ir instrumetnation

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IR INSTRUMANTATION PRESENTED BY: PALAK V. CHOKSHI GUIDED BY: MR. DHARMENDRA A. BARIA & MR.NISHIT S. PATEL DHARMAJ DEGREE PHARMACY COLLEGE

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AMPLIFIER Detector RECORDER Ra diation source Sample holder Prism INFRARED SPECTROMETER INSTRUMENTATION

Components of Infrared spectrophotometers : 

Components of Infrared spectrophotometers IR RADIATION SOURCE ii) MONOCHROMATORS iii) SAMPLE HOLDER iv) DETECTORS

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IR RADIATION SOURCE

1) Infrared Source: 

1) Infrared Source Sources are the hot bodies which continuously emitting the radiation- black body Usually inert solid material electrically heated to 1500 – 2200K; maximum radiation 5000 – 5900 cm-1 (2 to 1.7 μ m)

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SOURCE FOR NEAR IR REGION { 2.5 to 0.78 μ m} Tungsten-Halogen Lamps Incandescent wire sources

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1) Rhodium wire 2) Tungsten filament 3) Nichrome wire Sources with lower intensity but longer life Rhodium wire: Sealed in ceramic cylinder Nichrome wire: Heated to about 1100k Incandescent wire sources need no cooling.

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SOURCE FOR MID IR REGION Nernst glower : { 1 – 9 μ m} rare earth oxides of Cerium, Zirconium & Ytterium , formed in to cylinder(about 2 cm long & 1-3 mm in diameter) electrically heated to 1200K to 2200K Adv: Radiation intensity isapproximately twice that of nichrome wire coils & Globar sources. Can be handle in the air, no chances of oxidation. Disadv : Has negative coefficient of temperature therefore needs ancillary heat supply

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2) Globar source: { 5 μm} silicon carbide rod ( 5 cm in length & 0.5 cm in diameter) ; heated to 1300K to 1500K Adv: positive co-efficient of resistance Disadv : less intense source than the Nernst glower.

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SOURCE FOR FAR IR REGION { > 50 μm } Mercury arc lamp: This device consists of a quartz jacketed tube containing mercury vapor at a pressure greater than 1 atm. Passage of electricity through the vapor forms an internal plasma source that provides continuous radiation in the far IR region.

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Carbon dioxide laser monochromatic radiation; CO2 laser emits at 1100 – 900 cm-1 {11-9 μm} pollution control In remote-sensing application( lidar)

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MONOCHROMATORS

2) MONOCHROMATORS: 

2) MONOCHROMATORS Monochromators are used to convert the polychromatic light into a monochromatic light. Components of monochromators a) Entrance slit (to get narrow source) b) Collimator (to render the light parallel) c) Grating or Prism (to disperse radiation) d) Collimator (to reform the image of entrance slit) e) Exit slit (to fall on sample cell)

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MONOCHROMATOR

TYPES OF MONOCHROMATORS   : 

TYPES OF MONOCHROMATORS 1 ) Prisms a. Refractive type b. Reflective type 2 ) Gratings a. Diffraction grating b. Transmission grating

1) Prisms   : 

1) Prisms The resolution depends on the size & refractive index of the prism. Materials transparent to the IR radiation are used for the construction. Near IR:(1-5 μm) LIF MID IR:(5-15 μm) KBr FAR IR : (15-40 μm ) CsBr

a) Refractive type     : 

a ) Refractive type The light from the source through the entrance slit falls on a collimator. The parallel radiation from the collimator is dispersed according to the wavelength. The required radiation in the exit slit can be selected by rotating the prism or by keeping the prism stationery & moving the exit slit.

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Refractive type

b) Reflective type   : 

b) Reflective type The working principle is similar to the Refractive type prisms except that, a reflective surface is present on one side of the prism. Thus the dispersed radiation gets reflected & can be collected on the same side of the source of the light.

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Reflective type

2) Gratings : 

2) Gratings Gratings are more effective in converting a polychromatic light to monochromatic light. Resolution of + 0.1 nm could be achieved by using gratings.

