{"id":40,"date":"2024-04-04T04:31:17","date_gmt":"2024-04-04T01:31:17","guid":{"rendered":"https:\/\/sisu.ut.ee\/heritage-analysis\/31-ir-spectroscopy\/"},"modified":"2024-07-18T14:41:36","modified_gmt":"2024-07-18T11:41:36","slug":"31-ir-spectroscopy","status":"publish","type":"page","link":"https:\/\/sisu.ut.ee\/heritage-analysis\/31-ir-spectroscopy\/","title":{"rendered":"3.1. IR Spectroscopy"},"content":{"rendered":"<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p id=\"yui_3_17_2_1_1522669877965_2414\">In this\u00a0course, a general introduction to FT-IR spectroscopy will be given. Based on the types of materials (paints, varnishes, textiles, conservation materials, etc.), practical tips, examples and short explanation of interpretation of IR spectra of organic and inorganic materials will be presented. Capabilities of ATR-FT-IR spectroscopy and FT-IR microscopy\u00a0(or\u00a0IR microscopy) for analysing real-life samples taken from historical and archaeological objects will be demonstrated.\u00a0<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><strong>1. General aspects of Infrared (IR) spectroscopy<\/strong><\/span><\/h2>\n\n\n\n<p><span lang=\"EN-GB\">IR spectroscopy was first widely used by chemists in the 1950s. The advent of Fourier transform infrared spectroscopy (FT-IR) in the 1980s revolutionised the field with a high signal-to-noise ratio and good resolution. Since then, FT-IR has became commonly used for the analysis of artistic samples<span style=\"font-size: 11.6667px;\">\u00a0<\/span><\/span>[1]<span lang=\"EN-GB\">. Various advantages of Fourier Transform Infrared Spectrometer, as well as different sampling techniques and operation, modes enable investigation of different types of materials and perform high-level qualitative and quantitative analysis. <\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">FT-IR spectroscopy has several advantages as a chemical analysis technique [<\/span>2\u20134]<span lang=\"EN-GB\">:<\/span><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><span lang=\"EN-GB\">It is a universal technique: solids, liquids, gases, powders, polymers are all routinely analysed.\u00a0IR spectroscopy gives useful information about organic and also inorganic compounds.<\/span><\/li>\n\n\n\n<li><span lang=\"EN-GB\">IR spectra are information-rich: the peak positions, intensities, widths, and shapes in a spectrum provide useful information.<\/span><\/li>\n\n\n\n<li><span lang=\"EN-GB\">IR spectroscopy is a fast and relatively inexpensive technique.<\/span><\/li>\n\n\n\n<li><span lang=\"EN-GB\">IR spectra can be obtained with minimal to no sample preparation.<\/span><\/li>\n<\/ul>\n\n\n\n<p><span lang=\"EN-GB\">FT-IR spectroscopy also has some disadvantages [<\/span>4]<span lang=\"EN-GB\">:<\/span><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><span lang=\"EN-GB\">In the IR spectrum of the complex mixtures, the absorption bands usually overlap.<\/span><\/li>\n\n\n\n<li><span lang=\"EN-GB\">Complex mixtures are generally impossible to analyse without reference IR spectra of pure materials.<\/span><\/li>\n\n\n\n<li><span lang=\"EN-GB\">IR spectroscopy is not a very sensitive technique.<\/span><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>1.1. Infrared (IR) spectroscopy: fundamentals<\/em><\/span><\/h2>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span style=\"line-height: normal;\">Infrared (IR) spectroscopy is a vibrational spectroscopy technique which provides information about characteristic molecular vibrations, from which structural information about materials can be elucidated. IR spectroscopy is a powerful approach for analysing various organic and inorganic materials because, with the exception of some homonuclear molecules (O<sub>2<\/sub>, N<sub>2<\/sub>, Cl<sub>2<\/sub>), most materials absorb infrared radiation. Most of the cultural heritage materials (paints, varnishes, fibres, clays, polymers, synthetic glues, etc.) can be analysed with IR spectroscopy.<\/span><\/p>\n\n\n\n<p><span style=\"line-height: normal;\">The infrared (IR) spectral range is in the electromagnetic spectrum between the visible and microwave regions <\/span>[5]<span style=\"line-height: normal;\"> and extends from 14000 cm<sup>\u20131<\/sup> to 10 cm<sup>\u20131<\/sup>. It is divided into three regions: the <b>near-infrared<\/b> [14000\u20134000 cm<sup>\u20131<\/sup> (0.7\u20132.5 \u03bcm)], <b>mid-infrared<\/b> [4000\u2013400 cm<sup>\u20131<\/sup> (2.5\u201325 \u03bcm)] and <b>far-infrared<\/b> [about 400\u201310 cm<sup>\u20131<\/sup> (25\u20131000 \u03bcm)] [2,6].\u00a0The most frequently used region for chemical analysis, especially for the qualitative analysis,\u00a0is the mid-infrared region. The far infrared region is useful for molecules containing heavy atoms such as inorganic and metal-organic compounds. Also the lattice vibrations in crystals are found in the far infrared region [<\/span>4].