{"id":155,"date":"2018-11-28T11:02:57","date_gmt":"2018-11-28T11:02:57","guid":{"rendered":"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/?post_type=chapter&#038;p=155"},"modified":"2019-05-01T05:01:12","modified_gmt":"2019-05-01T05:01:12","slug":"spectroscopic-instrumentation","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/chapter\/spectroscopic-instrumentation\/","title":{"rendered":"Spectroscopic Instrumentation"},"content":{"raw":"<div><span style=\"float: right\"><a href=\"https:\/\/youtu.be\/6LxV2Seo2Xw\" target=\"_blank\" rel=\"noopener\"><img src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"epgp books\" width=\"75px\" height=\"75px;\" \/><\/a>\r\n<\/span><\/div>\r\n<div>\r\n\r\n<strong>\u00a0 \u00a0 Learning Objectives<\/strong>\r\n\r\n&nbsp;\r\n\r\nSpectroscopy is the study of interaction of electromagnetic radiation with the matter.\r\n<ul>\r\n \t<li style=\"text-align: justify\">It is used for investigating molecular characteristics of the sample of interest. In this module we study about two most common spectroscopy method<\/li>\r\n \t<li>UV\/Visible spectroscopy and Infra-red spectroscopy<\/li>\r\n \t<li style=\"text-align: justify\">First we will study about the basic principle of measurement and basic of instrumentation behind the technique.<\/li>\r\n<\/ul>\r\n<strong>\u00a0 \u00a0 Introduction<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">Spectroscopic methods are large group of analytical methods that are based on atomic and molecular spectroscopy. In general terms spectroscopy is the branch of science that deals with the interaction of various types of radiation with matter. This field of investigation started with the studies involved in interaction between electromagnetic radiation and matter, but at present the field has been broadened to include interactions between matter and other forms of energy, for example acoustic waves and beams of particles such as ions and electrons. Therefore, Spectrometry and spectrometric methods refer to the measurement of intensity of radiation with a photoelectric transducer or other type of electronic devices.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">Most of the commercially available spectrophotometers are based on electromagnetic radiation. This type of energy can take several forms and is most easily recognizable as light or radiant heat. Based on the frequency and wavelength range electromagnetic spectrum is classified into various classes, gamma rays have smallest wavelength in the range of 1 pm and radiowaves can have wavelength has long as 100 Mm (Mm \u2013 Mega Meter; Mega = 10-6).<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">In this session, we will limit ourselves to UV\/Vis and IR range. We will study about instrumentation and basic physics behind molecular absorption spectroscopy.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Ultraviolet \/Visible Spectroscopy<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Principle Behind UV\/Vis Spectroscopy<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">UV\/Vis spectroscopy falls into the category of molecular absorption spectroscopy. This technique primarily focuses on <\/span>absorption<span style=\"text-align: initial;font-size: 1em\"> characteristics of molecules within the electromagnetic spectral range of 160 to 780 nm. It is based on the measurement of Transmittance (T) or Absorbance (A) of solutions contained in <\/span>transparent<span style=\"text-align: initial;font-size: 1em\"> cell having <\/span>path<span style=\"text-align: initial;font-size: 1em\"> length of b cm. The concentration of an absorbing analyte is linearly related to absorbance.<\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Experimentally observed transmittance and absorbance can be approximated with the following equations \u2013<\/span><\/p>\r\n&nbsp;\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-159\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-84.png\" alt=\"\" width=\"335\" height=\"124\" \/>\r\n<p style=\"text-align: justify\">\u00a0 \u00a0where Po is the power of radiation passing through the solvent and P is the power of radiation passing through the analyte present in solvent.<\/p>\r\n&nbsp;\r\n\r\nThe relation between the absorbance and transmittance is given by the following equation\r\n\r\n&nbsp;\r\n\r\nA = 2 \u2013 log %T --------------(3)\r\n\r\n&nbsp;\r\n\r\nThe extent to which absorbance will take place is mathematically explained by <em>Beer\u2019s<\/em> <em>law <\/em>according to which \u2013\r\n\r\nA = \uf065bc -------------(4)\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">Where measured absorbance is directly proportional to molar absorbtivity with units of L mol-1 cm-1, <em>b<\/em> is the path length in cm i.e. width of the sample holder and <em>c<\/em> is the concentration of the compound in the solvent mol L-1.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">A limitation to the Beer\u2019s law is that it can describe absorption behavior at relatively low concentration of <\/span>analyte<span style=\"text-align: initial;font-size: 1em\">. At high concentration usually greater than 0.01M, the average distance between the molecules responsible for absorption very less. At high concentration molecules start affecting charge distribution of their adjacent molecule. This alters molecules ability to absorb radiation at a given wavelength. As the extent of absorption depends on concentration, this phenomenon causes deviation in the linear relationship between absorbance and concentration. Deviation in <\/span>the Beer\u2019s<span style=\"text-align: initial;font-size: 1em\"> law may also there due to because it depends upon the refractive index of the medium. If any changes in concentration can lead to alteration of <\/span>refractive<span style=\"text-align: initial;font-size: 1em\"> index of the solution, deviations in the Beer\u2019s law maybe observed.