Instrument - Time-of-flight Chemical Ionization Mass Spectrometer using CF3O- reagent (Wennberg)
Time-of-flight Chemical Ionization Mass Spectrometer using CF3O- reagent (Wennberg)
What is being measured:
volatile acids, hydroperoxides, polar oxygenated VOCs
Custom (Tofwerks TOF)
Data recording software:
Data analysis software:
Raw data time resolution:
Analysis data averaging:
Sensitivity to temperature (and correction method, if applicable):
Few ions have temperature-dependent sensitivities. This is corrected for by their T-dependent calibration factors
Sensitivity to relative humidity (and correction method, if applicable):
All ions have some sensitivity to RH. This is corrected for by the RH-dependent calibration factors for each ion.
Sample preparation method:
Sample residence time (chamber to instrument) (seconds):
Length of tubing (cm):
Instrument flow rate:
Tubing inner diameter:
Chemical identification method:
TOF mass spectrometry does not give insight into the chemical identity. However, CF3O- can distinguish acids by their unique ionization. Also, lower-m/z ions are generally better known. Best guesses to chemical identities are reported (e.g., "acetic acid" or "isoprene hydroxy nitrates (ISOPN)" when the chemicals have been studied previously through calibration with authentic standards or other means. Only the molecular formula is reported (or just the m/z, e.g. "mass 102") when the chemical identities are uncertain.
Data analysis method:
Data in HDF form are processed by a custom script in Matlab.
Quantification is done after baseline subtraction (observed during the background period before reaction), applying the RH and/or T dependent calibration factors, and correcting for dilution.
Calibration is performed in a number of ways, e.g., gravimetric analysis of permeation tubes, injecting known amounts of chemicals into Teflon "pillow bags", coupling with a quantitative instrument (e.g., TD-LIF), cross-calibrating with a quantitative instrument (e.g., FT-IR), or theoretical calculations of ion-molecule collision kinetics. For more information, please see the SI of Nguyen and Crounse et al., PNAS, 2014.
Calibration drift estimate:
Uncertainty estimation method:
Uncertainties are estimated by propagating errors from the calibration method and dilution ratios. Generally, ions that are directly calibrated have uncertainties of ~ 30%, and those whose calibrations depend on theoretical calculations have uncertainties exceeding 50%. Inquire with PI for more information.
Link to supplemental information:
Crounse 2006: https://pubs.acs.org/doi/abs/10.1021/ac0604235 Nguyen and Crounse 2014 Table S1: https://www.pnas.org/content/pnas/suppl/2015/01/16/1418702112.DCSupplemental/pnas.1418702112.sapp.pdf