Voltage Scanning As Trace Gas Calibration Method For Chemical Ionization Mass Spectrometry
Literature Seminar abstract
Gas-phase measurement techniques are key to understanding the chemistry of atmospherically relevant compounds, such as volatile organic compounds (VOCs) and oxidized nitrogen species. Time-of-flight chemical ionization mass spectrometry (ToF-CIMS) paired with iodide (I–) chemical ionization (CI) is useful for gas-phase atmospheric measurements—providing a high degree of sensitivity, selectivity, and time resolution. Iodide CI selectively ionizes various gas-phase oxidized organic/nitrogenous compounds via ion-molecule clustering reactions.1 Authentic calibration standards of atmospherically relevant compounds are often not readily available, making the task of quantifying these compounds in ambient air an instrumental challenge.1,2 ToF-CIMS users have developed an approach for estimating instrumental sensitivity without the use of calibration standards. This technique, known as voltage scanning, takes advantage of the instrument’s ability to either transmit or dissociate ion-molecule clusters by systematically varying electric field strengths applied within the ion-optics region.1,2 Strongly bound (high binding enthalpy) ion-molecule clusters are less likely to dissociate in the ion-optics region at a given electric field strength, and are therefore more likely to be detected by the instrument. Increased detection of ion-molecule clusters results in higher overall instrumental responses, and therefore higher sensitivities.1 Quantum mechanical calculations of cluster binding enthalpy (BE) of various iodide-analyte clusters correlate with measured ToF-CIMS sensitivities, allowing for reasonable estimations of sensitivity from cluster BE (and vice versa).1,3 Estimations of cluster BE, and therefore sensitivity, can ultimately be derived from voltage scanning experiments by monitoring cluster dissociation as a function of the electric field strength within the ion-optics region.1 Voltage scanning holds promise as a standard-free calibration method for ToF-CIMS, and could greatly increase users’ abilities to quantify important gas-phase atmospheric constituents.
- Lopez-Hilfiker, F. D.; Iyer, S. Meas. Tech. 2016, 9, 1505-1512.
- Brophy, P.; Farmer, D. K. Meas. Tech. 2016, 9, 3969-3986.
- Iyer, S.; Lopez-Hilfiker, F. D. Phys. Chem. A 2016, 120, 576-587.
Speaker: Jimmy Mattila
Speaker Institution: Colorado State University
Event Date: 09-27-2017
Event Time: 4:00 PM
Event Location: Chemistry A101
Mixer Time: 3:45 PM
Mixer Location: Chemistry B101E
Host: D. Farmer