<\/p>\n\n\n\n<p><span style=\"line-height: normal;\">Infrared spectroscopy is a vibrational spectroscopy: infrared radiation lies in the same frequency range as the vibrational frequencies of molecules. All molecules have a set of specific frequencies at which they vibrate corresponding to discrete energy levels (vibrational modes). There are three types of vibrational modes in molecules: <b>stretching<\/b>, <b>bending<\/b> and <b>torsional<\/b> modes <\/span>[5]<span style=\"line-height: normal;\">. In order for a vibrational mode to be active in the infrared region, the vibration must cause oscillation of\u00a0the permanent dipole moment of the molecule. The alternating electrical field (oscillating electromagnetic field) of the radiation interacts with fluctuations in the dipole moment of the molecule. If the frequency of the radiation matches the vibrational frequency of the molecule then radiation can be absorbed, causing a change in the amplitude of molecular vibration (in quantum mechanical terms: molecule transits from its vibrational ground state to an excited state). <\/span>[2,7,8]<span style=\"line-height: normal;\"> The IR spectrum provides energy\/frequency information about the IR radiation absorbed or transmitted, which is related to its molecular structure\u00a0and can be highly characteristic\u00a0<\/span>[7]<span style=\"line-height: normal;\">. <\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">In chemical analysis infrared spectroscopy is almost exclusively used as absorption spectroscopy. When infrared (IR) radiation is passed through a sample, <\/span><span lang=\"EN-GB\">the frequencies corresponding to the active vibrational modes of the molecules of the sample are, to some extent, absorbed, while other frequencies are transmitted through the sample without being absorbed by the sample<\/span>\u00a0[5,8]<span lang=\"EN-GB\">.<\/span> <span lang=\"EN-GB\">The absorption intensity depends on the probability that the infrared photon energy is transferred to the molecule, which in turn depends on molecular structure: the intensity of the absorption band is proportional to the square of the rate of dipole moment change during the vibration. [<\/span>4,6,7]\u00a0In simplified terms, it can be said that the higher is the polarity (i.e. dipole moment) of a bond and the larger is the number of such bonds in a molecule, the more intense is its stretching vibration signal observed in the IR spectrum. Examples:<\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p>\n<\/div>\n\n\n\n<ul class=\"wp-block-list\">\n<li>C=O bond is highly polar and its stretching vibrations are often among the strongest signals in the IR spectrum.<\/li>\n\n\n\n<li>C-H bonds have low to medium polarity, but because in typical organic molecules, there are lots of C-H bonds, the signals corresponding to their stretching vibrations are often among the strongest in the IR spectrum.<\/li>\n\n\n\n<li><p>C=C and C-C bonds have low polarity and their bonds are mostly either very weak or undetectable in the IR spectrum.<\/p><\/li>\n<\/ul>\n\n\n\n<p><span lang=\"EN-GB\">In complex samples, radiation of a large number of\u00a0various wavelengths can be absorbed depending on the chemical composition of the sample. The instrument output is an <b>IR spectrum<\/b> (see <b>Fig 1.<\/b>) in which the intensity of IR radiation absorbed or transmitted is plotted on the y-axis against frequency or wavenumber (or wavelength) of the radiation on the x-axis [<\/span>7]<span lang=\"EN-GB\">. In infrared spectroscopy, units called <strong>wavenumbers<\/strong> are normally used to denote different types of radiation. The wavenumber, usually expressed in cm<sup>\u20131<\/sup>,\u00a0is the number of waves that fit into 1 cm and is the reciprocal of wavelength in cm. [<\/span>2,7]<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-large is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"791\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-1024x791.png\" alt=\"Fig. 1. Transmittance and absorbance spectra of Rabbitskin glue\" class=\"wp-image-122\" style=\"width:980px;height:auto\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-1024x791.png 1024w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-300x232.png 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-768x593.png 768w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-1536x1187.png 1536w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-2048x1583.png 2048w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/transmittance_absorbance_rabbitskin_glue-1920x1484.png 1920w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\"><figcaption class=\"wp-element-caption\">Fig. 1. Transmittance and absorbance spectra of Rabbitskin glue<\/figcaption><\/figure>\n\n\n\n<p>\u00a0In the following video, the fundamentals of IR spectroscopy are shortly explained and examples are given.<\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>1.2. Infrared (IR) spectroscopy: basics of instrumentation<\/em><\/span><\/h2>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span style=\"line-height: normal;\">Two major designs of IR spectrometers exist: dispersive spectrometers and Fourier transform spectrometers<\/span> [9]<span style=\"line-height: normal;\">. Nowadays, the prevalent type is the <b>Fourier Transform Infrared Spectrometer<\/b> (FT-IR) and we limit our discussion to this design. <\/span><\/p>\n\n\n\n<p><span style=\"line-height: normal;\">The main components of FT-IR spectrometer are presented on the following scheme:<\/span><\/p>\n<\/div>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1164\" height=\"164\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ftir_skeem_01.jpg\" alt=\"FT-IR