<\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Instrumentation<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Instruments for measuring absorption in UV\/Visible range of electromagnetic spectrum are made up of (1) electromagnetic radiation source (2) wavelength selectors (3) sample containers (4) radiation transducers and (5) signal processors and readout devices.<\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">For molecular absorption <\/span>studies<span style=\"text-align: initial;font-size: 1em\"> a continuum source is required whose power doesn\u2019t change sharply over <\/span>considerable<span style=\"text-align: initial;font-size: 1em\"> range of wavelengths. Different types of sources are available in the market; they are hydrogen &amp; deuterium lamps, tungsten filament lamps <\/span>and<span style=\"text-align: initial;font-size: 1em\"> xenon arc lamps. Cells or cuvettes required for holding the sample and solvent are constructed out of special material that also allows radiation to pass through to pass through in the spectral region of interest. They normally made up of quartz or fused silica and are transparent to UV (below 350 nm) and visible region of the spectra. For <\/span>visible<span style=\"text-align: initial;font-size: 1em\"> region of the <\/span>spectra<span style=\"text-align: initial;font-size: 1em\"> Plastic containers are also used.<\/span><\/p>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-160\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85.png\" alt=\"\" width=\"501\" height=\"130\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center\"><strong>Figure 1. <\/strong>Single Beam Spectrophotometer<\/p>\r\n\r\n<\/div>\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">\u00a0 The two most commonly available spectrophotometers are Single beam and Double Beam spectrophotometer. Single beam spectrophotometer consists of <\/span>radiation<span style=\"text-align: initial;font-size: 1em\"> source, filter or monochromator, matched cells that can be interposed alternatively in the path of <\/span>radiation<span style=\"text-align: initial;font-size: 1em\"> beam, a photo detector, an amplifier and a read out device. The basic design single beam spectrophotometer is shown in figure 1. These systems have interchangeable tungsten\/deuterium lamp sources and are equipped with <\/span>high resolution<span style=\"text-align: initial;font-size: 1em\"> grating monochromator with variable slits. Photomultiplier tubes are used as transducers and its output is digitized, for printing, plotting and storing data in <\/span>useful<span style=\"text-align: initial;font-size: 1em\"> form.<\/span><\/p>\r\n\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-161\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86.png\" alt=\"\" width=\"497\" height=\"180\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center\"><strong>Figure 2. <\/strong>Double Beam Spectrophotometer<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">The Double-Beam spectrophotometer is similar to single beam but there are additional beam splitters that can direct radiation beam to reference and sample cells simultaneously. This is can be observed in figure 2. The signals from the two photodetector go to the difference amplifier and finally to readout device. They offer an advantage of compensating any short-term fluctuations from the radiation source and any drift in transducer and amplifier. They are also known to compensate for variations in the source intensity with the wavelength.<\/p>\r\n&nbsp;\r\n\r\n<strong>Infrared (IR) Spectroscopy<\/strong>\r\n\r\n&nbsp;\r\n\r\n<strong>Principle Behind Infrared Spectroscopy<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">The infrared region of the spectrum encompasses wavelengths from 0.78 to 1000 m. From the standpoint of application and instrumentation infrared is divided into near-,\u00a0<span style=\"text-align: initial;font-size: 1em\">mid- and far-infrared radiation. Though the most commonly used range in <\/span>infrared<span style=\"text-align: initial;font-size: 1em\"> region is between 2.5 to 15 m. A linear wavenumber scale i.e. cm-1 is preferred in infrared spectroscopy due to the <\/span>directly<span style=\"text-align: initial;font-size: 1em\"> proportionality between this quantity and both energy and frequency. In <\/span>practice<span style=\"text-align: initial;font-size: 1em\"> it is the frequency of absorption of radiation that is responsible for molecular vibrational frequency during the measurement. Absorption of IR radiation is largely confined to molecular species that have small energy difference between various vibrational states. If the radiation frequency exactly matches the natural vibrational frequency of the molecule, a net energy transfer takes place. This results change in amplitude of the molecular vibration and absorption of radiation is the consequence.<\/span><\/p>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-162\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-87.png\" alt=\"\" width=\"295\" height=\"348\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center\"><strong>Figure 3. <\/strong>Types of Molecular Vibrations. Note:+ indicates motion from page towards the reader; - indicates motion away from the reader.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">Similarly, any rotation of asymmetric molecules around their center of mass can lead to periodic dipole fluctuation that interact with IR radiation. There is no net change in the dipole moment occur during vibrational or rotation of homonuclear species such as N2, Cl2 or O2. Compounds like these cannot absorb IR radiation, whereas all other molecular species can. Various kinds of molecular vibrations that can take place in a\u00a0<span style=\"text-align: initial;font-size: 1em\">simple triatomic molecule <\/span>are<span style=\"text-align: initial;font-size: 1em\"> shown in <\/span>the figure<span style=\"text-align: initial;font-size: 1em\"> 3. Broadly they are classified as Stretching and Bending Vibrations.