Short name:
TOF-CIMS: Formic Acid

Full name:
CF3O- Time of Flight Chemical Ionization Mass Spectrometer

What is being measured:

Sampling Protocol:
Online

Manufacturer:
Custom

Model:
Custom

Instrument year :
None specified

Data recording software:
Tofwerks software

Data analysis software:
Matlab

Raw data time resolution:
0.1 seconds

Analysis data averaging:
1 seconds

Detection limit:
10 ppt

Sensitivity to temperature (and correction method, if applicable): :
For H2O2, there is some sensitivity to temperature which is corrected by applying a temperature-sensitivity curve

Sensitivity to relative humidity (and correction method, if applicable): :
For nearly every analyte, there is a sensitivity to RH, which is corrected in the data processing by applying a compound-specific humidity-sensitivity curve

Sampling method:
Direct sampling

Sample preparation method:
None

Sample residence time (chamber to instrument) (seconds):

Length of tubing (cm):
0.02

Instrument flow rate:
2

Tubing inner diameter:

Tubing material:
FEP Teflon

Chemical identification method:
The molecular formula of analytes are determined using their accurate masses in the TOF analyzer. Certain analytes have specific ion chemistry (e.g., acids that undergo fluoride transfer) which helps confirm identify where no isobaric compounds are expected.

Data analysis method:
The HDF data are processed with a custom Matlab code (JD Crounse) using ToF reduction code 0.2. With this code, data are background subtracted, signal averaged, and segregated by m/z. Metadata are also collected and processed.

Quantification method:
First a water correction to the sensitivity is applied using mirror water. The CIMS signals are normalized by the fluorine reagent and divided by the sensitivity (norm cts/pptv) to get the mixing ratio.

Calibration method:
The individual analyte sensitivities are determined from commercial or synthesized standard compounds where available, using gravimetric and spectrometric methods. These analytes have lower uncertainties for the quantification. For other analytes, the relative sensitivities are determined from kinetic parameters calculated by Kjaergaard and coworkers. For these analytes, the quantification uncertainty is higher as noted.

Calibration drift estimate:
Low (on the order of weeks)

Calibration schedule:
Prior to experiments

Uncertainty estimation method:
Most of the uncertainties are in the methods used to obtain a known mixing ratio of the compound (usually in a Teflon pillow bag). Even if we can get FT-IR spectra of the gas with known cross sections, losses to the walls may occur. Errors have been propagated from reasonable sources of uncertainties and are noted. A blanket 50% of mixing ratio + 100 pptv is assumed.

Known interferences:

Link to supplemental information:

Additional notes:

Measurement uncertainty:

Measurement units: