Infrared emission spectrometry

Compounds can be characterized by infrared transmission, reflection, photoacoustic, and emission spectroscopy. Of these techniques, infrared emission spectrometry is by far the least commonly used in most analytical chemistry laboratories. There is a number of reasons for this state of affairs ... 

There are, however, several occasions when transmission, reflection, or photoacoustic spectra of remote samples simply cannot be measured and emission spectroscopy is the only possible way to obtain qualitative or quantitative information. In this chapter a brief outline of the theory and practice of infrared emission spectrometry is given. 

As noted above, it is difficult to account for the effect of temperature gradients across the sample, which makes quantification by infrared emission spectrometry rather inaccurate. A clever way of not merely getting around the problem of temperature gradients but actually benefiting from them has been described in a series of papers by Jones and McClelland [5-10]. The technique developed by these two workers is known as transient infrared spectroscopy (TIRS) and can be subclassified into two techniques, known as transient infrared emission spectroscopy (TIRES) [5,7] and transient infrared transmission spectroscopy (TIRTS) [8]. In both of these two techniques, the deleterious effect of self-absorption is minimized by avoiding the condition of thermal equilibrium that has been assumed for previous sections of this chapter. 

In summary, although infrared emission spectrometry is by no means as widely used as absorption, reflection, or even photoacoustic spectrometry, the capability of emission spectroscopy for remote, noncontact analysis of samples should not be overlooked. 

In infrared emission spectrometry, very weak infrared radiation of emission from a sample itself is to be measured. Consequently, infrared emission measurements have requirements considerably different from transmission and reflection measurements. It is not desirable to use a complicated optical apparatus for emission measurements. 

Thus, infrared emission spectrometry is a useful method of analysis over a wide temperature range, if the background emission can be corrected appropriately. 

Table 5.2 Summary of selected analytical methods for molecular environmental geochemistry. AAS Atomic absorption spectroscopy AFM Atomic force microscopy (also known as SFM) CT Computerized tomography EDS Energy dispersive spectrometry. EELS Electron energy loss spectroscopy EM Electron microscopy EPR Electron paramagnetic resonance (also known as ESR) ESR Electron spin resonance (also known as EPR) EXAFS Extended X-ray absorption fine structure FUR Fourier transform infrared FIR-TEM Fligh-resolution transmission electron microscopy ICP-AES Inductively-coupled plasma atomic emission spectrometry ICP-MS Inductively-coupled plasma mass spectrometry. Reproduced by permission of American Geophysical Union. O Day PA (1999) Molecular environmental geochemistry. Rev Geophysics 37 249-274. Copyright 1999 American Geophysical Union...

Other frequently used methods for determining fluoride include ion and gas chromatography [150,204,205] and aluminium monofluoride (AIF) molecular absorption spectrometry [206,207]. Less frequently employed methods include enzymatic [208], catalytic [209], polarographic [210] and voltammetric methods [211], helium microwave-induced [212] or inductively coupled plasma atomic emission spectrometry [213], electrothermal atomic absorption spectrometry [214], inductively coupled plasma-mass spectrometry [215], radioactivation [216], proton-induced gamma emission [217], near-infrared spectroscopy [218] and neutron activation analysis [219]. 

In reviewing the literature one becomes aware that about 12 years ago the petroleum industry was undergoing partial transition into a synthetic chemicals industry and this is reflected in the variety of analyses required. Production of synthetic rubber, 1,3-buta-diene, isobutene, isobutane, styrene, diisobutene, alkylate, iso-octane, copolymer, cumene, and toluene was greatly aided by instrumental analysis including ultraviolet, infrared, mass and emission spectrometry. Without these methods many of the analyses would be entirely impractical because of tediousness, long elapsed time for results, and general expense of operation. 

In emission spectrometry, the sample is the infrared source. Materials emit infrared radiation by virtue of their temperature. KirchhofF s law states that the amounts of infrared radiation emitted and absorbed by a body in thermal equilibrium must be equal at each wavelength. A blackbody, which is a body having infinite absorptivity, must therefore produce a smooth emission spectrum that has the maximum possible emission intensity of any body at the same temperature. The emissivity, 8, of a sample is the ratio of its emission to that of a blackbody at the same temperature. Infrared-opaque bodies have the same emissivity at all wavelengths so they emit smooth, blackbody-like spectra. On the other hand, any sample dilute or thin enough for transmission spectrometry produces a structured emission spectrum that is analogous to its transmission spectrum because the emissivity is proportional to the absorptivity at each wavelength. The emissivity is calculated from the sample emission spectrum, E, by the relation... 

Infrared emission spectroscopy can be used for the laboratory study of heated samples as one would encounter in pyrot reactions or in the detonation of primary expls. One difficulty associated with the measurement of emission spectra of condensed phase samples is that the temp of the sample has to be uniform, or else radiation emitted from elements situated below the surface will be absorbed by the cooler particles near the surface. Emission spectrometry finds application in the study of flames and smoke... 