scheme\" class=\"wp-image-125\" style=\"width:1100px;height:auto\" title=\"ftir_skeem_01.jpg\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ftir_skeem_01.jpg 1164w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ftir_skeem_01-300x42.jpg 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ftir_skeem_01-1024x144.jpg 1024w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ftir_skeem_01-768x108.jpg 768w\" sizes=\"auto, (max-width: 1164px) 100vw, 1164px\"><\/figure>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span style=\"line-height: normal;\"><i>I<\/i><sub>0<\/sub> \u2013 Intensity of radiation entering a sample <\/span><\/p>\n\n\n\n<p><span style=\"line-height: normal;\"><i>I<\/i> \u2013 Intensity of radiation transmitted by the sample<\/span><\/p>\n<\/div>\n\n\n\n<p>\u00a0<\/p>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span style=\"line-height: normal;\">The heart of an FT-IR instrument is a two-beam Michelson Interferometer. In the interferometer, the IR beam is split in two using a half-transparent window known as the beamsplitter. The two beams travel different distances (and the difference is gradually changed). The beams are thereafter merged into one, and because of interference, it will be a <strong>pulsating<\/strong> beam. And very importantly, the pulsation pattern will mimic the pattern of frequencies in the IR beam reaching the detector. The interferometer is controlled by the frequency of a visible light laser. In general terms, FT-IR is a method of obtaining infrared spectra by first collecting an <b>interferogram (<\/b><b><i>time-domain<\/i><\/b><b><i> spectrum<\/i><\/b><b>)<\/b> of the sample signal using Michelson Interferometer. Then a mathematical transformation, called the Fourier Transform (FT), is applied to the interferogram to obtain the <b><i>frequency domain <\/i><\/b><b><i>spectrum<\/i><\/b>. This spectrum is then compared to a reference spectrum measured without the sample (called background) to obtain the absorbance or transmittance spectrum, which are the spectrum types, commonly used for chemical analysis (Fig. 1).\u00a0<\/span>[2,4,6,7]<\/p>\n\n\n\n<p><span style=\"line-height: normal;\">In the FT-IR spectrometer,\u00a0radiation containing\u00a0all thr IR spectrum frequencies emitted by the <strong>IR source<\/strong> (thermal sources are usually used, for example, Globar<sup>\u00ae<\/sup>) reach the<strong> detector<\/strong> (e.g. DTGS or MCT) simultaneously and are converted to the IR spectrum. This results in considerable time saving (the Fellgett advantage) and much higher signal-to-noise ratio advantage (Jacquinot\u2019 advantage) over dispersive instruments<\/span> [6]<span style=\"line-height: normal;\">. Additionally, the wavenumber scale of an FT-IR instrument is reliably fixed by the wavelength of the controlling <strong>laser<\/strong> (Connes\u2019 advantage). This enables performing multiple scans and averaging the spectra to further improve the signal-to-noise ratio. <\/span><\/p>\n<\/div>\n\n\n\n<p><\/p>\n\n\n\n<p>More information about the FT-IR spectrometer and the main components is given in the following video.<\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\">2. Sampling techniques used with FT-IR spectroscopy<\/span><\/h2>\n\n\n\n<p><\/p>\n\n\n\n<p><span lang=\"EN-GB\">FT-IR spectroscopy can be used with a number of sampling techniques and modes of operation. The most widespread of them are <\/span><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><b style=\"font-size: revert; text-align: var(--bs-body-text-align);\">Transmission spectroscopy<\/b><span style=\"font-size: revert; font-weight: var(--bs-body-font-weight); text-align: var(--bs-body-text-align);\"> (samples are solutions of KBr pellets)<\/span> <\/li>\n\n\n\n<li><strong>Attenuated Total Reflection<\/strong>(ATR, samples without any treatment can be used)<\/li>\n\n\n\n<li><strong>Specular reflectance<\/strong>\u00a0and\u00a0<strong>diffuse reflectance spectroscopy (DRIFTS)<\/strong><\/li>\n<\/ul>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><\/p>\n\n\n\n<p><span lang=\"EN-GB\">Also <\/span><b><span lang=\"EN-GB\">gas chromatography\/FT-IR spectroscopy<\/span><\/b><b><span lang=\"EN-GB\"> (GC\/FT-IR)<\/span><\/b><span lang=\"EN-GB\">, <b>thermogravimetry\/<\/b><\/span><b><span lang=\"EN-GB\">FT-IR spectroscopy<\/span><\/b><b><span lang=\"EN-GB\"> (TG\/FT-IR)<\/span><\/b><span lang=\"EN-GB\"> have been used. <\/span><span lang=\"EN-GB\">In recent years <b>FT-IR microspectroscopy<\/b> (also called FT-IR microscopy) has gained popularity due to the opportunity to analyse very small samples by using different sampling techniques (ATR, reflectance, transmission), including the mapping and imaging approaches. The greatest advances with FT-IR microspectroscopy have been made by using <b>synchrotron (SR)<\/b> radiation to enhance signal-to-noise ratio and spatial resolution of <b>FT-IR (SR-\u00b5FTIR)<\/b>.<\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">Each of these techniques has its advantages and disadvantages. The technique selected depends on such factors as the information required, the nature of the material being analysed, also the size of the sample. Below we look more closely at ATR and reflectance FT-IR spectroscopy, as well as at FT-IR microspectroscopy.