<\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Quantum Treatment of Vibrations<\/strong><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Molecular vibrations like <\/span>coupling<span style=\"text-align: initial;font-size: 1em\"> of vibrations between atoms involving bonds to a single central atom are analogous to <\/span>mechanical<span style=\"text-align: initial;font-size: 1em\"> model used in describing simple harmonic oscillator. The natural frequency of an oscillator can then be described mathematically as<\/span><\/p>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-163\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-88.png\" alt=\"\" width=\"226\" height=\"66\" \/>\r\n<p style=\"text-align: justify\">where k is the force constant that depends on the stiffness the spring, in our case it depends on the strength of the bond, is the reduced mass where two masses m1 &amp; m2 are connected by a spring ( in our case molecular bond) can be written as =m1.m2\/(m1 + m2).<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">Let us assume that the transitions in the vibrational energy levels are brought about by absorption of radiation, provided that the energy level of the radiation matches the difference in the energy level E between the vibrational quantum states, plus that the vibration causes fluctuation in the dipole. This difference in energy level can be written as<\/p>\r\n<img class=\"aligncenter size-full wp-image-164\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-89.png\" alt=\"\" width=\"301\" height=\"55\" \/>\u00a0 \u00a0 where <em>h<\/em> is the Planck Constant.\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">The frequency of radiation <em>v<\/em> that can bring change identical to the classical vibrational frequencies of the bond <em>v<\/em><em>m<\/em> can be derived from the equations 5 &amp; 6 and is written as<\/p>\r\n<img class=\"aligncenter size-full wp-image-165\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-90.png\" alt=\"\" width=\"312\" height=\"63\" \/>\r\n<p style=\"text-align: justify\">\u00a0 \u00a0The Wavenumber \u00a0\u00a0\u0305 is reciprocal of wavelength in centimeters and is directly proportional to the frequency and the energy of the radiation.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Thus it may be written as \u00a0\u00a0\u0305<\/span><em style=\"text-align: initial;font-size: 1em\">= kv<\/em><span style=\"text-align: initial;font-size: 1em\">, where <\/span><em style=\"text-align: initial;font-size: 1em\">k<\/em><span style=\"text-align: initial;font-size: 1em\"> is the constant dependent on the medium and wavenumber is equal to the reciprocal of velocity c of the electromagnetic radiation.<\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Now if we wish to express the equation 7 in wavenumber then it may be written as<\/span><\/p>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"aligncenter size-full wp-image-166\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91.png\" alt=\"\" width=\"362\" height=\"62\" \/>\u00a0 \u00a0 \u00a0where \u00a0\u00a0\u0305is the wavenumber of an absorption peak in cm-1, <em>k<\/em> is the force constant of the bond in Newtons per meter (N\/m), c is the velocity of light in cm\/s and is the reduced mass.\r\n\r\n&nbsp;\r\n\r\n<strong>IR Instruments<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">There 3 types of infrared instruments available from commercial sources (1) dispersive grating spectrophotometers that are used primarily for qualitative measurements (2) multiplex instruments employing Fourier transform and suited both for qualitative and quantitative measurements (3) non-dispersive photometers that have been developed for quantitative determination of a variety of organic species in the atmosphere by adsorption, emission, and reflectance spectroscopy.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">Most widely used spectrophotometer for laboratory-based investigation is Fourier transform Infrared (FTIR) spectrophotometers because of their speed, reliability and convenience.<\/p>\r\n&nbsp;\r\n\r\n<img class=\"aligncenter size-full wp-image-167\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-92.png\" alt=\"\" width=\"227\" height=\"218\" \/>\r\n\r\n&nbsp;\r\n<p style=\"text-align: center\"><strong>Figure 4<\/strong>. A single beam FTIR Spectrometer (Courtesy Perkin-Elmer)<\/p>\r\n\r\n<\/div>\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">\u00a0 The basic design of Single beam FTIR spectrophotometer is given in figure 4. The majority of FTIR instruments are based on Michelson Interferometer. An interferometer uses patterns formed by waves to measure characteristics of the waves themselves or of the material that reflects, refracts or transmits waves.<\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Infrared sources (lamps) consist of inert solid that is heated electrically to a temperature between 1500 and 2200 K. A Continuum radiation approximating to that of a blackbody is emitted from the source. Various kind of IR source that <\/span>are<span style=\"text-align: initial;font-size: 1em\"> used in IR instruments are<\/span><\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Nernst Glower \u2013 It is composed of rare earth oxides formed into <\/span>cylinder<span style=\"text-align: initial;font-size: 1em\"> of diameter 1 to 2 mm and length upto 20 mm.<\/span><\/li>\r\n \t<li style=\"text-align: justify\">Globar Source \u2013 It is a silicon carbide rod, usually about 50 mm in length and 5 mm diameter<\/li>\r\n \t<li style=\"text-align: justify\">Incandescent Wire Source \u2013 It is tightly<span style=\"text-align: initial;font-size: 1em\"> wound spiral of Nichrome wire heated to about 1100 K by an electrical current.