Disruption of a three-component solution as a novel strategy for Cu and Ni extraction from vegetable oils for their determination by GF AAS

In this work, we propose a novel approach for extracting Cu and Ni from vegetable oils (which can be expanded to other metals). The method is based on the transference of the analytes to an aqueous acid phase due to the disruption of a three-component solution. The extraction was carried out in two steps. In the first step, a three-component solution was prepared comprising the sample, 1-octanol, and HNO3 solution. Next, the homogeneous system was disrupted by adding 1.0 mL of deionized water, and two phases were formed. The aqueous extract deposited in the bottom of the flask was collected with a micropipette, and Cu and Ni were determined by graphite furnace atomic absorption spectrometry (GF AAS). The developed method presented limits of quantification (LOQ) of 0.25 and 0.17 ng g-1 for Cu and Ni, respectively, and was successfully applied in the analysis of eleven oil samples from different origins.

Single-vial preconcentration and cold vapor generation for the determination of Hg(II) in water samples of different salinities

In this work, a single-vial methodology for the extraction and cold vapor generation of mercury(II) was developed, followed by the determination of the analyte by atomic absorption spectrometry, with application in water samples of different salinities. L-cystine-modified Fe3O4 nanoparticles (2LcysMNP) were used as sorbent material in the magnetic solid phase extraction (MSPE) in the same flask in which the mercury vapor generation step was performed using a handmade gas-liquid separator developed in our laboratory. The main conditions for extraction, pre-concentration, and cold vapor generation of mercury were optimized. Under the optimized conditions, detection and quantification limits of 0.04 and 0.12 μg L-1, respectively, were achieved with a relative standard deviation of 7.5%. The single-vial system allowed for a preconcentration factor of 30 and an enrichment factor of 24. The accuracy of the method was evaluated by applying it to certified reference materials, and the obtained values were not significantly different from the expected values according to the Student's t-test. Verification of non-specific interferences was assessed by recovery tests, resulting in recoveries ranging from 81 to 111% for water samples of different salinities.

Microwave-Assisted Digestion of Polyurethane Foam as an Alternative to Elution: Solid Phase Extraction of Cd(II) and Pb(II) for Their Determination in Swimming Pool Waters

In this work, a separation/preconcentration method is proposed for the determination of Cd(II) and Pb(II) in swimming pool waters, using ammonium pyrrolidine dithiocarbamate (APDC) as a complexing agent and unloaded polyurethane foam (PUF) as a sorbent. The proposed method was optimized, and the defined optimal conditions were a pH of 7, 30 min of shaking time, 400 mg of PUF, and 0.5% (m/v) of the APDC solution. The release of Cd(II) and Pb(II) from the solid phase was achieved through the total digestion of PUF using a microwave-assisted acid approach with a 10.5 mol·L^-1 HNO₃ solution. The methodology was applied to four samples of swimming pool water for the determination of Cd(II) and Pb(II) using graphite furnace atomic absorption spectrometry (GF AAS). The limits of detection and quantification obtained were 0.02 and 0.06 μg·L^-1 for Cd(II) and 0.5 e 1.8 μg·L^-1 for Pb(II), respectively. We analyzed four samples of swimming pool waters, finding Cd concentrations between 0.22 and 1.37 μg·L^-1. On the other hand, only one sample presented Pb concentration above the limit of quantification (11.4 μg·L^-1). Recovery tests were performed by spiking the samples with known concentrations of the analytes, and recovery percentages between 82% and 105% were obtained.

In-syringe dispersive liquid-liquid microextraction

Dispersive liquid-liquid microextraction (DLLME) has recently been widely used in the separation and preconcentration of various chemical species. Among the various approaches using DLLME are systems that use a syringe as an extraction environment. In this review, details of some methods that use this approach are presented. The ways to promote dispersion, analytical characteristics, and the advantages and disadvantages of the methods, among other aspects, are discussed critically. Finally, some trends in the use of in-syringe microextraction systems are described.

Extraction of permethrin from impregnated fabrics for determination by ultra-high performance liquid chromatography with diode array detection

Permethrin is a synthetic pyrethroid insecticide that is largely used in the impregnation of fabrics employed for different purposes. This paper reports a detailed study on the conditions for its extraction from fabrics and for its determination by ultra-high performance liquid chromatography with diode array detection (UHPLC-DAD). Several parameters that could affect the extraction efficiency of permethrin were evaluated, such as the extraction time, agitating mode (mechanical or ultrasound-assisted), solvent type (methanol or acetonitrile), concentration, and volume. Under optimized conditions, the extraction was performed for 10 min using a 2 × 2 cm piece of impregnated fabric and 5 mL of pure methanol. The flask containing the sample and the solvent was shaken mechanically using a horizontal roller mixer. The accuracy of the method was assessed by a recovery test, which presented satisfactory results ranging from 86.8% to 95.2%. The method was employed in the analysis of nine samples of commercial fabrics of different colors and grammages that were impregnated with permethrin. The concentration of permethrin found in these samples varied between 25.6 ± 4.2 and 934 ± 119 mg m^-2.

