Course: B.Tech.

Subject: Engineering Chemistry

Unit: V(B)

Molecular Spectroscopy: the interaction of

electromagnetic radiation (light) with matter (organic

compounds).

This interaction gives specific structural information.

It gives Identification of any compound.

Optical spectroscopies

Techniques for determining the elemental composition of an analyte by its

electromagnetic or mass spectrum

Mass spectrometries

ICP-MS SIMSAASAES

Fluoresc-

ence

Spectros-

copy

Flame AAS GFAAS

ICP-OES

UV IR

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.

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, l10 nm 1000 nm 0.01 cm 100 m~0.01 nm~.0001 nm

1

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.

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)

IR

Stretching Bending

Principle:

2

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

GC-MS

LC-MS

HPLC-MS

GC-MS-MS

LC-MS-MS

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.

MS is now in very common use in analytical laboratories

that study

physical,

chemical,

biological properties of a great variety of compounds.

1.www.schome.ac.uk

2.www.shodor.org

3. Principles of instrumental analysis 6th ed by Skoog,

Holler, Crouch

Thank you…………