<\/span><\/li>\r\n \t<li style=\"text-align: justify\">Mercury arc \u2013 It consists of quartz<span style=\"text-align: initial;font-size: 1em\"> jacketed tube containing mercury vapor at <\/span>pressure<span style=\"text-align: initial;font-size: 1em\"> greater than one atmosphere.<\/span><\/li>\r\n \t<li style=\"text-align: justify\">An ordinary Tungsten filament lamp<\/li>\r\n \t<li style=\"text-align: justify\">A Carbon Dioxide Laser Source<\/li>\r\n<\/ul>\r\n<div>\r\n\r\n\u00a0 \u00a0 The basic design of Single beam FTIR spectrophotometer is given in figure 4.\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\"><strong>Advantages. <\/strong>Optics of FTIR instruments has much larger energy throughput (one or two orders of magnitude) than dispersive instruments. They have limited throughput due to the use of narrow slit widths. It should be noted that interferometer is free the problem of stray radiation because each IR frequency is effectively chopped at different frequency. That means any radiation other than the frequency that is to be radiated onto the sample is removed by interferometer.<\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">FTIR is a powerful instrument that has extensive application in the field of chemistry required for analysis of unknown component in the sample of interest. This instrument is particularly useful for<\/p>\r\n\r\n<ol>\r\n \t<li style=\"text-align: justify\">Very high-resolution work involving gaseous mixtures having complex spectra resulting from superposition of vibrational and rotational bands.<\/li>\r\n \t<li style=\"text-align: justify\">The study of analytes having high absorbances<\/li>\r\n \t<li style=\"text-align: justify\">The study of substances with weak absorption bands ( e.g. compounds absorbed on catalyst surface)<\/li>\r\n \t<li style=\"text-align: justify\">Fast scanning investigations involving kinetic studies or detection of chromatographic effluents<\/li>\r\n \t<li style=\"text-align: justify\">Collecting IR data from very small samples<\/li>\r\n \t<li style=\"text-align: justify\">Obtaining reflection spectra<\/li>\r\n \t<li style=\"text-align: justify\">IR emission studies<\/li>\r\n<\/ol>\r\n<\/div>\r\n<strong>\u00a0 \u00a0 Summary<\/strong>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">In this module we studied about two most important types of spectrophotometry methods. First, we studied about UV\/Visible Spectrophotometry and we briefly studied about Beer\u2019s law that describes the absorption characteristics of molecules in the path of the UV\/Visible radiation. Second, we studied about Infrared Spectrophotometry where we studied about different types of molecular bending vibrations responsible for absorption of radiation at particular wavenumber or frequency.<\/p>\r\n\r\n<table>\r\n<tbody>\r\n<tr>\r\n<td><strong>you can view video on Spectroscopic Instrumentation<\/strong><\/td>\r\n<td><a href=\"https:\/\/youtu.be\/6LxV2Seo2Xw\" target=\"_blank\" rel=\"noopener\"><img class=\"alignnone wp-image-120\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"\" width=\"36\" height=\"36\" \/><\/a><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<strong>References :-<\/strong>\r\n<ol>\r\n \t<li style=\"text-align: justify\">Electrical and Electronic Measurements and Instrumentation, <em>Sawhney A. K.<\/em>, Dhanpat Rai &amp; Sons, Reprint 1985<\/li>\r\n \t<li style=\"text-align: justify\">Measurements and Instrumentation, <em>Bakshi U.A., Bakshi A.V.,<\/em> Technical Publications, 2009<\/li>\r\n \t<li style=\"text-align: justify\">Principles of instrumental analysis, <em>Skoog, Douglas A., F. James Holler, and<\/em> <em>Stanley R. Crouc,. <\/em>Cengage learning, Edition 2017<\/li>\r\n \t<li style=\"text-align: justify\">Instrumentation, measurement and analysis. <em>Nakra, B.C. and Chaudhry, K.K.,<\/em> Tata McGraw-Hill Education, 2003.<\/li>\r\n \t<li style=\"text-align: justify\">Measurement and instrumentation: theory and application, <em>Morris, A. S., &amp;<\/em> <em>Langari, R<\/em>. , Academic Press, 2012.<\/li>\r\n<\/ol>","rendered":"<div><span style=\"float: right\"><a href=\"https:\/\/youtu.be\/6LxV2Seo2Xw\" target=\"_blank\" rel=\"noopener\"><img decoding=\"async\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"epgp books\" width=\"75px\" height=\"75px;\" \/><\/a><br \/>\n<\/span><\/div>\n<div>\n<p><strong>\u00a0 \u00a0 Learning Objectives<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p>Spectroscopy is the study of interaction of electromagnetic radiation with the matter.<\/p>\n<ul>\n<li style=\"text-align: justify\">It is used for investigating molecular characteristics of the sample of interest. In this module we study about two most common spectroscopy method<\/li>\n<li>UV\/Visible spectroscopy and Infra-red spectroscopy<\/li>\n<li style=\"text-align: justify\">First we will study about the basic principle of measurement and basic of instrumentation behind the technique.<\/li>\n<\/ul>\n<p><strong>\u00a0 \u00a0 Introduction<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Spectroscopic methods are large group of analytical methods that are based on atomic and molecular spectroscopy. In general terms spectroscopy is the branch of science that deals with the interaction of various types of radiation with matter. This field of investigation started with the studies involved in interaction between electromagnetic radiation and matter, but at present the field has been broadened to include interactions between matter and other forms of energy, for example acoustic waves and beams of particles such as ions and electrons. Therefore, Spectrometry and spectrometric methods refer to the measurement of intensity of radiation with a photoelectric transducer or other type of electronic devices.