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Unformatted text preview: 1 Chemistry 223: Experiment 12 Determination of lead and zinc in water samples by F- AAS References : 1. C, Chapter. 20 . 2. H7, Chapter 21, 3. Kellner, Chap 8 4. SWH, Chaps. 24 5. Standard method for examination of water and waste water. EPA. 6. http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/aa.html I. Purpose of the experiment Atomic line absorption spectra are used for analyzing various metals. Atomic absorption spectrophotometry ("AAS") offers sensitivity, selectivity and simplicity and was developed by CSIRO Melbourne scientists around 1955. "AAS" is an important tool in analytical laboratories. Using this technique, students will be determine Pb and Zn in water samples by flame atomic absorbance spectroscopy. Students will also be familiar with QA/QC for the analytical procedure through the example of analyzing Pb and Zn in soluble species and total concentrations in water samples. II. Introduction Flame atomic absorption spectroscopy (F-AAS) is a very common technique for detecting metals and metalloids in solid and aqueous samples. It is very reliable and simple to use. The technique is based on the fact that ground state metals absorb light at specific wavelengths. Metal ions in a solution are converted to atomic state by means of a flame. Light of the appropriate wavelength is supplied and the amount of light absorbed can be measured against a standard curve. AAS quantitatively measures the concentrations of elements present in a liquid sample. It utilizes the principle that elements in the gas phase absorb light at very specific wavelengths which gives the technique excellent specificity and detection limits. The sample may be an aqueous or organic solution, indeed it may even be solid provided it can be dissolved successfully. The liquid is drawn in to a flame where it is ionised in the gas phase. Light of a specific wavelength appropriate to the element being analyzed is shone through the flame, the absorption is proportional to the concentration of the element. Quantification is achieved by preparing standards of the element. The technique of (FAAS) requires a liquid sample to be aspirated, aerosolized, and mixed with combustible gases, such as acetylene and air or acetylene and nitrous oxide. The mixture is ignited in a flame whose temperature ranges from 2100 to 2800 o C. During combustion, atoms of the element of interest in the sample are reduced to free, unexcited ground state atoms, which absorb light at characteristic wavelengths. The characteristic wavelengths are element specific and accurate to 0.01-0.1nm. To provide element specific wavelengths, a light beam from a lamp whose cathode is made of the element being determined is passed through the flame. A device such as a photonmultiplier can detect the amount of reduction of the light intensity due to absorption by the analyte, and this can be directly related to the amount of the element in the sample. 2 Flame atomic absorption hardware is divided into six fundamental groups that have two major...
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