1 Detecção Amperométrica/Voltamétrica em Sistemas FIA e Cromatográficos Empregando Eletrodo de...

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Detecção Amperométrica/Voltamétrica em Sistemas FIA

e Cromatográficos Empregando Eletrodo de Diamante

Dopado com Boro

LABORATÓRIO DE ANALÍTICA•BIOANALÍTICA•BIOSSENSORES•ELETROANALÍTICA &•SENSORES

DQUFSCar

Orlando Fatibello FilhoDepartamento de Química, Universidade

Federal de São Carlos,Caixa Postal 676, 13560-970 São Carlos – SP

bello@ufscar.br; www.ufscar.br/labbes

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Prof. Dr. Romeu C. Rocha-Filho (DQ-UFSCar)

Prof. Dr. Leonardo S. Andrade (DQ-UFG-Catalão)

Dr. Roberta Antigo Medeiros (DQ-UFSCar)

M.Sc. Bruna Cláudia Lourenção (DQ-UFSCar)

Prof. Dr. Quezia B. Cass (DQ-UFSCar)

Prof. Dr. Adriana Evaristo de Carvalho (DQ-UFMS)

Prof. Dr. Élen R. Sartori (DQ-UEL)

Prof. Dr. Giancarlo Richard Salazar-Banda (ITP-Un. Tiradentes)

Prof. Dr. Luis A. Avaca (Guarujá, SP)

Financial Support and Acknowledgements

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Boron-doped diamond electrode

corrosion stable in very aggressive media

very low and stable background current

very low adsorption of organic/inorganic species

extreme electrochemical stability in both alkaline and

acid media

high response sensitivity

very wide working potential window (3.5 V)

K. Pecková et al. Critical Reviews in Analytical Chemistry. 39 (2009) 148

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Approximate potential ranges for platinum, mercury, carbon and boron-doped diamond (BDD) electrodes

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Experimental

Working electrode: Boron-doped diamond film (8000 ppm) on a silicon wafer from Centre Suisse de Electronique et de Microtechnique SA (CSEM), Neuchatêl, Switzerland

Cathodic pretreatment: –1.0 A cm–2 for 180 s in a 0.5 M H2SO4 solution

Anodic pretreatment: +1.0 A cm-2 for 180 s in a 0.5 M H2SO4 solution

Counter electrode: Pt wire

Reference electrode: Ag/AgCl (3.0 M KCl)

Potentiostat/galvanostat: Autolab PGSTAT-30 (Ecochemie) controlled with the GPES 4.0 software

Electrochemical pre-treatments

L.S. Andrade, G. R. Salazar-Banda, R. C. Rocha-Filho, O. Fatibello-Filho, Cathodic Pretreatment of Boron-Doped Diamond Electrodes and Their Use in Electroanalysis, In: Synthetic Diamond Films: Preparation, Electrochemistry, Characterization, and Applications, (Eds. E. Brillas and C. A. Martínez-Huitle), John Wiley & Sons, Inc., Hoboken, NJ, USA, 2011.

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Characteristics of the procedure:

simple and rapid low cost good intra- and inter-day repeatabilities

Electrochemical pre-treatments

Cathodic pre-treatment

Hydrogen-terminated BDD(HT-BDD)

Anodic pre-treatment

G.R. Salazar-Banda, L.S. Andrade, P.A.P. Nascente, P.S. Pizani,R.C. Rocha-Filho, L.A. Avaca. Electrochimica Acta, 51 (2006) 4612.

Oxygen-terminated BDD(OT-BDD)

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Flow Injection analysis system

Potentiostat/galvanostat: Autolab PGSTAT-30 (Ecochemie)

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Flow electrochemical cell

Working electrode :BDD

8000 ppm; 0.33 cm2

Reference electrode Ag/AgCl

(3.0 mol L–1 KCl)

Counter electrode : stainless steel tube

E. M. Richter et al. Quim. Nova, 26(6) (2003) 839.L. Andrade et al. Anal. Chim. Acta 654 (2009) 127.

Results and discussion

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Simultaneous Square-Wave Voltammetric Determination of Phenolic Antioxidants (BHA and BHT) in Food Using a Boron-Doped Diamond Electrode

R.A. Medeiros, R.C. Rocha-Filho, O. Fatibello-Filho, Food Chemistry, 123 (2010) 886.

