1-Introduction to Spectroscopy

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PharmaceuticalAnalysis II : 

PharmaceuticalAnalysis II Imtiaz Khalid Mohammed imtiaz@cybermed.edu.my : +603 8313 7042 : +6016 492 8175

contents : 

contents Introduction to Spectroscopy Ultraviolet (UV) Spectroscopy Visible Spectroscopy and Colorimetry Fluorimetry and Phosphorimetry Atomic Absorption Spectroscopy (AAS) Infra-Red (IR) Absorption Spectroscopy Nuclear Magnetic Resonance (NMR) Spectroscopy Mass Spectroscopy (MS) Polarimetry and Circular Dichroism (CD) Spectroscopy X-ray Spectroscopy Basic Drug Instrumental Analysis Structural Elucidation 2

Course objectives : 

Course objectives On completion of the course the student will have: An appreciation of the science and the role of Pharmaceutical Analysis in both qualitative and quantitative Analysis; An understanding of the principles and applications associated with drug, medicine and pharmaceuticals by spectroscopic methods; An appreciation of the scope and limitations of various techniques for identification, the determination of molecular structure and the analysis of complex mixtures; An appreciation of the application of modern instrumental techniques to aid in understanding the structure of drug, medicine and pharmaceutical materials. 3

READINGS : 

READINGS Pharmaceutical Analysis by David G. Watson, 2nd Edition, 2005. Analytical Chemistry by Gary D. Christian, 6th Edition, 2004. Pharmaceutical Analysis by David C. Lee & Michael Webb, 1st Edition, 2003. Vogel’s Text Book of Quantitative Chemical Analysis, 6th Edition, 2004. Practical Pharmaceutical Chemistry, Part two, A. H. Beckett & J. B. Stenlake – 4thEdition. Organic Chemistry by I. L. Finar Vol. II – 5th Edition Instrumental Methods of Analysis – Hobert H. Willard, 7th Edition. Pharmaceutical Analysis – Modern Methods – Part A & B, James W. Munson – 2001. Principles of Instrumental Analysis by Donglas A. Skoog, James, J. Leary, 4th Edition. Fundamentals of Mathematical Statistics, S.C. Gupta and V.K. Kapoor. Spectrometric identification of Organic Compounds, Robert. M. Silverstein et al, 7th Edition, 1981. Organic Spectroscopy – William Kemp, 3rd Edition. Stereo Chemistry – Conformation and Mechanism by P. S. Kalsi, 2nd Edition. Spectroscopy of Organic Compounds by P. S. Kalsi. 4

INTRODUCTION TO SPECTROSCOPY : 

INTRODUCTION TO SPECTROSCOPY 5

learning objectives : 

learning objectives Explain what is meant by spectroscopic methods of chemical analysis. Define each of the following: Absorption, emission, fluorescence, refraction, dispersion, scattering and refraction. Define each of the following: Wavelength, frequency, wave number, and velocity. Describe the relation between wavelength and electromagnetic radiation. Deduce Jablonski’s diagram and its use. Explain the frequency of spectral line. 6

Terminology : 

Terminology Spectroscopy = study of the interaction between light and matter. Spectra = plots of radiant intensity versus wavelength or frequency Spectroscope = instrument for viewing spectrum Spectrograph = instrument for recording spectrum (e.g. on photographic film) Spectrometer = instrument for recording spectrum as a function of radiant energy Spectrophotometer = spectrometer with associated electronics which provides the ratio or a function of ratio (e.g. log) of the two beams as a function of spectral wavelength. 7

Properties of EM radiation : 

Energy propagated through space or through a material medium in the form of electromagnetic waves. e.g. radio frequency, microwaves, infrared radiation, visible light, ultraviolet, X-rays, and gamma rays. 2. EM radiation exhibits wave-like properties such as reflection, refraction, diffraction and interference. 3. EM radiation also exhibits particle-like properties in that its energies occur in discrete packets (quanta or photons). 4. All types of radiation travel at the same speed but vary in frequency, wavelength and their interaction with matter. 5. Unlike other wave phenomena (e.g. sound), EM radiation can move through a vacuum. 8 Properties of EM radiation

WAVE PROPERTIES OF EM RADIATION : 

WAVE PROPERTIES OF EM RADIATION Electric and magnetic fields that undergo in-phase, sinusoidal oscillations at right angle to one another and to the direction of propagation. 9

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WAVE PROPERTIES OF EM RADIATION : 

WAVE PROPERTIES OF EM RADIATION 11

WAVE PARAMETERS : 

WAVE PARAMETERS 12

PARTICLES PROPERTIES OF EM RADIATION : 

PARTICLES PROPERTIES OF EM RADIATION Einstein’s work with photoelectric effect. EM waves carry quantized energy in the form of photons. Energy in EM related to both frequency () and wavelength (). E = h E= energy of photons in ergs = frequency in cycles/second h = Plank’s constant = 6.63 x 1034 Js E = h = hc/ = hc 13

QUANTUM THEORY : 

QUANTUM THEORY Every elementary particle (atom, ion or molecule) exists in discrete energy states, E0, E1, E2 , E3 etc. At room temperature most particles are in their lowest energy level E0 (ground state). When atoms absorb photon of radiation, they can be promoted to higher energy levels E1, E2 , E3 etc. Only occur if the photon matches exactly the energy difference (E) between the ground state and the higher energy states, i.e. E = (En  E0) = h = hc/ Promoted atoms are said to be in the excited states. M + h → M* 14

QUANTUM THEORY : 

QUANTUM THEORY M + h → M* After brief period (106 to 109), the excited species relaxes and return to it ground state, releasing it’s excess energy in the form of heat. M* → M + heat Relaxation can also occur by photochemical decomposition of M*→ new species, or by the reemission of light (fluorescence or phosphorescence) 15

