Atmos | Heatable long pathlength gas cells

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. Why Atmos™?

• 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 (80 psi - 5.44 bar for 20m version)
• Retrofittable heating jacket option for up to 200 °C

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

• Atmos Datasheet
• Atmos Gas Cells Manual
• Atmos Heating Jacket Quick Start Guide and Warnings Manual
• Atmos Heating Jackets Manual

• (Atmos Gas Transmission) AN18-08: Analyzing Car Exhaust Fumes with the Atmos Gas cell