Chemistry
Infrared Spectrometer
An infrared spectrometer is a scientific instrument used to analyze the chemical composition of substances by measuring the absorption of infrared radiation. It works by passing infrared light through a sample and detecting the wavelengths that are absorbed. This information can be used to identify functional groups and chemical bonds present in the sample.
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10 Key excerpts on "Infrared Spectrometer"
eBook - PDF- J.H. Richardson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The significant point, however, is that while absorption intensities vary from one group to another, they follow well-known laws, so that if a pure specimen of a material is available, quantita-tive analysis based on band intensities is always possible for that material. It is these subtle interactions and shadings in molecular dynamics that account for the uniqueness of infrared spectra, even for structurally similar molecules, and provide many significant clues about the electronic struc-ture of molecules. 2 Instrumentation The function of an Infrared Spectrometer is to measure (and usually plot) the absorption of the sample as a function of wavelength. The usual range of wavelength, chosen to reflect the most common and useful vibra- 260 A. LEE SMITH tional frequencies of organic molecules as well as the limitations of the optical materials used, is ^4000-600 cm -1 (2.5-16 μΐη).* Spectrometers may be either dispersive or nondispersive. In the former class are those instruments using gratings or prisms as the dispersing ele-ments. Nondispersive types include Fourier transform spectrometers, which will be discussed in Section 2.2, and variable frequency filter spec-trometers, which use a continuously variable interference filter instead of a conventional monochromator. 2.1 DISPERSIVE SPECTROMETERS 2.1.1 Spectrometer Design In many respects Infrared Spectrometers resemble other spectrometers used in the visible or ultraviolet region. There are, however, certain key differences which should be thoroughly understood by anyone attempting to use an Infrared Spectrometer for any but the crudest measurements. The design parameters of Infrared Spectrometers are dictated by one simple fact: They must operate in an energy-starved spectral region. Be-cause blackbody sources must be used, and because infrared detectors are grossly inefficient, it is of prime importance that the spectrometer be de-signed for maximum energy transmission.
eBook - PDFInfrared Spectroscopy
Life and Biomedical Sciences
- Theophile Theophanides(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
16 FT-IR Spectroscopy in Medicine Vasiliki Dritsa National Technical University of Athens, NTUA Greece 1. Introduction Infrared spectroscopy has been widely applied for the characterisation of various substances. Due to its sensitivity to the chemical information and architecture of the molecule, infrared spectroscopy can play an important role in new applications such as in the life-science field and not only in the traditional fields of physics and chemistry. Spectroscopic techniques are simple, reproducible, non-destructive without particular sample preparation. As a result, they provide information for the functional groups, bonds and molecular structure. Herschel discovered the existence of infrared radiation when he tried to measure the heat produced by separate colors of a rainbow spectrum in 1800. He noted that the highest temperature fell beyond the red end of the spectrum, implying the existence of invisible light beyond the red. Herschel termed this light calorifi c rays . Infrared spectra originate on the vibrational motions of atoms in chemical bonds within molecules. When a beam of light containing the IR radiation band is passed through a sample, light energy from the photons is absorbed by the chemical bonds and excites the vibrational motions. As a molecule absorbs radiation at a specific frequency, it produces a band in the infrared spectrum at the corresponding wavenumber. The approximate position of an infrared absorption band is determined by the vibrating masses and the chemical bonds (single, double, triple). Τ he exact position of the band depends also on electron withdrawing or donating effects of the intra- and intermolecular environment and coupling with other vibrations. The strength of absorption increases with increasing polarity of the vibrating atoms. The modes of vibration in a molecule that can absorb infrared radiation are many and increase with increasing complexity of the molecule.
