AGNES: A NEW ANALYTICAL TECHNIQUE FOR MEASURING FREE METAL ION CONCENTRATIONS'

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AGNES A NEW ANALYTICAL TECHNIQUE FOR MEASURING
FREE METAL ION CONCENTRATIONS.
ElectrochemistryUniversità di Pavia (Italy)
Encarna CompanysUniversitat de Lleida (Spain)
May 2007
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Inert complexes with NTA and
EDTA Precipitation and irreversibility Zn2
Oxalate Induced electrodic adsorption Cd2 I-
and Cd2 PAA Application of AGNES to natural
systems Problems and perspectives
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INERT COMPLEXES Cd2 NTA and Zn2 NTA
Cd
Zn
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INERT COMPLEXES Zn2 EDTA
Zn
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Inert complexes with NTA and
EDTA Precipitation and irreversibility Zn2
Oxalate Induced electrodic adsorption Cd2 I-
and Cd2 PAA Application of AGNES to natural
systems Problems and perspectives
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TESTING PRECIPITATION AND IRREVERSIBILITY Zn2
Oxalate
Oxalate
-
-
without precipitation
with precipitation
J. Electroanal. Chem. (2005) 576 21-32
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Inert complexes with NTA and
EDTA Precipitation and irreversibility Zn2
Oxalate Induced electrodic adsorption Cd2 I-
and Cd2 PAA Application of AGNES to natural
systems Problems and perspectives
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INDUCED ELECTRODIC ADSORPTION Cd2 I-
SIMPLE LIGANDS IODIDE (I-)
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INDUCED ELECTRODIC ADSORPTION Cd2 PAA
MACROMOLECULAR LIGANDS POLIACRYLIC ACID (PAA)
n
AGNES Y 100 (2P), ISE, I 0.1 M
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Application of AGNES to
natural systems Complexation of Zn, Cd and Pb to
Humic Acids Heavy metal speciation in
wines Free metals in seawaters Problems and
perspectives
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COMPLEXATION OF METAL TO HUMIC ACID
Interest? Toxicity and bioaccumulation of
heavy metals in natural systems? The Free Ion
Activity Model (Tessier et al. 1994) or the
Biotic Ligand Model (Campbell et al. 2002Paquin
et al. 2002) highlight the free concentration as
more relevant than the total metal
concentration? Complexation of metals to
Natural Organic Matter (humic acids)
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COMPLEXATION OF METAL TO HUMIC ACID
Specific or covalent binding
Non-specific or electrostatic binding
Donnan model
NICA isotherm
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COMPLEXATION OF METAL TO HUMIC ACID
Donnan model. Electrostatic binding
Donnan
VD is required
NLPB
A new expression for VD based on NLPB
Colloids and Surfaces A (2007). In press
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COMPLEXATION OF METAL TO HUMIC ACID
NICA isotherm. Specific binding
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Data treatment Iterative procedure
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COMPLEXATION OF METAL TO HUMIC ACID
Zn, Cd and Pb to Purified Aldrich Humic Acid
Cd
Zn
Good fitting! Parameters similar to literature
values
Pb
? pH 4 ? pH 5 pH 6 ? pH 7
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Application of AGNES to
natural systems Complexation of Zn, Cd and Pb to
Humic Acids Heavy metal speciation in
wines Free metals in seawaters Problems and
perspectives
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FREE METAL IN NATURAL MEDIA Zn2 in wine
? Effect of ethanol
DPP
? Decrease in the diffusion coefficient, DM
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FREE METAL IN NATURAL MEDIA Zn2 in wine
? AGNES in ethanolic media
How to calibrate in EtOH media?

• 1. Calibration in aquatic media ? wh , with
  a known wY
• 2. Determination of the EtOHEpic of a DPP

3. Determination of the h in ethanolic media,
EtOHh
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FREE METAL IN NATURAL MEDIA Zn2 in wine
? AGNES in ethanolic media
How to measure in EtOH media?
4. Set the required parameters, t1,a, t1,b,
to reach AGNES conditions
Y 50
t1,a 5 s
t1,a 2.5 s
Selected PARAMETERS t1,a 2.5 s t1,b 1000 s
1 Potential
5. Determination of the free metal
concentration cM
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FREE METAL IN NATURAL MEDIA Zn2 in wine
? Free metal in wine with AGNES (preliminary
results)
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FREE METAL IN NATURAL MEDIA Zn2 in wine
? Possible intermetallic precipitation
Zn0 Cu0 ? Cu0Zn0 ?
Results indicate that intermetallic
precipitation should not be a problem in wine
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FREE METAL IN NATURAL MEDIA Zn2 in wine
? High Zn concentration
AGNES reoxidation
High cZn
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Application of AGNES to
natural systems Complexation of Zn, Cd and Pb to
Humic Acids Heavy metal speciation in
wines Free metals in seawaters Problems and
perspectives
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FREE METAL IN NATURAL MEDIA Zn2 in sea water
? The new blank SHIFTED BLANK
ASV
? E
? Esb
Zn
Cd
Pb
E1 (Y500)
E1,sb (Y0.01)
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FREE METAL IN NATURAL MEDIA Zn2 in sea water
Talanta 71 (2007) 1795
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INDEX
Principles of AGNES Amperometric
implementation Strategies to reduce the
deposition time Validation of AGNES with
synthetic solutions Application of AGNES to
natural systems Complexation of Zn, Cd and Pb to
Humic Acids Heavy metal speciation in
wines Free metals in seawaters Problems and
perspectives
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PROBLEMS AND PERSPECTIVES

• Cu determination with AGNES
• Sb3 and Sb5 speciation
• AGNES in river water (low ionic strength)
• High metal concentrations
• AGNES with MFE (Mercury Film Electrodes)
• AGNES in solutions containing mixtures
• Bi electrodes
• Cinetic information from AGNES experiments

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AGNES REFERENCES
1 J.Galceran, E.Companys, J.Puy, J.Cecília,
J.L.Garcés, AGNES a new electroanalytical
technique for measuring free metal ion
concentration. J. Electroanal. Chem. 566 (2004)
95. 2 E.Companys, J.Cecília, G.Codina,
J.Puy, J.Galceran, Determination of Zn2
concentration with AGNES using different
strategies to reduce the deposition time. J.
Electroanal. Chem. 576 (2005) 21. 3
J.Galceran, C.Huidobro, E.Companys, G.Alberti,
AGNES a technique for determining the
concentration of free metal ions. The case of
Zn(II) in coastal Mediterranean seawater. Talanta
71 (2007) 1795. 4 G.Alberti, R.Biesuz,
C.Huidobro, E.Companys, J.Puy, J.Galceran. A
comparison between the determination of free
Pb(II) by two techniques AGNES and Resin
Titration. Submitted to Anal. Chim. Acta, 2007.
5 C.Huidobro, E.Companys, J.Puy, J.Galceran,
J.P.Pinheiro. The use of microelectrodes with
AGNES. Submitted to J. Electroanal. Chem.,
2007.6 E.Companys, J.Puy, J.Galceran, Humic
acid complexation to Zn and Cd determined with
the new electroanalytical technique AGNES.
Submitted to Environ. Sci. Technol., 2007.