Dispersive infrared method

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. 

An alternative method for the determination of particulate organic carbon in marine sediments is based on oxidation with potassium persulfate followed by measurement of carbon dioxide by a Carlo Erba non-dispersive infrared analyser [152,153]. This procedure has been applied to estuarine and high-carbonate oceanic sediments, and results compared with those obtained by a high-temperature combustion method. 

In this method volatile organic matter in seawater is concentrated on a Tenax GC solid adsorbent trap and dry-ice trap in series. The trapped organic material is then desorbed and oxidised to carbon dioxide, which is measured with a non-dispersive infrared analyser. A dynamic headspace method was used for the extraction with the assistance of nitrogen purging. Dynamic headspace analysis [184] is an efficient extraction procedure. The efficiency of extraction... 

With the exception of instrumental dry combustion methods [32], the techniques referred to above for the analysis of organic (and total) carbon in sediments are time consuming (e.g. 2-3h). An instrumental technique described by Van Hall and Stenger [33] makes use of a non-dispersive infrared detector and measures the carbon dioxide resulting from the combustion of the carbonaceous compounds. Total and inorganic carbon can be differentiated by the use of different combustion columns and temperatures. 

Later chapters detail application of the present method to electron spectroscopy for chemical analysis (Chapter 5), high-resolution dispersive infrared spectroscopy (Chapter 6), and tunable-diode-laser spectroscopy (Chapter 7). Because the heart of the method is the repeated application of simple convolution, the method has been adapted to the processing of images (Kawata et al, 1978 Kawata and Ichioka, 1980a Saghri and Tescher, 1980 Maitre, 1981 Gindi, 1981). 

A feasible solution for this complex challenge is to implement at least two analytical methods with which the course of the reaction can be followed a fast first method that allows qualitative control of the status of the catalyst performance and a second accurate, and in most cases more time consuming, analysis method that will allow a detailed evaluation of catalyst performance. The two analysis methods can be run on one analytical unit, e.g. a gas chromatograph with two different analysis protocols, or separate analytical units such as a gas chromatograph for accurate performance evaluation in combination with a non-dispersive infrared unit for fast qualitative analysis. 

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. 

With this particular example of a located, invariable charge model, Barriol used a method that would be frequently used in his laboratory, particularly in the many studies on the Onsager model to work on a very simple model and to adjust it punctually for one case or another. Other authors calculated the atomic polarizability of a molecule according to a dynamic model based on absorption and dispersion infrared measurements. But the problem is to determine the charge value participating effectively in polarization. [36] Barriol, for his part, did work on the simple model of located, invariable charges, with very disputable hypotheses Things are certainly not like this, but there are some difficulties to find a more elaborated model, with which it would be possible to do calculations. [37]... 

Figure 1 illustrates a data path in a typical ratio-recording, dispersive infrared spectrometer. The digitization of the analogue signal produced by the detector M.A. Ford, in Computer Methods in UV, Visible and IR Spectroscopy , ed. W.O. George and... 

Now, in order to employ a locked-in detection system, as in EMIRS, the modulation frequency of the potential at the electrode would have to be at least an order of magnitude greater than F(i). Thus, the potential modulation would have to be between 70 and 100 KHz, too great to allow sufficient relaxation time for most electrochemical processes to respond. As a consequence, lock-in detection has not been employed in in-situ FTIR studies and the sensitivity of SNIFTIRS is less than that of EMIRS. Nevertheless, the FT method does have the sensitivity necessary to detect monolayers, and submonolayers, of adsorbed species [55, 56]. This arises out of the very large improvements in S/N ratio available to FT (compared with dispersive) infrared spectrometry by the Jacquinot and Fellgett advantages. 

CO2 is a major vapor-phase MSS component exceeded only by N2. Its concentration is about 10% of the weight of the whole tobacco smoke (4145), similar to that of O2. The concentration of CO is next highest, being about 4% (4145). The ratio of CO2 to CO is considered to be an index (3482) of the combustibility of tobacco. The currently approved methods for the determination of CO are ISO Standard Methods 3308, 3402, 4387, 8454, 10315, and 10362-1. In these methods, CO is determined by non-dispersion infrared (NDIR) spectroscopy (19A02). 

