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

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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

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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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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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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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-0.45-1.2 -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

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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

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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

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[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