Interpretation & Application of X-ray diffraction

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Interpretation of Spectra & Application of X-ray diffraction Prepared by: Karan Mistry M.Pharm sem-1 Pharm tech.,IICP Guided by: Usmangani K.Chhalotiya Department of pharm.analysis, IICP 1

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X-ray absorption spectra When a narrow beam of X-rays is passed through a thin layer of matter, its intensity or power is generally diminished as a consequence of absorption and scattering. The effect of scattering is ordinarily small and can be neglected in those wavelength regions where appreciable absorption occurs. As shown in Figure, the absorption spectrum of an element like its emission spectrum, is simple and consists of a few well-defined absorption peaks. Here again, the wavelengths of the peaks are characteristic of the element and are largely independent of its chemical state. 2

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X-Ray absorption spectra for lead and silver 3

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Absorption of an X-ray quantum causes ejection of one of the innermost electrons from an atom and the consequent production of an excited ion. In this process, the entire energy hv of the radiation is partitioned between the kinetic energy of the electron and the potential energy of the excited ion. The highest probability for absorption arises when the energy of the quantum is exactly equal to the energy required to remove the electron just to the periphery of the atom, at that time the energy is suddenly absorb that is called as absorption edges. The Absorption Process 4

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The absorption spectrum for lead, shown in Figure, exhibits four peaks, the first occurring at 0.14 A. The energy of the quantum corresponding to this wavelength exactly matches the energy required to just eject the highest energy K electron of the element; immediately beyond this wavelength, the energy of the radiation is insufficient to bring about removal of a K electron, and an abrupt decrease in absorption occurs. At wavelengths lower than 0.14 A, the probability of interaction between the electron and the radiation diminishes and results in a smooth decrease in absorption. In this region, the kinetic energy of the ejected photoelectron increases continuously with the decrease in wavelength. 5

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The additional peaks at longer wavelengths correspond to the removal of an electron from the L energy levels of lead. Three sets of L levels, differing slightly in energy, exist (see Figure); three peaks are, therefore, observed. Another set of peaks, arising from ejections of M electrons, will be located at still longer wavelengths. Figure also shows the K absorption edge for silver, which occurs at 0.485 A. The longer wavelength for the silver peak reflects the lower atomic number of the element compared with lead. (1) 6

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Interpretation of Diffraction Patterns The identification of a species from its powder diffraction pattern is based upon the position of the lines (in terms of θ or 2 θ ) and their relative intensities. The diffraction angle 2 θ is determined by the spacing between a particular set of planes; with the use of the Bragg equation, this distance d is readily calculated from the known wavelength of the source and the measured angle; Line intensities depend upon the number and kind of atomic reflection centers that exist in each set of planes. 7

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Identification of crystals is empirical. ICDD publishes file cards that provide d spacings and relative line intensities for pure compounds; data for nearly 50,000 crystalline materials have been compiled. The cards are arranged in order of the d spacing for the most intense line; cards are withdrawn from this file on the basis of a d spacing that lies within a few hundredths of an angstrom of the d spacing of the most intense line for the analyte. 8

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If the sample contains two or more crystalline compounds, identification becomes more complex. Here, various combinations of the more intense lines are used until a match can be found. By measuring the intensity of the diffraction lines and comparing with standards, a quantitative analysis of crystalline mixtures is also possible . (2) 9

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Diffraction Pattern of venlafaxine (3) 10

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Application of X-ray diffraction 1. Structure of Crystals It gives information on the molecular structure of the sample. its most important use has been to measure the size of crystal planes. The patterns obtained are characteristic of the particulars compounds from which the crystal was formed. This method can also be used to distinguish between a mixture of crystal, which would give both diffraction patterns, and a mixed crystal, which would give a separate diffraction pattern. Identification of unknown crystal compounds. 12

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2. Polymer Characterization Powder method can be used to determine the degree of crystallinity of the polymer. The non-crystalline portion simply scatters the X-ray beam to give a continuous background, while the crystalline portion causes diffraction lines that are not continuous. 13

