Ricardo Jorgensen Cassella - Academia.edu (original) (raw)

Papers by Ricardo Jorgensen Cassella

Research paper thumbnail of Graphene oxide functionalized with <i>N</i>-methyl-<scp>d</scp>-glucamine as a novel sorbent for boron removal from produced and formation waters

RSC advances, 2024

This work describes the synthesis of a novel material based on graphene oxide (GO) for the select... more This work describes the synthesis of a novel material based on graphene oxide (GO) for the selective removal of boron in an aqueous medium. The material was obtained by functionalizing graphene oxide with N-methyl-D-glucamine (NMDG). This material, named NMDG@GO, was successfully characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, atomic force microscopy, and elemental analysis. The adsorption process was studied from a kinetic perspective using pseudo-first-order and pseudo-second-order models, with the pseudo-second-order model presenting a better fit. The adsorption process was studied using Langmuir and Freundlich isotherms, with the Freundlich model providing a better fit and an r 2 value of 0.9368. This result indicates that the adsorption process occurred in multilayers, considering a heterogeneous distribution of adsorption sites. The levels of the factor's adsorbent mass, pH, and time were optimized using a central composite design, with the optimal values achieved at 120 mg of material, pH = 2.0, and an agitation time of 40 min. Under these optimized conditions, it was possible to remove 22 to 35% of the boron present in saline waters from oil production (production and formation waters) using the developed adsorbent.

Research paper thumbnail of Ultrasensitive and rapid immuno-detection of human IgE anti-therapeutic horse sera using an electrochemical immunosensor

Analytical biochemistry, Dec 14, 2017

Antivenom allergy disease mediated by patient IgE is an important public health care concern. To ... more Antivenom allergy disease mediated by patient IgE is an important public health care concern. To improve detection of hypersensitive individuals prior to passive antibody therapy, an amperometric immunosensor was developed to detect reactive human IgE. Whole horse IgG3 (hoIgG3) was immobilized onto the surface of carbon or gold screen-printed electrodes through a cross-linking solution of glutaraldehyde on a chitosan film. Sera from persons with a known allergic response to hoIgG3 or non-allergic individuals was applied to the sensor. Bound human IgE (humIgE) was detected by an anti-humIgE antibody through a quantitative amperometric determination by tracking via the electrochemical reduction of the quinone generated from the hydroquinone with the application of a potential of 25 mV. The optimal immunosensor configuration detected reactive humIgE at a dilution of 1:1800 of the human sera that represent a detection limit of 0.5 pg/mL. Stability testing demonstrated that through 20 cy...

Research paper thumbnail of Use of a versatile, easy, and rapid atmospheric monitor (VERAM) passive samplers for pesticide determination in continental waters

Analytical and bioanalytical chemistry, 2016

The versatile, easy, and rapid atmospheric monitor (VERAM), a passive sampler device widely used ... more The versatile, easy, and rapid atmospheric monitor (VERAM), a passive sampler device widely used for air monitoring, was evaluated as passive sampler for the determination of 23 pesticides in water. Gas chromatography with mass spectrometry detection was employed for determination of pesticides after microwave-assisted-extraction and specific clean-up of deployed samplers. The proposed methodology reached method detection levels from 2 to 10 ng pesticide per sampler. Sampling rate (Rs) was determined for every pesticide from an uptake isotherm study performed at three different concentration levels (50, 125, and 250 ng L(-1)). The obtained RS values ranged from 0.06 to 0.76 L d(-1). The obtained limits of detection for a 24-h passive sampling were from 4 to 50 ng L(-1). The effect of water parameters, such as temperature, pH, and ionic strength, were evaluated for their effect on pesticides retention using VERAMs. Pesticide RS values were independent of the water composition and inc...

Research paper thumbnail of Comparação da Eficiência de Diferentes Técnicas (Esgotamento e Foulardagem) de Fixação de Permetrina em Tecidos Têxteis

Revista Virtual De Quimica, Feb 21, 2015

Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of... more Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of repellent is considered one of the most important means in terms of combating insect bites and the diseases transmitted that way. According to this trend, the use of repellents applied directly to the skin, and also impregnated into the fabrics used for making clothes have been frequently used and considered of great importance. Permethrin is a species commonly used for this purpose and such possibility exists due to two important facts: it has low toxicity by dermal adsorption and it presents high efficiency in repelling action. Several manufacturing methods are used to fix chemicals into the tissue. In this work, two different methods of fixation of permethrin into tissues were evaluated for their efficiency: exhaustion and padding. In the process of exhaustion, the fabric remains under stirring in bath, in contact with the solution of permethrin. In process of padding, the fabric passes through rollers so that the solution is forced to enter into it. The efficiency of fixation was assessed by quantificating impregnated permethrin and the results obtained indicated that exhaustion procedure was more efficient, when using the same initial concentration of permethrin at both processes, a greater concentration into the fabrics was achieved by exhaustion.

Research paper thumbnail of Comparison of the Eficiency of Different Techniques (Exhaustion and Padding) for the Fixation of Permethrin in Fabrics

Revista Virtual de Química, 2015

Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of... more Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of repellent is considered one of the most important means in terms of combating insect bites and the diseases transmitted that way. According to this trend, the use of repellents applied directly to the skin, and also impregnated into the fabrics used for making clothes have been frequently used and considered of great importance. Permethrin is a species commonly used for this purpose and such possibility exists due to two important facts: it has low toxicity by dermal adsorption and it presents high efficiency in repelling action. Several manufacturing methods are used to fix chemicals into the tissue. In this work, two different methods of fixation of permethrin into tissues were evaluated for their efficiency: exhaustion and padding. In the process of exhaustion, the fabric remains under stirring in bath, in contact with the solution of permethrin. In process of padding, the fabric passes through rollers so that the solution is forced to enter into it. The efficiency of fixation was assessed by quantificating impregnated permethrin and the results obtained indicated that exhaustion procedure was more efficient, when using the same initial concentration of permethrin at both processes, a greater concentration into the fabrics was achieved by exhaustion.