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Most of the commercially available spectrophotometers are based on electromagnetic radiation. This type of energy can take several forms and is most easily recognizable as light or radiant heat. Based on the frequency and wavelength range electromagnetic spectrum is classified into various classes, gamma rays have smallest wavelength in the range of 1 pm and radiowaves can have wavelength has long as 100 Mm (Mm \u2013 Mega Meter; Mega = 10-6).<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">In this session, we will limit ourselves to UV\/Vis and IR range. We will study about instrumentation and basic physics behind molecular absorption spectroscopy.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Ultraviolet \/Visible Spectroscopy<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Principle Behind UV\/Vis Spectroscopy<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">UV\/Vis spectroscopy falls into the category of molecular absorption spectroscopy. This technique primarily focuses on <\/span>absorption<span style=\"text-align: initial;font-size: 1em\"> characteristics of molecules within the electromagnetic spectral range of 160 to 780 nm. It is based on the measurement of Transmittance (T) or Absorbance (A) of solutions contained in <\/span>transparent<span style=\"text-align: initial;font-size: 1em\"> cell having <\/span>path<span style=\"text-align: initial;font-size: 1em\"> length of b cm. The concentration of an absorbing analyte is linearly related to absorbance.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Experimentally observed transmittance and absorbance can be approximated with the following equations \u2013<\/span><\/p>\n<p>&nbsp;<\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-159\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-84.png\" alt=\"\" width=\"335\" height=\"124\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-84.png 335w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-84-300x111.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-84-65x24.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-84-225x83.png 225w\" sizes=\"auto, (max-width: 335px) 100vw, 335px\" \/><\/p>\n<p style=\"text-align: justify\">\u00a0 \u00a0where Po is the power of radiation passing through the solvent and P is the power of radiation passing through the analyte present in solvent.<\/p>\n<p>&nbsp;<\/p>\n<p>The relation between the absorbance and transmittance is given by the following equation<\/p>\n<p>&nbsp;<\/p>\n<p>A = 2 \u2013 log %T &#8212;&#8212;&#8212;&#8212;&#8211;(3)<\/p>\n<p>&nbsp;<\/p>\n<p>The extent to which absorbance will take place is mathematically explained by <em>Beer\u2019s<\/em> <em>law <\/em>according to which \u2013<\/p>\n<p>A = \uf065bc &#8212;&#8212;&#8212;&#8212;-(4)<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Where measured absorbance is directly proportional to molar absorbtivity with units of L mol-1 cm-1, <em>b<\/em> is the path length in cm i.e. width of the sample holder and <em>c<\/em> is the concentration of the compound in the solvent mol L-1.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">A limitation to the Beer\u2019s law is that it can describe absorption behavior at relatively low concentration of <\/span>analyte<span style=\"text-align: initial;font-size: 1em\">. At high concentration usually greater than 0.01M, the average distance between the molecules responsible for absorption very less. At high concentration molecules start affecting charge distribution of their adjacent molecule. This alters molecules ability to absorb radiation at a given wavelength. As the extent of absorption depends on concentration, this phenomenon causes deviation in the linear relationship between absorbance and concentration. Deviation in <\/span>the Beer\u2019s<span style=\"text-align: initial;font-size: 1em\"> law may also there due to because it depends upon the refractive index of the medium. If any changes in concentration can lead to alteration of <\/span>refractive<span style=\"text-align: initial;font-size: 1em\"> index of the solution, deviations in the Beer\u2019s law maybe observed.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Instrumentation<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Instruments for measuring absorption in UV\/Visible range of electromagnetic spectrum are made up of (1) electromagnetic radiation source (2) wavelength selectors (3) sample containers (4) radiation transducers and (5) signal processors and readout devices.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">For molecular absorption <\/span>studies<span style=\"text-align: initial;font-size: 1em\"> a continuum source is required whose power doesn\u2019t change sharply over <\/span>considerable<span style=\"text-align: initial;font-size: 1em\"> range of wavelengths. Different types of sources are available in the market; they are hydrogen &amp; deuterium lamps, tungsten filament lamps <\/span>and<span style=\"text-align: initial;font-size: 1em\"> xenon arc lamps. Cells or cuvettes required for holding the sample and solvent are constructed out of special material that also allows radiation to pass through to pass through in the spectral region of interest. They normally made up of quartz or fused silica and are transparent to UV (below 350 nm) and visible region of the spectra. For <\/span>visible<span style=\"text-align: initial;font-size: 1em\"> region of the <\/span>spectra<span style=\"text-align: initial;font-size: 1em\"> Plastic containers are also used.<\/span><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-160\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85.png\" alt=\"\" width=\"501\" height=\"130\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85.png 501w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85-300x78.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85-65x17.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85-225x58.