- Kenneth Williamson, Katherine Masters(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
221 The types and molecular environment of functional groups in organic molecules can be identified by infrared (IR) spectroscopy. Like nuclear magnetic resonance (NMR) and ultraviolet (UV) spectroscopy, IR spectroscopy is nondestructive. More-over, the small quantity of sample needed, the speed with which a spectrum can be obtained, the relatively low cost of the spectrometer, and the wide applicability of the method combine to make IR spectroscopy one of the most common structural elucidation tools used by organic chemists. IR radiation consists of wavelengths that are longer than those of visible light. It is detected not with the eyes but by a feeling of warmth on the skin. When ab-sorbed by molecules, radiation of these wavelengths (typically 2.5–5 μ m) increases the amplitude of vibrations of the chemical bonds joining atoms. IR spectra are measured in units of frequency or wavelength. The wavelength is measured in micrometers 1 or microns, μ (1 μ m 5 1 3 10 2 6 m). The positions of absorption bands are measured in frequency units called wavenumbers ν , which are expressed in reciprocal centimeters, cm 2 1 , corresponding to the number of cy-cles of the wave in each centimeter. Infrared Spectroscopy CHAPTER 11 PRE-LAB EXERCISE: When an infrared (IR) spectrum is run, it is possible that the chart paper is not properly placed or that the spectrometer is not mechanically adjusted. Describe how you could calibrate an IR spectrum. Examine the scale carefully. Unlike UV and NMR spectra, IR spectra are inverted, with the strongest ab-sorptions at the bottom (called “peaks” although they look like valleys), and are not always presented on the same horizontal scale. Some spectrometers record the spectra on an ordinate linear in microns, but this compresses the low-wavelength region.
eBook - PDF- John H. Lawrence, Cornelius A. Tobias, John H. Lawrence, Cornelius A. Tobias(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
During the nineteen-forties physicists were at work on the necessary technical advances. It had by that time already become possible to produce synthetically the large high quality alkali halide crystals required for making prisms and windows. The next crucial development took place in the creation of high-sensitivity, rapid-response radiation detectors. With these devices it became possible to interrupt the light beam in a spectrometer at a frequency of several cycles per second, thus generating an alternating signal for which stable, all-electronic amplification and recording were feasible. Commercial infrared spec-trometers came into being, and except for special purposes it was no longer necessary for each laboratory to build its own instrument. The advent of the commercial spectrometer broadened the scope of infrared research tremendously. The availability of instruments which would yield large amounts of data quickly and easily was opportune for the application of infrared absorption in a variety of new fields. Whereas it had been chiefly in the hands of physicists and physical chemists, who were concerned with basic theoretical problems and implications of molecular vibration, it quickly spread to the laboratories of organic chemists, who have found it to be a valuable addition to their array of methods for characterizing compounds of either natural or synthetic origin. In petroleum chemistry particularly, the ability to distinguish isomeric hydrocarbons was recognized as a special virtue of this tool, 170 NORMAN Κ. FREEMAN and it was exploited to a high degree. The application of spectrophotome-try in the infrared provided an advantageous means for-quantitative analysis of hydrocarbon mixtures as well as of many other systems of diverse chemical nature. The chemistry of synthetic resins and high polymers has also benefited greatly from infrared methods of structure determination.
eBook - PDFChemical Analysis
Modern Instrumentation Methods and Techniques
- Francis Rouessac, Annick Rouessac, John Towey(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Chemical Analysis: Modern Instrumentation Methods and Techniques , Third Edition. Francis Rouessac and Annick Rouessac, translated by John Towey. © 2022 John Wiley & Sons Ltd. Published 2022 by John Wiley & Sons Ltd. Companion Website: www.wiley.com/go/Rouessac/Analysis3e Infrared and Raman Spectroscopy Chapter 10 I nfrared absorption spectroscopy is based on the study of electromagnetic radiation between 1 and 50 micrometres. This spectral range, divided into near, mid, and far infrared, is used to identify or quantify chemical compounds present in all sorts of samples. Raman spectroscopy is based on the scattering of a very small part of the light used to excite the sample. It provides comparable and additional information to that obtained from the mid or far infrared range, but the very low intensity of the Chapter 10: Infrared and Raman Spectroscopy 248 observed signals prevented the spread of this technique for a long time. These two nondestructive methods are accessible with a variety of versatile spectrometers and analysers designed to study target compounds. Many fields use these two techniques widely, ranging from industrial process analyses to field analyses as well as multipurpose laboratories. 10.1 THE ORIGIN OF LIGHT ABSORPTION IN THE INFRARED REGION In the near and the mid-infrared, the absorption of light by matter originates from the interaction between the radiation from a light source and the chemical bonds in the sample. More precisely, if the atoms situated at the two ends of a bond are animated by vibrational movement with respect to each other and are different from each other, they form an electric dipole that oscillates at a specific frequency. If such a nonsymmetrical bond is irradiated by a monochromatic light source whose frequency is the same as the dipole, then an interaction will occur with the dipole moment of the bond.
