Analytical methods for studying trace metal speciation in the natural environment

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Analytical methods for studying trace metal
speciation in the natural environment
As Hg Cr Sn Se Pb Cd Fe Cu Zn Ni Co
Al ..
(Analytiske metoder for speciering av
spormetaller i naturen)
Date 8 February 2006 Duration 45 minutes Target
groups 1st and 2nd year Chemistry students
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(No Transcript)
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Contents

• Chemical speciation and fractionation
• Analytical strategies and methodological
  approaches
• In-situ (on-field) speciation analysis in aquatic
  systems
• Conclusions

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• 1.
• Chemical Speciation and Fractionation

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Chemical Speciation and Fractionation

• Chemical species
• Speciation analysis
• Speciation of an element
• Fractionation

- Specific forms of an element Fe(II)/Fe(III)
As(III)/As(V) CuCl2/CuCO3 Hg/CH3HgCl
- Activity of identifying and measuring species
- Distribution amongst chemical species in a
system
- Analytes classification according to physical
or chemical properties
Acc. to Guidelines for terms related to chemical
speciation and fractionation of elements.
Definitions, structural aspects, and
methodological approaches (IUPAC
Recommendations, Pure Appl. Chem. 2000)
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Speciation of Metals

• Isotopic composition
• Electronic and oxidation state
• Inorganic compounds and complexes
• Organometalic compounds
• Organic and macromolecular complexes

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Benefits and Fields of Interest
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What is determining the biogeochemical impact of
the metal ions species in aqueous systems?

• Concentration
• Nature of considered organism
• Physico-chemical form
• Particulate ( gt 1 µm)
• Colloidal (1 nm 1 µm)
• Dissolved (lt 1 nm)
• Free metal ions
• Simple inorganic complexes
• Complexes with anthropogenic and natural ligands

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2. Analytical Strategies and Methodological
Approaches
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Analytical Strategy the Main Steps

1. Formulation of the problem
2. Sampling and sample preparation
3. Measurement of the analytical signal
4. Analytical signal interpretation (quantitative
   and qualitative)
5. Critical evaluation of the analytical
   performances and method validation

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What is relevant in a metal speciation study?
Groups of different species with similar
properties
Individual species

1. Formulation of the problem

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Bio-uptake of Metal Species in Soils

• Exchangeable fraction species most available for
  bio-uptake (reagent used acetic acid 0.11 M)
• Reducible fraction potentially available for
  plants (reagent used a reducing agent like
  hydroxylamine chloride)
• Oxidizable fraction potentially available for
  plants (reagent used an oxidizing agent like
  H2O2 and NH4COOCH3)
• Rezidual fraction contains naturally occurring
  minerals

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Bio-uptake of Metal Species in Aquatic Systems

• Free metal ions related to biological uptake
• Dynamic metal species (free metal ions and small
• labile complexes) potentially availably for
  organisms
• The particulate and colloidal species role in
• transport and residence time

The total extractable metals the reservoir of
metal in the test solution
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The Baia Mare Accident
!! Higher toxicity due to heavy metals (Cu(II),
Zn(II))
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Metal Species in Aquatic Systems

• Free metal ions related to biological uptake
• Dynamic metal species (free metal ions and small
• labile complexes) potentially availably for
  organisms
• The particulate and colloidal species role in
• transport and residence time

The total extractable metals the reservoir of
metal in the test solution
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2. Sampling and Sample Preparation
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What is influencing the species stability?

• Chemical factors
• Physical factors
• Biological factors

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Treatments for Sample Preservation

• Acidification
• Low-temperature
• Drying
• Freezing
• Pasteurization
• Lyophilization
• Adsorption on cartridges or solid-phase
  micro-columns
• Storage in the dark

Preservation of Sb samples - Acidification to
prevent hydrolysis - Extraction on solid-phase
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Artifacts in Sample Speciation
0.2 mM Pb2, pH 6
Fe(OH)3
Fe2
O2
PS film coated glass

• Precipitation
• Sorption onto the container walls

Glass cell
Adapted from J. P. Pinheiro et al., Anal.
Bioanal. Chem., 2004
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Analytical Methods for Trace Metal Analysis and
Speciation Analysis

• Measuring techniques
• Atomic spectroscopy
• Inductively coupled plasma-mass spectroscopy
  (ICP-MS)
• Neutron activation analysis (NAA)
• X-ray photoelectron spectroscopy
• Electroanalytical methods

• Separation/ extraction
• Chromatography (GC, LC, HPLC)
• Capillary electrophoresis
• Ion-chromatography
• L-L extraction
• Ion-exchange co-precipitation.

3. Measurement of the analytical signal
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IC-ICP-MS Chromatogram of 50 mg/L Arsenic Species
Hyphenated techniques for speciation
analysis Separation Excitation
Detection HPLC ICP MS GC ICP MS
IC ICP MS
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Metals speciation analysis by electroanalytical
techniques
Potentiometry
Voltammetry
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Ion-selective electrodes
Bioavailability Speciation

• Free metal ion activity, aI

• Speciation of Pb(II) and Cd(II) in drinking
  water
• Detection of free Cu(II) in sea water
• The uptake of Cd(II) species by plant roots

LOD 10-7 10-6 M 10-11 10-8 M
Acc. E. Bakker, E. Pretsch, Trends Anal. Chem.,
2005.
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Trace metal speciation analysis by voltammetry
Anodic stripping voltammetry (ASV) Adsorptive
stripping voltammetry (AdSV) Potentiometric
stripping analysis (PSA)
Anodic stripping voltammetry (ASV)
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• How is an ASV experiment working ?