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-85-350x91.png 350w\" sizes=\"auto, (max-width: 501px) 100vw, 501px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center\"><strong>Figure 1. <\/strong>Single Beam Spectrophotometer<\/p>\n<\/div>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">\u00a0 The two most commonly available spectrophotometers are Single beam and Double Beam spectrophotometer. Single beam spectrophotometer consists of <\/span>radiation<span style=\"text-align: initial;font-size: 1em\"> source, filter or monochromator, matched cells that can be interposed alternatively in the path of <\/span>radiation<span style=\"text-align: initial;font-size: 1em\"> beam, a photo detector, an amplifier and a read out device. The basic design single beam spectrophotometer is shown in figure 1. These systems have interchangeable tungsten\/deuterium lamp sources and are equipped with <\/span>high resolution<span style=\"text-align: initial;font-size: 1em\"> grating monochromator with variable slits. Photomultiplier tubes are used as transducers and its output is digitized, for printing, plotting and storing data in <\/span>useful<span style=\"text-align: initial;font-size: 1em\"> form.<\/span><\/p>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-161\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86.png\" alt=\"\" width=\"497\" height=\"180\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86.png 497w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86-300x109.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86-65x24.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86-225x81.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-86-350x127.png 350w\" sizes=\"auto, (max-width: 497px) 100vw, 497px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center\"><strong>Figure 2. <\/strong>Double Beam Spectrophotometer<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">The Double-Beam spectrophotometer is similar to single beam but there are additional beam splitters that can direct radiation beam to reference and sample cells simultaneously. This is can be observed in figure 2. The signals from the two photodetector go to the difference amplifier and finally to readout device. They offer an advantage of compensating any short-term fluctuations from the radiation source and any drift in transducer and amplifier. They are also known to compensate for variations in the source intensity with the wavelength.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Infrared (IR) Spectroscopy<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Principle Behind Infrared Spectroscopy<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">The infrared region of the spectrum encompasses wavelengths from 0.78 to 1000 m. From the standpoint of application and instrumentation infrared is divided into near-,\u00a0<span style=\"text-align: initial;font-size: 1em\">mid- and far-infrared radiation. Though the most commonly used range in <\/span>infrared<span style=\"text-align: initial;font-size: 1em\"> region is between 2.5 to 15 m. A linear wavenumber scale i.e. cm-1 is preferred in infrared spectroscopy due to the <\/span>directly<span style=\"text-align: initial;font-size: 1em\"> proportionality between this quantity and both energy and frequency. In <\/span>practice<span style=\"text-align: initial;font-size: 1em\"> it is the frequency of absorption of radiation that is responsible for molecular vibrational frequency during the measurement. Absorption of IR radiation is largely confined to molecular species that have small energy difference between various vibrational states. If the radiation frequency exactly matches the natural vibrational frequency of the molecule, a net energy transfer takes place. This results change in amplitude of the molecular vibration and absorption of radiation is the consequence.<\/span><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-162\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-87.png\" alt=\"\" width=\"295\" height=\"348\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-87.png 295w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-87-254x300.png 254w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-87-65x77.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-87-225x265.png 225w\" sizes=\"auto, (max-width: 295px) 100vw, 295px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center\"><strong>Figure 3. <\/strong>Types of Molecular Vibrations. Note:+ indicates motion from page towards the reader; &#8211; indicates motion away from the reader.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Similarly, any rotation of asymmetric molecules around their center of mass can lead to periodic dipole fluctuation that interact with IR radiation. There is no net change in the dipole moment occur during vibrational or rotation of homonuclear species such as N2, Cl2 or O2. Compounds like these cannot absorb IR radiation, whereas all other molecular species can. Various kinds of molecular vibrations that can take place in a\u00a0<span style=\"text-align: initial;font-size: 1em\">simple triatomic molecule <\/span>are<span style=\"text-align: initial;font-size: 1em\"> shown in <\/span>the figure<span style=\"text-align: initial;font-size: 1em\"> 3. Broadly they are classified as Stretching and Bending Vibrations.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong style=\"text-align: initial;font-size: 1em\">Quantum Treatment of Vibrations<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Molecular vibrations like <\/span>coupling<span style=\"text-align: initial;font-size: 1em\"> of vibrations between atoms involving bonds to a single central atom are analogous to <\/span>mechanical<span style=\"text-align: initial;font-size: 1em\"> model used in describing simple harmonic oscillator. The natural frequency of an oscillator can then be described mathematically as<\/span><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-163\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-88.png\" alt=\"\" width=\"226\" height=\"66\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-88.png 226w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-88-65x19.