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RGA Abacus

Three ways into the abacus: by species, by mass number, or by fingerprint.

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Reading a full spectrum? Spectrum Abacus →

Worked example: Water

Read from the reference base and preloaded. Base peak M18, four fragments as a percent of that peak, then the ratio test that settles the reading.

  • M18H₂O⁺100%
  • M17OH⁺23%
  • M1H⁺3%
  • M16O⁺/CH₄⁺1.1%
  • M2H₂⁺1%

If M17/M18 ≈ 0.23, water is main contributor

Ratio
M17 / M18
Expected
0.23 ± 0.05
Reading
If ~0.23, water is main source of M17

Source: NIST Chemistry WebBook, SRD 69 ; 70 eV electron impact ; normalised to base peak = 100. CAS 7732-18-5.
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Sources · 7
  1. [A]NIST Chemistry WebBook, Mass Spectra (70 eV electron impact).
  2. [A]NIST Electron-Impact Cross Section Database.
  3. [B]MKS Instruments, MicroVision 2 Residual Gas Analyzer : Operating Manual, 2019.
  4. [B]Solvay, Fomblin PFPE product documentation (M69 / M119 / M169 triplet).
  5. [B]DuPont / Chemours, Viton and Kalrez guides (thermal decomposition, M100 marker).
  6. [B]Dow Corning / Shin-Etsu, PDMS data (M73 / M147 / M207 triplet, silicone migration).
  7. [B]Gamma Vacuum / Agilent, Ion Pump manuals (noble-gas pumping, cathode sputtering).

Rated [A] primary standard data, [B] manufacturer documentation. 70 eV cracking patterns are nominal and vary 10-20% between instruments : validate against a known calibration gas before quantitative use.