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E0 E1 E2 E3 E4 E Excited states Ground state Absorption 16

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E0 E1 E2 E3 E4 E Excited states Ground state Emission 17

POLARIZATION OF ELECTROMAGNETIC RADIATION : 

POLARIZATION OF ELECTROMAGNETIC RADIATION Light source such as hot filament of a light bulb consists of multiple, randomly oriented light emitters. 3 kinds of electromagnetic waves (light) : Unpolarized light = electric-field vector oriented in all directions. Linearly (or plane) polarized light = electric-field vector oscillating in only one direction. Can be produced by a polarizer or from lasers that contain polarized optical components. Circularly polarized light = electric-field vector is rotating around the axis of light propagation. Right or left direction →Right or left circularly polarized 18

ELECTROMAGNETIC SPECTRUM : 

ELECTROMAGNETIC SPECTRUM EM radiation consists of photons of different energies → different spectral regions. Photons in all regions have the same EM nature but because of their very different energies, they interact with matter very differently. 19

SPECTRUM OF ELECTROMAGNETIC RADIATION : 

SPECTRUM OF ELECTROMAGNETIC RADIATION 20

SPECTRUM OF ELECTROMAGNETIC RADIATION : 

SPECTRUM OF ELECTROMAGNETIC RADIATION 21

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THE VISIBLE SPECTRUM : 

THE VISIBLE SPECTRUM When a beam of light is passed through a prism, a band of colours is formed (continuous spectrum). Visible part of EM spectrum (Visible range) Each colour corresponds to waves of a particular wavelength. 23

SPECTRUM OF ELECTROMAGNETIC RADIATION : 

SPECTRUM OF ELECTROMAGNETIC RADIATION 24

VISIBLE SPECTRUM : 

VISIBLE SPECTRUM 25

INTERACTION OF LIGHT WITH MATTER : 

INTERACTION OF LIGHT WITH MATTER EM carries energy and momentum that may be imparted when it interacts with matter. Absorption – light is captured Emission – light is released Transmission – light is allowed to pass through Reflection – light is bounced away Diffraction – exhibit wave nature Refraction – exhibit particle nature Interference – light is disturbed Scattering – light is dispersed Polarization – light vibration is restricted to one direction 26

ABSORPTION OF RADIATION : 

ABSORPTION OF RADIATION Absorption = chemical species in a transparent medium selectively attenuates (decreases the intensity of) certain frequencies of EM. Plot of intensity Vs ,  or  → absorption spectrum Two qualitative parameters : Transmittance Absorbance 27

ABSORPTION OF RADIATION : 

ABSORPTION OF RADIATION P0 P Transmittance ,T = P/P0 % T = P/P0  100 Absorbance,  log T = log P0/P 28 b

ATOMIC ABSORPTION : 

ATOMIC ABSORPTION When a beam of polychromatic radiation passes through a medium containing gaseous atoms, only a few frequencies is attenuated → line spectra e.g. Na absorption lines at 285, 330 and 590 nm. Due to electronic transitions from ground state 3s orbital to 3p, 4p and 5p orbitals. 29

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3.76 3.62 3.19 2.10 0.0 3s 3p 4s 3d 4p eV 5p 30

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MOLECULAR ABSORPTION : 

MOLECULAR ABSORPTION Molecules absorb/emit light over wider range of  → spectral bands Due to 3 types of quantized transitions : Electronic transitions Vibrational transitions Rotational transitions Relative energies Eel > Evib > Erot (10,000:100:1) E = (Eel + Evib + Erot)2  (Eel + Evib + Erot)1 Each E fixes the  at which each molecule absorbed. 32

MOLECULAR ABSORPTION : 

MOLECULAR ABSORPTION Molecular absorption spectra can be classified into 3 types: 1) Electronic spectra = due to changes in electronic transitions and also associated vibrational and rotational transitions → Ultraviolet-visible region (200-800nm) 2) Vibrational spectra = due to vibrational and rotational transitions → Infrared region (2.5-15 µm [400-4000cm-1]) 3) Rotational spectra = rotational transition only → microwave region (103 – 0.67 nm) 33

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MOLECULAR EMISSION : 

MOLECULAR EMISSION After absorption of UV light the excited molecular species are extremely short-lived and deactivation occurs due to : Internal collisions Cleavage of chemical bonds → photochemical reactions Re-emission as light (luminescence) Re-emission occur from molecules in which electron system is shielded, hence complete deactivation is discouraged. 2 associated phenomena : Fluorescence and phosphorescence. 35

MOLECULAR EMISSION : 

MOLECULAR EMISSION FLUORESCENCE Molecules on excitation possess higher vibrational energy → lost by internal collision → molecules return to ground electronic state → emission of light as fluorescence (106 – 109 seconds) PHOSPHORESCENCE Excited molecules that exhibit fluorescence are in singlet state (spin of  and  are antiparallel) At low temp, some molecules undergo intersystem crossover to a triplet state ( and  are parallel) → return to ground electronic state → phosphorescence (108 seconds) 36

MOLECULAR EMISSION : 

MOLECULAR EMISSION E(Absorption) > E(Fluorescence) > E(Phosphorescence) (Absorption) < (Fluorescence) < (Phosphorescence) Techniques of spectrofluorimetry and phosphorimetry measure intensity of light emitted from a system that has absorbed radiant energy. 37

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CLASSIFICATION OF SPECTROPHOTOMETRIC TECHNIQUES : 

CLASSIFICATION OF SPECTROPHOTOMETRIC TECHNIQUES 40

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