Research paper thumbnail of Multiple response optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry with sample injection as detergent emulsion

The present paper reports the optimization for Cu, Fe and Pb determination in naphtha by graphite... more The present paper reports the optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry (GF AAS) employing a strategy based on the injection of the samples as detergent emulsions. The method was optimized in relation to the experimental conditions for the emulsion formation and taking into account that the three analytes (Cu, Fe and Pb) should be measured in the same emulsion. The optimization was performed in a multivariate way by employing a three-variable Doehlert design and a multiple response strategy. For this purpose, the individual responses of the three analytes were combined, yielding a global response that was employed as a dependent variable. The three factors related to the optimization process were: the concentration of HNO 3 , the concentration of the emulsifier agent (Triton X-100 or Triton X-114) in aqueous solution used to emulsify the sample and the volume of solution. At optimum conditions, it was possible to obtain satisfactory results with an emulsion formed by mixing 4 mL of the samples with 1 mL of a 4.7% w/v Triton X-100 solution prepared in 10% v/v HNO 3 medium. The resulting emulsion was stable for 250 min, at least, and provided enough sensitivity to determine the three analytes in the five samples tested. A recovery test was performed to evaluate the accuracy of the optimized procedure and recovery rates, in the range of 88-105%; 94-118% and 95-120%, were verified for Cu, Fe and Pb, respectively.

Research paper thumbnail of Estuarine sediment quality assessment by Fourier-transform infrared spectroscopy

Vibrational Spectroscopy, 2010

Partial least squares Fourier-transform infrared (PLS-FTIR) models were developed for the quality... more Partial least squares Fourier-transform infrared (PLS-FTIR) models were developed for the quality assessment of estuarine sediments through the evaluation of several physico-chemical parameters. Models were based on the chemometric treatment of attenuated total reflection (ATR) spectra directly obtained from samples previously lyophilized and sieved through a lower than 63 m grid. Spectra were scanned from 3997 to 523 cm −1 , averaging 36 scans per spectrum with a nominal resolution of 8 cm −1. Models were built using reference data obtained for sediment samples collected from Ria de Arousa estuary. Hierarchical cluster classification of sediment ATR spectra was employed for the establishment of the independent calibration and validation sample sets. Several parameters, like trace element content (Sn, Pb, Cd, As, Sb and total Cr and also acid soluble, reducible and oxidizable Cr fractions), elemental composition (carbon (C), nitrogen (N) and hydrogen (H) content), pH, redox potential (Eh), together with the amount of fulvic and humic acids, were evaluated. Residual predictive deviation (RPD) values ranging from 1.79 to 2.28 were obtained for all trace elements with the exception of Pb, which exhibited a RPD value of 1.5, similar to those obtained for the different extractable fractions of Cr. Regarding the elemental analysis, excellent RPD values were also obtained for C and N, but for H only adequate values for screening purposes were achieved. Prediction errors for pH and Eh were 0.13 units and 30 mV, respectively, thus indicating the good prediction capabilities of the method. For humic substances, excellent results were obtained for humic acids when compared with fulvic ones. In short, direct ART-FTIR measurements on solid sediments allow a rapid screening of many components of sediments and quantitative data of the main physico-chemical parameters.

Research paper thumbnail of Determination of sulfide in waters by flow-injection solid phase spectrophotometry

Research paper thumbnail of Synthesis and application of a functionalized resin for flow injection/F AAS copper determination in waters

Talanta, 2005

This paper reports the development of a new strategy for low-level determination of copper in wat... more This paper reports the development of a new strategy for low-level determination of copper in water samples by using a flow-injection system coupled to solid-phase extraction (SPE) using flame atomic absorption spectrometry (F AAS) as detector. In order to preconcentrate copper from samples, a minicolumn packed with a styrene-divinylbenzene resin functionalized with (S)-2-[hydroxy-bis-(4-vinyl-phenyl)-methyl]pyrrolidine-1-carboxylic acid ethyl ester was used and the synthesis procedure is described. System operation is based on the on-line retention of Cu(II) ions at pH 9.0 ± 0.2 in a such minicolumn with posterior analyte elution with 2 mol l −1 HCl directly to the F AAS nebulizer. The influence of several chemical (sample pH, buffer concentration, HCl eluent concentration and effect of the ionic strength) and flow (sample and eluent flow rates and preconcentration time) variables that could affect the performance of this system were investigated as well as the possible interferents. At optimized conditions, for 2 min of preconcentration time (13.2 ml of sample volume), the system achieved a detection limit of 1.1 g l −1 , a R.S.D. 1% at 20 g g l −1 and an analytical throughput of 25 h −1 , whereas for 4 min of preconcentration time (26.4 ml of sample volume), a detection limit of 0.93 g l −1 , a R.S.D. 5.3% at 5 g l −1 and a sampling frequency of 13 h −1 were reported.

Research paper thumbnail of Direct determination of vanadium in high saline produced waters from offshore petroleum exploration by electrothermal atomic absorption spectrometry

Talanta, 2006

The present work reports the development of a methodology for the direct determination of vanadiu... more The present work reports the development of a methodology for the direct determination of vanadium in high saline waters derived from offshore petroleum exploration employing electrothermal atomic absorption spectrometry. Such waters, usually called produced waters, present complex composition containing various organic and inorganic substances. In order to attain best conditions (highest sensitivity besides lowest background) for the methodology, studies about the effects of several variables (evaluation of pyrolysis and atomization temperatures, type of chemical modifier, concentration of modifier and pyrolysis time) and the convenient calibration strategy were performed. Best conditions were reached with the addition of 10 g of NH 4 H 2 PO 4 as chemical modifier employing pyrolysis (during 10 s) and atomization temperatures of 1500 and 2700 • C, respectively. Obtained results indicated that, in this kind of sample, vanadium can be determined by standard addition method or employing an external calibration approach with standard solutions prepared in 0.8 mol l −1 NaCl medium. In order to evaluate possible matrix interferences, a recovery test was performed with five spiked samples of produced waters. The limit of detection, limit of quantification and relative standard deviation in 0.8 mol l −1 NaCl medium were also calculated and the derived values were 1.9 g l −1 , 6.3 g l −1 and 5.6% (at 10 g l −1 level), respectively.

