🗊Презентация Infrered spectroscopy

INFRERED SPECTROSCOPY PRESENTATION IS MADE BY STUDENT GROUP 33339/1 SVETLANA LEVINA

CONTENT Theory Instrumentation Fourier transform IR spectrometers(FTIR) Measurement techniques Mid-infrared (MIR) Near-infrared (NIR)

THEORY measurement of IR radiation absorbed by or reflected from a sample absorption of IR radiation is related to the changes of vibrational or rotational energy states of molecules applications: – analysis of gaseous, liquid or solid samples – identification of compounds – quantitative analysis information deduced from IR spectrum: – functional groups of molecules, constitution of molecules – interaction among molecules

VIBRATIONAL TRANSITIONS Fundamental (normal): change of vibrational quantum number ∆v = 1 high probability → high values of ε Overtones: the difference of vibrational quantum number ∆v = 2; 3… lower probability → low values of ε Combination: simultaneous change of two or more vibrational numbers for a polyatomic molecule

TYPES OF VIBRATION Stretching: the length of chemical bond (the inter-nuclear distance) is changed – symmetric – anti-symmetric Bending: the valence angle is changed – symmetric and anti-symmetric vibrations – vibrations in plane and vibrations out of plane

WHICH SUBSTANCES GIVE A SIGNAL IN IR SPECTRUM? YES

SPECTRAL REGIONS AND CORRESPONDING ANALITICAL TECHNIQUES

INSTRUMENTATION FOR IR SPECTROSCOPY Main components of an instrument

Sources of IR radiation Sources of IR radiation

FOURIER TRANSFORM IR SPECTROMETERS (FTIR)

MEASUREMENT TECHNIQUES IN IR SPECTROSCOPY TRANSMISSION TECHNIQUE the measurement of transmittance, absorbance ; REFLECTION TECHNIQUE the measurement of the radiation reflected from sample reflectance ; optical density OD = = - ATR TECHNIQUE attenuated total reflectance, or internal reflectance

Reflection techniques

ATR technique

Advantages of ATR

MID-INFRARED SPECROSCOPY (Mid IR) Mid IR region is divided into two sub-regions: Region of characteristic vibrations of functional groups 2.5–8 µm (4000–1250 ) contains the characteristic bands of individual bonds and functional groups that correspond mainly to stretching vibrations Fingerprint region 8–25 µm (1250–400 ) contains the bands corresponding mainly to bending vibrations the spectrum in this region characterizes each molecule as an integral whole

Steps of identification process 1. Searching for functional groups on the basis of characteristic vibrations (using tables) 2. Confrontation with the results of other tests • elementary analysis of the compound → stoichiometric formula of the compound • determination of molecular mass (from mass spectrum) → molecular formula of the compound → calculation of unsaturation index 3. Drawing of all possible structures that correspond to the presence of groups, molecular formula and unsaturation index 4. Comparison of the measured IR spectrum with the spectra of the suggested compounds found in an atlas or a database of spectra → identification 5. Verification of identity using other spectral methods (MS, NMR)

NEAR INFRARED SPECTROSCOPY (NIR) NIR region: 800 to 2500 nm or 12 500 to 4 000 NIR spectra contain less intensive signals – combination bands – overtone bands the change of vibration quantum number ∆v is 2; 3; 4…; if the fundamental vibration occurs at the wavelength of , the first overtone appears at the second at , the third at , etc., the strength of signal gradually decreases NIR spectra are measured by – transmission technique – diffusion-reflection technique – ATR technique

Making determinations of … in food analysis WATER FAT PROTEINS CARBOHYDRATES SUGARS ALCOHOLS

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