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-88-225x66.png 225w\" sizes=\"auto, (max-width: 226px) 100vw, 226px\" \/><\/p>\n<p style=\"text-align: justify\">where k is the force constant that depends on the stiffness the spring, in our case it depends on the strength of the bond, is the reduced mass where two masses m1 &amp; m2 are connected by a spring ( in our case molecular bond) can be written as =m1.m2\/(m1 + m2).<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Let us assume that the transitions in the vibrational energy levels are brought about by absorption of radiation, provided that the energy level of the radiation matches the difference in the energy level E between the vibrational quantum states, plus that the vibration causes fluctuation in the dipole. This difference in energy level can be written as<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-164\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-89.png\" alt=\"\" width=\"301\" height=\"55\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-89.png 301w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-89-300x55.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-89-65x12.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-89-225x41.png 225w\" sizes=\"auto, (max-width: 301px) 100vw, 301px\" \/>\u00a0 \u00a0 where <em>h<\/em> is the Planck Constant.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">The frequency of radiation <em>v<\/em> that can bring change identical to the classical vibrational frequencies of the bond <em>v<\/em><em>m<\/em> can be derived from the equations 5 &amp; 6 and is written as<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-165\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-90.png\" alt=\"\" width=\"312\" height=\"63\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-90.png 312w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-90-300x61.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-90-65x13.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-90-225x45.png 225w\" sizes=\"auto, (max-width: 312px) 100vw, 312px\" \/><\/p>\n<p style=\"text-align: justify\">\u00a0 \u00a0The Wavenumber \u00a0\u00a0\u0305 is reciprocal of wavelength in centimeters and is directly proportional to the frequency and the energy of the radiation.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Thus it may be written as \u00a0\u00a0\u0305<\/span><em style=\"text-align: initial;font-size: 1em\">= kv<\/em><span style=\"text-align: initial;font-size: 1em\">, where <\/span><em style=\"text-align: initial;font-size: 1em\">k<\/em><span style=\"text-align: initial;font-size: 1em\"> is the constant dependent on the medium and wavenumber is equal to the reciprocal of velocity c of the electromagnetic radiation.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Now if we wish to express the equation 7 in wavenumber then it may be written as<\/span><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-166\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91.png\" alt=\"\" width=\"362\" height=\"62\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91.png 362w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91-300x51.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91-65x11.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91-225x39.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-91-350x60.png 350w\" sizes=\"auto, (max-width: 362px) 100vw, 362px\" \/>\u00a0 \u00a0 \u00a0where \u00a0\u00a0\u0305is the wavenumber of an absorption peak in cm-1, <em>k<\/em> is the force constant of the bond in Newtons per meter (N\/m), c is the velocity of light in cm\/s and is the reduced mass.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>IR Instruments<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">There 3 types of infrared instruments available from commercial sources (1) dispersive grating spectrophotometers that are used primarily for qualitative measurements (2) multiplex instruments employing Fourier transform and suited both for qualitative and quantitative measurements (3) non-dispersive photometers that have been developed for quantitative determination of a variety of organic species in the atmosphere by adsorption, emission, and reflectance spectroscopy.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">Most widely used spectrophotometer for laboratory-based investigation is Fourier transform Infrared (FTIR) spectrophotometers because of their speed, reliability and convenience.<\/p>\n<p>&nbsp;<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-167\" src=\"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-92.png\" alt=\"\" width=\"227\" height=\"218\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-92.png 227w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-92-65x62.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-content\/uploads\/sites\/103\/2018\/11\/Untitled-92-225x216.png 225w\" sizes=\"auto, (max-width: 227px) 100vw, 227px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center\"><strong>Figure 4<\/strong>. A single beam FTIR Spectrometer (Courtesy Perkin-Elmer)<\/p>\n<\/div>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">\u00a0 The basic design of Single beam FTIR spectrophotometer is given in figure 4. The majority of FTIR instruments are based on Michelson Interferometer. An interferometer uses patterns formed by waves to measure characteristics of the waves themselves or of the material that reflects, refracts or transmits waves.