Several direct spectrophotometric methods are used for the sulphur dioxide measurement, including non-dispersive infrared absorption, ultraviolet absorption, molecular resonance fluorescence and second-derivative spectrophotometry. 

Analysis The analyses were performed on-line by infiured spectroscopy (IR) and mass spectrometry (MS). The former method used a dispersive infrared spectrometer (Perkin-Elmer 580B) with a multiple path cell (2.4m total path length) and a control... 

Hill and Powell (1968) have recently written a comprehensive text on non-dispersive infrared gas analysis. They have discussed applications and sampling techniques in science, medicine, and industry instrumentation and detecting systems and methods for producing calibration gas and vapor mixtures. 

There are various methods by which the impurities may be quantified, but dispersive infrared spectroscopy is often the method of choice.This method has serious shortcomings due to inherent problems with dispersive instruments such as poor resolution and poor wavenumber repeatability in the spectral regions of interest. A further criterion is that the wafer under test must be matched with a pure wafer of identical thickness. Only recently have FT-IR spectroscopic techniques been applied to the problem and considerable success has been realized. 

Fourier transform spectroscopy was used only by those relatively few spectroscopists who needed to overcome the difficulties of collecting spectra under conditions of very low signal levels.3-6 The inconveniences associated with this indirect method were tolerated in order to gain and to use the inherent advantages offered by this type of instrumentation over the more direct dispersive spectroscopic methods. The present commercialization of Fourier transform instrumentation, primarily for the infrared spectral region, has brought this form of spectroscopy out of the development and prototype laboratories and into widespread use. 

Development of a reliable method of measuring infrared spectra was an important subject of research in physics in the beginning of the twentieth century. William W. Coblentz (1873-1962) made a major contribution to the instrumentation of early infrared spectrometers and the compilation of the infrared spectra of many organic compounds in the period before 1930. At that time, alkali halide crystals were used as the prism for dispersing infrared radiation. 

The focus of this chapter is photon spectroscopy, using ultraviolet, visible, and infrared radiation. Because these techniques use a common set of optical devices for dispersing and focusing the radiation, they often are identified as optical spectroscopies. For convenience we will usually use the simpler term spectroscopy in place of photon spectroscopy or optical spectroscopy however, it should be understood that we are considering only a limited part of a much broader area of analytical methods. Before we examine specific spectroscopic methods, however, we first review the properties of electromagnetic radiation. 

As in all Fourier transform methods in spectroscopy, the FTIR spectrometer benefits greatly from the multiplex, or Fellgett, advantage of detecting a broad band of radiation (a wide wavenumber range) all the time. By comparison, a spectrometer that disperses the radiation with a prism or diffraction grating detects, at any instant, only that narrow band of radiation that the orientation of the prism or grating allows to fall on the detector, as in the type of infrared spectrometer described in Section 3.6. 

The use of CO is complicated by the fact that two forms of adsorption—linear and bridged—have been shown by infrared (IR) spectroscopy to occur on most metal surfaces. For both forms, the molecule usually remains intact (i.e., no dissociation occurs). In the linear form the carbon end is attached to one metal atom, while in the bridged form it is attached to two metal atoms. Hence, if independent IR studies on an identical catalyst, identically reduced, show that all of the CO is either in the linear or the bricked form, then the measurement of CO isotherms can be used to determine metal dispersions. A metal for which CO cannot be used is nickel, due to the rapid formation of nickel carbonyl on clean nickel surfaces. Although CO has a relatively low boiling point, at vet) low metal concentrations (e.g., 0.1% Rh) the amount of CO adsorbed on the support can be as much as 25% of that on the metal a procedure has been developed to accurately correct for this. Also, CO dissociates on some metal surfaces (e.g., W and Mo), on which the method cannot be used. 

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