Volumetric Gravimetric Procedures & Scintillation Counter, Radioimmunoassay

8/4/2019 Volumetric Gravimetric Procedures & Scintillation Counter, Radioimmunoassay

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VOLUMETRIC, GRAVIMETRICPROCEDURES

SCINTILLATION COUNTER &RADIOIMMUNOASSAY

Diana Mae CabreraPamela Marie Chua

BSMT IIIA



Volumetric Procedures

Also known as Titrimetry

Are quantitative analytical techniqueswhich employ a titration in comparing

an unknown and a standard.



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



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



Indicators:○ Internal Indicators – compounds

○ External Indicators – electrochemical devices

End point

- Point at which titration is stopped



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



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



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



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



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.



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



Gravimetric Procedures

It is the isolation of the pure form of

sample and its derivatives and thedetermination of its dry weight.



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.



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.



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.



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.



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



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.



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.



Diagram



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.



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.



BLOCK DIAGRAM



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



Radioimmuno Assay (RIA)

An immuno procedure involving the useof radioisotope

Is a very sensitive technique used tomeasure concentrations of antigens byuse of antibodies.



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.



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.



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.



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).



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.



References:

Volumetric Gravimetric Procedures & Scintillation Counter, Radioimmunoassay

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