2004 Progress Report: Speciation of chromium in environmental media using capillary electrophoresis with multiple wavlength UV/visible detection

EPA Grant Number: R828771C005
Subproject: this is subproject number 005 , established and managed by the Center Director under grant R828771
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: HSRC (2001) - Center for Hazardous Substances in Urban Environments
Center Director: Bouwer, Edward J.
Title: Speciation of chromium in environmental media using capillary electrophoresis with multiple wavlength UV/visible detection
Investigators: Stone, Alan T. , OMelia, Charles R.
Institution: The Johns Hopkins University
EPA Project Officer: Klieforth, Barbara I
Project Period: October 1, 2001 through September 30, 2002
Project Period Covered by this Report: October 1, 2003 through September 30, 2004
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management

Objective:

Capillary electrophoresis (CE) is a new analytical method that offers more reliable information than existing methods and allows entirely new species to be discerned. In some instances, detection limits can also be lowered. Our overall objective is to use capillary electrophoresis with photodiode array to detect dissolved chromium in contaminated waters.

The scientific literature provides procedures for the synthesis and purification of a variety of CrIII complexes with commercial aminocarboxylic acid chelating agents such as IDA, NTA, and EDTA. Previous reports have focused on using these standardized complexes to explore CrIII speciation. Our previous findings have considerable relevance for sites where contaminant mixtures (chromium and synthetic chelating agents) have been introduced into environmental media.

Chromium contamination without the presence of synthetic chelating agents is possible. The chelating properties of natural organic matter (NOM) merits consideration. Prior literature has reported that NOM is rich in oxygen-donor Lewis Base groups (e.g. carboxylic acid, alcohol, and phenol functional groups) but deficient in nitrogen-donor Lewis Base groups. The objectives of this research are to: (1) explore CrIII speciation in the presence of surrogate organics that possess the functional groups dominant in NOM; and (2) explore CrIII speciation in the presence of actual NOM.

Progress Summary:

Our first submitted paper (Carbonaro and Stone, 2004), which focuses on CrIII complexes with synthetic aminocarboxylic chelating agents, has been favorably reviewed by Analytical Chemistry; a revised draft currently is being prepared. During the past 12 months, our focus has been on ways that NOM affects chromium speciation, and the extent to which this speciation can be discerned by CE.

Salicylic acid has been used for more than 20 years as a low molecular-weight surrogate for NOM. Carboxylic acid groups and phenolic groups are believed to be the principal Lewis Base groups of terrestrially-derived NOM. The placement of the phenol group ortho- to the carboxylic acid group enables the fully deprotonated form, the salicylate dianion, to coordinate metal ions through a six-membered chelate ring. Our research has focused on salicylic acid plus the six more complex structures. 5,5’Methylenedisalicylic acid (VI) and pamoic acid (VII) are especially interesting; multiple functional groups on two rings might capture some of the complexity of real NOM.

Free, uncomplexed species at pH 7 predominantly consist of deprotonated carboxylate groups and protonated phenol groups. Metal ion coordination encourages deprotonation of the phenol group. The molecular charges of some of the possible complexes with CrIII are listed in Table 1.

Table 1. Molecular Charge of Some Possible CrIII Complexes

Molecular Charge of Some Possible Cr<sup>III</sup> Complexes

Buerge (1999) had analyzed cationic CrIII complexes of salicylic acid using CE in cation mode (acetate buffer). To aid in the detection of 1:1 complexes, we have replicated his approach and explored modifications (e.g. pH 7.0 phosphate or MOPS buffers). In each case, the representative chelating agent and CrIII inorganic salt are brought together at elevated temperature for a pre-specified contact time. Although peaks can be discerned in both cation-mode and anion-mode CE, interpretation must contend with (1) the absence of authentic standards for particular complex stoichiometries, and (2) the unavailability of thermodynamic information (i.e., equilibrium constants) that would allow us to calculate expected equilibrium concentrations corresponding to the different possible CrIII.L stoichiometries.