Research paper thumbnail of Multivariate optimization of a liquid–liquid extraction of the EPA-PAHs from natural contaminated waters prior to determination by liquid chromatography with fluorescence detection

Talanta, 2008

This paper reports the multivariate optimization of a liquid-liquid extraction procedure for the ... more This paper reports the multivariate optimization of a liquid-liquid extraction procedure for the determination of 15 EPA-polycyclic aromatic hydrocarbons (PAHs) by high-performance liquid chromatography with fluorescence detection. A Doehlert design was used to find optimum conditions for the procedure through Response Surface Methodology. Three variables (total volume of hexane, number of extraction steps and duration of such steps) were elected as factors in the optimization study. A principal component analysis (PCA) was run with optimized data, resulting in four groups of PAHs, ordered according to their molecular weight. Final working conditions were established in order to achieve a more robust methodology in relation to all fifteen PAHs under study. Best results could be observed when 77 mL of hexane were divided in four consecutive extraction steps with 18 min each. These experimental conditions were applied in the analysis of a spiked river water sample, and the recoveries varied between 80.9 and 106%, with an average value of 97.1 ± 6.8%. The application of the methodology to river water showed that the method has a good average precision for the studied PAHs.

Research paper thumbnail of Focussed microwave-assisted sample preparation: total phenol determination in petroleum refinery effluents by flow injection spectrophotometry

Microchemical Journal, 2004

This paper reports the development of a new approach for total phenol distillation using a focuss... more This paper reports the development of a new approach for total phenol distillation using a focussed microwave oven, aiming its determination in petroleum refinery effluents and sour waters. In the procedure, 25 ml of sample is distilled during 15 min at 210 W power. At ...

Research paper thumbnail of Combined use of Pd and HF as chemical modifiers for the determination of total chromium in produced waters from petroleum exploration by ET AAS

Microchemical Journal, 2008

This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the d... more This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the direct determination of total chromium in waters derived from petroleum exploration employing electrothermal atomic absorption spectrometry (ET AAS). Such waters, usually called as produced waters, have complex composition presenting a number of organic and inorganic substances. When obtained from offshore operations they

Research paper thumbnail of Polyurethane foam loaded with SDS for the adsorption of cationic dyes from aqueous medium: Multivariate optimization of the loading process

Journal of Hazardous Materials, 2009

This paper reports the development of a new procedure for the adsorption of four cationic dyes (R... more This paper reports the development of a new procedure for the adsorption of four cationic dyes (Rhodamine B, Methylene Blue, Crystal Violet and Malachite Green) from aqueous medium employing polyurethane foam (PUF) loaded with sodium dodecylsulfate (SDS) as solid phase. PUF loading process was based on the stirring of 200 mg PUF cylinders with acidic solutions containing SDS. The conditions for loading were optimized by response surface methodology (RSM) using a Doehlert design with three variables that were SDS and HCl concentrations and stirring time. Results obtained in the optimization process showed that the stirring time is not a relevant parameter in the PUF loading, evidencing that the transport of SDS from solution to PUF surface is fast. On the other hand, both SDS and HCl concentrations were important parameters causing significant variation in the efficiency of the resulting solid phase for the removal of dyes from solution. At optimized conditions, SDS and HCl concentrations were 4.0 × 10 −4 and 0.90 mol L −1 , respectively. The influence of stirring time was evaluated by univariate methodology. A 20 min stirring time was established in order to make the PUF loading process fast and robust without losing efficiency. The procedure was tested for the removal of the four cationic dyes from aqueous solutions and removal efficiencies always better than 90% were achieved for the two concentrations tested (2.0 × 10 −5 and 1.0 × 10 −4 mol L −1).

Research paper thumbnail of Optimization of an open-focused microwave oven digestion procedure for determination of metals in diesel oil by inductively coupled plasma optical emission spectrometry

Journal of Hazardous Materials, 2007

This work reports the optimization of a focused microwave assisted procedure for the wet acid dis... more This work reports the optimization of a focused microwave assisted procedure for the wet acid dissolution of diesel oil in order to allow the determination of metals in the samples by inductively coupled plasma optical emission spectrometry (ICP-OES). The dissolution process was monitored by measuring residual carbon content (RCC), also by ICP-OES, in the final solutions obtained after application of digestion program. All experimental work was performed using a commercial sample of diesel oil containing 85.74+/-0.13% of carbon. The initial dissolution program comprised three steps: (i) carbonization with H(2)SO(4); (ii) oxidation with HNO(3) and (iii) final oxidation with H(2)O(2). During work it was verified that the first step played an important role on the dissolution process of this kind of sample. It is therefore, necessary to give a detailed optimization of such step. Employing the optimized conditions it was possible to digest 2.5 g of diesel oil with a 40 min-heating program. At these conditions, residual carbon content was always lower than 5%. Optimized methodology was applied in the determination of metals in three diesel oil samples by ICP-OES. Recovery tests were also performed by adding 10 microg of metals, as organic standards, to the samples before digestion. Recovery percentages always higher than 90% were obtained for the metals of interest (Al, Cu, Fe and Ni), except for Zn, which presented recoveries between 70 and 78%.

