Research Project 5
| EPA Grant Number: | R828771-0-01 |
|
Title: |
Speciation of chromium in environmental media using capillary electrophoresis with multiple wavlength UV/visible detection |
| Investigators:
|
Principal Investigator: Alan T. Stone, Johns Hopkins University; Co-Investigator: Charles R. O'Melia, Johns Hopkins University |
| Institution: | Johns Hopkins University, Baltimore, MD |
| Project Period: | October 1, 2001 to September 31, 2004 |
| Description: |
| The speciation of chromium controls it's tendency to become adsorbed or precipitated, it's ability to be transported by water or wind borne particles, it's tendency to react with oxidants (e.g. O2, MnO2), reductants (e.g. FeII, natural organic matter), and ligands (e.g. carbonate, phosphate, natural organic matter) and it's toxicity towards humans and other organisms. The diphenylcarbazide (DPC) test for distinguishing CrVI from CrIII is currently the most commonly applied chromium speciation technique. |
| Objectives/Hypotheses: |
| In order to
resolve interference problems inherent in the DPC test and to gain new
information about CrIII speciation, we propose using: (i) capillary electrophoresis (CE) with multiple wavelength
UV-visible detection for identifying and quantifying CrVI and
CrIII dissolved species in surface waters, soil and sediment
interstitial waters, and in ground waters.
Small chromium-containing colloids are also found in many
samples. If time allows,
methods of characterizing these small colloids by CE will also be
investigated. We are presently the only U.S. group investigating the use of
CE for characterizing metal speciation.
Wayne Garrison (EPA, Athens, GA) is employing CE to characterize
natural and synthetic organic compounds. |
| Approach: |
| CE-based methods for accurately characterizing dissolved chromium in water and interstitial samples relevant to hazardous waste sites will be developed. CE efficiently resolves analytes based upon differences in molecular charge and hydrodynamic radii. We will investigate how (i) properties of the capillary wall and CE electrolyte medium; (ii) possible metal ion and ligand exchange reactions within the capillary; and (iii) non-chromium sample constituents affect the resolution and detection limit of CE. Authentic standards for CrIII complexes with low MW ligands likely to be encountered at hazardous waste sites will be synthesized; surface and subsurface water samples from pristine and chromium-contaminated field sites will be collected. Characterization of field samples of different pH, redox status, total chromium concentrations, and major constituent concentrations (total and dissolved iron, NOM, ionic strength) is an important part of this work. In the case of small colloids, the presence of FeIII and natural organic matter may affect colloidal charge and aggregation properties. |
| Expected Results: |
| A CE instrument equipped with diode-array UV-visible detector currently can be purchased for $50,000 and mastered in a few weeks by individuals lacking specialized training. Hence, CE-UV/VIS could become as common as GC-FID/ECD, HPLC-UV/VIS, and AAS in providing accurate information for risk assessment and risk management activities. We plan to demonstrate to environmental practitioners how new and accurate speciation information can be used to improve our understanding of the environmental behavior, health effects, and ecotoxicological effects of chromium. |