Atomic Absorption Spectroscopy Yash Purohit Block 4.
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Transcript of 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
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
"AAS Theory." AAS Theory. N.p., n.d. Web. 31 Mar. 2015. "Atomic Absorption Spectroscopy." Atomic Absorption Spectroscopy. N.p.,
n.d. Web. 31 Mar. 2015. "Atomic Absorption Spectroscopy." Chemical & Engineering News 60.8
(1982): 18. Web. 31 Mar. 2015. "Atomic Absorption Spectroscopy Learning Module." Atomic Absorption
Spectroscopy Learning Module RSS. N.p., n.d. Web. 31 Mar. 2015. Norheim, Gunnar. Arsenic Determination in Autopsy Material Using Atomic
Absorption Spectroscopy. N.p., n.d. Web. 31 Mar. 2015. "Tecmec Ltd - How Does Atomic Spectroscopy Work?" Tecmec Ltd - How
Does Atomic Spectroscopy Work? N.p., n.d. Web. 31 Mar. 2015.