Research paper thumbnail of Employment of polyurethane foam for the adsorption of Methylene Blue in aqueous medium

Journal of Hazardous Materials, 2008

This work presents a detailed study about the adsorption of Methylene Blue (MB) onto polyether ty... more This work presents a detailed study about the adsorption of Methylene Blue (MB) onto polyether type polyurethane foam (PUF). The adsorption process is based on the formation of a hydrophobic ionic-pair between cationic dye MB and dodecylsulfate anion (SDS), which present high affinity by PUF. Set-up employed in the study was built up by adjusting a 200mg cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium, kinetic and thermodynamic aspects and it was modeled by employing Langmuir and Freundlich isotherms. Obtained results showed that the ratio between SDS and MB concentrations plays an important role on the adsorption process. According to Langmuir isotherm, a maximum adsorption capacity of 7.20 x 10(-5) mol MBg(-1) was achieved when optimized operational conditions were employed. The adsorption rate seems to be regulated by an intraparticle diffusion mechanism. Adsorption process was spontaneous (negative DeltaG) at ambient temperature and presented an endothermic characteristic (positive DeltaH). Sequential extraction experiments were carried out by changing PUF plugs in 30 min time intervals and around 96% of the MB present in solution could be removed through consecutive extractions with six 200 mg PUF cylinders.

Research paper thumbnail of Separation of Malachite Green and Methyl Green cationic dyes from aqueous medium by adsorption on Amberlite XAD-2 and XAD-4 resins using sodium dodecylsulfate as carrier

Chemical Engineering Journal, 2011

This present work reports a study about the adsorption of some cationic dyes (Malachite Green and... more This present work reports a study about the adsorption of some cationic dyes (Malachite Green and Methyl Green) by polymeric resins called Amberlite XAD-2 and XAD-4, in a medium containing sodium dodecylsulfate (SDS). The effect of several parameters (SDS concentration, pH, ionic strength and temperature) on the adsorption of each dye by the resins was investigated. Also, the adsorption was characterized in relation to thermodynamic and kinetic aspects in order to define the nature of the process. For Malachite Green, the SDS concentration did not affect the adsorption efficiency, only changing the adsorption rate at the process occurs, happening faster in the presence of the surfactant. On the other hand, the adsorption efficiency of the Methyl Green was increased with the increase of the surfactant concentration when both Amberlite XAD-2 and XAD-4 resins were tested. For both dyes, the Amberlite XAD-4 resin showed higher efficiency than the Amberlite XAD-2. According to the obtained thermodynamic data, the adsorption of the dyes by the two resins appeared to be a physical process, once adsorption enthalpies values of approximately 20 kJ mol −1 were obtained in all cases. The kinetic study also showed that the whole adsorption process was governed by a pseudo first-order kinetics and that the adsorption rate was regulated by an intraparticle diffusion mechanism.

Research paper thumbnail of Development of an integrated flow injection system for the electro-oxidative leaching of uranium from geological samples and its spectrophotometric determination with Arsenazo III

Analytica Chimica Acta, 2008

This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric ... more This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric determination of uranium in ore samples. By associating a conventional flow injection system, used for uranium determination with Arsenazo III, with an on-line system for electro-oxidative leaching, a fully integrated system was assembled. The systems were integrated after achieving optimum conditions for uranium determination and leaching. According to the results obtained in the present work, a current density of 280 mA cm(-2) generated enough hypochlorite ions in the electrolyte solution (3.6 mol L(-1) HCl+2% (w/v) NaCl) to promote quantitative oxidation of U(IV) to U(VI) thus improving the extraction efficiency. The slurry density did not significantly affect the performance of the system and the increasing temperature resulted in a decrease in extraction efficiency. This methodology was applied in the determination of U(3)O(8) in four ore samples and the results obtained agreed with those obtained by ICP-MS after conventional wet acid digestion of the samples.

Research paper thumbnail of Multivariate optimization of the determination of zinc in diesel oil employing a novel extraction strategy based on emulsion breaking

Analytica Chimica Acta, 2011

This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination... more This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination by Flame Atomic Absorption Spectrometry (FAAS), proposed as a novel approach for these kinds of analyses and the multivariate optimization of the proposed procedure. The extraction of Zn is based on the emulsification of an aqueous solution containing Triton X-114 and HNO(3) with diesel oil samples followed by breaking of the emulsion by heating. The aqueous phase obtained after the emulsion breaking was collected and used for Zn quantification by FAAS. The methodology was optimized using a Doehlert design and the system variables were the concentrations of surfactant and HNO(3) in the solution employed in the emulsification and the temperature used in the emulsion breaking. The ratio between absorbance and the time required to break the emulsions was taken as response. Two sets of experiments, using different emulsifier agents, were run: the first one using Triton X-100 and the second one using Triton X-114. At optimized conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 5% w/v of Triton X-114 and 15% v/v of HNO(3) and broken by heating at 80 °C. The proposed analytical procedure was applied in the analysis of six real samples of diesel oil and a recovery test was carried out by spiking the samples with known amounts of Zn (25 and 50 μg L(-1)), added as organometallic oiled standard. Recovery percentages achieved in this test were between 92 and 109%.

Research paper thumbnail of Reversed Flow Injection System for the Spectrophotometric Determination of Cetylpyridinium Chloride in Pharmaceutical Products with Eriochrome Black T in Triton X-100 Medium

FIA研究懇談会会誌, 2010

This paper reports the development of a reversed FIA system for the spectrophotometric determinat... more This paper reports the development of a reversed FIA system for the spectrophotometric determination of cetylpyridinium chloride (CPC) in pharmaceutical products. The method is based on the reaction between CPC and Eriochrome Black T (EBT) with the formation of a product with strong absorption at 645 nm. At optimized conditions the reversed FIA system was able to process 40 samples per hour with a detection limit of 0.24 µg mL −1 and a quantification limit of 0.80 µg mL −1. Recovery rates between 92 and 107% were obtained in the analysis of pharmaceutical products using the proposed methodology.

