Environmental Electrochemistry: Analyses of Trace Element Biogeochemistry

406 Pages·2002·46.14 MB·English

by  Martial Taillefert

Environmental Electrochemistry
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
ACS SYMPOSIUM SERIES 811
Environmental Electrochemistry
Analyses of Trace Element Biogeochemistry
Martial Taillefert, EDITOR
Georgia Institute of Technology
Tim F. Rozan, EDITOR
University of Delaware
American Chemical Society, Washington, DC
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
Library of Congress Cataloging-in-Publication Data
Environmental electrochemisty : analyses of trace element biogeochemistry / Martial
Taillefert, editor, Tim F. Rozan, editor.
p. cm.—(ACS symposium series; 811)
Includes bibliographical references and index.
ISBN 0-8412-3774-3 (alk. paper)
1. Environmental chemistry—Congresses. 2. Electrochemistry—Congresses. 3.
Trace elements—Environmental aspects—Congresses. I. Taillefert, Martial, 1967 - II.
Rozan, Tim F., 1964 - III. American Chemical Society. Division of Environmental
Chemistry. IV. American Chemical Society. Meeting (220th: 2001 : Washington, D.C.).
V. Series.
TD193.E553 2002
628.01'54137—dc21 2001053392
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In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
Foreword
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In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
Preface
Electrochemistry has been used extensively in the past three decades to
determine the chemical composition of environmental samples from the water
column, sediments, soils, biofilms, and microbial mats. These electrochemical
methods have many advantages over other analytical techniques for
environmental research: (1) the techniques are non-destructive, which minimize
sample perturbation, (2) the data can be collected rapidly and reproducibly, (3)
the detection limits have appropriate sensitivity for most environmental
applications, (4) direct information on the chemical speciation can be obtained,
(5) the instrumentation can be very compact, which is attractive for field
deployment, and (6) the electrochemical sensors can be miniaturized, allowing
for non-invasive in-situ sampling. For these reasons, electrochemical methods
are extremely useful tools for understanding complex natural biogeochemical
processes, however, the present literature lacks a comprehensive publication,
which details the current multidisciplinary uses of electrochemistry in natural
environments.
The goal of this American Chemical Society (ACS) Symposium Series
publication is to demonstrate the usefulness of electrochemical methods in
environmental research. The chapters are based on a Symposium on
Electrochemical Methods for the Environmental Analysis of Trace Element
Biogeochemistry that was organized at the 200th ACS National Meeting in
Washington, D.C. in August 2000. The chapters present instrumental designs
and techniques currently being employed by researchers and cover a wide range
of environmental applications including trace metal measurements in the water
column of freshwater and marine environments, redox chemical species at
hydrothermal vents, in anoxic water bodies, sediments and microbial mats, major
cations and anions in extraterrestrial systems, metal complexing properties of
natural waters, and mineral-water interface processes.
The book is targeted to all scientist whose goal is to better understand
trace element cycling in aquatic systems, including environmental chemists and
engineers, geochemists, soil scientists, marine chemists, and environmental
microbiologists who require tools to characterize the chemistry of microbial
environments.
To cover this wide array of interests we have divided the book's 19
chapters into six sections: (1) development and application of electrochemical
techniques for in-situ measurements in the water column of lakes, rivers, and
xi
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
oceans; (2) development and application of electrochemical techniques for on
-line measurements in the water column of lakes, rivers, and oceans; (3)
development and application of electrochemical techniques for in-situ
measurements at the sediment-water interface in lakes and marine systems; (4)
applications of electrochemical techniques for sediment and microbial mat
measurements; (5) novel electrochemical technologies in development or
destined to be utilized in extraterrestrial environments; and (6) recent
applications of electrochemical techniques for metal complexation studies. Each
section comprises a number of different research examples where a variety of
analytical techniques (voltammetric, potentiometric, amperometric) have
successfully been used to help understand biogeochemical processes in diverse
environments. Chapters were categorized according to their main focus, and
some may apply to more than one section. Therefore, we encourage the reader to
consult each individual chapter.
Acknowledgments
The editors are grateful to the authors for their outstanding
contributions, to the referees who contributed significantly to the quality of this
book by reviewing each chapter, and finally to the acquisitions staff of the ACS
Books Department. Special thanks to Anne Wilson and Kelly Dennis for their
patience and support during the acquisition of this book and to Margaret Brown
for editing and production.
Martial Taillefert
School of Earth and Atmospheric Sciences
Georgia Institute of Technology
Atlanta, GA 30332-0340
Tim Rozan
College of Marine Studies
University of Delaware
Lewes, DE 19958-1298
xii
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
Chapter 1
Electrochemical Methods for the Environmental
Analysis of Trace Elements Biogeochemistry
Martial Taillefert1 and Tim F. Rozan2
1School of Earth and Atmospheric Sciences, Georgia Institute of Technology,
221 Bobby Dodd Way, Atlanta, GA 30332
2ColIege of Marine Sciences, University of Delaware, 700 Pilottown Road, Lewes, DE 19958
Since the 1970's, when the first in situ measurements of oxygen in the
oceans were reported, the development of electrochemical methods for the
analysis of trace element biogeochemistry in the environment has significantly
improved. From conductimetry to measure salinity, to amperometric and