eBook - PDF- Muhammad Akhyar Farrukh(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
This records all wavelengths in the IR range. After the two beams reflected by the mirrors recombine, they will travel different distances, and the recombination will lead to constructive and destructive interference. The result will be an interferogram. After the recombined beam has passed through the sample the detector will record the Fourier transform of the IR spectrum of the sample. The data obtained are then processed by a computer that performs an additional Fourier transform to back-transform the interferogram into an IR spectrum (Smith et al., 2011; Blum and John, 2012). Figure 2. A schematic representation of an interferometer used in FTIR spectrometers (adapted from Blum and John, 2012 with permission (originally published in Drug Test. Analysis, DOI: 10.1002/dta.374 )) The potential value of FTIR spectroscopy to a wide range of environmental applications has been demonstrated by numerous research studies. Some of them are presented below. A review by McKelvy and coworkers containing 132 references at the chapter related to environmental applications of infrared spectroscopy (McKelvy et al ., 1998) covers the published literature about relevant applications of infrared spectroscopy for chemical analysis. The literature research was made for the period November 1995 to October 1997. The review contains aspects about infrared accessories and sampling techniques, infrared techniques, applications of infrared spectroscopy in environmental analysis, synthesis chemistry, food and agriculture, biochemistry and also the books and reviews appeared in that period for this subject (McKelvy et al ., 1998). An other review concerning the near-infrared and infrared spectroscopy was made by Workman Jr. This review covers the period 1993-1999 and presents the application of the near infrared spectral region to all types of analyses (Workman Jr, 1999).
eBook - PDF- Douglas Skoog, Donald West, F. Holler, Stanley Crouch, Douglas Skoog(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
J. Pouchert, The Aldrich Library of Infrared Spectra, 3rd ed., Milwaukee, WI: Aldrich Chemical, 1981; NIST Chemistry WebBook, NIST Standard Reference Database Number 69, Gaithersburg, MD: National Institute of Standards and Technology, 2008 (http://webbook.nist.gov). 17 For more information, see D. A. Skoog, F. J. Holler, and S. R. Crouch, Principles of Instrumental Analysis, 7th ed., Boston, MA: Cengage Learning, 2018, Chap. 19. Producing Spectra with an FTIR Spectrometer Feature 23-7 described the basic operating principles of the Michelson interferometer and the function of the Fourier transform to produce a frequency spectrum from a measured interferogram. Figure 24F-1 shows an optical diagram for a Michelson interferometer similar to the one in the spectrom- eter depicted in Figure 24-21. The interferometer is actually two parallel interferometers, one to modulate the IR radia- tion from the source before it passes through the sample and FEATURE 24-1 DO NOT STARE INTO LASER OR VIEW DIRECTLY WITH OPTICA L INSTRUMENTS Interferometer Laser IR Source Beamsplitter Mirror Mirror Mirror Detector Sample Sample compartment Mirror Optical Path FIGURE 24F-1 Instrument diagram for a basic FTIR spectrometer. Radiation of all frequencies from the IR source is reflected into the interferometer where it is modulated by the moving mirror on the left. The modulated radiation is then reflected from the two mirrors on the right through the sample in the compartment at the bottom. After passing through the sample, the radiation falls on the detector. A data acquisition system attached to the detector records the signal and stores it in the memory of a computer as an interferogram. (Reprinted by permission of Thermo Fisher Scientific, Inc.) (continued ) Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Therefore, empirical meth- ods are often employed in quantitative infrared analysis, keeping experimental condi- tions constant. The baseline or ratio method is often used, and this is illustrated in Figure 11.11. A peak is chosen that does not fall too close to others of the test sub- stance or of other substances. A straight line is drawn at the base of the band, and P and P 0 are measured at the absorption peak. (The curve is upside down from the usual absorption spectrum because transmittance is recorded against wavelength.) Log P 0 ∕P is plotted against concentration in the usual manner. Unknowns are compared against standards run under the same instrumental conditions. This technique minimizes rel- ative errors that are in proportion to the sample size, but it does not eliminate simple additive errors, such as factors that offset the baseline. %T 0 100 Wavelength P 0 P FIGURE 11.11 Baseline method for quantitative determination in infrared region of spectrum. 11.8 Spectrometric Instrumentation A spectrometer or spectrophotometer is an instrument that will resolve polychro- matic radiation into different wavelengths and measure the light intensitry at one or more wavelengths. A block diagram of a spectrometer is shown in Figure 11.12. All spectrometers require (1) a source of continuous radiation over the wavelengths of interest, (2) a monochromator for dispersing the light into its component wavelengths and frequently, choosing a narrow band of wavelengths from the source spectrum, (3) a sample cell, (4) a detector, or transducer, for converting radiant energy into elec- trical energy, and (5) a device to read out the response of the detector. The sample may precede or follow the monochromator. Each of these, except the readout device, will vary depending on the wavelength region. The types of instrument components will depend on the wavelength region.
