University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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NIST 2109

Citations 1

"Selective Flow Injection Quantitation Of Ultra-trace Amounts Of Chromium(VI) Via Online Complexation And Preconcentration With APDC Followed By Determination By Electrothermal Atomic Absorption Spectrometry"
Anal. Chim. Acta 1998 Volume 366, Issue 1-3 Pages 163-176
Steffen Nielsen and Elo H. Hansen

Abstract: A rapid, sensitive and selective time-based flow injection (FI) pre-concentration procedure is described for the determination of ultra-trace amounts of Cr(VI) via online reaction with ammonium pyrrolidine dithiocarbamate (APDC) and formation of the Cr(VI)-PDC complex. The pre-concentration is effected by adsorption on the inner wall of a knotted reactor made from PTFE tubing. The complex is subsequently eluted with a monosegmented discrete zone of ethanol (55 µL), and the analyte is quantified by electrothermal atomic absorption spectrometry (ETAAS). The operations of the FI-system and the ETAAS-detector are synchronously coupled. Efforts were made to design a generic and versatile FI-ETAAS system that allows all necessary manipulatory operations to be executed online which, in addition to effective entrapment of the analyte in the pre-concentration unit, comprise washing the surface of the retained analyte to remove possibly interfering matrix components; quant. dissolution of the retained analyte in the smallest possible volume of eluent to satisfy the volumetric requirements of the graphite tube (platform); reproducible transport of the concentrate to the ETAAS instrument at minimal dispersion; and, finally, a thorough cleansing of all pertinent conduits in the FI-system to prevent carry-over between individual samples. A 19-fold enhancement in sensitivity of Cr(VI) was achieved after pre-concentration for 60 s at a sample flow rate of 5.0 mL min-1 as compared to direct introduction of 55 µL samples, yielding a detection limit (3s) of 4.2 ng L-1. The sample frequency was 21.2 samples per h. The proposed method was evaluated by analyzing drinking water, a NIST Cr(VI)-ref. material and synthetic sea water. A major contribution to successful operation of the system can, to a large extent, be ascribed to the incorporation of a newly developed mixing-point component, which is attached directly to the commercial available 8-port rotary valve.
Chromium(VI) Spectrophotometry Preconcentration Ammonium pyrrolidine dithiocarbamate Knotted reactor Complexation Interferences Reference material Mixing Tube wall immobilization