Nondispersive infrared

Reference methods for criteria (19) and hazardous (20) poUutants estabHshed by the US EPA include sulfur dioxide [7446-09-5] by the West-Gaeke method carbon monoxide [630-08-0] by nondispersive infrared analysis ozone [10028-15-6] and nitrogen dioxide [10102-44-0] by chemiluminescence (qv) and hydrocarbons by gas chromatography coupled with flame-ionization detection. Gas chromatography coupled with a suitable detector can also be used to measure ambient concentrations of vinyl chloride monomer [75-01-4], halogenated hydrocarbons and aromatics, and polyacrylonitrile [25014-41-9] (21-22) (see Chromatography Trace and residue analysis). 

The deterrnination of impurities in the hehum-group gases is also accompHshed by physical analytical methods and by conventional techniques for measuring the impurity in question (93), eg, galvanic sensors for oxygen, nondispersive infrared analysis for carbon dioxide, and electrolytic hygrometers for water. 

Organic Carbon. The total organic carbon (TOC) in a water sample is determined by injecting a microliter sample into a heated, packed tube in a stream of oxygen. The water is vapori2ed and carbon is converted to carbon dioxide, which is detected with a nondispersive infrared analy2er. 

EPA Method 6C is the instrumental analyzer procedure used to determine sulfur dioxide emissions from stationaiy sources (see Fig. 25-30). An integrated continuous gas sample is extracted from the test location, and a portion of the sample is conveyed to an instrumental analyzer for determination of SO9 gas concentration using an ultraviolet ( UV), nondispersive infrared (NDIR), or fluorescence analyzer. The sample gas is conditioned prior to introduction to the gas analyzer by removing particulate matter and moisture. Sampling is conducted at a constant rate for the entire test rim. 

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. 

The sampling system consists of a condensate trap, flow-control system, and sample tank (Fig. 25-38). The analytical system consists of two major subsystems an oxidation system for the recovery and conditioning of the condensate-trap contents and an NMO analyzer. The NMO analyzer is a gas chromatograph with backflush capabihty for NMO analysis and is equipped with an oxidation catalyst, a reduction catalyst, and an FID. The system for the recovery and conditioning of the organics captured in the condensate trap consists of a heat source, an oxidation catalyst, a nondispersive infrared (NDIR) analyzer, and an intermediate collec tion vessel. 

The primary reference method used for measuring carbon monoxide in the United States is based on nondispersive infrared (NDIR) photometry (1, 2). The principle involved is the preferential absorption of infrared radiation by carbon monoxide. Figure 14-1 is a schematic representation of an NDIR analyzer. The analyzer has a hot filament source of infrared radiation, a chopper, a sample cell, reference cell, and a detector. The reference cell is filled with a non-infrared-absorbing gas, and the sample cell is continuously flushed with ambient air containing an unknown amount of CO. The detector cell is divided into two compartments by a flexible membrane, with each compartment filled with CO. Movement of the membrane causes a change in electrical capacitance in a control circuit whose signal is processed and fed to a recorder. 

Fig. 14-1. Nondispersive infrared (NDIR) analyzer, Source Bryan, R. J, Ambient air quality surveillance, in "Air Pollution," 3rd ed., Vol. Ill (A. C. Stern, ed.). Academic Press, New York, 1976, p. 375.

Describe the potential interferences (a) in the nondispersive infrared (NDIR) method for measuring CO and (b) in the chemiluminescent method for measuring NO2. 

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. 

Infrared (IR) spectroscopy offers many unique advantages for measurements within an industrial environment, whether they are for environmental or for production-based applications. Historically, the technique has been used for a broad range of applications ranging from the composition of gas and/or liquid mixtures to the analysis of trace components for gas purity or environmental analysis. The instrumentation used ranges in complexity from simple filter-based photometers to optomechanically complicated devices, such as Fourier transform infrared (FTIR) spectrometers. Simple nondispersive infrared (NDIR) insttuments are in common use for measurements that feature well-defined methods of analysis, such as the analysis of combustion gases for carbon oxides and hydrocarbons. For more complex measurements it is normally necessary to obtain a greater amount of spectral information, and so either Ml-spectrum or multiple wavelength analyzers are required. 