BHA = butylated hydroxyanisole; BHT = butylated hydroxytoluene

OCH3

OH

C(CH3)3

H2O

O

O

C(CH3)3

CH3OH H3O+

BHA

H2O

(CH3)3C C(CH3)3

O

CH3

H3O+2 e-

OCH3

C(CH3)3

O

H3O+ 2 e- 2H2O

+

BHT

(CH3)3C C(CH3)3

OH

CH3

1111

SWV curves obtained on an anodically (dashed line) and a cathodically (solid line) pre-treated BDD electrode, using a mixture of 10 µM BHA and 10 µM BHT. Supporting electrolyte: aqueous-ethanolic (30 % ethanol, v/v) 10 mM KNO3 solution (pHcond. = 1.5 adjusted with conc. HNO3).

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BHA: 0.60 – 10 M; LOD = 0.14 M

BHT: 0.60 – 10 M; LOD = 0.25 M

BHA

BHT

Highlight:LODs lower than those

previously reported

OCH3

OH

C(CH3)3

(CH3)3C C(CH3)3

OH

CH3

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Flow injection simultaneous determination of BHA and BHT with multiple pulse amperometric detection at a BDD electrode

Voltamogramas hidrodinâmicos obtidos para o BHA 0,10 mmol L-1 (A) e BHT 0,10 mmol L-1 (B), utilizando o eletrodo de BDD; vazão 2,4 mL min-1

e Vamostra = 350 µL

R.A. Medeiros; B.C. Lourenção; R.C. Rocha-Filho, O. Fatibello-Filho; Anal. Chem.,82 (2010) 8658.

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(A) MPA waveform applied to the cathodically pretreated BDD working electrode as a function of time. (B) Flow-injection pulse amperometric responses in triplicate for solutions containing 50 μmol L-1 BHA or BHT or both analytes simultaneously at this concentration. Supporting electrolyte: aqueous ethanolic (30% ethanol, v/v) 10 mmol L-1 KNO3 solution (pHcond =1.5) adjusted with concentrated HNO3); flow rate 2.4 mL min-1; injected volume 250 μL.

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FIA-MPA amperograms obtained after injections of solutions containing BHA (0.050-3.0 μmol L-1) and BHT (0.70-70 μmol L-1) simultaneously or different samples of mayonnaise (A-D). Supporting electrolyte: aqueous ethanolic (30% ethanol, v/v) 10 mmol L-1 KNO3 solution (pHcond =1.5) adjusted with concentrated HNO3); flow rate 2.4 mL min-1; injected volume 250 μL.

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Tabela-Resultados obtidos para o estudo de repetibilidade intra e entre-dias

Faixa linear: BHA - 0,050 a 3,0 µmol L–1

BHT - 0,70 a 70,0 µmol L–1

(I = IEdet.1, para o BHA)

I/µA= 0,00619 + 0,0559 [c/(µmol L–1)]; r = 0,998

(I = IEdet.2 – IEdet.1, para o BHT)

I/µA= 0,144 + 0,0503 [c/(µmol L−1)]; r = 0,999

Limites de Detecção: BHA: 3,0 10-8 mol L-1

BHT: 4,0 10-7 mol L-1

intra-diasRSDa (%)

entre-diasRSDb (%)

BHA (mol L-1)7,0 × 10-8 3,8 5,1

5,0 × 10-7 2,5 3,9

3,0 × 10-6 2,9 4,2

BHT (mol L-1)7,0 × 10-7 8,9 8,5

6,0 × 10-6 2,0 5,3

7,0 × 10-5 1,8 3,6

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Amostras BHA (mg/100 g) BHT (mg/100 g) BHA BHT

