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These above mentlOned techmques are presently conSidered as alternate test procedures and approval must be obtamed pnor to their use 2. Summary ofMethod 2.1 In direct asplratlOn atomic absorptlOn spectroscopy a sample IS aspirated and atomized m a flame A 11ght beam from a hollow cathode lamp whose cathode IS made of the element to be determmed IS drrected through the flame mto a monochromator, and onto a detector that measures the amount of 11ght absorbed AbsorptlOn depends upon the presence of free unexcited ground state atoms m the flame Smce the wavelength of the 11ght beam IS charactenstiC of only the metal bemg determmed, the 11ght energy absorbed bytheflameISameasureoftheconcentrationofthatmetalmthesample Thisprmclple is the basIs ofatOmlC absorptlOn spectroscopy 2.2 Although methods have been reported for the analysIs of so11ds by atomic absorption spectroscopy (Spectrochlm Acta, 24B 53, 1969) the techmque generally IS 11mlted to metals m solutlOn or solubl11zed through some form ofsample processmg 2 2 1 Pre11mmary treatment of wastewater and/or mdustnal effluents IS usually necessary because of the complexity and vanabl11ty of the sample matnx Suspended matenal must be subjected to a solublhzatlOn process before analysIs This process may vary because ofthe metals to be detefmlned and the nature ofthe sample bemg analyzed When the breakdown of orgamc matenal IS necessitated, the process should mclude a wet dlgestlOn with mtnc aCid 222 In those mstances where complete charactenzatlOn of a sample IS desired, the suspended matenal must be analyzed separately This may be accomphshed by filtratlOnandaCiddlgestlOnofthesuspendedmatenal Metalhcconstituentsmthis aCid digest are subsequently determmed and the sum of the dissolved plus suspended concentratlOns w111 then provide the total concentratlOns present The sample should be filtered as soon as possible after collection and the filtrate aCldlfied lmmedlately 2 2 3 The total sample may also be treated with aCid without pnor filtratlOn to measure what may be termed "total recoverable" concentratlOns 23 When usmg the furnace techmque m conJunctlOn with an atOmlC absorptlOn spectrophotometer, a representative ahquot of a sample IS placed m the graphite tube m the furnace, evaporated to dryness, charred, and atomized As a greater percentage of avallable analyte atoms are vaponzed and dissociated for absorptlOn m the tube than the flame, the use of small sample volumes or detection of low concentrations of elements IS possible The pnnclple IS essentially the same as with direct asprratlOn atomic absorptlOn except a furnace, rather than a flame, IS used to atomize the sample RadlatlOn from a given excited element IS passed through the vapor contammg ground state atoms of that element The mtenslty of the transmitted radlatlOn decreases m proportlOn to the amount ofthe ground state element m the vapor . MET ALS-2PDF Image | Methods for Chemical Analysis of Water and Wastes
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