Radiochemical methods

Radiochemical Methods
By
Mirza Khan (Pharm.D, M.Phil.)
Lecturer department of pharmacy
Pishin campus, UoB
Email: mirza_khan92@yahoo.com

Radiochemistry
The chemical study of radioactive elements
(radionuclides) both natural and artificial and
their use in the study of chemical processes is
known as radiochemistry.
Radionuclides:
An unstable form of chemical element that
releases radiation as it breaks down and
becomes more stable. They may be natural or
made in the laboratory.
Examples: carbon14, H3 etc.Mirza Khan

Radiochemical methods
It is the branch of analytical chemistry consisting of
different techniques used for the qualitative and
quantitative analysis of radioisotopes.
There are three types of radiochemical analysis:
1. Neutron Activation Analysis (NAA)
2. Isotope Dilution Method (IDM)
3. Radioimmunoassay (RIA)
Before going into detail discussion of these three
types of methods, we will briefly define some terms
related to Radiochemical methods:
Mirza Khan

Aspects of Radiochemistry
• Nuclide:
A particular nucleus characterized by its atomic
number and mass number.
• Radionuclide:
A radionuclide is a nuclide which is radioactive,
i.e. radiation is emitted by the spontaneous
transformation of the nucleus.
• Isotopes:
These are the nucleus with same atomic number
but different mass numbers.
Mirza Khan

• Stable & unstable nuclei:
The nuclei of the atoms with low atomic number
are most stable if the number of neutrons is equal
to slightly greater ( 1 more) than the number of
protons.
The nuclei with greater atomic number and having
unequal number of neutron and protons are
unstable.
• Radioactive isotopes:
The unstable isotopes (radioactive) undergo
spontaneous disintegration to form stable isotopes
by spontaneous emission of radiations.
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• Types of radiations:
There are following types of radiations emitted
from radioactive isotopes:
1) Alpha particles:
These are heavy and positively charged particles
which are equivalent to the nuclei of helium
atoms (4²He). They have low penetrating power
and have discrete energies typically 4MeV.
Mirza Khan

2) Beta particles:
These particles have the same mass as an
electron, most of them are negatively charged
(negatron) but some may be positively charged
(positron). Their penetration power is more than
alpha particles.
Mirza Khan

3) Gamma radiation:
• These radiations are emitted from the nucleus
of radioactive isotope
• These are sometimes called photons
• It is an EMR so it has no mass or charge and
travels with the speed of light.
• These are very penetrating rays.
Mirza Khan

• Radioactive decay
• It is the spontaneous breakdown of an atomic
nucleus resulting in the release of energy and
matter from the nucleus.
• In the process, they will release energy and
matter from their nucleus and often transform
into a new element. This process is called
transmutation.
• Transmutation can occur naturally or by
artificial means.
Mirza Khan

• NEUTRON ACTIVATION ANALYSIS (NAA)
Neutron activation analysis (NAA) is a nuclear
process used for determining the concentration
elements in a varieties of materials.
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• Principle of NAA
It is based on the neutron activation and
therefore requires source of neutron. The
sample is bombarded with neutrons, causing
them to be radioactive. The specific type of
gamma radiations (energies) and the number of
gamma rays emitted from the radioactive
sample are used for qualitative and quantitative
analysis respectively.
Mirza Khan

• Process & instrumentation of NAA
In neutron activation analysis , unknown sample
with stable nuclei is bombarded with a flux of
protons. As a result neutron is captured by the
nuclei of the sample and transformed into a
radioactive nucleus. This “neutron rich” radioactive
nucleus then decays, with a unique half life, by the
emission of beta particle. In most of the cases
gamma rays are also emitted along with beta decay
process.
Mirza Khan

• High resolution gamma ray spectrometer is
used to detect these gamma rays from
artificially induced radioactivity in the sample
for both qualitative and quantitative analysis.
• The energies of gamma rays are used for
qualitative analysis and the number of gamma
rays of a specific energy is used for
quantitative analysis.
• Example:
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• When a sample that contains iron is irradiated, a
fraction of the Fe-58 atoms in the sample will
capture neutron and become Fe-59. This Fe-59
atoms are radioactive and give beta- decay and
transform into Co-59.
• Gamma rays (1099 KeV) is emitted which is the
identification of presence of iron in the sample
and by measuring the number of 1099 KeV
gamma rays emitted from the sample can be
used for the quantification of iron in the sample.
Mirza Khan

• Applications of NAA
This technique has following applications:
• Environmental studies: it includes pollutants
in the ecosystem.
• Biotechnology: it includes development of
new pharmaceuticals and sorbents
• Trace metal analysis in medicine and forensic
science.
Mirza Khan

• ISOTOPE DILUTION METHOD
It is method of determining the quantity of
unknown substance by mixing it with isotopic
labeled compound.
It was first introduced by von Hevesy & Hofer in
1934.
Mirza Khan

• Isotope Dilution analysis
initially Amount Specific activity
X gram of substance
(Unknown quantity)
0
Y gram of labelled compound
(quantity known)
Si
Finally (x+y) gram mixture Sf
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Isotope Dilution Analysis
Mathematically,
Applying the law of conservation of activity
Final activity=initial activity
We know that,
Specific activity= s counts/min/g
Whereas, activity= S (mass in g)counts/min
So,
(X+Y)Sf= Ysi
XSf+Ysf=Ysi
Xsf=Y(Si-Sf)
X=y(si-sf)/sf
Mirza Khan

Isotope Dilution Analysis
Applications:
• It is used in the analysis of complex
biochemical substance, such as
Vitamin-D
Vitamin-B complex
Insulin
steroids
Mirza Khan

Radiochemical methods

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