Heatable Long Pathlength Gas Cells | FTIR Gas Testing
- Wide pathlength range (1m - 20m)
- Vacuum to 15 p.s.i. operation
- Ambient temperature operation
- Borosilicate glass body
- Anodised components
- Gold mirrors (protected)
- Viton or Kalrez 'O' ring seals
- KBr, CaF2 or ZnSe windows
- Purgeable transfer optics box
- Benchmark series baseplate mounting
- Additional mirror carriage assemblies
- Vacuum / gas inlet & outlet taps
- Pressure gauge
- Desiccant storage caps
- Purge bellows
Download the free datasheet in 'Documents' below.
Specac’s standard long pathlength gas cell range is now the new Atmos™ series of metal-bodied fixed-pathlength gas cells. They have been optimized using the latest optical modelling tools to give maximum 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™ range of cells are heatable to 200 °C with the addition of a heating jacket and temperature controller.
- Optimized optical path for unmatched signal-to-noise
- Low cell volume for fast gas exchange
- Ni-coated Al cell bodies for improved thermal transfer from heating jackets. Also holds higher gas pressure than glass.
- Inert stainless-steel mirror substrates and avoidance of glues to prevent outgassing
- 125 psi (8.6 bar) maximum cell pressure
- Retrofittable heating jacket option for up to 200 °C
Flexible specification long pathlength gas cells | Cyclone™ & Tornado™
These cells are available with glass or metal cell bodies and can be set to a range of pathlengths.
Model C2 C5 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™
- Cyclone™ cells can be supplied with a fitted heating jacket for studies of heated gases up to 200 °C (not available for model C20)
- An adjustable mirror carriage can be fitted to Cyclone™ cells to enable the user to vary the pathlength throughout the specified range.
- Tornado™ cells are a stripped back offering, supplied as standard without inlet or outlet tap valves. They are not heatable.
Which pathlength should I choose?
The absorbance of a gas depends on the distance travelled by the IR light beam through the gas sample. The relationship between absorbance, A, concentration, C, and pathlength, L, is given by Beer’s Law:
A = -log10 (I/I0) = a.C.L
Atmospheric concentrations of gases are usually expressed in C.L units of ppm.m – the number of molecules that would be encountered by the infrared beam across a 1.0 m path.
A gas at 0.1 ppm atmospheric concentration will absorb as much IR light over a pathlength of 100 m as would the same gas at 1 ppm over 10 meters or at 10 ppm over 1 meter.
Accordingly, the pathlength of cell should be chosen to give absorbance values within the spectrometer’s linear range for a given concentration. The following table may be taken 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
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