Detecção Amperométrica/Voltamétrica em Sistemas FIA e Cromatográficos Empregando Eletrodo de Diamante Dopado com Boro LABORATÓRIO DE ANALÍTICA BIOANALÍTICA BIOSSENSORES ELETROANALÍTICA & SENSORES DQ UFSCar LABBES Orlando Fatibello Filho Departamento de Química, Universidade Federal de São Carlos, Caixa Postal 676, 13560-970 São Carlos – SP bello@ufscar.br; www.ufscar.br/labbes

Financial Support and Acknowledgements 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)

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

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

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.

Hydrogen-terminated BDD Oxygen-terminated BDD Electrochemical pre-treatments Characteristics of the procedure: simple and rapid low cost good intra- and inter-day repeatabilities Cathodic pre-treatment Anodic pre-treatment Hydrogen-terminated BDD (HT-BDD) Oxygen-terminated BDD (OT-BDD) 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.

Flow Injection analysis system Potentiostat/galvanostat: Autolab PGSTAT-30 (Ecochemie) Flow Injection analysis system 7

Flow electrochemical cell Working electrode : BDD 8000 ppm; 0.33 cm2 Counter electrode : stainless steel tube Reference electrode Ag/AgCl (3.0 mol L–1 KCl) E. M. Richter et al. Quim. Nova, 26(6) (2003) 839. L. Andrade et al. Anal. Chim. Acta 654 (2009) 127.

Results and discussion

Boron-Doped Diamond Electrode Simultaneous Square-Wave Voltammetric Determination of Phenolic Antioxidants (BHA and BHT) in Food Using a Boron-Doped Diamond Electrode BHA = butylated hydroxyanisole; BHT = butylated hydroxytoluene 10 R.A. Medeiros, R.C. Rocha-Filho, O. Fatibello-Filho, Food Chemistry, 123 (2010) 886.

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). 11

LODs lower than those previously reported BHA BHT Highlight: LODs lower than those previously reported BHA: 0.60 – 10 M; LOD = 0.14 M BHT: 0.60 – 10 M; LOD = 0.25 M

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.

(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.

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.

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 Tabela-Resultados obtidos para o estudo de repetibilidade intra e entre-dias intra-dias RSDa (%) entre-dias RSDb (%) 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

BHA: texp = 1,54 e BHT: texp = 1,66 tcrítico = 3,18 Tabela- Resultados obtidos na determinação simultânea de BHA e BHT em produtos alimentícios empregando-se HPLC e MPA-FIA Amostras BHA (mg/100 g) BHT (mg/100 g) BHA BHT Maionese HPLCa MPAa 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 -5,9 0,0 3 2,3±0,2 2,2±0,2 1,8±0,2 1,8±0,3 -4,3 4 2,3±0,1 2,1±0,3 1,4±0,2 1,3±0,1 -8,7 -7,1 a n = 3 b Erro (%) = 100 × (valor amperométrico - valor HPLC) / valor HPLC teste t-pareado BHA: texp = 1,54 e BHT: texp = 1,66 tcrítico = 3,18 R.A. Medeiros; B.C. Lourenção; R.C. Rocha-Filho, O. Fatibello-Filho; Anal. Chem., 82 (2010) 8658.

Paracetamol (A) and caffeine (B) in pharmaceuticals Differential pulse voltammetry Paracetamol: 0.50 – 83 M LOD = 0.049 M Caffeine: 0.50 – 83 M LOD = 0.035 M Highlight: LODs lower than those reported; higher sensitivity and larger linear concentration range of the AC 17 M 38 M B.C. Lourenção, R.A. Medeiros, R.C. Rocha-Filho, L.H. Mazo, O. Fatibello-Filho. Talanta, 78 (2009) 748. 19

A Simple Strategy for Simultaneous Determination of Paracetamol and Caffeine Using Flow Injection Analysis with Multiple 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.

Simultaneous differential pulse voltammetric determination of ascorbic acid and caffeine in pharmaceutical formulations using a boron-doped diamond electrode 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. B.C. Lourenção, R.A. Medeiros, R.C. Rocha-Filho, O. Fatibello-Filho. Electroanalysis, 22, 1717 (2010) 22

higher repeatability of the BDD electrode Repeatability study GC BDD 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) electrode RSD = 1.0 % for boron-doped diamond (BDD) electrode Highlight: higher repeatability of the BDD electrode B.C. Lourenção; R.A. Medeiros; R.C. Rocha-Filho; O. Fatibello-Filho; Electroanalysis, 22 (2010) 1717

(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

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

Profs. Romeu Leonardo Quezia Giancarlo Dr. Adriana Dr. Élen M.Sc. Bruna M.Sc. Roberta