Research paper thumbnail of Graphene oxide functionalized with <i>N</i>-methyl-<scp>d</scp>-glucamine as a novel sorbent for boron removal from produced and formation waters

RSC advances, 2024

This work describes the synthesis of a novel material based on graphene oxide (GO) for the select... more This work describes the synthesis of a novel material based on graphene oxide (GO) for the selective removal of boron in an aqueous medium. The material was obtained by functionalizing graphene oxide with N-methyl-D-glucamine (NMDG). This material, named NMDG@GO, was successfully characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, atomic force microscopy, and elemental analysis. The adsorption process was studied from a kinetic perspective using pseudo-first-order and pseudo-second-order models, with the pseudo-second-order model presenting a better fit. The adsorption process was studied using Langmuir and Freundlich isotherms, with the Freundlich model providing a better fit and an r 2 value of 0.9368. This result indicates that the adsorption process occurred in multilayers, considering a heterogeneous distribution of adsorption sites. The levels of the factor's adsorbent mass, pH, and time were optimized using a central composite design, with the optimal values achieved at 120 mg of material, pH = 2.0, and an agitation time of 40 min. Under these optimized conditions, it was possible to remove 22 to 35% of the boron present in saline waters from oil production (production and formation waters) using the developed adsorbent.

Research paper thumbnail of Ultrasensitive and rapid immuno-detection of human IgE anti-therapeutic horse sera using an electrochemical immunosensor

Analytical biochemistry, Dec 14, 2017

Antivenom allergy disease mediated by patient IgE is an important public health care concern. To ... more Antivenom allergy disease mediated by patient IgE is an important public health care concern. To improve detection of hypersensitive individuals prior to passive antibody therapy, an amperometric immunosensor was developed to detect reactive human IgE. Whole horse IgG3 (hoIgG3) was immobilized onto the surface of carbon or gold screen-printed electrodes through a cross-linking solution of glutaraldehyde on a chitosan film. Sera from persons with a known allergic response to hoIgG3 or non-allergic individuals was applied to the sensor. Bound human IgE (humIgE) was detected by an anti-humIgE antibody through a quantitative amperometric determination by tracking via the electrochemical reduction of the quinone generated from the hydroquinone with the application of a potential of 25 mV. The optimal immunosensor configuration detected reactive humIgE at a dilution of 1:1800 of the human sera that represent a detection limit of 0.5 pg/mL. Stability testing demonstrated that through 20 cy...

Research paper thumbnail of Use of a versatile, easy, and rapid atmospheric monitor (VERAM) passive samplers for pesticide determination in continental waters

Analytical and bioanalytical chemistry, 2016

The versatile, easy, and rapid atmospheric monitor (VERAM), a passive sampler device widely used ... more The versatile, easy, and rapid atmospheric monitor (VERAM), a passive sampler device widely used for air monitoring, was evaluated as passive sampler for the determination of 23 pesticides in water. Gas chromatography with mass spectrometry detection was employed for determination of pesticides after microwave-assisted-extraction and specific clean-up of deployed samplers. The proposed methodology reached method detection levels from 2 to 10 ng pesticide per sampler. Sampling rate (Rs) was determined for every pesticide from an uptake isotherm study performed at three different concentration levels (50, 125, and 250 ng L(-1)). The obtained RS values ranged from 0.06 to 0.76 L d(-1). The obtained limits of detection for a 24-h passive sampling were from 4 to 50 ng L(-1). The effect of water parameters, such as temperature, pH, and ionic strength, were evaluated for their effect on pesticides retention using VERAMs. Pesticide RS values were independent of the water composition and inc...

Research paper thumbnail of Comparação da Eficiência de Diferentes Técnicas (Esgotamento e Foulardagem) de Fixação de Permetrina em Tecidos Têxteis

Revista Virtual De Quimica, Feb 21, 2015

Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of... more Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of repellent is considered one of the most important means in terms of combating insect bites and the diseases transmitted that way. According to this trend, the use of repellents applied directly to the skin, and also impregnated into the fabrics used for making clothes have been frequently used and considered of great importance. Permethrin is a species commonly used for this purpose and such possibility exists due to two important facts: it has low toxicity by dermal adsorption and it presents high efficiency in repelling action. Several manufacturing methods are used to fix chemicals into the tissue. In this work, two different methods of fixation of permethrin into tissues were evaluated for their efficiency: exhaustion and padding. In the process of exhaustion, the fabric remains under stirring in bath, in contact with the solution of permethrin. In process of padding, the fabric passes through rollers so that the solution is forced to enter into it. The efficiency of fixation was assessed by quantificating impregnated permethrin and the results obtained indicated that exhaustion procedure was more efficient, when using the same initial concentration of permethrin at both processes, a greater concentration into the fabrics was achieved by exhaustion.

Research paper thumbnail of Comparison of the Eficiency of Different Techniques (Exhaustion and Padding) for the Fixation of Permethrin in Fabrics

Revista Virtual de Química, 2015

Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of... more Due to lack of knowledge of chemoprophylaxis for most diseases transmitted by insects, the use of repellent is considered one of the most important means in terms of combating insect bites and the diseases transmitted that way. According to this trend, the use of repellents applied directly to the skin, and also impregnated into the fabrics used for making clothes have been frequently used and considered of great importance. Permethrin is a species commonly used for this purpose and such possibility exists due to two important facts: it has low toxicity by dermal adsorption and it presents high efficiency in repelling action. Several manufacturing methods are used to fix chemicals into the tissue. In this work, two different methods of fixation of permethrin into tissues were evaluated for their efficiency: exhaustion and padding. In the process of exhaustion, the fabric remains under stirring in bath, in contact with the solution of permethrin. In process of padding, the fabric passes through rollers so that the solution is forced to enter into it. The efficiency of fixation was assessed by quantificating impregnated permethrin and the results obtained indicated that exhaustion procedure was more efficient, when using the same initial concentration of permethrin at both processes, a greater concentration into the fabrics was achieved by exhaustion.

