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Applications of IR (Infrared) Spectroscopy in Pharmaceutical Industry

1. Infrared spectroscopy can be used to qualitatively and quantitatively analyze compounds. It is used to identify unknown substances by comparing their IR spectra to reference standards. 2. The "fingerprint" region from 1200-700 cm-1 is particularly useful for identification because small molecular differences result in significant spectral changes in this region. Computer search systems can also identify compounds by matching IR spectra to profiles of pure compounds. 3. IR spectroscopy allows determination of molecular structures by identifying the presence or absence of functional groups from their characteristic absorption bands. It can also be used to study the progress of chemical reactions.

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APPLICATIONS OF IR SPECTROSCOPY Presented by: Muhammed Fahad 1st M.Pharm
QUALITATIVE ANALYSIS 2
1. Identification of Substances • To compare spectrums. • No two samples will have identical IR spectrum. • Criteria: Sample and reference must be tested in identical conditions, like physical state, temperature, solvent, etc. • Disadvt: Enantiomers cannot be distinguished (spectrum are identical). 3
The “Fingerprint” Region (1200 to 700 cm-1): • Small differences in structure & constitution of molecule  result in significant changes in the peaks in this region. • Hence this region helps to identify an unknown compound.
Computer Search Systems: • Newer IR instruments offer computer search systems to identify compounds from stored infrared spectral data. • The position and magnitudes of peaks in the spectrum is compared with profiles of pure compounds stored. • Computer then matches profiles similar to that of the analyte and result is displayed.
2. Determination of Molecular Structure • Used along with other spectroscopic techniques. • Identification is done based on position of absorption bands in the spectrum. • Eg.: C=O at 1717 cm-1. • Absence of band of a particular group indicates absence of that group in the compd. 8
3. Studying Progress of Reactions • Observing rate of disappearance of characteristic absorption band in reactants; or • Rate of increasing absorption bands in products of a particular product. • Eg.: O—H = 3600-3650 cm-1 C=O = 1680-1760 cm-1 9
4. Detection of Impurities • Determined by comparing sample spectrum with the spectrum of pure reference compound. • Eg.: ketone impurity in alcohols. • Detection is favoured when impurity possess a strong band in IR region where the main substance do not possess a band. 10
5. Isomerism in Organic Chemistry (i) Geometrical Isomerism: • trans isomers give a simpler spectrum than cis due to symmetry. (ii) Conformers (Rotational Isomers): • Identified with the help of high resolution IR spectrometers. 11
Contd… • E.g.: Ethanol normal OH – 3636 cm-1 weak band – 3622 cm-1 12
(iii) Tautomerism: Existence of 2 or more chemical compds capable of intercovertion , usually by exchanging a hydrogen atom between the 2 atoms. e.g.: Thiocarboxylic acid 13
6. Functional Group Isomerism • Isomerism shown by compounds having same molecular formula but different functional groups. Eg: CH3–O–CH3 and CH3–CH2–OH (Diethyl ether) (Ethanol) OH = 3500-3100 cm-1 14
7. APPLICATIONS OF IR SPECTROSCOPY TO INORGANIC COMPLEXES Difficulties: 1. High modes of vibration: Since they contain more than 5 atoms; hence min. 10 modes of vibrations. 2. Lower symmetry of Complexes: Due to formation of ligand & polynuclear complexes. 3. Formation of chelates: Large no. of new bands appear. 15
APPLICATIONS OF IR SPECTROSCOPY TO INORGANIC COMPLEXES Assumptions (not always true): 1. Complex formation only affects the vibrations of the ligand slightly. 2. Vibrations do not undergo coupling with other vibrations of another ligand. 3. When ligand is coordinated with another atom, it will not change the symmetry of the ligand. 16
Geometrical Isomerism: Eg: Bipyridyl cobalt (III) chloride [Co(Bipy)2(Cl2)Cl] 2 isomers – trans isomer has more symmetry than cis isomer. Hence complex spectrum is expected for cis isomer. 17 APPLICATIONS OF IR SPECTROSCOPY TO INORGANIC COMPLEXES
