototype; Volatility; Probe; Mixture; Particle; Accuracy; Test; Formic acid; Volatilization; Oxidation; Composition; Hydrocarbon; Instruments; Orifice; Impactor; Desorption; Acetate; Chemical ionization; Positive ion; Gases; Sensitivity; Reagents; Aerosols; Negative ion; Gas phase; Time-of-flight mass spectrometers; Formation mechanism
• ISSN: 0278-6826; 1521-7388
• DOI: 10.1080/02786826.2012.712236

We describe a new instrument, chemical ionization (CI) high-resolution time-of-flight mass spectrometer (ToFMS) coupled to a micro-orifice volatilization impactor (MOVI-HRToF-CIMS). The MOVI-HRToF-CIMS instrument is unique in that, within a compact field-deployable package, it provides (1) quantifiable molecular-level information for both gas and particle-phase organic species on timescales ranging from ≤1 s for gases to 10-60 min for particle-phase compounds that can be used to efficiently probe oxidation and secondary organic aerosol (SOA) formation mechanisms, and (2) relative volatility information of the detected compounds simultaneously estimated using the programmed thermal desorption information obtained from the MOVI. We demonstrate the capabilities of a prototype instrument using known test compounds and complex mixtures generated from the oxidation of biogenic and anthropogenic hydrocarbons. We present spectra obtained using both negative and positive ion CI with acetate (CH 3 C(O)O − ) and protonated water clusters (H 3 O + ·(H 2 O) n ), respectively, as reagent ions. The instrument has high mass resolving power (R = 5000 above m/Q 250 Th) and mass accuracy (±20 ppm) enabling estimation of compound elemental composition. Instrument sensitivity in negative ion mode was tested using formic acid as a representative gas-phase compound, and that for particle-phase compounds was tested using palmitic, azelaic, and tricarballylic acids. With a heated MOVI inlet, an ion count rate of ∼15 Hz is achieved when sampling 1 pptv (= 1 pmol/mol) of formic acid (or other monocarboxylic acids) under typical operating conditions. This sensitivity translates to detection limits less than 1 ng/m 3 for carboxylic acids in the particle-phase. We also discuss the remaining challenges with this instrument to broadly characterizing gaseous and particulate oxygenated organic compounds in situ. Copyright 2012 American Association for Aerosol Research