Research paper thumbnail of Multiple response optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry with sample injection as detergent emulsion

The present paper reports the optimization for Cu, Fe and Pb determination in naphtha by graphite... more The present paper reports the optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry (GF AAS) employing a strategy based on the injection of the samples as detergent emulsions. The method was optimized in relation to the experimental conditions for the emulsion formation and taking into account that the three analytes (Cu, Fe and Pb) should be measured in the same emulsion. The optimization was performed in a multivariate way by employing a three-variable Doehlert design and a multiple response strategy. For this purpose, the individual responses of the three analytes were combined, yielding a global response that was employed as a dependent variable. The three factors related to the optimization process were: the concentration of HNO 3 , the concentration of the emulsifier agent (Triton X-100 or Triton X-114) in aqueous solution used to emulsify the sample and the volume of solution. At optimum conditions, it was possible to obtain satisfactory results with an emulsion formed by mixing 4 mL of the samples with 1 mL of a 4.7% w/v Triton X-100 solution prepared in 10% v/v HNO 3 medium. The resulting emulsion was stable for 250 min, at least, and provided enough sensitivity to determine the three analytes in the five samples tested. A recovery test was performed to evaluate the accuracy of the optimized procedure and recovery rates, in the range of 88-105%; 94-118% and 95-120%, were verified for Cu, Fe and Pb, respectively.

Research paper thumbnail of Estuarine sediment quality assessment by Fourier-transform infrared spectroscopy

Vibrational Spectroscopy, 2010

Partial least squares Fourier-transform infrared (PLS-FTIR) models were developed for the quality... more Partial least squares Fourier-transform infrared (PLS-FTIR) models were developed for the quality assessment of estuarine sediments through the evaluation of several physico-chemical parameters. Models were based on the chemometric treatment of attenuated total reflection (ATR) spectra directly obtained from samples previously lyophilized and sieved through a lower than 63 m grid. Spectra were scanned from 3997 to 523 cm −1 , averaging 36 scans per spectrum with a nominal resolution of 8 cm −1. Models were built using reference data obtained for sediment samples collected from Ria de Arousa estuary. Hierarchical cluster classification of sediment ATR spectra was employed for the establishment of the independent calibration and validation sample sets. Several parameters, like trace element content (Sn, Pb, Cd, As, Sb and total Cr and also acid soluble, reducible and oxidizable Cr fractions), elemental composition (carbon (C), nitrogen (N) and hydrogen (H) content), pH, redox potential (Eh), together with the amount of fulvic and humic acids, were evaluated. Residual predictive deviation (RPD) values ranging from 1.79 to 2.28 were obtained for all trace elements with the exception of Pb, which exhibited a RPD value of 1.5, similar to those obtained for the different extractable fractions of Cr. Regarding the elemental analysis, excellent RPD values were also obtained for C and N, but for H only adequate values for screening purposes were achieved. Prediction errors for pH and Eh were 0.13 units and 30 mV, respectively, thus indicating the good prediction capabilities of the method. For humic substances, excellent results were obtained for humic acids when compared with fulvic ones. In short, direct ART-FTIR measurements on solid sediments allow a rapid screening of many components of sediments and quantitative data of the main physico-chemical parameters.

Research paper thumbnail of Determination of sulfide in waters by flow-injection solid phase spectrophotometry

Research paper thumbnail of Synthesis and application of a functionalized resin for flow injection/F AAS copper determination in waters

Talanta, 2005

This paper reports the development of a new strategy for low-level determination of copper in wat... more This paper reports the development of a new strategy for low-level determination of copper in water samples by using a flow-injection system coupled to solid-phase extraction (SPE) using flame atomic absorption spectrometry (F AAS) as detector. In order to preconcentrate copper from samples, a minicolumn packed with a styrene-divinylbenzene resin functionalized with (S)-2-[hydroxy-bis-(4-vinyl-phenyl)-methyl]pyrrolidine-1-carboxylic acid ethyl ester was used and the synthesis procedure is described. System operation is based on the on-line retention of Cu(II) ions at pH 9.0 ± 0.2 in a such minicolumn with posterior analyte elution with 2 mol l −1 HCl directly to the F AAS nebulizer. The influence of several chemical (sample pH, buffer concentration, HCl eluent concentration and effect of the ionic strength) and flow (sample and eluent flow rates and preconcentration time) variables that could affect the performance of this system were investigated as well as the possible interferents. At optimized conditions, for 2 min of preconcentration time (13.2 ml of sample volume), the system achieved a detection limit of 1.1 g l −1 , a R.S.D. 1% at 20 g g l −1 and an analytical throughput of 25 h −1 , whereas for 4 min of preconcentration time (26.4 ml of sample volume), a detection limit of 0.93 g l −1 , a R.S.D. 5.3% at 5 g l −1 and a sampling frequency of 13 h −1 were reported.

Research paper thumbnail of Direct determination of vanadium in high saline produced waters from offshore petroleum exploration by electrothermal atomic absorption spectrometry

Talanta, 2006

The present work reports the development of a methodology for the direct determination of vanadiu... more The present work reports the development of a methodology for the direct determination of vanadium in high saline waters derived from offshore petroleum exploration employing electrothermal atomic absorption spectrometry. Such waters, usually called produced waters, present complex composition containing various organic and inorganic substances. In order to attain best conditions (highest sensitivity besides lowest background) for the methodology, studies about the effects of several variables (evaluation of pyrolysis and atomization temperatures, type of chemical modifier, concentration of modifier and pyrolysis time) and the convenient calibration strategy were performed. Best conditions were reached with the addition of 10 g of NH 4 H 2 PO 4 as chemical modifier employing pyrolysis (during 10 s) and atomization temperatures of 1500 and 2700 • C, respectively. Obtained results indicated that, in this kind of sample, vanadium can be determined by standard addition method or employing an external calibration approach with standard solutions prepared in 0.8 mol l −1 NaCl medium. In order to evaluate possible matrix interferences, a recovery test was performed with five spiked samples of produced waters. The limit of detection, limit of quantification and relative standard deviation in 0.8 mol l −1 NaCl medium were also calculated and the derived values were 1.9 g l −1 , 6.3 g l −1 and 5.6% (at 10 g l −1 level), respectively.

