Short name:
HR-ToF-CIMS

Full name:
High Resolution Time of Flight Chemical Ionization Mass Spectrometer

What is being measured:

Sampling Protocol:
Online

Manufacturer:
Aerodyne

Model:
NA

Instrument year :
2015

Data recording software:
ToFDAQ

Data analysis software:
Igor Pro

Raw data time resolution:
1 Hz

Analysis data averaging:

Detection limit:
4 pptv (formic acid)

Sensitivity to temperature (and correction method, if applicable): :
NA

Sensitivity to relative humidity (and correction method, if applicable): :
Sensitivity to RH is compound-specific. Correction involves passing carrier UHP nitrogen through a water bubbler before it joins the sampled gas in the instrument's IMR region. This results in a stream of gas in the IMR region at a stable RH of around 60%.

Sampling method:
Direct sampling

Sample preparation method:

Sample residence time (chamber to instrument) (seconds):
5.70

Length of tubing (cm):
0.015

Instrument flow rate:
2

Tubing inner diameter:

Tubing material:
PFA Teflon

Chemical identification method:
The sampled gas comes into contact with Iodide ions that are produced by a methyl iodide permeation tube within the instrument. In the Ion-Molecule Reaction region, the I- ions form adducts with the sampled gas primarily as I- + C2H6O -> C2H6OI-. The negatively-charged adducts are then passed through a vacuum region where voltages are applied. Based on the relative time of flight of each individual chemical species, we can determine the mass-to-charge ratio of the species. The high mass resolution allows us to do high-resolution identification of compounds within a single unit m/z.

Data analysis method:
An instrument-specific calibration curve is present that allows us to determine m/z of compounds based on their ToF at a 1Hz time resolution. After the initial data processing is done (determining average peak shape, subtracting instrument baseline, etc.), we integrate the data using Igor's Tofware and then we obtain graphs of signal (in ions/s) vs. unit m/z. We can then carry out high-resolution identification of peaks at specific m/z based on our knowledge of the kind of reactants and products that may be found in the experiment.

Quantification method:
Currently our instrument is only used qualitatively for most compounds but we are working on a calibration technique. We normalize all signals against the primary ion (I-) to take into account fluctuations in its concentration.

Calibration method:

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

Calibration schedule:
As Needed

Uncertainty estimation method:
NA

Known interferences:
There are compounds that interact more strongly with I- than the different VOCs we measure (eg: Cl2, chlorinated compounds). These can cause significant depletion in I- affecting other observed adducts.

Link to supplemental information:

Additional notes:

Measurement uncertainty:

Measurement units: