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Trace metal Trace metal complexation incomplexation innatural watersnatural waters
- - PseudopolarographyPseudopolarography- - Metal complexing capacity Metal complexing capacity
(MCC)(MCC)Dario Omanović, Dario Omanović, Petra Cmuk, Petra Cmuk, Ivanka PižetaIvanka Pižeta
Center for Marine and Environmental Research, Center for Marine and Environmental Research, Ruđer Bošković Institute,Ruđer Bošković Institute, CroatiaCroatia
Yoann Louis, Rudy NicolauYoann Louis, Rudy NicolauLaboratoire PROTEE, Université de Toulon et du Var
-BP 132, 83957 La Garde, France
Cedric GarnierCedric GarnierLPTC, Université Bordeaux I, 351 Crs. de la Libération,
F-33405 Talence CEDEX, France
Distribution of trace Distribution of trace metalsmetalsOperationally defined:Operationally defined:
• Particulate - > 0.45 Particulate - > 0.45 µµmm• Dissolved - < 0.45 Dissolved - < 0.45 µµmm• Colloidal Colloidal -- between 1 kD and 0.45 between 1 kD and 0.45 µµmm• Truly dissolved - < 1 kD Truly dissolved - < 1 kD
Distribution of trace Distribution of trace metalsmetalsPhysico-chemical classification:Physico-chemical classification:
• Inorganic complexesInorganic complexes• Organic complexesOrganic complexes• Associated to particles Associated to particles
Distribution of trace Distribution of trace metalsmetalsMethodological (electrochemical) classification:Methodological (electrochemical) classification:
• Labile complexesLabile complexes– Mostly inorganic complexes (Cl-, OH-, SO42-, ...)Mostly inorganic complexes (Cl-, OH-, SO42-, ...)– Fast dissociation rateFast dissociation rate– Mostly reducableMostly reducable
• Inert complexes Inert complexes – Mostly organic complexesMostly organic complexes– Very stable – high stability constantVery stable – high stability constant– Only Only partlypartly reducable reducable
Electrochemical Electrochemical characteristicscharacteristicsLabile complexesLabile complexes InertInert complexes complexes
Construction of Construction of pseudopolarogrampseudopolarogram
0
2
4
6
8
10
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14
16
-0.65-0.60
-0.55-0.50
-0.45-1.2 -1.0 -0.8 -0.6 -0.4
struja
/ A
potencijal / Vpotencijal akumulacije / V
potencijal akumulacije / V-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
struja
/ A
0
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0
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-0.65-0.60
-0.55-0.50
-0.45-1.2 -1.0 -0.8 -0.6 -0.4
struja
/ A
potencijal / Vpotencijal akumulacije / V
potencijal akumulacije / V-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
struja
/ A
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0
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-0.65-0.60
-0.55-0.50
-0.45-1.2 -1.0 -0.8 -0.6 -0.4
struja
/ A
potencijal / Vpotencijal akumulacije / V
potencijal akumulacije / V-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
struja
/ A
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-0.65-0.60
-0.55-0.50
-0.45-1.2 -1.0 -0.8 -0.6 -0.4
struja
/ A
potencijal / Vpotencijal akumulacije / V
potencijal akumulacije / V-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
struja
/ A
0
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0
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-0.65-0.60
-0.55-0.50
-0.45-1.2 -1.0 -0.8 -0.6 -0.4
struja
/ A
potencijal / Vpotencijal akumulacije / V
potencijal akumulacije / V-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
struja
/ A
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0
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-0.65-0.60
-0.55-0.50
-0.45-1.2 -1.0 -0.8 -0.6 -0.4
struja
/ A
potencijal / Vpotencijal akumulacije / V
potencijal akumulacije / V-1.4 -1.3 -1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4
struja
/ A
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Voltammograms Pseudopolarogram
Model titrations – one Model titrations – one ligandligand
added [Cd2+]x107 / M
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
foun
d [C
d2+]x
107 /
M
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5Theoretical