8. Shape of Symmetry of a Molecule • E.g.: Nitrogen dioxide, NO2 If linear --> only 2 bands should be present. If bent --> 3 bands should be present. Actual spectrum shows 3 peaks at 750, 1323 and 1616 cm-1. • Similarly, IR spectrum was used to determine structures of XeF2, XeF4 & XeF6  linear, square planar and octahedral resp.: 18
9. Identification of Functional Groups Due to the presence of functional group region. E.g.: (3500-3100 cm-1) (1700 cm-1) 19
10. Presence of Water in Sample • If lattice water is present, spectra will contain 3 characteristic bands  at 3600-3200 cm-1, 1650 cm-1 and 600-300 cm-1. 20
11. Measurement of Paints & Varnishes • Measured by ‘reflectance analysis’ • Advt: Measure IR absorbance of paints on appliances or automobiles without destroying the surface. • Make and year of car can be determined from IR spectral analysis. 21
12. Examination of Old Paintings & Artifacts • Help to determine fake “masterpieces”. • Varnish & paints from old items (statues, canvas, etc.) are analysed by IR spectroscopy. • Presence of new paint traces implies the “masterpiece” is fake. 22
13. In Industry 1. Determine impurities in raw materials (to ensure quality products). 2. For Quality Control checks; to determine the % of required product. 3. Identification of materials made in industrial research labs, or materials of competitors. E.g.: Impurity in bees wax (with petroleum wax) 23
14. Analysis of Petroleum HCs, Oil & Grease contents • These contain C–H bonds. Absorption at 3100-2700 cm-1. • ‘Freons’—Fluorocarbon-113; do not contain C–H bond. • Thus, quantity of HCs, oil & grease in freons is determined by measuring C–H absorption at 2930 cm-1. 24
15. Quantitative Analysis of Multicomponent Mixtures of Sulfur-oxygen Anions by ATR Spectroscopy • FTIR-ATR help to determine sulfur-oxygen anions in aqueous solutions. S–O stretching band at 1350-750 cm-1. • ATR uses water resistant cells, have short & reproducible effective path length. 25
16. Characterization of Heterogenous Catalysts by Diffuse Reflectance Spectroscopy • Diffuse Reflectance Spectroscopy help to determine nature of molecules attached to catalyst surfaces. E.g.: characterization of olefin polymerization catalysis with silica gel; diff. types of Si–OH bonds are determined. 26
17. Analysis of Multilayered Polymeric Film using FTIR Spectroscopy • Determine identities of polymer materials in multilayered film. • FTIR helps in quick characterization. 27
Other Applications 1. Determination of unknown contaminants in industry using FTIR. 2. Determination of cell walls of mutant & wild type plant varieties using FTIR. 3. Biomedical studies of human hair to identify disease states (recent approach). 4. Identify odour & taste components of food. 5. Determine atmospheric pollutants from atmosphere itself. 28
QUANTITATIVE ANALYSIS 29
QUANTITATIVE ANALYSIS • Based on the determination of one of the functional groups. E.g.: concn of hexanol in hexane-hexanol mixture. A = -log I1/I0 = abc (Beer-Lambert’s law) A = Absorbance I0 = Intensity of radiation before entering the sample I1 = Intensity of radiation after leaving the sample a = Absorptivity of the solution b = Initial path length of the sample cell c = concn. of the solution If ‘b’ & ‘a’ are const., then ‘A’ α ‘c’ 30
2 methods to determine ‘A’ and conc. ‘c’: 1. Cell-in cell-out Method: Std. calibration curve method 2. Baseline Method:  selection of suitable absorption band  P0 & P are measured  Abs, log (P0/P) plotted against conc; determine unknown 31
Baseline Method: 32
Advantages: 1. Common possible errors are eliminated. 2. Same cell is used for all determinations. 3. All measurements are done on points defined by the spectrum; hence no dependence on λ intensity. 4. Eliminate changes in instrument sensitivity and source intensity. 33
Using KBr Pellets (Disk Technique):  Uniform pellets of similar weight & thickness  Known wts. of KBR + known qty of test  Calibration curve plotted  Disks are weighed and thickness measured Using Internal Std. (pot. thiocyanate):  Dried, ground with KBr to make a conc of 0.2% by wt of thiocyanate.  Calibration curve plotted.  Ratio of thiocyanate absorption at 2125 cm-1 to a chosen band of test is plotted vs conc. 34
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