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&EPA United States Environmental Protection Agency Research and Development Test Method Environmental MOnitoring and Support Laboratory CinCinnati OH 45268 Chromium, Dissolved Hexavalent (Atomic Absorption, Furnace Technique)-Method 218.5 1 Scope and ApplicatIon 1 1 ThIs method covers the determination of dIssolved hexavalent G chromium (Cr +) In drinking and surface waters The method may also be applicable to certain domestic and industrial wastes after fIltratIOn provided that potential Interfernng substances are taken Into account (See 4 1 ) 1 2 The method may be used to analyze samples containing from 5 to G 100 /1g of Cr + per liter The range of the method may be extended upward by dilution 3 Sample Handling and PreservatIon 3 1 For sample handling cleaning glassware and the filtration procedure see part 4 1 of the AtomIc Absorption Method section of thiS manual 3 2 The sample must not be preserved by aCidification, but Instead transported and stored until time of analysIs atAOC G 3 3 Stability of Cr + In environmental samples IS n ot completely understood at thIS time The chemical nature of the sample matrix can have a definite affect on the chemistry of chromium Therefore the analysIs should be carned out as soon as possIble but no longer than 24 hours after collection Summary of Method aCid After separation, the supernate G IS drawn off and the Cr precipitate resolubllized In nitriC aCid as trivalent 3 chromium (Cr +) and quantifIed by furnace atomic absorption 2 2 Hexavalent chromium may also be analyzed by the chelationI extractIOn technique (see Method 218 4 or the procedure described In 9 2 of the Atomic AbsorptIon methods found In thiS manual) 2 The method IS based on the 2 1 separation of CrG+ from the sample by copreclpltatlon of lead chromate wIth lead sulfate In a solution of acetic 4 2185-1 Dec 1982 Interferences 4 2 Samples With eIther sulfate or chlOride concentratIons above 1000 mg/llter should be diluted before analYSIS 4 3 The potential reductIOn of CrG+ from highly reductive substances Increases as pH IS lowered When sulfltes and sulfIdes are present the The possible Interference from 4 1 other elements which form stable chromates IS not known at thIS tImePDF Image | Methods for Chemical Analysis of Water and Wastes
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