Atomic Absorption Spectroscopy

Yash Purohit

Block 4

AAS UsesMeasures the light absorbed by the atoms of a

sample then compares it to a set of known standard concentration

It used in different ways for different fields of workMining:

Measure the concentration of metals such as gold to know whether to mine there

Food and drug inspections To measure concentration of certain harmful things in

food and drugs

AAS Uses Continued Environmental:

It is also used in air samples to see if lead or mercury is present

Petrochemical:  analyzing products for metals and other substances

that can have adverse affects such as oil and gasPharmaceutical:

For quality control so not to much of a substance is put into the drug

How It Works Sample is introduced into the machine Nitrous oxide flows into the machine where the

solution is, in the nebuliser, and creates a vacuum The solution in that vacuum is converted into a gas With the gas is forced into the flame, which is a

really high temperature (2000°C) This atomizes it and separates the particles

Now a light usually a hollow cathode lamp is shined into the center of the flame

Any light not absorbed is passed into the monochromator and detector

Atomizers FlameElectro thermalVapor generation (cold and heated) PlasmaArc and spark

Types of Data Even with small amounts of the element over 65

different elements can be detected Using the wavelengths absorbed and set absorbance

spectrum we can find out the element (qualitative) The concentration of an element can also be

determined by using known standard concentration solutions (quantitative) You would use 5 known concentration solutions and

get their absorbance then make a calibration curve Next put the unknown to find the absorbance Beer-Lambert law A=abc

Relation to Forensic Science

Used in a variety of analyses in forensics scienceLike in food poisoning cases you could us AAS to

check of toxic material. For example chocolate it is used to find toxic

cadmium You would take small but representative sample of

the food would need to be turned it into gas by heating it then put in the machine

Different wavelengths of light will be shined at the gas and flame

Relation to Forensic Science continued

Also gunshot residue some one suspected of shooting could have there hand and clothes swabbed to check for high amounts of lead and other elements found in gun powder Similar to the food the gun powder would have to be

turned into a gas then put in the machine Different wave lengths will be sent to see which is

absorbed Since each element is different based on which are

absorbed you can figure out the element

Relation to Forensic Science continued

Very important for forensics science is soil samples. If soil is found on a person AAS can be used to find

the elements that are most abundant in the soil Then it will be traced to a location with similar

amounts of the element in the soil. Obviously done through comparing the sample you

have to others taken

Real Life Case Use Suicide case of a 52 year old womenShe took some poison that was said to have

arsenic trioxide (As2O3)Blood, bile and liver samples were taken from the

dead women Then using AAS the samples were analyzed to find

the elements in the samplesAfter that, reference sample solutions were made

with known amounts of arsenic trioxide in them Calibration curve was made to then find

concentration of the unknown

Chemical PrinciplesThe solution is put into the machine where it under

goes a phase change and only the elements remain

After they are forced into the flame a light is shined at the center where the free atoms are The electrons then absorb certain wavelengths and

go from the ground state to higher states Since every element has a different absorption

spectrum that is just for that element you can figure out which element or elements are present

Safety When starting the flame be careful it is extremely

hot and make sure to close the latch in front of the flame

Gases being used in vacuum like nitrous oxide when broken down can help start fires

Do not view the flame directly or you could go blindMake sure vents are properly working so the gas

can removed When using AAS starting fires and causing

explosions are the biggest safety issues.

InterferenceMachine interference could be the spectral lines of

two or more elements are over lapping one another In this case you would not be able to find the

elements present Chemical interference occurs when analyte do not

atomize completely For example an analysis for a sample of calcium you

have Calcium Chloride and Calcium Sulfate in a sample one atomizes but the other does not, the absorbance reading is worthless

Limitations Basically is only good for metals, non-metals have

to be analyzed indirectly Only a bit over 60 elements on the periodic table

will be rapidly detected Multiple elements cannot be detected at once For most flame atomic absorption the detection is

between 1microgram per liter and 3000microgram per liter Do not seem like to much but compared to others the

samples are bigThere is really no bias for this

Advantages Machine is fairly easy to use after the sample has

been put inVery few interferences Since there are different atomizers different types

of sample can be taken Solids, liquids, and gases Some machines are fasters than other and other get

more accurate data High precision data regardless of which type is

used

Disadvantages For flame atomic absorption only solutions can be

analyzed Graphite furnace atomic absorption has low

precisionFor all types a calibration curve needs to be

formed for quantitative analysisOne element has to be determined at a time

because each requires a special light source

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