<\/span><\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>2.1. General aspects of ATR-FT-IR spectroscopy<\/em><\/span><\/h2>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span lang=\"EN-GB\">Attenuated total reflection (ATR) <\/span><span lang=\"EN-GB\">has been developed since 1959 <\/span><span lang=\"EN-GB\"> and is now probably the most common sampling technique in FT-IR spectroscopy<\/span>\u00a0[6].<span lang=\"EN-GB\">\u00a0ATR enables qualitative and quantitative analysis of samples with little or no sample preparation. In principle, it is a non-destructive technique. ATR is easily miniaturized so that high-quality spectra can be scanned of samples with a diameter far less than a millimetre.<\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">I<\/span><span lang=\"EN-GB\">n this technique, the sample is placed in contact with the internal reflection element (IRE), also called ATR crystal,<\/span><span lang=\"EN-GB\"> and IR radiation from the source is directed through the IRE to its surface that is in contact with the sample at a certain angle (<\/span><i><span lang=\"EN-GB\">\u03b8<\/span><\/i><span lang=\"EN-GB\">) so that<\/span><span lang=\"EN-GB\"> the light is totally reflected (see <b>Fig. 2<\/b>) [3].<\/span><span lang=\"EN-GB\">\u00a0In order to observe total internal reflection, the angle of the incident radiation <i>\u03b8<\/i> must exceed the <i>critical angle<\/i> <i>\u03b8<sub>c<\/sub>. <\/i>This angle is a function of the refractive indices of both the sample and the ATR crystal. The critical angle is defined as [<\/span>4]<span lang=\"EN-GB\">:<\/span><\/p>\n<\/div>\n\n\n\n<figure class=\"wp-block-image aligncenter is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"484\" height=\"286\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/critical_angle_.jpg\" alt=\"Critica angle\" class=\"wp-image-126\" style=\"width:203px;height:auto\" title=\"critical_angle_.jpg\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/critical_angle_.jpg 484w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/critical_angle_-300x177.jpg 300w\" sizes=\"auto, (max-width: 484px) 100vw, 484px\"><\/figure>\n\n\n\n<p class=\"has-text-align-left\"><span lang=\"EN-GB\">where, <i>n<sub>1<\/sub><\/i> is the refractive index of the ATR crystal and <i>n<sub>2<\/sub><\/i> is the refractive index of the sample. <\/span><\/p>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span lang=\"EN-GB\">Importantly, the refractive index of the crystal must be higher than that of the sample in order for the total reflection can occur. Therefore, h<\/span><span lang=\"EN-GB\">igh refractive index materials are chosen for the ATR crystal<\/span><span lang=\"EN-GB\">. The hardness of the material is also an important characteristic because in order to obtain good contact with the sample, the sample has to be strongly pressed against the crystal.<\/span><\/p>\n\n\n\n<p><span style=\"line-height: normal;\">The following ATR crystal materials are most commonly used: <b>diamond<\/b> (very hard, insoluble, inert; wavenumber range: 40 000\u2013200 cm<sup>-1<\/sup>; <i>n<\/i><sub>1<\/sub>=2.4), <b>zinc selenide<\/b> (a hard and brittle crystal, water-insoluble, slightly soluble in acids; wavenumber range: 10 000\u2013550 cm<sup>-1<\/sup>; <i>n<\/i><sub>1<\/sub>=2.4), <b>germanium<\/b> (a hard and brittle crystal, chemically inert; wavenumber range: 20 000\u2013600 cm<sup>-1<\/sup>; <i>n<\/i><sub>1<\/sub>=4.0).\u00a0<\/span>[3-5]<\/p>\n\n\n\n<p><span lang=\"EN-GB\">Upon internal reflection, a part of the IR beam (so-called <i>evanescent wave<\/i>) penetrates into the sample to a depth of a few micrometers (<em>d<\/em><sub>p<\/sub>) and is partially (depending on the composition of the sample) absorbed by the sample. The result is a selective attenuation of the radiation at those wavelengths at which the sample absorbs [<\/span>4,10,11]<span lang=\"EN-GB\">. So generally, due the interaction of the sample with the penetrating beam, the beam loses energy at those wavelengths where the sample absorbs\u00a0infrared radiation\u00a0and thus the infrared spectrum\u00a0of the sample\u00a0is obtained.<\/span><\/p>\n<\/div>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1037\" height=\"575\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/atr.jpg\" alt=\"ATR theory\" class=\"wp-image-127\" style=\"width:781px;height:auto\" title=\"Fig. 2. Schematic representation of total internal reflection.\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/atr.jpg 1037w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/atr-300x166.jpg 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/atr-1024x568.jpg 1024w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/atr-768x426.jpg 768w\" sizes=\"auto, (max-width: 1037px) 100vw, 1037px\"><figcaption class=\"wp-element-caption\">Fig. 2. Schematic representation of total internal reflection.