B.tech. ii engineering chemistry unit-5 B spectroscopic techniques

1. Course: B.Tech.
Subject: Engineering Chemistry
Unit: V(B)

2. Molecular Spectroscopy: the interaction of
electromagnetic radiation (light) with matter (organic
compounds).
 This interaction gives specific structural information.
 It gives Identification of any compound.

3. Optical spectroscopies
Techniques for determining the elemental composition of an analyte by its
electromagnetic or mass spectrum
Mass spectrometries
ICP-MS SIMS
AASAES
Fluoresc-
ence
Spectros-
copy
Flame AAS GFAAS
ICP-OES
UV IR

4. General introduction to IR
Spectroscopy is the study of the interaction of matter with
the electromagnetic spectrum.
1. Electromagnetic radiation displays the properties of both particles and waves
2. The particle component is called a photon.
3. The energy (E) component of a photon is proportional to the frequency. Where
h is Planck’s constant and n is the frequency in Hertz (cycles per second)
E = hn
4. The term “photon” is implied to mean a small, massless particle that contains a
small wave-packet of EM radiation/light – we will use this terminology in the
course.

5. The entire electromagnetic spectrum
Energy (kcal/mol)
300-30 300-30 ~10-4> 300 ~10-6
Frequency, n in Hz
~1015 ~1013 ~1010 ~105~1017~1019
Wavelength, l
10 nm 1000 nm 0.01 cm 100 m~0.01 nm~.0001 nm
1

6.  Infrared spectroscopy (IR spectroscopy) is the
spectroscopy that deals with the infrared region of the
electromagnetic spectrum, that is light with a longer
wavelength and lower frequency than visible light.

7.  The infrared portion of the electromagnetic spectrum is
usually divided into three regions:
 near- IR 14000–4000 cm−1 (0.8–2.5 μm)
 mid- IR 4000–400 cm−1 (2.5–25 μm)
 far- IR 400–10 cm−1 (25–1000 μm)

8. IR
Stretching Bending
Principle:

9. 2

10. The infrared spectrum of a sample is recorded by passing a beam
of infrared light through the sample.
When the frequency of the IR is the same as the vibrational
frequency of a bond, absorption occurs.
Examination of the transmitted light reveals how much energy
was absorbed at each frequency (or wavelength).
Alternatively, the whole wavelength range is measured at once
using a Fourier transform instrument and then a transmittance or
absorbance spectrum is generated using a dedicated procedure.
Analysis of the position, shape and intensity of peaks in this
spectrum reveals details about the molecular structure of the
sample.

11.  This technique works almost exclusively on samples
with covalent bonds.
 Simple spectra are obtained from samples with few IR
active bonds and high levels of purity.
 More complex molecular structures lead to more
absorption bands and more complex spectra.
 The technique has been used for the characterization of
very complex mixtures.

12.  Infrared spectroscopy is a simple and reliable technique
widely used in research and industry.
 It is used in
 quality control,
 dynamic measurement,
 monitoring applications such as the long-term
unattended measurement of CO2 concentrations in
greenhouses

13.  It is also used in forensic analysis in both criminal and
civil cases,
 for example in identifying polymer degradation.
 It can be used in determining Explosives also.

14.  Nuclear magnetic resonance (NMR) is a physical
phenomenon in which nuclei in a magnetic field absorb
and re-emit electromagnetic radiation.
 This energy is at a specific resonance frequency which
depends on the strength of the magnetic field and the
magnetic properties of the isotope of the atoms.

15.  The principle of NMR usually involves two sequential
steps:
 The alignment (polarization) of the magnetic nuclear
spins in an applied, constant magnetic field H0.
 The perturbation of this alignment of the nuclear spins
by employing an electro-magnetic, usually radio
frequency (RF) pulse.
 The required perturbing frequency is dependent upon
the static magnetic field (H0) and the nuclei of
observation.

16.  Mass spectrometry (MS) is an analytical chemistry
technique that helps identify the amount and type of
chemicals present in a sample by measuring the mass-
to-charge ratio and abundance of gas-phase ions.
 A mass spectrum (plural spectra) is a plot of the ion
signal as a function of the mass-to-charge ratio.

17.  The spectra are used to determine the elemental or
isotopic signature of a sample, the masses of particles and
of molecules, and to elucidate the chemical structures of
molecules, such as peptides and other chemical
compounds.
 Mass spectrometry works by ionizing chemical
compounds to generate charged molecules or molecule
fragments and measuring their mass-to-charge ratios.

18.  In a typical MS procedure, a sample, which may be
solid, liquid, or gas, is ionized, for example by
bombarding it with electrons.
 This may cause some of the sample's molecules to
break into charged fragments.
 These ions are then separated according to their mass-
to-charge ratio, typically by accelerating them and
subjecting them to an electric or magnetic field: ions of
the same mass-to-charge ratio.

19.  The ions are detected by a mechanism capable of detecting
charged particles, such as an electron multiplier.
 Results are displayed as spectra of the relative abundance
of detected ions as a function of the mass-to-charge ratio.
 The atoms or molecules in the sample can be identified by
correlating known masses to the identified masses or
through a characteristic fragmentation pattern.

20.  GC-MS
 LC-MS
 HPLC-MS
 GC-MS-MS
 LC-MS-MS

21.  Mass spectrometry has both qualitative and quantitative
uses.
 These include identifying
 unknown compounds,
 determining the isotopic composition of elements in a
molecule,
 determining the structure of a compound by observing
its fragmentation.

22.  MS is now in very common use in analytical laboratories
that study
 physical,
 chemical,
 biological properties of a great variety of compounds.

23. 1.www.schome.ac.uk
2.www.shodor.org
3. Principles of instrumental analysis 6th ed by Skoog,
Holler, Crouch

24. Thank you…………