potentiometric sensors that can measure a single analyte, to voltammetric sensors
that can measure several species during the same scan, a variety of
electrochemical techniques have been utilized to better understand
biogeochemical processes in the environment. These techniques have been
integrated into a variety of devices for laboratory experimentation and in situ
deployment (or online measurements). The development of microsensors has
significantly contributed to the application of these techniques in sediments,
biofilms, and microbial mats, where data can now be collected at the micrometer
scale. Electrochemical techniques have also been adapted to measure the
chemical speciation of trace elements in natural environments following physical
and chemical separations. Finally, the complexation properties of most naturally
occurring ligands have been determined by electrochemical measurements
performed on synthetic and natural samples.
This first chapter is intended to familiarize the reader with the
electrochemical terminology, techniques, current applications, and future
directions in environmental chemistry and biogeochemistry research.
2 © 2002 American Chemical Society
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
3
Electrochemical Techniques and Sensors
Potentiometry
In potentiometry, the difference of potential between two electrochemical
cells is measured with a high impedence voltmeter in the absence of appreciable
currents. The difference in potential is measured between a reference electrode,
usually a Ag/AgCl or a Hg/HgCl electrode, and an indicator electrode. The
2
boundary potential, or the difference in potential between the external and the
internal solution at the indicator electrode, is sensitive to the activity of ions
according to the Nernst equation.
Potentiometric sensors commonly used in the environment include
membrane electrodes to determine the pH (1-3), or S2" (4-6), molecular
electrodes to determine pC0 (3, 7), and ion selective electrodes (ISEs) to
2
determine N0" (5-70), N0" (10, 11), NH+ (10, 12), Ca2+ (10), C02' (10), or
3 2 4 3
free metal activities (13, 14). Unfortunately, interferences prevent the use of
N0" and NH+ electrodes in marine environments. Finally, the detection limits
3 4
of ISEs are usually not suitable for the determination of free metals in natural
environments, but the recent development of polymer membrane ISEs (75,16) is
promising to increase their sensitivity.
Coulometry
Coulometry is based on the oxidation and reduction of an analyte for a
sufficient period of time to assure its quantitative conversion to a new oxidation
state. Two coulometric methods are used to analyze environmental samples:
chronopotentiometry and chronoamperometry. In chronopotentiometry, an
element is electrolytically preconcentrated at an electrode and the potential is
recorded at a reference electrode as a function of time upon addition of a
chemical reactant (17, 18) or application of a constant current (e.g., 19, 20). The
first technique, called potentiometric stripping analysis (PSA), is usually used to
analyze trace metals in freshwater (21) and seawater (22), as well as for metal
complexation studies (23). The second technique, called constant current
stripping analysis (CCSA), has been used to analyze trace metal concentrations
in aquatic systems (19, 20).
In chronoamperometry, an element is electrolytically preconcentrated at an
electrode by applying a constant potential and the current of the reaction is
simultaneously recorded at an auxiliary electrode as a function of time (24). To
our knowledge, the application of chronoamperometry for the analysis of
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.
4
environmental samples is limited. A chronoamperometric method has been used
to measure organic compounds in the environment (25), and recently, a
biosensor has been developed to determine NH+ by the intermediate of a
4
chronoamperometric measurement of NADH involved with NH+ in the
4
reduction of an enzyme (26).
Amperometry
In amperometry, the current is measured at an auxiliary electrode when a
constant potential is applied between a reference electrode, usually silver/silver
chloride, and the indicative electrode.
The most common amperometric sensor is the oxygen electrode, or Clark
electrode (27, 28), which has been routinely deployed to measure concentrations
of oxygen in aquatic systems (e.g, 4, 28-34). Another amperometric sensor has
been built to detect N0 in biofilms (35). Recently, bioelectrochemical sensors
2
have been developed to measure N0" in marine sediments (36) and CH in
3 4
sediments and biofilms (37). These biosensors use a N0 microelectrode (35)
2
and an oxygen microelectrode (4), respectively, as indirect electrochemical
detector. The N0" biosensor contains a microbial community between a
3
membrane and the N0 electrode which reduces N0" and N0" to N0. This
2 3 2 2
biosensor does not suffer from chloride interference and can be used in marine
environments. The CH biosensor contains aerobic methane oxidizers which
4
consume 0. The decrease in 0 is inversely proportional to the CH
2 2 4
concentration.
An amperometric microsensor has been developed for on-line measurements
of HS (38, 39). Dissolved sulfide is detected indirectly by measuring the
2
reoxidation current of ferrocyanide produced by sulfide reduction of
ferricyanide. In contrast to potentiometric sensors, this electrode does not suffer
from oxygen interferences because oxygen does not react with ferricyanide.
Voltammetry
In voltammetry, the potential is ramped between a working electrode and a
reference electrode. At a particular potential, the analyte is oxidized or reduced
at the working electrode and the current resulting from this reaction is measured
at an auxiliary electrode. Voltammetric techniques are attractive to measure
chemical species in the environment because they can detect several analytes in
the same potential scan, they have low detection limits, and generally do not
suffer from matrix problems (e.g., high salinity) (40). Voltammetry in the
environment is mostly used with mercury electrodes, because their analytical
In Environmental Electrochemistry; Taillefert, M., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 2002.