NDIR nondispersive infrared PLSR partial least squares regression... 

Other infrared absorption techniques are also used in ambient air measurements, including tunable diode laser spectroscopy (TDLS), nondispersive infrared (NDIR) spectroscopy, and matrix isolation spectroscopy. These are discussed in more detail later. 

FIGURE 11.9 Schematic diagram of nondispersive infrared device (adapted from Skoog et al., 1998). 

Braden B, Haisch M, Duan LP et al (1994) Clinically feasible stable-isotope technique at a reasonable price - analysis of 13C02/12C02-abundance in breath samples with a new isotope selective nondispersive infrared spectrometer. Zeitschrift fur Gastroenterologie 32(12) 675-678... 

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

Air drawn through a vacuum pump into the gas cuvette of a nondispersive infrared spectrophotometer IR absorption by CO is measured using two parallel IR beams through sample and reference cell and a selective detector, detector signal amplified concentration of analyte determined from a calibration curve prepared from standard calibration gases (ASTM Method D 3162-91, 1993). 

There are two main approaches to the oxidation of OC in water samples to C02 combustion in an oxidizing gas and UV-promoted or heat-catalyzed chemical oxidation. Other approaches are sometimes used, but are much less widespread.11 Carbon dioxide, which is released from the oxidized sample, can be detected in several ways, including conductivity detection, nondispersive infrared (NDIR) detection, or conversion to methane and measurement with a flame ionization detector (FID).1213 The limits of detection in TOC determination can be as low as 1 pg L 1, and the dynamic range can span many orders of magnitude. The precision of the method is usually very good, and the analysis can be completed in a few minutes. Another advantage is the very small amount of sample required—from 10 to 2000 pL. 

CO and C02 are removed from the air, which is then directed through a suitable catalyst to a nondispersive infrared detector (NDIR)... 

The elemental composition (C, H, N) of the cell mass was measured in a Leco CHN-2000 analyzer (St. Joseph, MI), while the oxygen content was obtained by the difference after correction for ash. Total organic carbon (TOC) of fermentation medium at the beginning and end of fermentations was analyzed with a TOC analyzer (Shimadzu 5050A Kyoto, Japan) by the combustion technique with nondispersive infrared detection. 

Organic/elemental carbon speciation is performed on yg-sized samples using a thermal evolution technique (11) in which carbon is evolved in 2 discrete steps at 400°C in He and at 650<>C in 10% 02/He, then measured as OO2 by nondispersive infrared (NDIR) spectroscopy (Beckman Model 865). 13c/12c measurements are made by... 

The carbon dioxide (COz) analyzer types include (1) nondispersive infrared (NDIR), (2) gas filter correlation (GFC), and (3) Orsat, having measurement accuracies from 0.2 ppm to 1-2% FS for NDIR and 1-2% FS for gas filter cor-... 

Fig. 15.1. Concentrations of carbon dioxide were measured with a continuously recording nondispersive infrared gas analyzer at Mauna Loa Observatory, Hawaii. The dots indicate average monthly concentrations. (Reprinted with permission from B. Hileman, Carbon dioxide levels in the atmosphere are increasing exponentially, Chem. Eng. News, April 27,1992. pp. 7-19. Copyright 1992 American Chemical Society.)...

Measurements of the total carbon content (TC) of water, which consists of 1C and TOC (TC = IC-i-TOC), are usually based on the catalytic combustion of the water sample in the presence of oxygen to yield the TC value. Alternatively, the determination of TOC is possible by a photochemical method, i.e. the VUV-initiated oxidation of organic matter in the low pg L concentration range with formation of CO2 (Huber and Frimmel, 1991). The CO2 resulting from both procedures is analyzed quantitatively in a nondispersive infrared analyzer (NDIR). 

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