added 1x10-7 M NTA
without NTA
0.1 M NaClO4, pH = 8.5
Model titrations – one Model titrations – one ligandligand
Experimental:
CdCC = 0.970×10-7 Mlog Kapp = 8.37
Theoretical:
CdCC = 1×10-7 Mlog Kapp = 8.44
Model titrations – two Model titrations – two ligandsligands
Stability constantsStability constants@ @ µµ = 0.1 M: = 0.1 M:
Log Log KK CdNTACdNTA = 9.76 = 9.76
Log Log KK CdEDTACdEDTA = 16.4 = 16.4
Theoretically:ΔErev = 0.059*log K / n
Exp. for CdNTA:ΔE = 0.320 Vlog K = 10.8
Model titrations – two Model titrations – two ligandsligands
Eacc = -0.75 VCdCC = 0.973×10-7 M
Eacc = -1.15 VCdCC = 0.503×10-7 M
added [Cd2+]x107 / M0 1 2 3 4
foun
d [C
d2+]x
107 /
M
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
theoretical
5x10-8 M NTA5x10-8 M N-8 M EDTA
without NTA
0.1 M NaClO4, pH = 8.5
Eacc = -1.15 V
Eacc = -0.75 V
Seawater sample – addition of NTASeawater sample – addition of NTA
CADMIUMCADMIUM
• Fast complexation with Fast complexation with NTANTA
• Two separate peaks of Two separate peaks of labile Cd and CdNTAlabile Cd and CdNTA
Seawater sample – addition of Seawater sample – addition of EDTAEDTA
CADMIUMCADMIUM
• Very slow complexation Very slow complexation with EDTA (cca. 3 h)with EDTA (cca. 3 h)
• Two separate peaks of Two separate peaks of labile Cd and CdEDTAlabile Cd and CdEDTA
accumulation potential / V-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0
anod
ic p
eak
curr
ent /
nA
0
1
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8
without added Cu+ 5x10-8 M Cu2+
Seawater sample – “not clean” Seawater sample – “not clean” (Šibenik)(Šibenik)
[Cu2+]ux108 / mol dm-3
0 2 4 6 8 10 12 14
i p / n
A
0
2
4
6
8
10
12
[Cu2+]n x108 / mol dm-30 2 4 6 8
[Cu2+
] n / ([
Cu2+
] u - [C
u2+] n)
0.0
0.5
1.0
1.5
2.0R2 = 0,9994
EEaccacc = -0.45 V = -0.45 V
No separated well defined wavesNo separated well defined waves CuCC = 4.2CuCC = 4.2××1010-8-8 M MLog Log KKappapp = 9.2 = 9.2
CopperCopper
Seawater sample – “clean” Seawater sample – “clean” (Zlarin)(Zlarin)CopperCopper
Two well separated waves:Two well separated waves: - labile copper complexes- labile copper complexes @ E = -0.34 V @ E = -0.34 V - inert copper complexes- inert copper complexes @ E = -1.40 V@ E = -1.40 V
Experimental setup - Experimental setup - parametersparameters
Eacc = -1.6 V, tacc = 300 sEacc = -0.45 V, tacc = 300 s Eacc = -0.45 V, tacc = 297 sandEacc = -1.6 V, tacc = 3 s
Copper - “clean“ seawater Copper - “clean“ seawater (Zlarin)(Zlarin)
Experimental setup - Experimental setup - parametersparametersCopper - “clean“ seawater Copper - “clean“ seawater
(Zlarin)(Zlarin)
Seawater sample – “clean” Seawater sample – “clean” (Zlarin)(Zlarin)CadmiumCadmium
withoutwithout well separated waves well separated waves
ConclusionConclusion• Pseudopolarography is a tool for the characterisation of Pseudopolarography is a tool for the characterisation of
an interaction of trace metal ions in natural samplesan interaction of trace metal ions in natural samples• It is the “fingerprint” of the sampleIt is the “fingerprint” of the sample• The position and the shape of the waves give us The position and the shape of the waves give us
additional information about complexing ability of the additional information about complexing ability of the particular natural sampleparticular natural sample
• It is very useful in complexing capacity determination It is very useful in complexing capacity determination measurementsmeasurements
• The composition of natural water samples is very The composition of natural water samples is very complex and, unfortunatelly, it is very hard to obtain complex and, unfortunatelly, it is very hard to obtain behaviours like in model solutionsbehaviours like in model solutions
• Additional efforts should be done to resolve problems Additional efforts should be done to resolve problems associated with the experimental setup as well as to associated with the experimental setup as well as to interpret data regarding both pseudopolarograms and interpret data regarding both pseudopolarograms and metal complexing capacity determinationmetal complexing capacity determination