Heatable Long-Pathlength Gas Cells for FTIR Gas Testing

The standard long pathlength gas cell range available from Specac is now the latest Atmos™ series of metal-bodied fixed-pathlength gas cells.

These cells have been improved using new optical modeling tools to provide the highest signal-to-noise.

Model A2.5 A5 A10 A20
Pathlength (m) 2.5 5.0 10 20
Base pathlength (mm) 104 139 250 455
Number of passes 24 36 40 44
Volume (L) 0.27 0.63 2.12 3.68

The Atmos™ series can be heated to 200 °C with the inclusion of a temperature controller and heating jacket.

Why Atmos™?

  • Low cell volume to facilitate rapid gas exchange
  • Improved optical path for unparalleled signal-to-noise
  • Retrofittable heating jacket option for up to 200 °C
  • Maximum cell pressure of 125 psi (8.6 bar)
  • Includes inert stainless-steel mirror substrates and does not contain glues, thus preventing outgassing
  • Ni-coated Al cell bodies enable better thermal transfer from heating jackets; the Atmos™ series also holds higher gas pressure when compared to glass

Flexible Specification Long-Pathlength Gas Cells—Cyclone™ and Tornado™

Cyclone™ and Tornado™ cells are available with metal or glass cell bodies and can be configured to a range of pathlengths.

Model C2 C5 or
C10 or
C20 or
Pathlength settings (m) 0.5—2.5
in 0.5 m steps
in 1.0 m steps
in 1.06 m steps
in 2.0 m steps
Base pathlength (mm) 125 250 264 500
Number of passes 4—20 4—32 8—40 4—40
Volume (L) 0.19 1.33 2.60 4.30


Cyclone™ Versus Tornado™

  • Tornado™ cells are a stripped-back offering, delivered as standard without outlet or inlet tap valves; they cannot be heated.
  • Cyclone™ cells can be delivered with a fitted heating jacket for analyses of heated gases of up to 200 °C (unavailable for model C20)
  • A modifiable mirror carriage can be installed into the Cyclone™ cells to allow users to change the pathlength throughout the given range.

Which Pathlength to Choose?

Gas absorbance relies on the distance traveled by the IR light beam across the gas sample. The association between pathlength (L), concentration (C), and absorbance (A) is given by Beer’s Law, as shown below:

A = -log10 (I/I0) = a.C.L

The concentrations of gases in the atmosphere are generally expressed in C.L units of ppm⋅m—the number of molecules encountered by the infrared beam across a 1.0-m path.

A gas at 0.1 ppm atmospheric concentration will be able to absorb as much IR light over 100-m pathlength as would the same gas at 10 ppm over 1 m or at 1 ppm over 10 m.

Therefore, the cell’s pathlength should be selected to give absorbance values within the linear range of the spectrometer for a specified concentration. The table given below can be considered as a guide:

Gas name formula v (cm-1) ppm.m absorbance
Carbon dioxide CO2 2360 100 0.40
Carbon monoxide CO 2170 100 0.04
Methane CH4 3020 100 0.10
C2 to C6 n-alkanes   2960 100 0.10
Nitrogen dioxide NO2 1630 100 0.15
Nitric oxide NO 1900 100 0.015
Sulfur dioxide SO2 1370 100 0.09
Hydrogen sulfide H2S 1300 1000 0.002
Ammonia NH3 960 100 0.12
Hydrogen chloride HCl 2940 100 0.04
Water H2O 1650 1000 0.20
Vinyl chloride CH2CHCl 950, 900 100 0.06
Acetaldehyde CH3CHO 2750 100 0.015
Benzene C6H6 670 10 0.09
Toluene C6H5CH3 730, 690 100 0.10
Methanol CH3OH 1040 100 0.10
Ethanol CH3CH2OH 1050 100 0.05
Carbonyl sulfide COS 2070 100 0.40
Nitrous oxide N2O 2235 100 0.15
Sulfur hexafluoride SF6 950 10 0.40



  • Ambient temperature operation
  • Vacuum to 15 p.s.i. operation
  • Wide pathlength range (1–20 m)
  • Anodized components
  • Borosilicate glass body
  • Benchmark series baseplate mounting
  • Purgeable transfer optics box
  • ZnSe, CaF2, or KBr windows
  • Kalrez or Viton “O” ring seals
  • Gold mirrors (protected)

Optional Features

  • Purge bellows
  • Pressure gauge
  • Desiccant storage caps
  • Vacuum/gas inlet and outlet taps
  • Extra mirror carriage assemblies


Specac - Introduction to FTIR

Other Equipment by this Supplier

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.