<\/figcaption><\/figure>\n\n\n\n<p class=\"has-text-align-center\"><\/p>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span style=\"line-height: normal;\">Only the surface layer of the sample is analysed since the beam penetrates just a few micrometers into the sample <\/span>[5]<span style=\"line-height: normal;\">. Due to the low depth of penetration, there must be good contact between the sample and the ATR crystal surface. <\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">The depth to which the evanescent wave (or IR radiation) extends into the sample is called the depth of penetration (<i>d<\/i><sub>p<\/sub>). The depth of penetration (of the evanescent wave) is the distance from the crystal-sample interface where the intensity of the evanescent wave decays to 1\/e of its original value. It can be estimated by the following eq [<\/span>4,12,13]<span lang=\"EN-GB\">:<\/span><\/p>\n<\/div>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1045\" height=\"320\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/depth_of_penetration_01.jpg\" alt=\"depth of penetration\" class=\"wp-image-129\" style=\"width:490px;height:auto\" title=\"depth_of_penetration_01.jpg\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/depth_of_penetration_01.jpg 1045w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/depth_of_penetration_01-300x92.jpg 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/depth_of_penetration_01-1024x314.jpg 1024w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/depth_of_penetration_01-768x235.jpg 768w\" sizes=\"auto, (max-width: 1045px) 100vw, 1045px\"><\/figure>\n\n\n\n<p class=\"has-text-align-center\"><\/p>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span style=\"color: black;\"><span style=\"font-style: italic;\">d<\/span><\/span><span style=\"color: black;\"><span style=\"vertical-align: sub;\">p<\/span><\/span><span style=\"color: black;\"> \u2013 depth of penetration<\/span><\/p>\n\n\n\n<p><span style=\"color: black;\"><span style=\"font-style: italic;\">n<\/span><\/span><span style=\"color: black;\"><span style=\"vertical-align: sub;\">1<\/span><\/span><span style=\"color: black;\"> \u2013 the refractive index of the ATR <\/span><span style=\"color: black;\">crystal<\/span><\/p>\n\n\n\n<p><span style=\"color: black;\"><span style=\"font-style: italic;\">n<\/span><\/span><span style=\"color: black;\"><span style=\"vertical-align: sub;\">2<\/span><\/span><span style=\"color: black;\"> \u2013 the refractive index of the <\/span><span style=\"color: black;\">sample<\/span><\/p>\n\n\n\n<p><span style=\"color: black;\"><i>\u03bb\u00a0<\/i>\u2013 the wavelength of the IR radiation <\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\"><i>\u03b8<\/i><\/span> <span style=\"color: black;\">\u2013 <\/span><span style=\"color: black;\">angle of incidence of the IR radiation<\/span><\/p>\n<\/div>\n\n\n\n<p><\/p>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span lang=\"EN-GB\">Changes in the angle of incidence of the infrared radiation have an effect on the depth of penetration and thus the ATR spectrum of the sample. In most devices it is not possible to vary the angle continuously, usually 30\u00b0, 45\u00b0 and 60\u00b0 are employed [<\/span>14]<span lang=\"EN-GB\">. The angle of incidence must be chosen to exceed the critical angle<\/span> <span lang=\"EN-GB\">in order to have internal reflection and produce an ATR spectrum.<\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">ATR-IR and transmission\u00a0spectra are similar, but not identical [<\/span>11,13]<span lang=\"EN-GB\">. The depth of penetration (and thus the effective path length) is dependent on the wavelength and refractive index of the sample (which in turn depends on wavelength, see below). The depth of penetration is proportional to wavelength, and therefore, an increase in depth of penetration is observed at higher wavelengths (lower wavenumbers). This leads to the increase of the intensity of the bands at low wavenumbers relative to high wavenumbers and is one of the causes of differences between the ATR-IR spectra and transmission IR spectra. [<\/span>4,5]<\/p>\n\n\n\n<p><span lang=\"EN-GB\">The refractive index also affects the depth of penetration of the evanescent wave into the sample. By increasing the refractive index of the ATR crystal, the depth of penetration will decrease. This will decrease the effective pathlength and therefore decrease the absorbance of the spectrum [15].<\/span><span lang=\"EN-GB\">\u00a0The refractive index of a material is also a function of wavelength. In the IR spectral region the change of refractive index with wavelength is not monotonous. At certain wavelengths, large nonlinearities are observed. [<\/span>4,16]<span lang=\"EN-GB\"> Absorption bands that occur near such nonlinearities can be significantly different from those observed in the transmission mode. This is another cause of differences between IR spectra obtained using transmission and ATR modes.<\/span><\/p>\n<\/div>\n\n\n\n<p><\/p>\n\n\n\n<p>In the following video, main aspects of ATR-FT-IR spectroscopy are shortly explained and examples are given.<\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>Analysis with\u00a0ATR-FT-IR spectroscopy<\/em><\/span><\/h2>\n\n\n\n<p>In the following video, Dr Signe Vahur demonstrates how to perform\u00a0analysis of different materials (paint sample, textile piece, paper sheet froma book, pigment powder and liquid varnish) using ATR-FT-IR spectrometer\u00a0 in the Mid-IR and Far-IR region.