Infrared gas analyser

A dry combustion-direct injection apparatus was applied to water samples by Van Hall et al. [51 ]. The carbon dioxide was measured with a non-dispersive infrared gas analyser. Later developments included a total carbon analyser [97], a diffusion unit for the elimination of carbonates [98], and finally a dual tube which measured total carbon by combustion through one pathway and carbonate carbon through another. Total organic carbon was then calculated as the difference between the two measurements [99]. 

The various combustion methods differ primarily in the method of measuring the carbon dioxide generated from the organic carbon. The first really sensitive carbon dioxide detector and the one still most used is the non-dispersive infrared gas analyser. The detecting element senses the difference in absorption of infrared energy between a standard cell filled with a gas with no absorption in the infrared, and a sample cell. Water vapour is the only serious interference, hence the carbon dioxide must be dried before any measurements are made. 

When rebreathing systems are used for the delivery of xenon, its concentration within the system needs to be closely monitored. Infrared gas analysers cannot detect xenon, since it is a single atom, and as it is chemically inert its physical properties must be utilised. Mass spectrometry is the most accurate method but it is expensive and it is impractical for clinical use. A calibrated katharometer combined with a galvanic oxygen sensor is a satisfactory alternative which provides a reasonably accurate measure ( 1%). 

Hashimoto, S. (2002). A simple technique to analyze a small volume of soil C02 gas using an infrared gas analyser. Soil Biol. Biochem. 34, 273-275. 

For example, a portable infrared gas analyser allows direct monitoring of gases and vapours in the workplace Figure 18.4). The principle utilised is that many gases and vapours will absorb infrared radiation and under... 

Figure 18.4 Portable infrared gas analyser. (Courtesy Foxboro Analytical Ltd)...

It appears there would be several advantages in using the proposed infrared method analyses could be performed much faster using the IR method. An IR scan takes 45 seconds versus -16 minutes by the NI0SH GC method. The IR method is adapted to charcoal tubes sampled by current recommended techniques. The majority of laboratories have infrared spectrometers and the simplest of models will do utilization of the IR method would relieve pressure of the heavily used gas chromatographs. The... 

Gas Analysis. Most of the analyses were carried out either on the average" sample taken during an experiment or on a sample extracted from the total gas sample. Some spot samples were also taken to investigate the variation in composition during an experiment. The gas analyses were carried out mainly using either gas chromatographic or infrared methods, but in some cases the... 

Analyses. The analytical methods used were described earlier (9). Gas analyses were performed with a modified Orsat apparatus—a method which can be considered satisfactory only if the gases are to be used as fuel, which was the intention for the first generation of AST recovery systems. No analytical differentiation of the unsaturated hydrocarbons can be obtained with the concentrated sulfuric acid used to absorb the so-called illuminants. Subsequent semiquantitative infrared analyses of gas samples indicated that approximately half of the illuminants are ethylene, and more than one-third are acetylene, with some other unsaturated compounds also present. A gas chromatograph is now being calibrated to determine individual unsaturated hydrocarbons quantitatively and to identify various trace gas components. 

Another important application of infrared gas analysis is for trace analysis, such as for the analysis of a dilute mixture (in the ppm range) or an environmental specimen. In such cases, individual analytes are measured from the high ppb levels to the lO s or lOO s of ppm. For such analyses, extended path lengths are required, and typically multipass gas cells from 1 to 20 m in path length are used. One very specific application is an open-path measurement for ambient air monitoring in manufacturing plants or in toxic waste sites in which no cell is used. Instead, a source and interferometer combination are focused on a remote detection system with the aid of special telescope optics. In such cases, several hundreds of meters of effective path length are used. 

The Philae lander carries ten scientific instruments panoramic, stereoscopic and descent camera a-p-x-ray spectrometer evolved gas analyser for elemental, molecular and isotopic composition infrared microscope comet acoustic surface and sounding experiment permittivity probe dust impact monitor multi-purpose sensor for surface and sub-surface science magnetometer plasma monitor comet nucleus sounding experiment drill and sample distribution system. 

Methods of EGA using selective sorption, condensation of effluent gases, infrared absorption and thermoparticulate analysis have been reviewed by Lodding [144]. The use of simple gas burette systems should not be forgotten and an Orsat gas analysis apparatus can provide useful measurements in studies of the decomposition of formates [169]. Problems have been encountered in the determination of water released Kiss et al. [170—172] have measured the formation of this compound from infrared analyses of the acetylene evolved following reaction of water with calcium carbide. Kinetic data may be obtained by wet methods ammonia, determined by titration after absorption in an aqueous solution, has been used to measure a—time values for the decomposition of ammonium salts in a fluidized bed [173],... 

Installing an excess of anal)dical equipment and sample ports for example, an online near-infrared analyser may take the place of a gas and liquid sample port and associated GC equipment. 

In modern times, most analyses are performed on an analytical instrument for, e.g., gas chromatography (GC), high-performance liquid chromatography (HPLC), ultra-violet/visible (UV) or infrared (IR) spectrophotometry, atomic absorption spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), mass spectrometry. Each of these instruments has a limitation on the amount of an analyte that they can detect. This limitation can be expressed as the IDL, which may be defined as the smallest amount of an analyte that can be reliably detected or differentiated from the background on an instrument. 

Wade and Quinn [12] measured the hydrocarbon content of sea surface and subsurface samples. Hydrocarbons were extracted from the samples and analysed by thin-layer and gas-liquid chromatography. The hydrocarbon content of the surface micro layer samples ranged from 14 to 599 pg/1 with an average of 155 pg/1, and the concentration in the subsurface samples ranged from 13 to 239 pg/1 and averaged 73 pg/1. Several isolated hydrocarbon fractions were analysed by infrared spectrometry and each fraction was found to contain a minimum of 95% hydrocarbon material, including both alkenes and aromatics. 

Rasmussen [82] describes a gas chromatographic analysis and a method for data interpretation that he has successfully used to identify crude oil and bunker fuel spills. Samples were analysed using a Dexsil-300 support coated open tube (SCOT) column and a flame ionisation detector. The high-resolution chromatogram was mathematically treated to give GC patterns that were a characteristic of the oil and were relatively unaffected by moderate weathering. He compiled the GC patterns of 20 crude oils. Rasmussen [82] uses metal and sulfur determinations and infrared spectroscopy to complement the capillary gas chromatographic technique. 

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