3 steps experiment I. Accumulation/Preconcentra
tion (Mz ze- M0(Hg)) II.
Equilibration III. Measurement of the analytical
signal (M0(Hg)) Mz ze-)
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Strengths and advantages of the voltammetric
techniques

• Accuracy
• Sensitivity
• Simplicity
• Low detection limit (ppm - ppt)
• Well-suited for automatic in situ speciation
• Allow to determine the complexing properties of
  model or naturally occurring complexants

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5. Critical evaluation of the analytical
performances and methods validation

• To test accuracy and traceability
• Use of CRM (Certified Reference Materials)

 
Example of simple certified reference
materials for speciation analysis of arsenium and
chromium in water samples
Supplier Name Material Certificate
BCR CRM 626 Solution Arsenobetaine
BCR CRM 544 Lyophilized solution Cr(III), Cr(VI)
NIST SRM 2108 Solution Cr(III)
NIST SRM 2109 Solution Cr(VI)
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Why validation methods are important?
In situ detection of O2, Fe(II), Mn(II) in
sediments porewaters with unprotected Au/Hg WE
(100 µm)
Acc. G. W. Luther III et al., Environ. Sci.
Technol. 33 (1999) 4352
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• 3.
• In-situ (on-field) speciation analysis
• in aquatic systems

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In-situ voltammetric analyzers

• ATMA (Automated Trace Metal Analyzer)
• VIP (Voltammetric In situ Profiler)
• MPCP (Multi Physical-Chemical Profiler)

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• ATMA
• PSA measurements
• Electrodes a mercury film deposited on a glassy
  carbon
• rod or a thin gold electrode
• Used for measuring As(III) Cr(VI) Cu(II)
  Hg(II) Se(IV).

Automated Trace Metal Analyzer (ATMA) Acc. to
Space and Naval Warfare Systems Center, San
Diego, USA (2002)
Interferences from matrix (organics, solids,
other metals) can have a dramatic effect on the
accuracy of the instrument
Caution in use on unpredictable or unknown
effluents
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In situ trace metal speciation based on
bioanalogical sensors VIP (Voltammetric In situ
Profiler)MPCP (Multi Physical-Chemical Profiler)

• Gel protected voltammetric microelectrodes
• - GIME -
• Gel Integrated Microelectrode
• - CGIME -
• Complexing Gel Integrated Microelectrode
• - PLM mTAS -
• Permeation Liquid Membrane Total Analytical
  System

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Model of metal uptake by a biological cell




Bulk solution

Diffusive boundary layer
Cell wall layer
Cell membrane
kint, M
Cell interior
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GIME (gel-integrated micro-sensor)
Test solution (volume)
Agarose gel
Ir
Si3N4
Hg (5 µm)
Silicon
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CGIME (complexing gel-integrated micro-sensor)
Test solution (volume)
Agarose gel
Resin
Ir
Si3N4
Hg (5 µm)
Silicon
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From voltammetric sensors to in situ probes
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VIP Voltammetric In situ Profiler www.idronaut.
it

• Based on an array of interconnected GIME sensors
  covered with a 300 mm thick agarose antifouling
  gel
• Measures the concentration of dynamic fraction of
  trace metals (Cu(II), Pb(II), Cd(II), Zn(II),
  Mn(II), Fe(II))

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Voltammetric in situ profiler (VIP)
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MPCP
MPCP (Multi Physical-Chemical Profiler) a system
for in-situ trace metal speciation Acc. to M.-L.
Tercier-Waeber/ Marine Chemistry 2005

• Speciation of Cu, Cd, Pb
• Pressure
• pH
• Temperature
• O2
• Conductivity
• Salinity
• Redox potential
• Turbidity
• Chlorophyll a

• Environmental monitoring and pollution control
• Biogeochemical studies

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MPCP 3 channels configuration
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Speciation analysis of copper with MPCP
Acc. to M.-L. Tercier-Waeber/ Marine Chemistry
2005
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Conclusions- In situ voltammetric speciation
analysis have many advantages- It demands
improvement of the voltammetric devices
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• 4.
• Conclusions

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Interdisciplinarity and Speciation Analysis
Environmental Chemistry
Analytical Chemistry

• Transport processes
• Consumptive processes
• (chemical reactions and biological uptake)

Geochemistry
Biology and Biochemistry
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Summary
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Suggestions for further reading

• R. Cornelis, J. Caruso, H. Crews, K. Heuman
  (Eds.), Handbook of Elemental Speciation
  Techniques and Methodology, Wiley, N. Y., 2005.
• J. Buffle, G. Hoarvai (Eds.), In situ Monitoring
  of Aquatic Systems Chemical Analysis and
  Speciation, IUPAC Ser. Anal. Phys. Chem. Environ.
  Syst., Vol. 6, Wiley, Chichester, UK, 2000.
• D. M. Templeton, F. Ariese, R. Cornelis, L-G.
  Danielsson, H. Muntau, H. P. van Leeuwen, R.
  Lobinski, Guidelines for terms related to
  chemical speciation and fractionation of
  elements. Definitions, structural aspects, and
  methodological approaches, Pure Appl. Chem. 72
  (2000) 1453-1470.
• E. Prichard, G. M. MacKay, J. Points (Eds.),
  Trace Analysis a structured approach to
  obtaining reliable results, Royal Society of
  Chemistry, Cambridge, 1996.
• Institute for Reference Materials and
  Measurements (http//www.irmm.jrc.be/html/homepage
  .htm)
• The European Virtual Institute for Speciation
  Analysis (EVISA) (http//www.speciation.net/)

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Many shall pass through and learning shall be
increased
Multi pertransibunt et augebitur scientia
The Great Instauration, Francis Bacon