What is AAS/Atomic Absorption Spectroscopy?

Double Beam AAS Schematic Diagram
Double Beam AAS Schematic Diagram

Atomic Absorption Spectroscopy is an instrumental analysis technique for rapid trace metal analysis.It is based on element specific wavelength light absorption by ground state atoms in the flame or electrothermal graphite furnace. It finds immense applications in the analysis for trace metals in soils, lakes, rivers, oceans, and drinking water, pharmaceuticals, foods and beverages, geological and mineralogical samples, petroleum products, biological fluids and specimens and forensic analysis. It is common to get results in ppm levels and a higher sensitivity of ppb levels when we using graphite furnace atomisation.

Why not start with a short video?

An illustrated video will depict the changes that take place when a sample containing a trace metal is aspirated into a flame. Such physical changes are accompanied by changes in absorption of light by ground state atoms and measurement of absorption signal for quantitative estimations is illustrated in the video.

Glossary of AAS terms

The glossary will help you to understand the terminology in case you aren’t already familiar with the technique.

Atomic Absorption SpectroscopyStudy of element specific light absorption by ground state atoms for estimation of concentration of the element in the sample solution.
AtomisationProcess of reduction of sample to ground state atoms by application of heat by means of a flame or a graphite furnace.
AtomThe smallest particle of an element or compound. It comprises of a central nucleus containing neutral particles called neutrons and positively charged protons. The electrons revolve the central nucleus in shells of different energy levels. The number of electrons equals the number of protons in the neutral atom.
Atomic Emission SpectroscopyQualitative identification and quantification of element by emission of characteristic wavelength of light on excitation of an element by means of a flame or plasma
Atomic Fluorescence SpectroscopyMeasurement of light emitted on decay of elements from excited states.Measurement is made at an angle to the optical beam path so that the detector sees only the fluorescence in the flame and not incidental light from the lamp.
AbsorbanceThe amount or fraction of incident light absorbed by the ground state atoms. It is directly proportional to the number of ground state atoms in the beam path and also on the optical path length of the flame in accordance to Beer Lambert law of light absorption
Absorbance unita ratio of intensity of transmitted flight to the intensity of incident light. It is a unit less quantity but is commonly expressed in absorbance units (EU)
Aspirationlosses of reduction of liquid sample stream into fine droplets for introduction into the flame
AcetyleneCommonly used gas as fuel to support combustion of the flame.Provides temperatures in the range 2150-23000C
ArgonGas used commonly as a filling gas in hollow cathode lamps and as sample carrier in graphite furnace analysis
AirUsed as oxidant in combination with acetylene as fuel gas to support the flame
Air compressorDevice for delivery of air to the atomic absorption spectrometer. Oil less air compressor is preferred as contamination from oil is thereby avoided
BurnerA component of AAS system made of solid metal body having slit on the flat top surface to provide the flame required for atomisation of the sample
Blaze angleIt is the angle of cut of a mechanically ruled grating at which the angle of incidence is equal to the angle of reflection so that light intensity is greatest with minimal loss due to diffraction. For greater efficiency dual blazed ratings are used which provide greater light throughput over the wavelength range of the spectrometer
Backgroundany extraneous light other than the transmitted light that reaches the detector and affects the signal absorption
Background correctionMeans applied to reduce the effects of background on the signal
ConcentrationThe amount of element present in a unit volume of solution.Usually expressed as ppm (mg/lit) or ppb (μg/lit)
Characteristic concentrationConcentration of an element expressed in mg/lit required to produce a 1% absorbance or 0.004 absorbance signal. Knowledge of characteristic concentration helps predict the concentration range required to produce optimum absorbance levels for analysis
CollimationCondensation of beam of light as per size requirement
CathodeAn electrode inside the lamp made from the pure metal whose analysis is required in the sample solution
ChopperA half transparent half opaque disc that rotates in the beam path to split the beam so as to alternately allow its passing through the sample or around it to give effective double beam performance
Cold vapour mercury analyserAnalyser fo mercury without using a heated sample cell as mercury is only element which exists as a liquid at room temperature
Deuterium sourcesA broadband light source for providing background correction in flame analysis
DetectorA component of the system that records the intensity of the transmitted light. Photomultiplier tube is the commonly used detector in AAS
Double beam systemOptical arrangement which alternately permits the light beam to pass through the sample and round it as a reference beam.
