Post on 17-Apr-2015
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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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