In a more direct approach, we have spiked solutions prepared from freeze-dried Great Dismal Swamp NOM with chromate anion (CrO42-). During the first 24 hours, the peak corresponding to the chromate anion declines and is gradually replaced by three well-defined peaks. Over a period of several days, these peaks also decay. The transient nature of these peaks intrigues us and forces us to consider several new questions:

  • What reductant moieties within NOM are capable of reducing CrVI?
  • Does the chromium remain coordinated to the organic compound responsible for its reduction?
  • How can we confirm that the peaks correspond to CrIII and not CrIV or CrV species?
  • Would NOM from locations other than the Great Dismal Swamp yield similar peaks?

References:

Buerge I. Influence of pH, organic ligands, and mineral surfaces on the reduction of chromium(VI) by iron(II). Ph.D. Dissertation, ETH, Zurich, Switzerland, 1999.

Future Activities:

We will focus our future work on new chromium species created in the chromate plus NOM reaction. Spectral features recorded by the diode array detector may offer important clues regarding peak identity. Using other low molecular weight surrogates for NOM also may be informative, especially surrogates that represent possible reductant moieties (e.g. catechols and saccharides).


Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other subproject views: All 5 publications 1 publications in selected types All 1 journal articles
Other center views: All 108 publications 22 publications in selected types All 20 journal articles
Type Citation Sub Project Document Sources
Journal Article Carbonaro RF, Stone AT. Speciation of chromium(III) and cobalt(III) (Amino)carboxylate complexes using capillary electrophoresis. Analytical Chemistry. 2005;77(1):155-164. R828771C005 (2004)
not available

Supplemental Keywords:

chromium, capillary electrophoresis, natural organic matter, toxics, exposure, hazardous substances, chemical detection technique, assessment, cleanup, risk communication,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Waste, Water, Hydrology, Chemical Engineering, Environmental Chemistry, Geochemistry, Health Risk Assessment, Risk Assessments, Analytical Chemistry, Hazardous Waste, Physical Processes, Chemistry and Materials Science, Ecological Risk Assessment, Ecology and Ecosystems, Hazardous, Engineering, Chemistry, & Physics, Environmental Engineering, electrochemical technology, fate and transport, hazardous waste treatment, aquatic ecosystem, chemical exposure, contaminant transport, contaminant dynamics, fate and transport , analytical measurement methods, environmental risks, exposure, chemical composition, chemical detection techniques, ecotoxicological effects, adsorption, chemical kinetics, human exposure, chromium speciation, groundwater contamination, chemical releases, capillary elecrophoresis, capillary electrophoresis, hydrodynamics, groundwater, hazardous substance contamination

Relevant Websites:

http://www.jhu.edu/hsrc Exit

Progress and Final Reports:

Original Abstract
  • Final

  • Main Center Abstract and Reports:

    R828771    HSRC (2001) - Center for Hazardous Substances in Urban Environments

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R828771C001 Co-Contaminant Effects on Risk Assessment and Remediation Activities Involving Urban Sediments and Soils: Phase II
    R828771C002 The Fate and Potential Bioavailability of Airborne Urban Contaminants
    R828771C003 Geochemistry, Biochemistry, and Surface/Groundwater Interactions for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts
    R828771C004 Large Eddy Simulation of Dispersion in Urban Areas
    R828771C005 Speciation of chromium in environmental media using capillary electrophoresis with multiple wavlength UV/visible detection
    R828771C006 Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas
    R828771C007 The Center for Hazardous Substances in Urban Environments (CHSUE) Outreach Program
    R828771C008 New Jersey Institute of Technology Outreach Program for EPA Region II
    R828771C009 Urban Environmental Issues: Hartford Technology Transfer and Outreach
    R828771C010 University of Maryland Outreach Component
    R828771C011 Environmental Assessment and GIS System Development of Brownfield Sites in Baltimore
    R828771C012 Solubilization of Particulate-Bound Ni(II) and Zn(II)
    R828771C013 Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
    R828771C014 Research Needs in the EPA Regions Covered by the Center for Hazardous Substances in Urban Environments
    R828771C015 Transport of Hazardous Substances Between Brownfields and the Surrounding Urban Atmosphere