title: Matrix isolation with an ion transfer device for interference-free simultaneous spectrophotometric determinations of hexavalent and trivalent chromium in a flow-based system.
abstract: Chromium speciation by spectrophotometric determination of hexavalent chromium (Cr(VI)) with diphenylcarbazide (DPC) has several problems. These include: (1) the inability to directly detect trivalent chromium (Cr(III)) with DPC, (2) positive interference in Cr(VI) determination by other metal cations and (3) negative interference by any reducing agent present in the sample. These are addressed with an ion transfer device (ITD) in a flow injection analysis system. We previously developed the ITD for electrodialytic separations. Here we separate oppositely charged Cr(III) and Cr(VI) species by the ITD into two different acceptor solutions within ~5 s. The acceptor solutions consist of buffered H2O2to oxidize the Cr(III) to Cr(VI). Then DPC is added to either acceptor to measure Cr(III) and Cr(VI) spectrophotometrically. The system was optimized to provide the same response for Cr(VI) and Cr(III) with limits of detection (LODs, S/N=3) of 0.5 μg L-1for each and a throughput rate of 30 samples h-1. The ITD separation was also effective for matrix isolation and reduction of interferences. Potential cationic interferences were not transferred into the anionic Cr(VI) acceptor stream. Much of the organic compounds in soil extracts were also eliminated as evidenced from standard addition and recovery studies.
authors.affiliation: Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan. Electronic address: ohira@sci.kumamoto-u.ac.jp.
authors.forename: Shin-Ichi
authors.initials: SI
authors.lastname: Ohira
authors.affiliation: Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan.
authors.forename: Koretaka
authors.initials: K
authors.lastname: Nakamura
authors.affiliation: Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan.
authors.forename: Mitsuki
authors.initials: M
authors.lastname: Chiba
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Arlington, 700 Planetarium Place, Arlington, TX 76019 USA.
authors.forename: Purnendu K
authors.initials: PK
authors.lastname: Dasgupta
authors.affiliation: Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Toda
keywords: Chromium; Diphenylcarbazide; Electrodialysis; Flow injection analysis; Soil extracts; Spectrophotometry