Maionese HPLCa MPAa HPLCa MPAaErro (%)b Erro (%)b

1 2,0±0,1 2,1 ±0,2 1,1±0,1 1,2±0,3 5,0 9,1

2 1,7±0,2 1,6±0,1 1,3±0,2 1,3±0,2 -5,9 0,0

3 2,3±0,2 2,2±0,2 1,8±0,2 1,8±0,3 -4,3 0,0

4 2,3±0,1 2,1±0,3 1,4±0,2 1,3±0,1 -8,7 -7,1

Tabela- Resultados obtidos na determinação simultânea de BHA e BHT em produtos alimentícios empregando-se HPLC e MPA-FIA

teste t-pareado

BHA: texp = 1,54 e BHT: texp = 1,66 tcrítico = 3,18

a n = 3b Erro (%) = 100 × (valor amperométrico - valor HPLC) / valor HPLC

R.A. Medeiros; B.C. Lourenção; R.C. Rocha-Filho, O. Fatibello-Filho; Anal. Chem., 82 (2010) 8658.

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Paracetamol (A) and caffeine (B) in pharmaceuticals

B.C. Lourenção, R.A. Medeiros, R.C. Rocha-Filho, L.H. Mazo, O. Fatibello-Filho.

Talanta, 78 (2009) 748.

Differential pulse voltammetry

Paracetamol: 0.50 – 83 M

LOD = 0.049 M

Caffeine: 0.50 – 83 M

LOD = 0.035 MHighlight:

LODs lower than those reported; higher sensitivity and larger linear concentration range of the AC

17 M

38 M

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A Simple Strategy for Simultaneous Determination ofParacetamol and Caffeine Using Flow Injection Analysis withMultiple Pulse Amperometric Detection

W. C. Silva, F.P. Pereira, M.C. Marra, D. T. Gimenes, R.R. Cunha, R.A.B. da Silva, R. A.A. Munoz, E. M. Richter, Electroanalysis, 23 (2011) 2764.

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Simultaneous differential pulse voltammetric determination of ascorbic acid and caffeine in pharmaceutical formulations using a boron-doped diamond electrode

B.C. Lourenção, R.A. Medeiros, R.C. Rocha-Filho, O. Fatibello-Filho.

Electroanalysis, 22, 1717 (2010)

DPV responses for 0.029 M AA and 0.79 M caffeine in 0.1 M H2SO4 on (1) cathodically pretreated BDD electrode and (2) glassy-carbon electrode.

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0.4 0.6 0.8 1.0 1.2 1.4 1.6

10

15

20

25

30

35

40

45

50

I/A

E/V vs Ag/AgCl

0.4 0.6 0.8 1.0 1.2 1.4 1.60

10

20

30

40

50

60

70

I/A

E/V vs Ag/AgCl

Repeatability study for 0.029 M Ascorbic acid (n = 10) + 0.79 M caffeine in 0.1 M H2SO4

RSD = 8.7 % for glassy-carbon (GC) electrodeRSD = 1.0 % for boron-doped diamond (BDD) electrode

Repeatability study

GC BDD

Highlight:higher repeatability of the BDD

electrode

B.C. Lourenção; R.A. Medeiros; R.C. Rocha-Filho; O. Fatibello-Filho; Electroanalysis, 22 (2010) 1717

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(A) Diagram of the multicommutated stop-flow system: V1 and V2: solenoid valves;

A: sample or standard solution; C: carrier solution (BR buffer pH 7.0). (B) Transient DPV signals in triplicate for sulfamethoxazole (1.0 – 8.0 mg L–1) and

trimethoprim (0.2 – 1.6 mg L–1) determination in pharmaceuticals.

Sampling

Rate = 30 h-1

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Conclusions

HT-BDD electrodes present an improved electrochemical activity towards many analytes

Background current for HT-BDD electrodes is one order of magnitude lower than that for glassy-carbon electrodes, leading to an improved signal-to-background ratio

HT-BDD electrodes present higher sensitivity, precision, and accuracy, and lower LOD and response time than glassy-carbon electrodes

No deactivation of the BDD electrode was observed in the flow injection system / HPLC coupled with amperometric/voltammetric detection

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Profs. Romeu Leonardo Quezia Giancarlo

Dr. Adriana Dr. Élen M.Sc. Bruna M.Sc. Roberta

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