Research paper thumbnail of Multivariate optimization of a liquid–liquid extraction of the EPA-PAHs from natural contaminated waters prior to determination by liquid chromatography with fluorescence detection

Talanta, 2008

This paper reports the multivariate optimization of a liquid-liquid extraction procedure for the ... more This paper reports the multivariate optimization of a liquid-liquid extraction procedure for the determination of 15 EPA-polycyclic aromatic hydrocarbons (PAHs) by high-performance liquid chromatography with fluorescence detection. A Doehlert design was used to find optimum conditions for the procedure through Response Surface Methodology. Three variables (total volume of hexane, number of extraction steps and duration of such steps) were elected as factors in the optimization study. A principal component analysis (PCA) was run with optimized data, resulting in four groups of PAHs, ordered according to their molecular weight. Final working conditions were established in order to achieve a more robust methodology in relation to all fifteen PAHs under study. Best results could be observed when 77 mL of hexane were divided in four consecutive extraction steps with 18 min each. These experimental conditions were applied in the analysis of a spiked river water sample, and the recoveries varied between 80.9 and 106%, with an average value of 97.1 ± 6.8%. The application of the methodology to river water showed that the method has a good average precision for the studied PAHs.

Research paper thumbnail of Focussed microwave-assisted sample preparation: total phenol determination in petroleum refinery effluents by flow injection spectrophotometry

Microchemical Journal, 2004

This paper reports the development of a new approach for total phenol distillation using a focuss... more This paper reports the development of a new approach for total phenol distillation using a focussed microwave oven, aiming its determination in petroleum refinery effluents and sour waters. In the procedure, 25 ml of sample is distilled during 15 min at 210 W power. At ...

Research paper thumbnail of Combined use of Pd and HF as chemical modifiers for the determination of total chromium in produced waters from petroleum exploration by ET AAS

Microchemical Journal, 2008

This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the d... more This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the direct determination of total chromium in waters derived from petroleum exploration employing electrothermal atomic absorption spectrometry (ET AAS). Such waters, usually called as produced waters, have complex composition presenting a number of organic and inorganic substances. When obtained from offshore operations they

Research paper thumbnail of Polyurethane foam loaded with SDS for the adsorption of cationic dyes from aqueous medium: Multivariate optimization of the loading process

Journal of Hazardous Materials, 2009

This paper reports the development of a new procedure for the adsorption of four cationic dyes (R... more This paper reports the development of a new procedure for the adsorption of four cationic dyes (Rhodamine B, Methylene Blue, Crystal Violet and Malachite Green) from aqueous medium employing polyurethane foam (PUF) loaded with sodium dodecylsulfate (SDS) as solid phase. PUF loading process was based on the stirring of 200 mg PUF cylinders with acidic solutions containing SDS. The conditions for loading were optimized by response surface methodology (RSM) using a Doehlert design with three variables that were SDS and HCl concentrations and stirring time. Results obtained in the optimization process showed that the stirring time is not a relevant parameter in the PUF loading, evidencing that the transport of SDS from solution to PUF surface is fast. On the other hand, both SDS and HCl concentrations were important parameters causing significant variation in the efficiency of the resulting solid phase for the removal of dyes from solution. At optimized conditions, SDS and HCl concentrations were 4.0 × 10 −4 and 0.90 mol L −1 , respectively. The influence of stirring time was evaluated by univariate methodology. A 20 min stirring time was established in order to make the PUF loading process fast and robust without losing efficiency. The procedure was tested for the removal of the four cationic dyes from aqueous solutions and removal efficiencies always better than 90% were achieved for the two concentrations tested (2.0 × 10 −5 and 1.0 × 10 −4 mol L −1).

Research paper thumbnail of Optimization of an open-focused microwave oven digestion procedure for determination of metals in diesel oil by inductively coupled plasma optical emission spectrometry

Journal of Hazardous Materials, 2007

This work reports the optimization of a focused microwave assisted procedure for the wet acid dis... more This work reports the optimization of a focused microwave assisted procedure for the wet acid dissolution of diesel oil in order to allow the determination of metals in the samples by inductively coupled plasma optical emission spectrometry (ICP-OES). The dissolution process was monitored by measuring residual carbon content (RCC), also by ICP-OES, in the final solutions obtained after application of digestion program. All experimental work was performed using a commercial sample of diesel oil containing 85.74+/-0.13% of carbon. The initial dissolution program comprised three steps: (i) carbonization with H(2)SO(4); (ii) oxidation with HNO(3) and (iii) final oxidation with H(2)O(2). During work it was verified that the first step played an important role on the dissolution process of this kind of sample. It is therefore, necessary to give a detailed optimization of such step. Employing the optimized conditions it was possible to digest 2.5 g of diesel oil with a 40 min-heating program. At these conditions, residual carbon content was always lower than 5%. Optimized methodology was applied in the determination of metals in three diesel oil samples by ICP-OES. Recovery tests were also performed by adding 10 microg of metals, as organic standards, to the samples before digestion. Recovery percentages always higher than 90% were obtained for the metals of interest (Al, Cu, Fe and Ni), except for Zn, which presented recoveries between 70 and 78%.