<\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>2.2. General aspects of specular reflectance and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)<\/em><\/span><\/h2>\n\n\n\n<p><span lang=\"EN-GB\">The reflectance techniques used in FT-IR can be broadly divided into ATR, Diffuse and Specular reflectance. The ATR technique was discussed above. Below, diffuse and specular reflectance techniques are discussed. In the case of both <b>diffuse<\/b> and <b>specular reflectance<\/b> techniques, the radiation interacts directly with the sample surface. The sample type determines how the IR radiation is reflected from the sample surface. It can be reflected similarly as from a mirror,\u00a0which is known as <strong>specular reflection<\/strong>, or scattered in different directions, known as <strong>diffuse reflection<\/strong> (see <b>Fig. 3<\/b>). <\/span><\/p>\n\n\n\n<p class=\"has-text-align-center\"><\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full is-resized\"><img loading=\"lazy\" decoding=\"async\" width=\"1063\" height=\"354\" src=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/diffuse_specular_reflection.jpg\" alt=\"Fig.3.\" class=\"wp-image-130\" style=\"width:763px;height:auto\" srcset=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/diffuse_specular_reflection.jpg 1063w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/diffuse_specular_reflection-300x100.jpg 300w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/diffuse_specular_reflection-1024x341.jpg 1024w, https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/diffuse_specular_reflection-768x256.jpg 768w\" sizes=\"auto, (max-width: 1063px) 100vw, 1063px\"><figcaption class=\"wp-element-caption\">Fig. 3. Comparison of diffuse and specular reflection<\/figcaption><\/figure>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><b><span lang=\"EN-GB\">Diffuse reflectance<\/span><\/b><span lang=\"EN-GB\"> is commonly known as <b>DRIFTS<\/b> (Diffuse reflectance infrared Fourier transform spectroscopy). As shown in <b>Fig. 3<\/b> <b>diffuse reflectance<\/b> is produced by rough surfaces. The radiation is diffusely reflected, i.e. it can go in many directions from the surface. Before being reflected, the IR radiation penetrates into the sample to a depth (typically few micrometers), which is dependent on the reflective and absorptive properties of the analysed sample. The sample partially absorbs the radiation (depending on the molecular structure). The partially weakened radiation is then diffusely re-emitted from the sample and collected on a mirror that focuses energy coming from the sample onto the detector.<\/span><\/p>\n\n\n\n<p>DRIFTS is typically used for measuring IR spectra from uneven\u00a0(rough)\u00a0surfaces or from powders. In the latter case, a small amount of sample can be added into a special sample cup on a sliding metal strip. When using powdery solids, strongly absorbing sample might require dilution in a non-absorbing IR-transparent matrix (for example KBr).\u00a0Preparation of samples is not always necessary:\u00a0from powders,\u00a0soils, textile fibres, printed papers, etc. spectra can be measured also directly [17]. Spectra recorded in DRIFTS mode are somewhat similar to spectra acquired with transmission mode, however they differ from transmission spectra by the intensity ratios of the peaks.<\/p>\n<\/div>\n<\/div>\n\n\n\n<p><\/p>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><b><span lang=\"EN-GB\">Specular reflectance<\/span><\/b><span lang=\"EN-GB\"> is defined as light reflected from a smooth surface (such as a mirror, coated metal surface, etc.) at a definite angle (see <b>Fig. 3.<\/b>)<\/span> <span lang=\"EN-GB\">Specular reflectance occurs only when the reflected angle of radiation equals the angle of incidence. The amount of reflected light depends upon the angle of incidence of the external light radiation source, the refractive index, surface roughness and absorption properties of the sample [<\/span>18]<span lang=\"EN-GB\">.<\/span> <span lang=\"EN-GB\">Specular reflectance is typically used to measure coating thicknesses etc. on smooth reflective surfaces.<\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">For the measurement of specular reflection, the sample is usually placed on a highly reflective plate, e.g. polished gold or mirror. For obtaining good reflectance spectrum, it is important that the surface is as smooth as possible and the radiation beam is as focused as possible on the selected analysis area of the sample. Also, when recording spectra in reflection mode there are significant losses of energy during the measurement and the best possible detector sensitivity is needed so that the obtained spectra are not noisy. <\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">Specular reflectance spectra are different from the spectra acquired with transmission or ATR mode. Specular reflectance spectra can be converted to roughly match spectra obtained in the transmission mode using the Kramers-Kronig transformation. It is a mathematical transformation that can be applied to any specular reflectance spectrum to eliminate the effect of variations in the refractive index of the sample and to obtain more interpretable spectra. However, we recommend\u00a0that for the interpretation, it is reasonable to compare the reflectance spectrum of the sample to a reference spectrum of the pure material also obtained in the reflectance mode. <\/span><\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>2.3.\u00a0General aspects of FT-IR microspectroscopy<\/em><\/span><\/h2>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><span lang=\"EN-GB\">FT-IR microspectroscopy (also called FT-IR microscopy) enables to analyse very small samples with very high locality \u2013 with spot sizes down to few micrometers in diameter. An important additional possibility of this technique is mapping function that allows doing mapping in selected areas of the sample on the basis of their spectral features.