DesolvationRefrom sample droplets by heat inside the flame
Exhaust ventilation systemAn assembly for removal of hot corrosive combustion gases and vapours arising from the flame
Electrode/discharge lampa lamp used for analysis of volatile elements.It is a high energy light source which has a longer life than corresponding hollow cathode lamps.
ExcitationExcitation of a ground state atom to higher energy states by means of electromagnetic radiation
End CapRemovable cover of spray chamber that serves to introduce sample into spray chamber and also hold the nebuliser
Flow spoilerA device inside spray chamber used for removal of large droplets of sample
FlameAtomisation system which uses a flame. Commonly air – acetylene gas mixture or nitrous oxide – acetylene for higher temperature combustion
FlashbackReverse movement of flame inside burner towards spray chamber due to greater proportion of oxidant or even pure oxygen in flame. It often results to a loud explosion and damage to spray chamber
FurnaceA graphite tube about a cm long with a hole on top for atomisation of sample using electrical heating of the tube
FIASFlow injection analysis system for automated analysis using hydride generation
Graphite furnacesame as furnace
GratingA light dispersing device used in the monochromator
Hollow cathode lampA light source used for AAS analysis which is specific for metal to be analysed in the sample. For some elements multielement hollow cathode camps are also used
Hydride generation techniqueUsed for analysis of volatile hydride forming elements such as As, Bi, Ge, Pb, Sb, Se, Sn, Te.
Impact beadA device inside spray chamber for removal of large sized droplets from sample stream
InterferenceEffects resulting in variation of results due to spectral or non-spectral interferences
L’vov platformsmall platform made from solid pyrolytically coated graphite which is placed at bottom inside graphite tube. Sample is put into a depression in the platform. Permits uniform heating and delays atomisation till stable temperature conditions are preached inside the furnace
MonochromatorA device used for dispersion of incident light using prism or grating, reflecting mirrors and a combination of entrance and exit slits for isolation of required wavelength and collimation of the light beam
Mirror'sLight reflecting component of monochromator with a aluminium or gold coated surface to reduce corrosion damage and provide high reflectivity
MHSMercury hydride system for analysis of volatile elements by hydride formation
Matrix interferenceInterference arising due to differences in parameters such as viscosity, surface tension between sample and standards solutions
Microwave Reaction SystemAutomated digestion of samples in closed tubes using sonic waves. It offers advantages of speed of f digestion, cost and freedom from toxic vapours
Matrix modifierSubstance used for reduction of chemical interferences
NebuliserA device for producing an aerosol of sample inside spray chamber
OrificeSmall bore tube opening
PolychromaticA light dispersion device using an array of detectors for simultaneous detection of elements in a sample
Photomultiplier tube detectorA detection device used in AAS which amplifies the current produced by impact of photons on a light sensitive surface
PrismA light dispersing element
QuartzA UV transparent material used for making hollow cathode lamp and graphite tube end windows
Slit widthWidth of monochromator entry and exit slits expressed in millimeters
STPFStabilised temperature platform furnace is a combination of instrumental and analysis factors for providing high accuracy of results
Transverse heatingHeating of graphite furnace perpendicular to its axis to provide uniform heating of graphite tube along its length
UV rangeWavelength range 180 - 350 nm. Most elements have specific absorption bands in this region
Zeeman background correctionAdvanced background correction used in graphite furnace analysis involving application of a magnetic field perpendicular to the graphite furnace. Effective for background correction of complex matrices.
Refresh your concepts by registering for the free course which will provide you an introduction to the technique and even prepare you for an interview if you are applying for a job in the laboratory equipped with AAS systems.

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Want to read all the AAS free course modules right now? Here are all links to all the modules for you!
  1. Introduction to Atomic Absorption Spectroscopy course
  2. Module 1 : Scope of Spectroscopic Analysis
  3. Module 2 : Evolution of Atomic Absorption Spectroscopy
  4. Module 3 : Introduction to AAS component parts
  5. Module 4 : Types of Light Sources in AAS
  6. Module 5 : Flame Atomic Absorption Spectroscopy
  7. Module 6 : Graphite Furnace Atomic Absorption Spectroscopy
  8. Module 7 : Dispersion and Resolution of Light in Atomic Absorption Spectroscopy
  9. Module 8 : Interferences in Atomic Absorption Spectroscopy
  10. Module 9 : Background correction in Atomic Absorption Spectroscopy
  11. Module 10 : 10 Interview questions in Atomic Absorption Spectroscopy
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