Lucio Angnes

Publications (103) View all

• Article: Amperometric detection of benzoyl peroxide in pharmaceutical preparations using carbon paste electrodes with peroxidases naturally immobilized on coconut fibers.

  J V B Kozan, R P Silva, S H P Serrano, A W O Lima, L Angnes
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  ABSTRACT: This paper describes the applications of a new carbon paste electrode containing fibers of coconut (Cocus nucifera L.) fruit, which are very rich in peroxidase enzymes naturally immobilized on its structure. The new sensor was applied for the amperometric quantification of benzoyl peroxide in facial creams and dermatological shampoos. The amperometric measurements were performed in 0.1 mol L(-1) phosphate buffer (pH 5.2), at 0.0 V (versus Ag/AgCl). On these conditions, benzoyl peroxide was rapidly determined in the 5.0-55 micromol L(-1), with a detection limit of 2.5 micromol L(-1) (s/n=3), response time of 4.1 s (90% of the steady state) and sensitivity limit of 0.33 A mol L(-1) cm(-2). The amperometric results are in good agreement with those obtained by spectrophotometric technique, used as a standard method.
  Biosensors & bioelectronics 10/2009; 25(5):1143-8. · 5.43 Impact Factor
• Article: Thermal behavior study and decomposition kinetics of salbutamol under isothermal and non-isothermal conditions

  Fabiana S. Felix, L. C. Cides da Silva, L. Angnes, J. R. Matos
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  ABSTRACT: The thermal decomposition of salbutamol (β2 — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E act=130 kJ mol−1 (for standard sample) and E act=252 kJ mol−1 (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min−1). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min−1). The calculated values were E act=134 kJ mol−1 (for standard sample) and E act=139 kJ mol−1 (for pharmaceutical sample).
  Journal of Thermal Analysis and Calorimetry 02/2009; 95(3):877-880. · 1.60 Impact Factor
• Article: Biosensing hydrogen peroxide utilizing carbon paste electrodes containing peroxidases naturally immobilized on coconut (Cocus nucifera L.) fibers.

  J V B Kozan, R P Silva, S H P Serrano, A W O Lima, L Angnes
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  ABSTRACT: A novel unmediated hydrogen peroxide biosensor based on the incorporation of fibrous tissue of coconut fruit in carbon paste matrix is presented. Cyclic voltammetry and amperometry were utilized to characterize the main electrochemical parameters and the performance of this new biosensor under different preparation and operation conditions. The resulting H2O2-sensitive biosensors respond rapidly (7 s to attain 90% of the signal), was operated at -0.15 V, presented linear response between 2.0x10(-4) and 3.4x10(-3) mol L(-1), the detection limit was estimated as 4.0x10(-5) mol L(-1). Its operation potential was situated between -0.2 and 0.1 V and the best pH was determined as 5.2. Electrodes containing 5% (w/w) of coconut fiber presented the best signal and their lifetime was extended to 3 months. The apparent Michaelis-Menten constant KM(app) and Vmax were estimated to be 8.90 mmol L(-1) and 6.92 mmol L(-1) microA(-1), respectively. The results obtained for determination of hydrogen peroxide in four pharmaceutical products (antiseptic solution, contact lenses cleaning solution, hair coloring cream and antiseptic dental rinse solution) were in agreement with those obtained by the spectrophotometric method. An additional advantage of these biosensors is the capacity to measure hydrogen peroxide even in samples with relatively low pH. To demonstrate the enzymatic activity of the coconut tissue, a very simple way was created during this work. Coconut fibers were immersed in H2O2 solution between two glass slides. Sequential images were taken to show the rapid generation of O2, attesting the high activity of the enzymes.
  Analytica chimica acta 06/2007; 591(2):200-7. · 4.31 Impact Factor
• Article: Electroanalysis of Crude Oil and Petroleum-Based Fuel for Trace Metals:  Evaluation of Different Microwave-Assisted Sample Decompositions and Stripping Techniques

  Rodrigo A. A. Munoz, Paulo R. M. Correia, Angerson N. Nascimento, Cíntia S. Silva, Pedro V. Oliveira, Lucio Angnes
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  ABSTRACT: Electroanalytical stripping techniques have been well-used for trace-metal determinations, because of their remarkable sensitivity and selectivity. However, when these techniques are applied for organic materials, such as crude oil and petroleum-based fuels, the samples must be decomposed. This paper evaluates the use of different microwave ovens for the decomposition of crude oil and diesel fuel to determine the content of copper, lead, mercury, and zinc in the digestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2, operated at atmospheric pressure, and a closed-vessel microwave (CVM) oven using HNO3/H2O2, operated under pressure in a vessel, were evaluated. Square-wave stripping voltammetry (SWSV) and stripping chronopotentiometry (SCP) at gold film electrodes were applied for copper, lead, and mercury. Potentiometric stripping analysis (PSA) at mercury film electrodes was applied for copper, lead, and zinc. SWSV was more affected by residual organic matter, especially for lead determination. SCP presented higher sensitivity for copper and mercury at gold electrodes. PSA at mercury electrodes was preferred for lead and zinc determination. Better detection limits were attained for FM-digested solutions, after 0.8−1.0 g of sample can be digested, in contrast to the low quantities (0.10−0.25 g) used when pressurized vessels were explored. Nevertheless, the loss of mercury was verified when samples were decomposed in the FM oven.
  12/2006;
• Article: Disposable nickel screen‐printed sensor based on dimethylglyoxime‐containing carbon ink

  Joseph Wang, Valberes B. Nascimento, Jianmin Lu, Deog Su Park, Lucio Angnes
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  ABSTRACT: Disposable complexing (preconcentrating) sensor strips for trace nickel have been fabricated by doping the screen-printed carbon ink with ligand dimethylglyoxime (DMG). The carbon ink is shown to be a useful matrix for incorporating the DMG, with the ligand maintaining its attractive coordination chemistry following the printing and firing processes. The response is characterized with respect to the ink composition, preconcentration period and potential, solution conditions and other variables. A short (30 s) accumulation period yields a detection limit of 5 μg/L nickel. The highly stable response indicates great promise for use as reusable devices. Measurement of nickel in a river water sample is demonstrated. Such incorporation of ligands into screen-printed carbon inks provides a promising route for thick-film sensors based on the preconcentration/voltammetric strategy.
  Electroanalysis 04/2005; 8(7):635 - 638. · 2.87 Impact Factor