eBook - PDF- Gerald Oster, Arthur W. Pollister, Gerald Oster, Arthur W. Pollister(Authors)
- 2013(Publication Date)
- Academic Press(Publisher)
INFRARED SPECTROPHOTOMETRY 291 mation as vibrations of different parts, or chemical groups, of the molecule. If the molecular system has regular or favored intermolecular associations it is also an approximation to consider the vibrations as due only to indi-vidual molecules; one must consider the system as a whole. It is not surprising then that as the molecular environments are varied, as by changes of state, temperature, pressure, externally applied fields, different solvents, etc., there are changes in the spectra of the molecular system. In the gaseous state, densities are at most of the order of Kooo of the densities of the liquid or solid, and intermolecular distances are increased by about a factor of 10. At lower pressures intermolecular distances are further increased, decreasing the frequency of intermolecular collisions and in general making negligible intermolecular associations. The molecule is now free to rotate, with different rotational energies corresponding to differ-ent rotational inertias about the three principal molecular axes. These rotational energies are quantized, so that a molecule has characteristic pure rotation absorption bands in the microwave electromagnetic region near one centimeter wave length, or a wave number of 1 cm' 1 or a frequency of 3 X 10 10 cycles per second (0.03 megamegacycles). Microwave spectroscopy utilizes primarily radio rather than optical techniques; see Gordy (1953). Molecules may simultaneously have rotational and vibra-tional energies, so that as different molecules change from one particular vibrational energy state to another they may change to different rotational energy states.
- Rohit Bhargava, Ira W. Levin, Rohit Bhargava, Ira W. Levin, Rohit Bhargava, Ira W. Levin(Authors)
- 2008(Publication Date)
- Wiley-Blackwell(Publisher)
Cell. Mol. Biol. 44 , 109–115. [17] Chalmers, J. M., Everall, N. J., Schaerberle, M. D., et al. (2002) FT-IR imaging of polymers: an industrial appraisal. Vib. Spectrosc. 30 , 43. [18] Lyon, R. C., Lester, D. S., Lewis, E. N. et al. (2002) Near infrared spectral imaging for quality assurance of pharmaceutical products: analysis of tablets to assess powder blend homogeneity. AAPS PharmSciTech. 3 (3), 17. [19] Clarke, F. (2004) Extracting process related information from pharmaceutical dosage forms using near infrared microscopy. Vib. Spectrosc. 34 , 25–35. [20] Barer, R., Cole, A. R. H. and Thompson, H. W. (1945) Infra-Red spectroscopy with the reflecting microscope in physics, chemistry and biology. Nature 163 , 193. [21] Harthcock, M. A. and Atkin, S. C. (1988) Appl. Spectrosc. 42 , 3. [22] Taylor, S. K. and McClure, W. F. (1990) NIR imaging spectroscopy: measuring the distribution of chemical components. In Near Infrared Spectroscopy (M. Iwamoto and S. Kawano, eds), Korin Publishing Co. Ltd., Japan, pp. 393–404. [23] Treado, P. J., Levin, I. W. and Lewis, E. N. (1992) Near-infrared acousto-optic fil-tered spectroscopy: a solid state approach to chemical imaging, Appl. Spectrosc. 46 , 553–9. [24] Robert, P., Bertrand, D., Devaux, M. F. and Sire, A. (1992) Identification of chemical constituents by multivariate near-infrared spectral imaging. Anal. Chem. 64 664–7. [25] Treado, P. J., Levin, I. W. and Lewis, E. N. (1994) Indium antimonide (InSb) focal plane array (FPA) detection for near-infrared imaging microscopy. Appl. Spectrosc. 48 , 607–15. [26] Lewis, E. N. and Levin, I. W. (1995) Real-time, mid-infrared spectroscopic imaging microscopy using indium antimonide focal-plane array detection. Appl. Spectrosc. 49 , 672–8. [27] Lewis, E. N., Levin, I.
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