Atomic Absorption Spectroscopy Yash Purohit Block 4

AAS Uses § Measures 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 work § Mining: § 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 gas § Pharmaceutical: § 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 § Flame § Electro thermal § Vapor generation (cold and heated) § Plasma § Arc 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 science § Like 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 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 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 women § She took some poison that was said to have arsenic trioxide (As 2 O 3) § Blood, bile and liver samples were taken from the dead women § Then using AAS the samples were analyzed to find the elements in the samples § After 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 Principles § The 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 blind § Make sure vents are properly working so the gas can removed § When using AAS starting fires and causing explosions are the biggest safety issues.

Interference § Machine 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 1 microgram per liter and 3000 microgram per liter § Do not seem like to much but compared to others the samples are big § There is really no bias for this

Advantages § Machine is fairly easy to use after the sample has been put in § Very 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 precision § For all types a calibration curve needs to be formed for quantitative analysis § One element has to be determined at a time because each requires a special light source

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