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Infrared sources (lamps) consist of inert solid that is heated electrically to a temperature between 1500 and 2200 K. A Continuum radiation approximating to that of a blackbody is emitted from the source. Various kind of IR source that <\/span>are<span style=\"text-align: initial;font-size: 1em\"> used in IR instruments are<\/span><\/p>\n<ul>\n<li style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Nernst Glower \u2013 It is composed of rare earth oxides formed into <\/span>cylinder<span style=\"text-align: initial;font-size: 1em\"> of diameter 1 to 2 mm and length upto 20 mm.<\/span><\/li>\n<li style=\"text-align: justify\">Globar Source \u2013 It is a silicon carbide rod, usually about 50 mm in length and 5 mm diameter<\/li>\n<li style=\"text-align: justify\">Incandescent Wire Source \u2013 It is tightly<span style=\"text-align: initial;font-size: 1em\"> wound spiral of Nichrome wire heated to about 1100 K by an electrical current.<\/span><\/li>\n<li style=\"text-align: justify\">Mercury arc \u2013 It consists of quartz<span style=\"text-align: initial;font-size: 1em\"> jacketed tube containing mercury vapor at <\/span>pressure<span style=\"text-align: initial;font-size: 1em\"> greater than one atmosphere.<\/span><\/li>\n<li style=\"text-align: justify\">An ordinary Tungsten filament lamp<\/li>\n<li style=\"text-align: justify\">A Carbon Dioxide Laser Source<\/li>\n<\/ul>\n<div>\n<p>\u00a0 \u00a0 The basic design of Single beam FTIR spectrophotometer is given in figure 4.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\"><strong>Advantages. <\/strong>Optics of FTIR instruments has much larger energy throughput (one or two orders of magnitude) than dispersive instruments. They have limited throughput due to the use of narrow slit widths. It should be noted that interferometer is free the problem of stray radiation because each IR frequency is effectively chopped at different frequency. That means any radiation other than the frequency that is to be radiated onto the sample is removed by interferometer.<\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">FTIR is a powerful instrument that has extensive application in the field of chemistry required for analysis of unknown component in the sample of interest. This instrument is particularly useful for<\/p>\n<ol>\n<li style=\"text-align: justify\">Very high-resolution work involving gaseous mixtures having complex spectra resulting from superposition of vibrational and rotational bands.<\/li>\n<li style=\"text-align: justify\">The study of analytes having high absorbances<\/li>\n<li style=\"text-align: justify\">The study of substances with weak absorption bands ( e.g. compounds absorbed on catalyst surface)<\/li>\n<li style=\"text-align: justify\">Fast scanning investigations involving kinetic studies or detection of chromatographic effluents<\/li>\n<li style=\"text-align: justify\">Collecting IR data from very small samples<\/li>\n<li style=\"text-align: justify\">Obtaining reflection spectra<\/li>\n<li style=\"text-align: justify\">IR emission studies<\/li>\n<\/ol>\n<\/div>\n<p><strong>\u00a0 \u00a0 Summary<\/strong><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">In this module we studied about two most important types of spectrophotometry methods. First, we studied about UV\/Visible Spectrophotometry and we briefly studied about Beer\u2019s law that describes the absorption characteristics of molecules in the path of the UV\/Visible radiation. Second, we studied about Infrared Spectrophotometry where we studied about different types of molecular bending vibrations responsible for absorption of radiation at particular wavenumber or frequency.<\/p>\n<table>\n<tbody>\n<tr>\n<td><strong>you can view video on Spectroscopic Instrumentation<\/strong><\/td>\n<td><a href=\"https:\/\/youtu.be\/6LxV2Seo2Xw\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-120\" src=\"http:\/\/epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/2018\/11\/download.png\" alt=\"\" width=\"36\" height=\"36\" \/><\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>References :-<\/strong><\/p>\n<ol>\n<li style=\"text-align: justify\">Electrical and Electronic Measurements and Instrumentation, <em>Sawhney A. K.<\/em>, Dhanpat Rai &amp; Sons, Reprint 1985<\/li>\n<li style=\"text-align: justify\">Measurements and Instrumentation, <em>Bakshi U.A., Bakshi A.V.,<\/em> Technical Publications, 2009<\/li>\n<li style=\"text-align: justify\">Principles of instrumental analysis, <em>Skoog, Douglas A., F. James Holler, and<\/em> <em>Stanley R. Crouc,. <\/em>Cengage learning, Edition 2017<\/li>\n<li style=\"text-align: justify\">Instrumentation, measurement and analysis. <em>Nakra, B.C. and Chaudhry, K.K.,<\/em> Tata McGraw-Hill Education, 2003.<\/li>\n<li style=\"text-align: justify\">Measurement and instrumentation: theory and application, <em>Morris, A. S., &amp;<\/em> <em>Langari, R<\/em>. , Academic Press, 2012.<\/li>\n<\/ol>\n","protected":false},"author":3,"menu_order":10,"template":"","meta":{"_acf_changed":false,"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["prof-vinay-gupta"],"pb_section_license":""},"chapter-type":[],"contributor":[58],"license":[],"class_list":["post-155","chapter","type-chapter","status-publish","hentry","contributor-prof-vinay-gupta"],"part":3,"_links":{"self":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/155","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/users\/3"}],"version-history":[{"count":6,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/155\/revisions"}],"predecessor-version":[{"id":517,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/155\/revisions\/517"}],"part":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/parts\/3"}],"metadata":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/155\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/media?parent=155"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapter-type?post=155"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/contributor?post=155"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/license?post=155"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}