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Sinusoidal groove profile Laminar groove profile Triangular groove profile

a) Diffraction gratings   : 

a) Diffraction gratings Gratings consist of lines or grooves drawn on materials such as glass, plastic, alkali metal halides. Replica gratings are made from master gratings with a epoxy resin and are removed after setting. The surface is made reflective by depositing aluminum on the surface. PRINCIPLE : For radiations of different wavelength, the angle of dispersion is different. Thus at a grating the separation of light occurs because light of different wavelengths is dispersed at different angle.

b) Transmission gratings         : 

b) Transmission gratings The working principle is similar to the diffraction grating but refraction takes place instead of reflection. The desired wavelength can be obtained by either moving the grating with a fixed slit or by moving the slit & keeping the grating constant.

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SAMPLE HOLDER

3) SAMPLE HOLDER: 

3) SAMPLE HOLDER material containing the sample must be transparent to IR radiation . 1)sampling of solids 2)sampling of liquids 3)sampling of gases

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1) Sampling of solids Solids run in solution Solid film Mull technique Pressed pellet technique

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Solids run in solution: Solids dissolved in a non- aqueous solvent. A drop of the solution is placed on the alkali metal disk and the solvent allow evaporating, leaving a thin film of the solute, or the entire solution is placed in the liquid sample cell. b) Solid film: If a solid is amorphous in nature the sample is deposited on the surface of a KBr or NaCl cell by evaporation of a solution of the solid. This technique is useful for rapid qualitative analysis.

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c) Mull technique: finely ground solid sample is mixed with Nujol to make a thick paste which is then made to spread between IR transmitting windows. Although Nujol is transparent throughout IR region, yet it has the disadvantage that it has the absorption maxima at 2915, 1462, 1376 and 719 cm -1 .

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d) Pressed pellet technique: Mainly used for qualitative work small amount of finely ground solid sample is intimately mixed with about 100 times its weight of powdered potassium bromide. The finely ground mixture then passed under very high pressure (25000psig) in a press to form a small pellets. The resulting pellets are transparanent to IR radiation.

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device for pressing the mixture of KBr and solid sample to form a pellet

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Advantages: Eliminate the problem of bands which appear in nujol. Resolution is superior KBR pellets can be preserved

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2) Sampling of liquids Sample that are liquids at room temperature are usually put frequently with no preparation, into rectangular cell made of NaCl, KBr and their IR spectra are obtained directly. double beam work, “matched cell” are generally employed. One cell will contain the sample while other will have a solvent used in the sample.

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3) Sampling of gases similar to the cell of liquid samples, surfaces in the light path are made of KBr, NaCl. the cells are larger; usually they are about 10 cm long; when gas sample present in small amount. Cell is made up of glass and end walls of KBr or NaCl. GLC is coupled with IR to analyse the elutes from GLC.

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Detectors

4) DETECTORS : 

4) DETECTORS Detectors for different IR regions are: Near IR region – Lead sulfide photoconductive. Mid IR region – Thermopile, thermistor, pyroelectric Detectrs. Far IR region – Golay cell, pyroelectric detectors

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Types of detectors 1. Thermal detectors 2. Photon detectors i ) BOLOMETER i ) PHOTOCONDUCTIVITY CELL ii) THERMOCOUPLE ii) SEMICONDUCTOR iii) THERMISTORS iv) GOLAY CELL

Thermal detectors i) BOLOMETER: 

Thermal detectors i) BOLOMETER Principle : A bolometer is based upon the fact that the electrical resistance of a metal conductor changes with increasing temperature. working : Bolometer consists of a thin metal conductor. When radiation falls on this conductor, its temperature changes . As the resistance of a metallic conductor changes with temperature, the degree of change in resistance is regarded as a measure of the amount of radiation that has fallen on the bolometer.

ii) THERMOCOUPLE : 

ii) THERMOCOUPLE Principle : An electric current will flow when two dissimilar metal wires are connected together at both ends and a temperature differential exists between the two ends. The electricity, which flows, is directly proportional to the energy differential between the two connections .

