28 Aug 2019

New Heatable FTIR Gas Cell

Specac are pleased to introduce its latest range of heatable long pathlength gas cells, the Atmos™ range of fixed pathlength, metal bodied cells. Specac are a long-standing supplier of accessories for infrared analysis, having been in business for almost 50 years, and regularly work with scientists and chemists all over the world. Specac was recognised for its global scale and ambition in 2018 with the prestigious Queen’s Award for Enterprise.

Why Atmos™?

The new Atmos™ long pathlength gas cells from Specac are ideally suited to IR measurement of gaseous species at low concentrations.

The principal advantage of the Atmos cell is its high temperature, high pressure capability: its metal-bodied construction contains gas pressures up to 125 psi and allows for efficient heating of the cell up to 200 °C using a separate heating jacket. This enables heated gases (such as combustion gases) to be studied while avoiding the condensation of vapours such as water.

In addition, the geometry of the cells has been carefully optimised to maximise signal-to-noise, boosting the limits of detection, and to reduce the overall volume of the cell for rapid gas exchange.

The Atmos™ is available in four factory-set and pre-aligned pathlength configurations: 

  • Atmos™ A2.5 cell is 2.5 m 
  • Atmos™ A5 cell is 5.0 m 
  • Atmos™ A10 cell is 10.0 m 
  • Atmos™ A20 cell is 20.0 m

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

Visit the FTIR Gas Cell page for more information or request a quote for this product.