UMD CHEM 425 - AASLabreport (10 pages)

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AASLabreport



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AASLabreport

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Pages:
10
School:
University of Maryland, College Park
Course:
Chem 425 - Instrumental Methods of Analysis

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AAS Intro Atomic Absorption Spectroscopy AAS is an analytical laboratory technique that converts the analyte of study into a gaseous state for quantitative determination of the chemical species using the Beer Lambert Law1 AAS relies on the quantum principle that the ground state energy of an atom absorbs a discrete amount of electromagnetic radiation before it is excited to a higher state energy This radiation is absorbed in the form of a wavelength with each element corresponding to its own wavelength thus giving AAS a great degree of selectivity1 This is done by exciting the free atoms via optical radiation using a special hollow cathode lamp containing the element of interest allowing for the precision required for the excitation wavelength2 Another advantage of using AAS is it s easy use and relatively inexpensive cost when compared to other types of high precision spectroscopy However AAS also contains its disadvantages Since AAS relies on the nebulization of the analyte only solutions can be analyzed In addition AAS has less sensitivity than a graphite furnace which allows for analysis of smaller samples between 5 60 L whereas AAS requires samples in the range of 1 3 mL2 AAS can only be used for quantitative analysis of an element whereas atomic emission or atomic fluorescence are quantitative and qualitative instruments The first step in analyzing a chemical s atomic components is to atomize the sample1 For this lab the sample was atomized via a high temperature flame that was generated via a mixture of compressed air and fuel specifically an air acetylene flame at a temperature of about 2 300 C1 Once the liquid sample is decomposed into its atomic constituents the hollow cathode lamp is shined and allowed to pass through a collimating lens at the sample s corresponding absorption wavelength The absorption of light by the atomic components is then used to determine the sample s concentration once it passes through a monochromator wavelength selector This is because the absorption of the light from the hollow cathode lamp is linearly proportional to the sample concentration via the Beer Lambert relationship shown in Figure A4 up to a range of 0 1 to 0 8 units another disadvantage of AAS as our least concentrated standard had an absorbance below 0 12 A general scheme for the setup and instrumentation is illustrated in Figure B below5 Figure A Beer Lambert Law visual representation of incident light and relationship to concentration4 Figure B Atomic Absorption Spectrometer Block Diagram5 For this experiment we were interested in using the atomic absorption spectrometer in order to better understand the effectiveness of releasing agents towards overcoming matrix effects and chemical interferences This will be done by first completing a routine AAS analysis on trace amounts of the metal calcium in millipore water containing diluted HCl These results will then be compared with calcium solutions consisting of various added reagents that were



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