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3.State of anneal in metals A property of metals than can be determined by X-ray diffraction is the state of anneal. Well-annealed metals are in well-ordered crystal form and give sharp diffraction lines. If the metal is subjected to drilling, hammering, or bending, it becomes "worked", or fatigued," that is, its crystals become broken and the X-ray pattern more diffuse . 4.Particle size Determination A variety of X-ray techniques may be used to determine the size of particles or crystallites : (a) Spot counting method (b) Broadening of diffraction lines (c) Low-angle scattering 14

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5. Applications of Diffraction Methods to complexes (a) Determination of Cis-Trans Isomerism X-ray diffraction study has been used to make the distinction between cis and trans isomers of a complex. (b) Determination of Linkage Isomerism By X-ray studies, it becomes possible to identify linkage isomers of complexes. Sometimes knowledge of the position of hydrogen atoms is useful. 15

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6.Miscellaneous Application Soil classification based on crystallinity. Different types of soils, such as various types of clays and sands, exhibit different types and degrees of crystallinity. Analysis of industrial dusts can be effected, and their relationship to industrial disease ascertained, by means of x-ray diffraction studies. X-ray diffraction can also be used to assess the weathering and degradation of natural and synthetic minerals. By designed experiments, the factors responsible for the degradation can be revealed. Corrosion products can be studied by this method. Tooth enamel and dentine can be examined by x-ray diffraction. (4) 16

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Application of X-ray Absorption method The various applications are as follows: (a) Quantitative Analysis: This is based upon the simple fact that there is a large difference in the mass absorption coefficient of an element on either side of an absorption edge. (b) Qualitative Analysis: Different elements absorb the X-rays to different degrees. This property has been widely used to detect broken bones, impurities, segregations, etc. The above property has been widely used in industry and medicine. 17

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(c) Other Application (1) This has been used to locate trace elements, such as barium and iodine in the body. These elements are taken by the patient. Then, their movements in the body are followed by X-ray absorption. This method helps the doctor to detect the activity of the body tissue towards barium or iodine. (2) This has been used to detect below holes or the segregation of impurities such as oxides in welds and other joints. These blow holes reveal that the weld is weak and may be breaking in use. (3) This has been widely used to measure the volume of liquids in closed vessels or pipes without opening or breaking the vessels or pipes. (5) 18

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Application of x-ray fluorescence In Agriculture- For the determination of trace elements in plants and foods; The detection of insecticides on fruit and leaves; The continuous determination of phosphorus in fertilizer; And the characterization of soils. 19

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In medicine – For the direct determination of sulfur in protein. The sulfur content of each of the many different forms in which protein exists in human blood varies considerably, X -ray fluorescence indicates protein distribution and provides a diagnostic link for the medical practitioner; For determination of chloride in blood serum; For the determination of strontium in blood serum and bone tissue. 20

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In mining and metallurgy For the analysis of ores, concentrates, and drilled core; The continuous determination of silica in flowing slurries of ores; The simple determination of lead in lead-tin alloys; The determination of chromium in stainless steels, manganese in plain steels, and tungsten in high-speed steels; The elemental analysis of slags and the direct analysis of platinum and gold in plating solutions; 21

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Other applications:- The determination of additives in motor oil by determining barium, zinc, phosphorus, calcium, and chloride, and The determination of lead or sulfur in gasoline. The determination of the elements of the bearings in the used motor oil, which can be performed by X-ray fluorescence, In the rubber industry, the determination of the vulcanizing element, sulfur, can be done by X-ray fluorescence. This is a means of ensuring the production of high-quality rubber. In space technology, the analysis of new alloys and ceramics can be carried out by X-ray fluorescence . (6) 22

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References D. A. Skoog, F. James Holler, Timothy A. Nieman, Principles of Instrumental Analysis,5 th ed., Thomson asia Pte Ltd., (1998) 276 D. A. Skoog, F. James Holler, Timothy A. Nieman, Principles of Instrumental Analysis,5 th ed., Thomson asia Pte Ltd., (1998) 294 By SICART G. R. Chatwal, S. K. Anand, Instumental Methods of Chemical Analysis, Himalaya publishing house., (2007) 2.326 G. R. Chatwal, S. K. Anand, Instumental Methods of Chemical Analysis, Himalaya publishing house., (2007) 2.314 G. R. Chatwal, S. K. Anand, Instumental Methods of Chemical Analysis, Himalaya publishing house., (2007) 2.337 23

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