Atomic Emission Spectroscopy (AES) Devon Brown SUPA Forensics Block 4

What Is AES? A method of chemical analysis that measures the intensity of light emitted by the atoms of elements at specific wavelength

Chemical Principles Electrons from a higher energy level drop to a lower energy level Electron emits a photon of light to dispose of extra energy

How it Works Flame, spark, or plasma excites the electrons Electrons jump to a higher energy level As electrons return to ground state, they release a photon Instrument measures intensity of photons and their wavelength Determines elements present and they’re quantity

Emission Lines The frequency of an atom moving from a high energy level to a lower energy level Wavelengths of photons emitted create lines Each element has unique emission lines Qualifies elements present in sample

Emission Band Graph of the intensity of the light emitted from a sample Intensity is a function of the wavelength Separates various elements by color (like emission lines) Quantifies the amount of an element in a sample

Flame Atomic Emission Spectroscopy Sample is in the form of a sprayed solution or gas Flame heat evaporates solvent and breaks chemical bonds Produces free atoms of the material Heat changes atoms into electrically charge particles Emit light as they lose energy Wavelength of light characteristic to specific element Light dispersed by a prism and detected in spectrometer

Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) Inductively coupled plasma produces excited ions Ions and atoms radiate electromagnetically charged particles Wavelengths produced correspond to a definite element

Uses Determine the proportional quantity of a particular element in a given sample Determine the elemental composition of an unknown sample Study structures of atoms Analyzing motor oils Determine the presence of arsenic in food and metals in wine Study trace elements that are bound to proteins

AES in Forensic Science

Uses Analyze trace elements in soil Determine origin Determine the composition of metallic and glass samples Determine origin and/or manufacturer Confirm a poison Detect a drug

Evidence Preparation: samples must be converted into highly excited free atoms Solid samples (glass, soil, metal alloy) Directly vaporize sample Excite sample by using a laser pulse or spark between electrodes Introduced to a exciting source by a semiliquid mixture or melted by a laser in a stream of gas Liquid samples (bodily fluids, unknown solution) Reduced to a fine spray Carried to exciting source by flowing gas

Safety and Hazard Issues Chemicals tested can be very dangerous Keep away any flammable materials Extreme temperatures Glass and metal samples can have sharp edges Biological samples can contain poisonous materials and disease

Difficulties/Interference Self-absorption Flame’s temperature is greatest at center – concentration of excited atoms greater at center Atoms around outer edges not in the same state Excited atom emits a photon – grounded atoms in outer regions of flame may absorb photon Decrease the emission intensity

Limitations Originally: High possibility of chemical interaction Need a fairly large sample Sensitivity of instruments low Instability of atomization source Cannot conduct simultaneous or multi-elemental analyses With the development of technology, most of these limitations have been overcome.

Advantages Disadvantages Equipment is more expensive Several elements can be recorded at once Higher temperatures means lower inter-element interference Several elements can be analyzed from a very small sample Nonmetals can be determined by plasma Low concentration refractory compounds can be determined High concentration range for plasma sources Equipment is more expensive Procedure is more complicated More time consuming Higher operating costs

Works Cited “Atomic Spectroscopy.” Andor: An Oxford Instruments Company. www.andor.com. Web. March 29, 2015. Banerjee, Prasenjit. “Atomic Emission Spectroscopy.” Chemistry Learner. www.chemistrylearner.com. Web. March 17, 2012. March 30, 2015. Cylinder, Drew. “Atomic Spectra.” UC Davis Chemwiki. chemwiki.ucdavis.edu. Web. March 29, 2015 Harvey, Davis. “Atomic Emission Spectroscopy.” UC Davis Chemwiki. chemwiki.ucdavis.edu. Web. March 29, 2015. Rosen, Vasiliy, Ph.D. “Atomic Spectroscopy: Basic Principles and Instruments.” Slideshare. www.slideshare.net. Web. March 28, 2011. March 29, 2015. Scheeline, Alexander and Spudich, Thomas M. “Atomic Emission Spectroscopy.” Analytical Science Digital Library. www.asdlib.org. Web. March 30, 2015. Spencer, James T, Ph.D. An Introduction to Forensic Science: The Science of Criminalistics. Cengage Learning. 2007-2012. March 29, 2015 Stone, David C, Ph.D. “Atomic Spectroscopy: Intrumentation, Techniques, and Theory.” Chemistry University of Toronto. www.chem.utoronto.ca. Web. May 7, 2012. March 29, 2015. Troy, David B. The Science and Practice of Pharmacy. Remington. 2006. books.google.com. Web. March 30, 2015.