<\/span><\/p>\n\n\n\n<p><span lang=\"EN-GB\">In the FT-IR microspectroscopy systems, an optical microscope can be coupled to an FT-IR spectrometer or these can be together in the same equipment. Infrared microscopes use reflecting optics such as Cassegrain objectives (these are used in conventional optical microscopes) [<\/span>17].<span lang=\"EN-GB\"><sup>\u00a0<\/sup>With FT-IR microspectroscopy different sampling techniques like <b>transmission<\/b>, <b>reflectance<\/b> and <b>ATR<\/b> modes can be used. <\/span><\/p>\n<\/div>\n\n\n\n<p><\/p>\n\n\n\n<p><span lang=\"EN-GB\">In the following video the main aspects of FT-IR microspectroscopy are discussed and transmission, reflectance and ATR modes and their capabilities are compared.<\/span><\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>Analysis with FT-IR microspectroscopy<\/em><\/span><\/h2>\n\n\n\n<p>In the following video, Dr Signe Vahur demonstrates how to analyse samples (cross-section of the paint sample, paper sheet with ink, painted wallpaper) using FT-IR microspectrometer in the ATR and reflectance modes.<\/p>\n\n\n\n<p><\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\">3. Interpretation of IR spectra of different materials<\/span><\/h2>\n\n\n\n<p><\/p>\n\n\n\n<p>Identification of the composition of the studied material is often based on the comparison of its IR spectrum with a spectral library of reference materials. Many papers [13,16,19-23] and books [2,4,5,8,24-26] have been published from where IR spectra are available.\u00a0<br>Our cultural heritage work group has also created an online database [19] with more than 150 cultural heritage-, art- and conservation-related ATR-FT-IR spectra measured in the extended region of 4000-80 cm<sup>\u20131<\/sup> (mid-IR and far-IR region). The database is freely available here: <a title=\"\" data-url=\"https:\/\/spectra.chem.ut.ee\/\" href=\"https:\/\/spectra.chem.ut.ee\/\" target=\"_blank\" rel=\"noopener\">https:\/\/spectra.chem.ut.ee\/<\/a>. This spectral collection has over 200 daily visits on working days. Also, another highly valuable online database has been made available by the Infrared &amp; Raman Users Group (IRUG) \u2013 <a title=\"\" data-url=\"http:\/\/irug.org\/\" href=\"http:\/\/irug.org\/\" target=\"_blank\" rel=\"noopener\">http:\/\/irug.org\/<\/a> \u2013 from where different IR (and also Raman) spectra of cultural heritage materials can be obtained free of charge.<\/p>\n\n\n\n<p><\/p>\n\n\n<p><\/p><div class=\"accordion mb-3\">\n        <div class=\"accordion-item accordion-item--white\">\n        <h2 class=\"accordion-header\" id=\"accordion-69d96ce28555b-heading\">\n            <button class=\"accordion-button collapsed\" type=\"button\" data-bs-toggle=\"collapse\" data-bs-target=\"#accordion-69d96ce28555b-collapse\" aria-expanded=\"true\" aria-controls=\"accordion-69d96ce28555b-collapse\"><span style=\"font-size: 16px;\"><strong>References <\/strong>(click here)<\/span><\/button>\n        <\/h2>\n        <div id=\"accordion-69d96ce28555b-collapse\" class=\"accordion-collapse collapse\" aria-labelledby=\"accordion-69d96ce28555b-heading\">\n            <div class=\"accordion-body\">\n<ol>\n<li>Perez-Alonso, M.; Castro, K.; Madariaga, J. Vibrational Spectroscopic Techniques for the Analysis of Artefacts with Historical, Artistic and Archaeological Value. <em>Curr. Anal. Chem.<\/em> <strong>2006<\/strong>, <em>2<\/em> (1), 89\u2013100. https:\/\/doi.org\/10.2174\/157341106775197385.<\/li>\n<li>Smith, B. C. <em>Infrared Spectral Interpretation: A Systematic Approach<\/em>; CRC Press: Boca Raton etc., 1999.<\/li>\n<li>Willard, H. H.; Merritt, Jr., L. L.; Dean, J. A.; Settle, Jr., F. A. <em>Instrumental Methods of Analysis<\/em>; Wadsworth Publishing Company: Belmont, 1988.<\/li>\n<li>Vahur, S. <em>Expanding the Possibilities of ATR-FT-IR Spectroscopy in Determination of Inorganic Pigments<\/em>. PhD thesis, University of Tartu, Tartu, Estonia, 2010.<\/li>\n<li>Derrick, M. R.; Stulik, D.; Landry, J. M. <em>Infrared Spectroscopy in Conservation Science; Scientific tools for conservation<\/em>; Getty Conservation Institute: Los Angeles, 1999.<\/li>\n<li><em>Ullmann\u2019s Encyclopedia of Industrial Chemistry. Vol. B 5, Analytical Methods 1, 5.<\/em>, completely rev. ed.; G\u00fcnzler, H., Ed.; VCH Verlagsgesellschaft: Weinheim, 1994.<\/li>\n<li><em>Forensic Examination of Glass and Paint: Analysis and Interpretation<\/em>; Caddy, B., Ed.; Taylor &amp; Francis: London, 2001.<\/li>\n<li>Kemp, W. <em>Organic Spectroscopy<\/em>, 3rd ed.; Macmillan Press LTD: Basingstoke\u202f; London, 1992.<\/li>\n<li>Skoog, D. A.; West, D. M.; Holler, F. J.; Crouch, S. R. <em>Skoog and West\u2019s Fundamentals of Analytical Chemistry<\/em>, 9th edition, Cengage technology edition.; Cengage Learning: Hampshire, 2014.<\/li>\n<li>van der Weerd, J. <em>Microspectroscopic Analysis of Traditional Oil Paint<\/em>. Ph.D. thesis, University of Amsterdam, AMOLF, Amsterdam, 2002.<\/li>\n<li>Harvey, D. <em>Modern Analytical Chemistry<\/em>; McGraw-Hill: Boston, 2000.<\/li>\n<li>Averett, L. A.; Griffiths, P. R.; Nishikida, K. Effective Path Length in Attenuated Total Reflection Spectroscopy. <em>Anal. Chem.