IR spectroscopy/Infrared Spectroscopy/ IR spectrophotometer (Principle,Instrumentation&applications)

Описание: This video explains the types of IR regions, principle, instrumentation and applications of Infra red spectroscopy. In detail it explains about each component in it. It also explains the working of IR spectrophotometer. It explains the instrumentation of double beam IR spectrophotometer.
Infra-red spectroscopy is the interaction of Infra-red (IR) radiation with molecules to undergo vibrational excitation from lower to higher vibrational energy level. Each covalent bond present in the molecule absorbs IR radiation of a specific frequency/energy, which corresponds to the energy required for the vibration of that bond.
Near –Infrared (NIR) – 14000-4000 cm-1
Quantitative analysis –mixture of aromatic amines, food grain industry determination of fats, proteins, sugar, oils, moisture, iodine number etc.
Mid-Infrared – 4000 - 400 cm-1 – Identification of functional groups, quantitative analysis and detecting impurities.
Functional group region – 1400 - 4000 cm-1
Finger print region – 400 - 1400 cm-1
Far- Infrared – 400 -10 cm-1 – Analysis of structure of molecules
Double BEAM IR spectrophotometer : Instrumentation & working of IR(Infrared spectrophotometer
Source of IR(Infrared spectrophotometer) – Electrical heating of the source to temperatures in the range 200-1200 oC generates IR radiation .
Nichrome heating coil wound on ceramic support
Nernst glower – a filament made of oxides of zirconium, yttrium, cerium and thorium
Globar silicon carbide (carborundum rod)
Double beam – Two equivalent beam of light is generated from the source, one passes through the test sample and other through the blank/reference.
Monochromator of IR(Infrared spectrophotometer) – The polychromatic light from the sample/reference is dispersed by the monochromator and reaches the detector.
The transmitted light after being absorbed by the sample is dispersed into its component frequencies. eg. Prism made of NaCl or KCl, diffraction grating etc.
Optical chopper – The reference and sample beams are alternately focused on the detector for optical comparison of transmitted light of reference and sample. It reflects or transmits the sample beam alternately into the monochromator.
Detector/transducer of IR(Infrared spectrophotometer)
Selective detector -eg. photocell, photoconductive cells or semiconductor devices (mercury-cadmium telluride detector). –
converts the radiation falling on the detector to electric current.
Non-selective detector – thermal detectors that convert thermal radiant energy into temperature sensitive response.
Thermocoup[e (EMF/voltage changes)
Thermistor and bolometer (changes in resistance)
Pyroelectric (change in electric polarisation)
Pneumatic cell (changes in pressure of enclosed gas)
Amplifier (optional) – It is used if the signal produced by the detector is weak

Recorder- Each frequency that passes through the sample is measured individually by the detector which slows the process of scanning the entire IR range.
Applications of IR spectroscopy Applications of Infrared spectrophotometer
Identification of unknown compound.
Determination of the molecular structure from the absorption peaks.
Detection of functional group.
Study of the progress of a reaction.
Determination of impurities (it will give extra peaks).
It is used in forensic department, biomedical applications, food industries, pollution control.
Bending vibrations
stretching vibration
symmetric stretching vibration
unsymmetric stretching vibration
wagging rocking twisting scissoring