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hv Infrared Metal A Metal B T 1 T 2 Hot junction Cold junction

iii) THERMISTORS : 

iii) THERMISTORS A thermistor is made of a fused mixture of metal oxides. As the temperature of the mixture increases, its electrical resistance decreases. This relationship between temperature and electrical resistance allows thermistors to be used as IR detectors.

iv) GOLAY CELL   : 

iv) GOLAY CELL WORKING: It consists of a small metal cylinder, which is closed by a blackened metal plate at one end and by a flexible metalized diaphragm at the other. The cylinder is sealed after filling with xenon. When IR radiation falls on the blackened metal plate, it heats the gas, which causes it to expand. The resulting pressure increase in the gas deforms the metalized diaphragm, which separates two chambers. Light from a lamp is made to fall on the diaphragm, which reflects light on to a photocell. Motion of the diaphragm changes the output of the cell. The intensity of the signal depends upon the power of the radiant beam incident on the gas cell.

Photon detectors i) PHOTOCONDUCTIVITY CELL : 

Photon detectors i) PHOTOCONDUCTIVITY CELL It consists of a thin layer of lead sulfide or lead telluride supported on glass and enclosed into an evacuated glass envelope. When IR radiation is focused on lead sulfide or lead telluride, its conductance increases and causes more current to flow.

ii) SEMICONDUCTOR DETECTORS     : 

ii) SEMICONDUCTOR DETECTORS Semiconductor are the materials that are insulators when no radiation falls on them, but which become conductors when radiation falls on them. Exposure to radiation causes a very rapid change in their electrical resistance & therefore a very rapid response to the IR signal.

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IR SPECTROPHOTOMETERS

a) SINGLE BEAM SPECTROPHOTOMETER : 

a) SINGLE BEAM SPECTROPHOTOMETER WORKING: In single beam spectrophotometer the radiation emitted from the source passes through the sample and then through a fixed prism and then through a rotating littrow mirror. Both prism and littrow select the desired wavelength and then allow to pass on to a detector. The detector measures the intensity of a radiation after it passes through the sample. APPLICATION: Knowing the original intensity of the radiation, one can measure how much of radiation has been absorbed . By measuring the degree of absorption at wavelengths, the absorption spectrum of the sample can be obtained.

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Exit slit IR source Sample holder Chopper Entrance slit Prism Littrow mirror Detector

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Disadvantages: intensity of the emission of the radiation source varies from point to point in IR absorption spectrum; therefore the resulting spectrum is considerably deformed. 2) When the sample is analyzed in solution, the bands of solvent appear on the spectrum. In this case a spectrum of the sample is obtained by subtracting the spectrum of the solvent from the resultant spectrum, the former must be recorded under identical conditions.

b) DOUBLE BEAM SPECTROPHOTOMETER : 

b) DOUBLE BEAM SPECTROPHOTOMETER The energy emitted by the radiation source is split by the instrument into two beams, which are energetically and optically identical. One of the beams passes through the sample and the other passes through the reference sample. When there is no sample in the reference beam it arrives at the detector unabsorbed. When there is no sample in the sample cell the half beam traveling along the sample beam is not absorbed and is equal to the reference beam. When these two equal half beams are recombined a steady signal reaches the detector.

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When the sample cell contain the sample the half beam traveling through if undergoes a decrease in the intensity and the two half beams are combined, they produce an oscillating signal which is measured by the detector. The signal from the detector is passed on to the recording unit through a servomotor.

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Sample cell Reference cell Rotating mirror section Recording unit Servomotor From detector Entrance slit Of monochromator IR source

REFERENCES: 

REFERENCES Dr. S. Ravi sankar; “Pharmaceutical analysis”; 3 rd Edition; Rx publication, Tirunelveli. Skoog, Holler, Crouch; “INSTRUMENTAL ANALYSIS”; Brooks/ cole , New delhi. Dr.A.V.KASTURE; “Pharmaceutical analysis”; Vol-III; Nirali prakashan.

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thank you