<\/em> <strong>2008<\/strong>, <em>80<\/em> (8), 3045\u20133049. https:\/\/doi.org\/10.1021\/ac7025892.<\/li>\n<li>Vahur, S.; Knuutinen, U.; Leito, I. ATR-FT-IR Spectroscopy in the Region of 500\u2013230 cm<sup>\u22121<\/sup> for Identification of Inorganic Red Pigments. <em>Spectrochim. Acta. A. Mol. Biomol. Spectrosc.<\/em> <strong>2009<\/strong>, <em>73<\/em> (4), 764\u2013771. https:\/\/doi.org\/10.1016\/j.saa.2009.03.027.<\/li>\n<li><em>Surface Analysis Methods in Materials Science<\/em>; O\u2019Connor, D. J., Sexton, B. A., Smart, R. St. C., Eds.; Springer Science &amp; Business Media, 2003.<\/li>\n<li><em>Introduction to Attenuated Total Reflection (ATR) Spectroscopy<\/em>; Thermo Fisher Scientific, 1998.<\/li>\n<li>Kendix, E. L.; Prati, S.; Joseph, E.; Sciutto, G.; Mazzeo, R. ATR and Transmission Analysis of Pigments by Means of Far Infrared Spectroscopy. <em>Anal. Bioanal. Chem.<\/em> <strong>2009<\/strong>, <em>394<\/em> (4), 1023\u20131032. https:\/\/doi.org\/10.1007\/s00216-009-2691-2.<\/li>\n<li><em>Handbook of Analytical Techniques<\/em>; G\u00fcnzler, H., Williams, A., Eds.; Wiley-VCH: Weinheim\u202f; New York, 2001.<\/li>\n<li>Stuart, B. <em>Infrared Spectroscopy: Fundamentals and Applications; Analytical techniques in the sciences<\/em>; J. Wiley: Chichester, West Sussex, England\u202f; Hoboken, NJ, 2004.<\/li>\n<li>Vahur, S.; Teearu, A.; Peets, P.; Joosu, L.; Leito, I. ATR-FT-IR Spectral Collection of Conservation Materials in the Extended Region of 4000-80 cm<sup>\u20131<\/sup>. <em>Anal. Bioanal. Chem.<\/em> <strong>2016<\/strong>, <em>408<\/em> (13), 3373\u20133379.<\/li>\n<li>Castro, K.; P\u00e9rez, M.; Rodr\u00edguez-Laso, M. D.; Madariaga, J. M. Peer Reviewed: FTIR Spectra Database of Inorganic Art Materials. <em>Anal. Chem.<\/em> <strong>2003<\/strong>, <em>75<\/em> (9), 214 A-221 A. https:\/\/doi.org\/10.1021\/ac031320e.<\/li>\n<li>Peets, P.; Leito, I.; Pelt, J.; Vahur, S. Identification and classification of textile fibres using ATR-FT-IR spectroscopy with chemometric methods. <em>Spectrochim. Acta. A. Mol. Biomol. Spectrosc.<\/em> <strong>2017<\/strong>, <em>173<\/em>, 175\u2212181.<\/li>\n<li>Peets, P.; Kaupmees, K.; Vahur, S.; Leito, I. Reflectance FT-IR spectroscopy as a viable option for textile fiber identification.<em> Herit. Sci.<\/em> <strong>2019<\/strong>,<em> 7<\/em> (1), 93.<\/li>\n<li>Madejov\u00e1 J, Komadel P. Baseline Studies of the Clay Minerals Society Source Clays: Infrared Methods. <em>Clays and Clay Minerals.<\/em> <strong>2001<\/strong>;<em>49<\/em>:410\u201332.<\/li>\n<li>Smith, B. C. <em>Fundamentals of Fourier Transform Infrared Spectroscopy<\/em>, 2nd ed.; CRC Press: Boca Raton, FL, 2011.<\/li>\n<li><em>Modern Analytical Methods in Art and Archeology<\/em>; Ciliberto, E., Spoto, G., Eds.; Wiley: New York, 2000.<\/li>\n<li>Larkin, P. J.<em> Infrared and Raman Spectroscopy: Principles and Spectral Interpretation<\/em>; Elsevier: Amsterdam [etc.], 2011.<\/li>\n<\/ol>\n<p><\/p><\/div>\n        <\/div>\n        <\/div>\n    <\/div>\n\n\n\n<p>The slides used in the videos can be downloaded from\u00a0here:<\/p>\n\n\n\n<div class=\"wp-block-group attached-files-group is-layout-constrained wp-block-group-is-layout-constrained\">\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-d0691eb1-c502-4567-b1e5-5a3e3cd409f8\" href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ir_fundamentals.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">IR_fundamentals.pdf<\/a><\/div>\n\n\n\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-d4d46cdc-3990-4796-9340-df2260d43439\" href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ir_basics_of_instrumentation.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">IR_basics_of_instrumentation.pdf<\/a><\/div>\n\n\n\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-6aa60653-bc68-44c0-998a-37dc5edbfa90\" href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/atr-ft-ir_theory.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">ATR-FT-IR_theory.pdf<\/a><\/div>\n\n\n\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-7121efa2-caf4-4ed6-868e-90fdfc2aeed5\" href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/ir_microspectroscopy.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">IR_microspectroscopy.pdf<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>In this\u00a0course, a general introduction to FT-IR spectroscopy will be given. Based on the types of materials (paints, varnishes, textiles, conservation materials, etc.), practical tips, examples and short explanation of interpretation of IR spectra of organic and inorganic materials will &#8230;<\/p>\n","protected":false},"author":151,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"class_list":["post-40","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages\/40","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/users\/151"}],"replies":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/comments?post=40"}],"version-history":[{"count":13,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages\/40\/revisions"}],"predecessor-version":[{"id":1162,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages\/40\/revisions\/1162"}],"wp:attachment":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/media?parent=40"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}