Long-Path Gas Cells - Cyclone

From Specac

The Cyclone™ series includes gas cells with fixed and optionally adjustable optical path lengths—which can be customized by the user—and offers a high-quality solution for analyzing infrared spectra of gases and vapors.

They are designed for use across a wide pressure range and are ideal for users who value precise measurement results, high-quality standards, and flexible expansion options.

Based on the White cell principle, in which light is reflected multiple times between specially arranged mirrors, Cyclone™ gas cells enable particularly efficient spectral analysis. The series is available in three different sizes, covering a wide range of requirements in research and industry.

In addition, we offer a wide selection of replacement parts for Cyclone™ gas cells to ensure long-term and reliable use. Custom solutions and non-standard designs are also available upon request, allowing individual requirements to be optimally met.

Features

Cell body from glas or metal
Path lengths from 0,5 m to 10 m
Variable or Fixed pathlength
Vacuum up to 15 psi
Different window materials available

Further information

Which pathlength should I choose?

Due to the low density of gases compared to liquids, special gas cells are used for IR measurements. For trace analysis of gaseous samples, path lengths of up to several meters must be used. Lambert-Beer's law helps to estimate the required path length.

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 d, is given by Beer’s Law:

A = -log10 (I/I₀) = ε∙c∙d

Atmospheric concentrations of gases are usually expressed in c∙d 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	ν(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	0.40
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

Applications

FTIR analysis of gases and vapors
Trace gas analysis (depending on path length, down to the ppm range or below)
Analysis of inorganic gases and organic vapors
Quantitative analyses based on the Beer-Lambert law
Method development through selection of suitable optical path lengths (model-dependent)
Laboratory analysis under defined pressure conditions