volumetric gravimetric procedures & scintillation counter, radioimmunoassay
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VOLUMETRIC, GRAVIMETRICPROCEDURES
SCINTILLATION COUNTER &RADIOIMMUNOASSAY
Diana Mae CabreraPamela Marie Chua
BSMT IIIA
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Volumetric Procedures
Also known as Titrimetry
Are quantitative analytical techniqueswhich employ a titration in comparing
an unknown and a standard.
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Titration - the unknown sample is madeto react with a known solution
Equivalence point - number ofequivalents of the known solutionadded equals the number of
equivalents of the unknown solution
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Types of Titration
Direct Titration – titrant reacts directlywith analyte
Residual Titration – back titration
- intermediate reactant is added in
excess of that required to exhaust theanalyte
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Indicators:○ Internal Indicators – compounds
○ External Indicators – electrochemical devices
End point
- Point at which titration is stopped
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Components
A standard solution of known concentrationwhich reacts with the analyte with a knownand repeatable stoichiometry
A device to measure mass or volume ofsample
A device to measure the volume of the
titrant added A pretreatment to remove interferents
A means by which the end point can be
determined
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Volumetric Methods
Aqueous Acid-Base Strong acid/Strong base – usual choice for a
titrant [methyl orange/red; phenolphthalein]
suitable for the analysis of any Bronsted acid or
base.
Non-aqueous Acid-Base
○ The sample is insoluble in water ○ Sample/titrants reacts with water in undesirable
ways
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Example Applications ofAcid-Base Titrations
Kjeldahl Analysis of Organic Nitrogen
- often used in the analysis of surface
water and wastewater.- widely used to determine the proteincontent of food samples
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Precipitation
relies on the formation of solid phasewith a very low solubility product
constant. 3 methods:
○ Precipitation type – Mohr‟s Method
○ Fajan‟s Method - Adsorption
○ Volhard Method
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Complexation or Chelation○ (sometimes chelatometry) is a form
of volumetric analysis in which the
formation of a colored complex is used toindicate the end point of a titration.Complexometric titrations are particularlyuseful for the determination of a mixture ofdifferent metal ions in solution.
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Oxidation/Reduction
a type of titration based on a redoxreaction between
the analyte and titrant. Redox titration may involve the use of
a redox indicator and/or a potentiometer.
Idiometric method – oxidation of iodideto iodine
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Gravimetric Procedures
It is the isolation of the pure form of
sample and its derivatives and thedetermination of its dry weight.
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Four Fundamental Types ofGravimetric Analysis:
Physical Gravimetry - involves the
physical separation and classification
of matter in environmental samples
based on volatility and particle size(e.g., total suspended solids).
Thermogravimetry - samples are
heated and changes in sample mass
are recorded. Volatile solids analysis isan important example of this type of
gravimetric analysis.
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Precipitative Gravimetric Analysis -relies on the chemical precipitationof an analyte.
Electrodeposition - involves theelectrochemical reduction of metalions at a cathode, and simultaneous
deposition of the ions on thecathode.
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Common Procedures inGravimetric Analysis:
Drying to a Constant Weight○ Hygroscopic – reagents that readily pick
up water
○ Deliquescent – absorb so much water thatthey will dissolve in it and form aconcentrated solution
Use of the Analytical Balance○ Analytical balance – generally used for
gravimetric analyses, and for thepreparation of standard solutions.
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Scintillation Counter
also known as Scintillometer
It is used to measure the disintegration
per minute of time of a radioisotope. An instrument which measures ionization
radiation and is extensively used inairborne and ground radiometric surveys.
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Types of radiation
1. Alpha-positively charged particles, resembles the
nucleus of a helium atom with a mass of 4.-have a very little of energy
2. Beta-resembles an electron with both negative
(B-) and positive (B+) charges but essentially nomass.
3. Gamma
-a form of electromagnetic energy with nomass, only energy
-exists in two forms: soft and hard gamma
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Types of Scintillation Counter
1. Solid Scintillation counter
- measures a gammaradiation using thallium activated
Nal crystal as scintillator and PM tubeas detector with preamplifier circuit.
2. Liquid scintillation counter
- measures beta radiationusing liquid flour as scintillator.
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Fact File
It utilizes the flash of light emitted when the
atoms of a suitable „phosphor‟ (e.g. a large
sodium iodide crystal „doped‟ with thallium)
are energized by gamma rays. The scintillation counter not only can
detect the presence of a particle, gamma
ray, or x-ray, but can measure the energy,
or the energy loss, of the particle or radiation in the scintillating medium. The
sensitive medium may be solid, liquid, or gas
but is usually one of the first two.
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Diagram
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UNDERSTANDING THE WORKING
One face of the scintillator isplaced in optical contact with thephotosensitive surface of the
photomultiplier or PIN diode. Inorder to direct as much as possibleof the light flash to the
photosensitive surface, reflectingmaterial is placed between thescintillator and the inside surface
of the container.
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In many cases it is necessary tocollect the light from a large areaand transmit it to the small surface ofa photomultiplier. In this case, a
“light pipe” leads the light signalfrom the scintillator surface to thephotomultiplier with only small loss.The best light guides and light fibers
are made of glass, plastic, or quartz.It is also possible to use lenses andmirrors in conjunction with scintillatorsand photomultipliers.
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BLOCK DIAGRAM
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Applications for scintillation
counters
Scintillation counters can be used tomeasure radiation in a variety ofapplications.
Medical imaging
National and homeland security
Border security
Nuclear plant safety
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Radioimmuno Assay (RIA)
An immuno procedure involving the useof radioisotope
Is a very sensitive technique used tomeasure concentrations of antigens byuse of antibodies.
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HISTORY
It was developed by Yalow andBerson to study blood volume andiodine metabolism.
later adapted the method to studyhow the body uses hormones,
particularly insulin, which regulates
sugar levels in the blood.
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Types of RIA
1. Unlabeled antigen (Ag)
- substance being analyzed
2. Radiolabeled Antigen (Ag)
-acts as label
3. Antibody
- provide binding site for thetwo antigens.
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The Technique
A mixture is prepared of
radioactive antigen
○ Because of the ease with which iodine atoms can beintroduced into tyrosine residues in a protein, the
radioactiveisotopes 125
I or 131
I are often used. antibodies ("First" antibody) against that antigen.
Known amounts of unlabeled ("cold") antigen areadded to samples of the mixture. These competefor the binding sites of the antibodies.
At increasing concentrations of unlabeled antigen,an increasing amount of radioactive antigen isdisplaced from the antibody molecules.
The antibody-bound antigen is separated (seebelow) from the free antigen in the supernatant
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The Technique
The radioactivity of each ismeasured.
From these data, a standard binding
curve, like this one shown in red, canbe drawn.
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The Technique
The samples to be assayed(the unknowns) are run in parallel.
After determining the ratio of bound
to free antigen ("cpm Bound/cpmFree") in each unknown, the antigenconcentrations can be read directly
from the standard curve (as shownabove).
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Uses of RIA
narcotics (drug) detection,
blood bank screening for the hepatitis (ahighly contagious condition) virus,
early cancer detection, measurement of growth hormone levels,
tracking of the leukemia virus,
diagnosis and treatment of peptic ulcers,and
research with brain chemicals calledneurotransmitters.
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