IS…the use of absorption, emission or scattering of electromagnetic
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10/27/2009 The usage of the atomic absorption spectrophotometer is very widespread, and is important for determining the abundance of almost 70 different elements The machine is mostly used to determine very low concentrations, of mainly metallic elements The cost for a new AAS can run anywhere from around 40,500.00 USD http://www.tradekey.com/product_view/id/390838.htm http://docs.google.com/gview?a=v&q=cache:vyowqbhTsXUJ: www.standardbase.com/tech/FinalHUTechAAS.pdf+Atomic+A bsorption+Spectrophotometer+%28AAS%29&hl=en&gl=us&s ig=AFQjCNHF8V2EJ65rH-axWe9GwX86z08PsQ IS…the use of absorption, emission or scattering of electromagnetic radiation by atoms or molecules to qualitatively or quantitatively study the atoms or molecules and d their h processes. An interaction of radiation with matter can cause transitions between energy levels… Widely used for the analysis of trace metals in a variety of matrices. Including concentration determination of metals in… Transition from higher level to a lower level is EMISSION Transition from a lower level to a higher level is ABSORPTION Water/wastewater and air Blood, urine, muscle tissue, hair . Oil, sediment and rocks Dating back to the 1800’s, scientists such as Kirchoff, Bunsen and Angstrom studied the composition of the sun based on emission of different wavelengths The idea of AAS works on this idea that matter will absorb light at the same wavelength at which it emits light. A scientist by the name of Woodson first applied these principles with his detection of Mercury in the 1900’s. The earliest scientist to used the idea similar to modern Atomic Absorption Spectrophotometry was named Walsh, and he suggested that the used of cathode lamps to provide emission of appropriate wavelengths, and he also suggested the use of flames to produce neutral atoms that would then absorb the emitted cathode light as they crossed the flame path. Elements that are completely detectable using an AAS include the following on the Periodic table, here that are marked in red LIMITATION: cant really analyze the concentrations of NON-metals Useful, because as geologist, we are interested in the amount of metals and their concentration in rock samples http://www.cee.vt.edu/ewr/environmental/teach/smprimer /aa/aa.html#Features 1 10/27/2009 AAS uses the idea that atoms at the ground state absorb light of characteristic wavelength passing through an atomic vapor layer of the element. Ground state metals absorb light g at specific p wavelengths Metal ions in a solution are converted to atomic state by means of a flame or graphite Light of the appropriate wavelength is supplied and the amount of light absorbed can be measured against a standard curve The process of converting a sample in solid, liquid or gas form into a free atom. Because the sample has usually gone under p preparation p and is in solution, there are two general methods used by scientists for atomization Flame Atomization Electrothermal Atomization Due to the extreme sensitivity of the instrument, only a small amount of sample is necessary when running the analysis AAS is a destructive technique, that is only solutions containing g the investigated g element can be usedÆ This supporting that AAS is used to determine concentrations of elements Solid samples are accurately weighed, dissolved (usually with strong acids) and then the solution is evaporated and all materials present in the sample are vaporized and dissociated to atoms at the very high temperature that is used by the AAS Flame Atomization Requires less expertise from the operator Better for analyzing samples with large concentrations which may be too large for the electro thermal method Subject to fewer interferences Less sensitive…good and bad… Electrothermal Atomization Good method of choice when you have a limited amount of sample Good to use when there is little concentration of the desired element in the given sample After atomization and the sample has become a mixture of free atoms and the combustible gas, the mixture is ignited in a variety of flame types Different flames are made by different mixtures of gas http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/aa.html# Features Some elements can only be converted to free atoms at high temperatures http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/ aa.html#Features The most common and reliable method for analysis by an Atomic Absorption Spectrophotometer 2 10/27/2009 http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/aa.html #Features Usually the apparatus includes… A light source that emits light with element specific wavelengths Atom cell Monochromator Detector Amplifier http://www.cee.vt.edu/ewr/environmental/teach/smprimer/a Signal Display a/aa.html#Features Data Station This stable light source emits a light that is specific to the element which is being analyzed. Some cathode lamps can be used for at most 3-4 different elements http://www.cee.vt.edu/ewr/environmental/teach/ smprimer/aa/aa.html#Features Its function is to convert the LIGHT signal, into an electric signal, which is processed further by a signal amplifier. - This signal can then be displayed for read-out and concentration determination MOST IMPORTANT: atomizes the sample and turns it into a fine mist as free atoms, where it then passes through the flame of a specific composition Not all of the sample makes it through the flame, part is disposed and gathered in the disposal contained located at the bottom Absorption of light is directly proportional to the number of atoms absorbing it. Deviations from the linear usually occur, and by measuring the deviations from the th curve you can determine d t i the th concentration of the metal in the sample The more concentrated the sample is, the higher absorbance is measured. Isolates the specific spectrum line emitted by the light source through spectral dispersion and focuses it on the… Any factor that can affect the ability of the instrument to give a correct reading include… The formation of compounds that don’t dissociate in the flame…usually occurs with Ca and Sr phosphates h h t Interferences due to differences b/t surface tension and viscosity of test solutions and standards BROADENING OF A SPECTRAL LINE… à Doppler effect à Lorentz Effect http://www.cee.vt.edu/ewr/environmen tal/teach/smprimer/aa/aa.html#Featur es 3 10/27/2009 Gonzalez, Georgina and Ma, Guihua., 1997. Flame Atomic Absorption Spectrometry. http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/aa.html#Features Tissue, Brian., 1996-2000. INTRODUCTION TO ANALYTICAL SPECTROSCOPY. http://www.files.chem.vt.edu/chem-ed/courses/spec/index.html Luca, Szalay., Atomic Absorption Spectrophotometry (AAS). Petrik Lajos Vocational y Environmental Sciences and Information Technology, gy School for Chemistry, Budapest, Hungary. 4
