Infrared analyzers

When the operating conditions are uniform and steady (there are no fluctuations in flow rate or in concentration of CO in the gas stream), the continuous sampling method can be used. A sampling probe is placed in the stack at any location, preferably near the center. The sample is extracted at a constant sampling rate. As the gas stream passes through the sampling apparatus, any moisture or carbon dioxide in the sample gas stream is removed. The CO concentration is then measured by a nondispersive infrared analyzer, which gives direct readouts of CO concentrations. 

FIGURE 13.46 Nondispersive Infrared analyzer based on (d) interference filters and (b) gas correlation cechnictues. M = mirror, D = detector, S source, F = filter disk. WO = motor, FB = baud pass filter. SD = synchronous detection. C = correlation cell. N nitrogen filter. 

Carbon monoxide and carbon dioxide can be measured using the FTIR techniques (Fourier transform infrared techniques see the later section on the Fourier transform infrared analyzer). Electrochemical cells have also been used to measure CO, and miniaturized optical sensors are available for CO 2 monitoring. 

The Pt film, with a surface area corresponding to NG=4.2-10 9 mol Pt, measured via surface titration of oxygen with C2H4,1,4 is exposed to po2 — 4.6 kPa, PC2H4 = 0.36 kPa at 370°C in a continuous flow gradientless (CSTR) reactor of volume 30 cm3. The rate of C02 formation is monitored via an infrared analyzer.1,4... 

Xiao H-K, Levine SP, D Arcy JB, et al. 1990. Comparison of the Fourier transform infrared (FTIR) spectrophotometer and the Miniature Infrared Analyzer (MIRAN ) for the determination of trichloroethylene (TCE) in the presence of Freon -113 in workplace air. Am Ind Hyg Assoc J 51 395-401. 

CO2 is measured by acidifying a seawater sample. This converts all the bicarbonate and carbonate ion into CO2. The CO2 gas is stripped out of the water sample by bubbling with an inert gas and then swept through either a coulometer or infrared analyzer for quantification. Alternatively, 2CO2 can be calculated from two easily measurable concentrations, pH and alkalinity. (See the online appendix on the companion website for the equations.)... 

The uncertainties are within one standard deviation. Because ultraviolet photometry carried out with the Dasibi instrument is relatively simple, it may be advisable to calibrate even infrared analyzers by means of the ultraviolet transfer standard. 

Light sources and detectors for near-infrared analyzers... 

Near-infrared Spectroscopy for Process Analytical Technology 127 5.3.4 Fourier transform near-infrared analyzers... 

Section 5.3 described a number of alternative design and implementation strategies for near-infrared analyzers, suitable for operation in a process analytical environment. However, none of these analyzers can operate without a robust, maintainable and repeatable sampling interface with the process sample under consideration. In addition to this question of the optical interface to the sample, there is a whole wider area of concern, which is how far the particular sample interface is representative of the sample in the process as a whole. This complex issue is not addressed here, and is dealt with separately in Chapter 3. 

Where is it possible or desirable to locate the near-infrared analyzer modnle What hazardous area certification requirements apply to both analyzer and sampling system ... 

Where physical stream switching is acceptable, this arrangement allows for multiple sampling fast loops to feed a single near-infrared analyzer, with stream switching controlled by the analyzer. The analyzer will most likely need to be hazardous area comphant, but may be either located in a dedicated analyzer shelter, or may be field-mounted. 

Carbon dioxide may be readily analyzed by various instrumental techniques, such as IR, GC, and GC/MS. Many portable infrared analyzers are available commercially for rapid, on site monitoring of CO2. Also, it can be analyzed by GC using a TCD or an FID. It readily may be identified by mass spectrometry from its characteristic ionic mass 44. Dissolved CO2 in water... 

The samples collected arc analyzed in an oil-content analyzer that is based on solvent-extraction principle, and the oil content is measured by a nundispersive infrared analyzer lhai gives digital output. This instrument measures the total oil content, including both free and dissolved oil Therefore, a typical value of 20 ppm is deducted from analyzer results to arrive at free-oil content in the sample. 

This instrument has evolved from ihe laboratory spectrophotometer to satisfy the specific needs of industrial process control. While dispersive instruments continue to be used in some applications, the workhorse infrared analyzers in process control are predominantly nondispersive infrared (NDIR) analyzers. The NDIR analyzer ean be used for either gas or liquid analysis. For simplicity, the following discussion addresses the NDIR gas analyzer, hut it should be recognized that the same measurement principle applies to liquids. The use of infrared as a gas analysis technique is certainly aided by the fact that molecules, such as nitrogen (N ) and oxygen tO , which consist of two like elements, do not absorb in the infrared spectrum. Since nitrogen and oxygen are the primary constituents of air. it is frequently possible to use air as a zero gas. 

Fig. 4. Nondispersive infrared analyzer with a Veingerov.type detector...

Fig. 6. Dual-beam infrared analyzer with j solid-state deteclor. (Inlnircd Industries. Inc)...

Fig. 8. Dual-channel nondispersive infrared analyzer with a solid- slate detector. Infrared Industries, Inc)...

The mass spectra were determined on a LKB 900U Model GC/MS instrument. The elemental analysis was obtained by a VG-model ZAB double focusing high resolution mass spectrometer. The infrared spectra were measured on a Perkin-Elmer 567 spectrophotometer and with a chromatographic infrared analyzer (CIRA 101). The ultraviolet spectra were determined by a UV-visible spectrophotometer (Hitachi Perkin Elmer Model 139). 

Non-dispersive infrared analyzers are usually employed to determine carbon dioxide concentration at atmospheric levels, as they are stable, user friendly, and suited to continuous monitoring. At the Istituto di Metrologia G. Colonnetti (IMGC), as in other metrology laboratories, the determination of the C02 concentration in air is carried out for different purposes in mass, length, and environmental measurements. As NDIR spectroscopy is not a primary method of analytical measurement it does not provide direct traceability to the SI it is hence necessary to refer the obtained results to traceable reference materials, namely PRMs of C02 in N2 at appropriate concentrations. 

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