Old-bond excitation may have been observed in infrared region emission studies of the reaction of O atoms with N0258. Interference spectrometry techniques have been used to examine the infrared emission that occurs when O (presumably 3P) is mixed with NO or N02, the reactions being... 

The components in a mixture separate in the column and exit from the column at different times (retention times). As they exit, the detector registers the event and causes the event to be recorded as a peak on the chromatogram. A wide range of detector types are available and include ultraviolet adsorption, refractive index, thermal conductivity, flame ionization, fluorescence, electrochemical, electron capture, thermal energy analyzer, nitrogen-phosphorus. Other less common detectors include infrared, mass spectrometry, nuclear magnetic resonance, atomic absorption, plasma emission. 

Particle diameter Inductively coupled plasma-optical emission spectrometry (ICP-OES) Fourier transform infrared spectrometry Mass spectrometry X-ray fluorescence Extended X-ray absorption fine structure (EXAFS) spectroscopy X-ray absorption near edge (XANES) spectroscopy Static and dynamic laser light scattering Scanning probe technologies... 

So far, we have been concerned mainly with emission of radiation from electronically excited states. Emission may also arise from vibrational transitions in various reaction systems. The species HO2 has long been postulated as an important chain carrier in combustion reactions, although emission from electronically excited HO2 has yet to be demonstrated unequivocally. However, Tagirov has observed radiation in flames at a frequency of 1305 cm which he ascribes to transitions from vibrationally excited HO2. Investigations of vibrational quenching processes are of great interest, and if the vibrationally excited species emit infrared radiation, then emission spectrometry may be the most satisfactory way of following the reaction. Davidson et describe a shock-tube study of the relaxation of... 

XRD, X-ray diffraction XRF, X-ray fluorescence AAS, atomic absorption spectrometry ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, Inductively coupled plasma/mass spectroscopy IC, ion chromatography EPMA, electron probe microanalysis SEM, scanning electron microscope ESEM, environmental scanning electron microscope HRTEM, high-resolution transmission electron microscopy LAMMA, laser microprobe mass analysis XPS, X-ray photo-electron spectroscopy RLMP, Raman laser microprobe analysis SHRIMP, sensitive high resolution ion microprobe. PIXE, proton-induced X-ray emission FTIR, Fourier transform infrared. 

The techniques of infrared emission, ultraviolet and visible absorption and emission, and time-of-flight mass spectrometry have also been utilized and will be discussed along with a general description of the shock tube method and various methods of data reduction and refinement. 

Gas monitoring systems should be chosen to suit their intended use since significant differences exist between available sensing technologies, price, and performance. There are basically two types of gas detection technologies. With instrumentation monitors, a sample of air is drawn through a piece of tubing, the sample draw line, to an analysis instrument, which is most commonly based on mass spectrometry, flame emission spectrometry, infrared spectrometry, or colorimetric (paper tape) response. 

Several spectroscopic methods have been used to monitor the levels of heavy metals in man, fossil fuels and environment. They include flame atomic absorption spectrometry (AAS), atomic emission spectroscopy (AES), graphite furnace atomic absorption sp>ectrometry (GFAAS), inductively coupled plasma-atomic emission sp>ectroscopy (ICP/AES), inductively coupled plasma mass spectrometry (ICP/MS), x-ray fluorescence sp>ectroscopy (XRFS), isotope dilution mass spectrometry (IDMS), electrothermal atomic absorption spectrometry (ETAAS) e.t.c. Also other spectroscopic methods have been used for analysis of the quality composition of the alternative fuels such as biodiesel. These include Nuclear magnetic resonance spectroscopy (NMR), Near infrared spectroscopy (NIR), inductively coupled plasma optical emission spectrometry (ICP-OES) e.t.c. 

Flame infrared emission (FIRE) spectrometry is a new technique that is useful in determining FAC in liquid bleach. In the FIRE method, solutions of sodium hypochlorite are acidified to produce aqueous CI2 (reactions [I] and [II] and Figure 1). Dissolved CI2 is liberated from solution in a purge tube and converted to vibrationally excited HCl molecules in a hydrogen-air flame. The intensity of the P-branch of the HCl stretching vibration at 3.8 pm is monitored with a simple filter infrared photometer that employs a lead selenide detector. 

Modern analytical such as infrared (IR) spectroscopy, liquid chromatography (LC), and gas-liquid chromatography (GLC) are in use for the identification of organic components, whilst the mineral constituents can be estimated by using X-ray fluorescence (XRF) spectrometry. X-ray diffraction (XRD), atomic absorption spectrometry (AAS), or inductively coupled plasma (ICP) atomic emission spectrometry (AES). 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

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