ana banica prøveforelesning 2006 1 analytical methods for studying trace metal speciation in the...
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Ana BANICA Prøveforelesning 2006
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Analytical methods for studying trace metal speciation
in the natural environment
(Analytiske metoder for speciering av spormetaller i naturen)
As Hg Cr Sn Se Pb Cd Fe Cu Zn Ni Co Al …..
Date: 8 February 2006Duration: 45 minutesTarget groups: 1st and 2nd year Chemistry students
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Contents
1. Chemical speciation and fractionation
2. Analytical strategies and methodological approaches
3. In-situ (on-field) speciation analysis in aquatic systems
4. 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
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)
- 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
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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 ( > 1 µm)• Colloidal (1 nm – 1 µm)• Dissolved (< 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?
Individual speciesGroups
of different species with similar properties
1.Formulation of the problem
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• 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
Bio-uptake of Metal Species in Soils
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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))
Surface-water sampling sites
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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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A major challenge in speciation analysis
Sampling – Sample preparation
SamplingTransportPre-treatmentPreservation
Contamination
Loss of analyte
Species transformation
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
O2Fe(OH)3
• Precipitation• Sorption onto the container walls
Fe2+
0 4 8 12 16 20 240
20
40
60
80
100
% to
tal c
onte
nt o
f Pb(
II)
time / h
Glass cell
PS film coated glass
Adapted from J. P. Pinheiro et al., Anal. Bioanal. Chem., 2004
Pb2+(aq) Pb2+
(ads)
0.2 M Pb2+, pH 6
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Analytical Methods for Trace Metal Analysis and Speciation Analysis
3. Measurement of the analytical signal
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….
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IC-ICP-MS Chromatogram of 50 g/L Arsenic Species
Dimethylarsinic acid (DMA, cacodylic acid)O||
H3C-As-CH3
| OH
Arsenic acid (As+5) O||
HO-As-OH|
OH
Arsenious acid (As+3)HO-As-OH
| OH
Monomethylarsonic acid (MMA)O||
H3C-As-OH|
OH
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
Free metal ion and labile formsconcentration
Free metal ion activitySample
Voltammetry
Potentiometry
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Ion-selective electrodes
Free metal ion activity, aI
IazF
RTkEMF ln
LOD: 10-7 – 10-6 M 10-11 – 10-8 M
BioavailabilitySpeciation
• 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
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)
E
time
(A)
E
time
(B)
E
time
(C)
Anodic stripping voltammetry (ASV)
Voltammetric cell PotentiostatCurrent – potential curves
i - E
WE
RE
AE
00,20,4E ,V
0
-4
4
8
12
Curr
en
t, µ
A Measuredsignal
in SWASV
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How is an ASV experiment working ?How is an ASV experiment working ?
3 steps experiment:
I. Accumulation/Preconcentration (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)
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)
Example of simple certified reference materialsfor speciation analysis of arsenium and chromium in water samples
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Acc. G. W. Luther III et al., Environ. Sci. Technol. 33 (1999) 4352
In situ detection of O2, Fe(II), Mn(II) in
sediments porewaters with
unprotected Au/Hg WE (100 μm)
Why validation methods are important?
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3.
In-situ (on-field) speciation analysis
in aquatic systems
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ATMA (Automated Trace Metal Analyzer)
VIP (Voltammetric In situ Profiler)
MPCP (Multi Physical-Chemical Profiler)In-situ voltammetric analyzers
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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).
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
Automated Trace Metal Analyzer (ATMA)
Acc. to Space and Naval Warfare Systems Center, San Diego, USA (2002)
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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 – TAS -Permeation Liquid Membrane – Total Analytical System
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Model of metal uptake by a biological cell
Bulk solution
Diffusive boundary layer
Cell membrane
Cell interior
Cell wall layer
kint, M
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GIME (gel-integrated micro-sensor)
M MYML+ L (KML)
+ Y (KMY)
M MYML
MX
M0
Agarose gel
Ir Si3N4
Silicon
Test solution(volume)
Hg (5 μm)
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CGIME (complexing gel-integrated micro-sensor)
M MYML+ L (KML)
+ Y (KMY)
M MYML
MX
M0
M - R
Agarose gel
Si3N4
Silicon
Ir
Test solution(volume)
Resin
Hg (5 μm)
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From voltammetric sensors to in situ probes
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• Based on an array of interconnected GIMEarray of interconnected GIME sensors covered with a 300 m thick agarose antifouling gel
• Measures the concentration of dynamic fractiondynamic fraction of trace metals (Cu(II), Pb(II), Cd(II), Zn(II), Mn(II), Fe(II))
VIP – Voltammetric In situ Profiler
www.idronaut.it
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Voltammetric in situ profiler (VIP)
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Environmental monitoring and pollution control
Biogeochemical studies
Speciation of Cu, Cd, Pb Pressure pH Temperature O2
Conductivity Salinity Redox potential Turbidity Chlorophyll a
MPCP (Multi Physical-Chemical Profiler) a system for in-situ trace metal speciation
Acc. to M.-L. Tercier-Waeber/ Marine Chemistry 2005
MPCP
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MPCP – 3 channels configuration
Channel 1
GIME
Dynamic fraction of trace metals
Channel 2
CGIME
Free metal ion
Channel 3
FIA - GIME
Total extractablemetal concentration
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Speciation analysis of copper with MPCP
0
20
40
60
80
100
120
1 2 34 5 67 8 910 11
% o
f la
b to
tal c
onc.
Cu in Breakwater marine costal area (UK) at 3 different times
FIA GIME CGIME
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
Analytical Chemistry
Environmental Chemistry
Biology and Biochemistry
Geochemistry
•Transport processes•Consumptive processes
(chemical reactions and biological uptake)
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Summary
Analysis of trace metals in the natural environment
Speciation analysis Fractionation
Location
Laboratory In situ
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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. Łobiński, “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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Multi pertransibunt et augebitur scientia
‘Many shall pass through and learning shall be increased’
The Great Instauration, Francis Bacon