A method to determine hexavalent chromium in environmental solid waste has been developed by using an ammonium complexation technique in ICP-AES. This method consists of a two-step extraction and the complexation of ammonium ion. An ammonium hydroxide solution was used to extract the chromium(VI) out of the fly ash sample into the solution. Interfering metal ions, such as Pb, Fe, and Zn in the fly ash sample, were effectively removed by extracting them as diethyldithio-carbamate (DDTC) complexes at pH 9.5 into an MIBK (methyl isobutyl ketone) solution. The pH of the aqueous phase of the sample is then transferred and adjusted to 6.0, and the Cr(VI) is extracted as its complex with MIBK prior to the organic ICP analysis. A method detection limit of 50 ng/g or better, as well as spike recoveries of 90 to 110% (at a spike concentration level of 500 ng/g), is obtained when this method is applied to determine chromium(VI) in fly ash samples.
J. David Hwang and Wen-Jwu Wang, "Determination of Hexavalent Chromium in Environmental Fly Ash Samples by an Inductively Coupled Plasma-Atomic Emission Spectrometer with Ammonium Ion Complexation," Appl. Spectrosc. 48, 1111-1117 (1994)