Research paper thumbnail of Employment of polyurethane foam for the adsorption of Methylene Blue in aqueous medium

Journal of Hazardous Materials, 2008

This work presents a detailed study about the adsorption of Methylene Blue (MB) onto polyether ty... more This work presents a detailed study about the adsorption of Methylene Blue (MB) onto polyether type polyurethane foam (PUF). The adsorption process is based on the formation of a hydrophobic ionic-pair between cationic dye MB and dodecylsulfate anion (SDS), which present high affinity by PUF. Set-up employed in the study was built up by adjusting a 200mg cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium, kinetic and thermodynamic aspects and it was modeled by employing Langmuir and Freundlich isotherms. Obtained results showed that the ratio between SDS and MB concentrations plays an important role on the adsorption process. According to Langmuir isotherm, a maximum adsorption capacity of 7.20 x 10(-5) mol MBg(-1) was achieved when optimized operational conditions were employed. The adsorption rate seems to be regulated by an intraparticle diffusion mechanism. Adsorption process was spontaneous (negative DeltaG) at ambient temperature and presented an endothermic characteristic (positive DeltaH). Sequential extraction experiments were carried out by changing PUF plugs in 30 min time intervals and around 96% of the MB present in solution could be removed through consecutive extractions with six 200 mg PUF cylinders.

Research paper thumbnail of Separation of Malachite Green and Methyl Green cationic dyes from aqueous medium by adsorption on Amberlite XAD-2 and XAD-4 resins using sodium dodecylsulfate as carrier

Chemical Engineering Journal, 2011

This present work reports a study about the adsorption of some cationic dyes (Malachite Green and... more This present work reports a study about the adsorption of some cationic dyes (Malachite Green and Methyl Green) by polymeric resins called Amberlite XAD-2 and XAD-4, in a medium containing sodium dodecylsulfate (SDS). The effect of several parameters (SDS concentration, pH, ionic strength and temperature) on the adsorption of each dye by the resins was investigated. Also, the adsorption was characterized in relation to thermodynamic and kinetic aspects in order to define the nature of the process. For Malachite Green, the SDS concentration did not affect the adsorption efficiency, only changing the adsorption rate at the process occurs, happening faster in the presence of the surfactant. On the other hand, the adsorption efficiency of the Methyl Green was increased with the increase of the surfactant concentration when both Amberlite XAD-2 and XAD-4 resins were tested. For both dyes, the Amberlite XAD-4 resin showed higher efficiency than the Amberlite XAD-2. According to the obtained thermodynamic data, the adsorption of the dyes by the two resins appeared to be a physical process, once adsorption enthalpies values of approximately 20 kJ mol −1 were obtained in all cases. The kinetic study also showed that the whole adsorption process was governed by a pseudo first-order kinetics and that the adsorption rate was regulated by an intraparticle diffusion mechanism.

Research paper thumbnail of Development of an integrated flow injection system for the electro-oxidative leaching of uranium from geological samples and its spectrophotometric determination with Arsenazo III

Analytica Chimica Acta, 2008

This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric ... more This work proposes a new procedure for on-line electro-oxidative leaching and spectrophotometric determination of uranium in ore samples. By associating a conventional flow injection system, used for uranium determination with Arsenazo III, with an on-line system for electro-oxidative leaching, a fully integrated system was assembled. The systems were integrated after achieving optimum conditions for uranium determination and leaching. According to the results obtained in the present work, a current density of 280 mA cm(-2) generated enough hypochlorite ions in the electrolyte solution (3.6 mol L(-1) HCl+2% (w/v) NaCl) to promote quantitative oxidation of U(IV) to U(VI) thus improving the extraction efficiency. The slurry density did not significantly affect the performance of the system and the increasing temperature resulted in a decrease in extraction efficiency. This methodology was applied in the determination of U(3)O(8) in four ore samples and the results obtained agreed with those obtained by ICP-MS after conventional wet acid digestion of the samples.

Research paper thumbnail of Multivariate optimization of the determination of zinc in diesel oil employing a novel extraction strategy based on emulsion breaking

Analytica Chimica Acta, 2011

This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination... more This paper describes the extraction/pre-concentration of Zn from diesel oil and its determination by Flame Atomic Absorption Spectrometry (FAAS), proposed as a novel approach for these kinds of analyses and the multivariate optimization of the proposed procedure. The extraction of Zn is based on the emulsification of an aqueous solution containing Triton X-114 and HNO(3) with diesel oil samples followed by breaking of the emulsion by heating. The aqueous phase obtained after the emulsion breaking was collected and used for Zn quantification by FAAS. The methodology was optimized using a Doehlert design and the system variables were the concentrations of surfactant and HNO(3) in the solution employed in the emulsification and the temperature used in the emulsion breaking. The ratio between absorbance and the time required to break the emulsions was taken as response. Two sets of experiments, using different emulsifier agents, were run: the first one using Triton X-100 and the second one using Triton X-114. At optimized conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 5% w/v of Triton X-114 and 15% v/v of HNO(3) and broken by heating at 80 °C. The proposed analytical procedure was applied in the analysis of six real samples of diesel oil and a recovery test was carried out by spiking the samples with known amounts of Zn (25 and 50 μg L(-1)), added as organometallic oiled standard. Recovery percentages achieved in this test were between 92 and 109%.

Research paper thumbnail of Reversed Flow Injection System for the Spectrophotometric Determination of Cetylpyridinium Chloride in Pharmaceutical Products with Eriochrome Black T in Triton X-100 Medium

FIA研究懇談会会誌, 2010

This paper reports the development of a reversed FIA system for the spectrophotometric determinat... more This paper reports the development of a reversed FIA system for the spectrophotometric determination of cetylpyridinium chloride (CPC) in pharmaceutical products. The method is based on the reaction between CPC and Eriochrome Black T (EBT) with the formation of a product with strong absorption at 645 nm. At optimized conditions the reversed FIA system was able to process 40 samples per hour with a detection limit of 0.24 µg mL −1 and a quantification limit of 0.80 µg mL −1. Recovery rates between 92 and 107% were obtained in the analysis of pharmaceutical products using the proposed methodology.