Characterization of HOCl Using Atmospheric Pressure Ionization Mass Spectrometry

HOCl is an important intermediate in stratospheric and tropospheric chemistry. Although it can be readily measured in laboratory systems at low pressures (≤20 Torr) using conventional electron impact ionization mass spectrometry, there is a need for a measurement technique that can operate at higher...

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Bibliographic Details
Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1999-10, Vol.103 (41), p.8231-8238
Main Authors: Caldwell, Tracy E, Foster, K. L, Benter, Thorsten, Langer, Sarka, Hemminger, John C, Finlayson-Pitts, Barbara J
Format: Article
Language:English
Subjects:
ATMOSPHERIC CHEMISTRY
ATMOSPHERIC PRESSURE
ENVIRONMENTAL SCIENCES
HYPOCHLOROUS ACID
IONIZATION
MASS SPECTROSCOPY
OZONE
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Summary:HOCl is an important intermediate in stratospheric and tropospheric chemistry. Although it can be readily measured in laboratory systems at low pressures (≤20 Torr) using conventional electron impact ionization mass spectrometry, there is a need for a measurement technique that can operate at higher pressures, up to 1 atm in air. One such technique seeing increasing use is atmospheric pressure ionization mass spectrometry (API-MS). We report here studies of the API-MS of ∼0.5−50 ppm HOCl at a total pressure of 1 atm and room temperature. Major peaks from the ion-adducts with Cl- and OCl- were observed. The Br- adduct of HOCl can also be generated using bromoform in the discharge region of the ion source. At the lower range of HOCl concentrations studied in air, the O2 - adduct and small parent peaks assigned to HOCl- were observed. The species present as minor impurities in the HOCl source (Cl2, Cl2O and HCl) can be readily distinguished through identification of the parent ion for Cl2, or as their adducts with Cl- and Br- for Cl2O and HCl. The identification of HOCl was confirmed using electron impact ionization time-of-flight mass spectrometry (EI-MS). HOCl was quantified using EI-MS to measure the Cl2 generated when the HOCl reacted heterogeneously on a water−ice/HCl surface and independently by photolysis of the HOCl to generate atomic chlorine, which was trapped using propene and measured as chloroacetone. The implications for the use of API-MS for measuring HOCl in laboratory systems and in ambient air are discussed.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp9906841