Accurate Methods of Gas Analysis
The earliest methods of detecting poisonous gases involved using birds such as canaries. This was mainly inside mines, where the presence of carbon monoxide, methane, and carbon dioxide had a harmful effect on the miners. The canaries, being sensitive to life threatening gases, would stop singing in the presence of such gases. This was a signal for the miners to evacuate.
Modern methods use several other means of detection, and are more accurate. These involve detecting gases accurately and analyzing them in different areas. For instance, households have carbon monoxide detectors to alert families of the presence of dangerous gases. Explosive detection in airports uses gas chromatography, while human breath analysis forms one of the diagnostic tools for patients in hospitals.
Most gases are frequently undetectable, unless they possess a peculiar odor. That makes the ability to analyze the composition of gases so crucial to human health and safety. By knowing the composition of the gases, we get a clue as to the operation of different processes operating and improving upon them. At present, there exist technologies for several optical, laser, and spectroscopic gas analysis. The major processes involve laser absorption spectroscopy, photoionization, and paramagnetism, involving different types of electronic components.
Laser Absorption Spectroscopy
Laser absorption spectroscopy is the operating principle behind several technologies involving gas analysis. The basic principle being different molecules absorb specific light waves, and the amount of energy a gas absorbs gives an indication of its composition. The characteristic absorption spectra offer very accurate gas detection and analysis. One of the laser-based instruments used is the Tunable Diode Laser Spectrometer (TDLS).
Tunable Diode Laser Spectrometer
With TDLS, it is possible to measure low concentrations of gases such as carbon dioxide, ammonia, water vapor, or methane. Within the instrument, a photodiode measures the reduction in signal intensity when the emission wavelength of the laser is adjusted to match the absorption lines of the target molecule. The measurement readings give an estimation of the concentration of the target gas.
For proper operation of the TDLS, it is important to select a suitable absorption line for the compound under study. This makes TDLS highly specific and sensitive. The ability of TDLS to measure several points simultaneously and its non-intrusive nature has been of great help in combustion diagnostics.
A similar technology involves infrared (IR) spectroscopy. By measuring the absorption of a light source through the gas sample, IR spectroscopy helps to analyze the gas composition. This technology focuses on the IR wavelengths that excite the molecules of the gas. Detection involves use of Fourier Transform Infrared Technology (FTIR). In actual use, a combination of light frequencies is directed towards a sample and the detectors within the instrument measure the light the gas absorbs. After repeating this process several times with different combination of light frequencies, a computer processes the raw absorption data and converts the result using a Fourier Transform algorithm. IR spectroscopy can measure more than 20 different gases simultaneously, and is very suitable for measuring carbon dioxide and organic compounds.
These very sensitive devices use IR spectroscopy for detecting ambient levels of atmospheric ammonia in the environment.