Passive sampling of toluene (and benzene) in indoor air using a semipermeable membrane device

The distribution and concentration of organic compounds in the environment have attracted great interest mainly due to their capability of bioaccumulation, dispersion, and danger to living organisms. Factors such as urbanization, population growth, and the emergence of new technologies contribute to the increase in pollutant emissions, especially volatile organic compounds (VOCs), such as benzene, toluene, ethylbenzene, and xylenes (BTEX). These compounds are emitted by several sources, becoming more common in work environments, influencing indoor air quality (IAQ), which can cause health damage, in addition to increasing the likelihood of cancer development. In this context, we developed a semipermeable membrane device (SPMD), consisting of low density polyethylene membrane (8 cm long × 3 cm wide), filled with 3 mL of acetonitrile, for passive sampling of toluene (and benzene) in gas phase. With this configuration, the SPMD needed 24 h exposure to the indoor air in order to achieve equilibrium. The target compounds were quantified in the acceptor phase by HPLC-DAD. The optimized SPMD was tested for the collection of toluene and benzene in six chemistry laboratories at Fluminense Federal University and in five nail salons in the city of Niterói, in the state of Rio de Janeiro, Brazil. The developed sampling method was able to identify the analytes in the indoor air of the studied environments, and was easy to operate, with no need to clean up the extracts, allowing their direct injection into the chromatographic system.

Evaluation of Copper and Manganese Concentrations in Commercial Fruit Juices and Nectars Consumed in Brazil by GF AAS

The present work proposes a simple method for direct determination of Cu and Mn in commercial fruit juices and nectars by graphite furnace atomic absorption spectrometry (GF AAS). We analyzed samples of different flavors (orange, mango, passion fruit, peach, and grape) and brands of Brazilian commercial fruit juices and nectars. We also carried out a study to define a suitable temperature program and to optimize the calibration conditions. It was possible to determine Cu and Mn in the samples just after a simple dilution of samples with a 0.70 mol L^-1 HNO₃ solution, except in the case of grape juice. We compared the results obtained with the proposed method to those obtained after a traditional treatment based on acid digestion in a microwave oven, and no significant differences were observed (except for grape juice). The accuracy of the method was assessed through a recovery test, which provided recovery percentages in the range of 81-117%. Precision was always better than 8%, and the limits of quantification for Cu and Mn were 6 μg L^-1 and 9 μg L^-1, respectively. We analyzed twenty-two samples, and the concentrations of Cu and Mn were in the range of 24.1-321 μg L^-1 and 116-3296 μg L^-1, respectively. Statistical analysis using a two-way analysis of variance (ANOVA) at 95% confidence level showed that flavor and brand impacted on the concentration of the analytes in the samples. Among the samples analyzed, the grape juice presented the highest concentrations of both Cu and Mn.

Extraction induced by microemulsion breaking as a novel tool for the simultaneous determination of Cd, Mn, Pb and Sb in gasoline samples by ICP-MS and discrete sample introduction

This study reports a simple and efficient method for the simultaneous determination of Cd, Mn, Pb, and Sb at trace levels in gasoline samples by discrete sample introduction in inductively coupled plasma mass spectrometry (ICP-MS), employing the extraction induced by microemulsion breaking as a sample preparation method. In this work, a microemulsion was formed by mixing 0.7 mL of the gasoline sample with 0.28 mL of ethanol and 0.02 mL of 7 mol L^-1 HNO₃ solution. Afterwards, 0.1 mL of ultrapure water was added to induce microemulsion breaking. This lead to the formation of two different phases: (i) a top organic phase and (ii) a bottom aqueous phase that contained acid, ethanol and the extracted analytes. After that, 20 μL of the bottom phase (extract) was collected, and the analyte concentrations were determined by discrete sample introduction in ICP-MS. Calibration curves with 20 μg L^-1 of Rh as an internal standard were set up to each analyte in the range from 1 up to 10 μg L^-1, wherein the standard solutions were prepared in the matrix-matched extract (70:25:5, ethanol: deionized water: 7 mol L^-1 HNO₃ solution). The optimization of the EIMB conditions was carried out by analyzing the effects of the parameters that could affect the extraction efficiency, such as the relation between the nature of the alcohol and the proportion of the volumes of the microemulsion constituents (sample, HNO₃ and alcohol), acid concentration, and the water volume used for the microemulsion breaking. The following limits of detection relative to the amount of sample were obtained: 0.03 (Cd), 0.49 (Mn), 0.07 (Pb) and 0.02 (Sb), all of them in μg L^-1. The accuracy of the method was evaluated by the analysis of spiked samples, because no certified gasoline reference material is available. The average recoveries achieved for every analyte ranged from 96% to 114%. The developed methodology was successfully applied to the determination of these metals in five commercial gasoline samples.

Development of an extraction method for the determination of inorganic anions (chloride, sulfate and phosphate) in edible oils from different origins by ion chromatography

The present work reports the development of ion chromatography conductivity based detection analytical method for the determination of some inorganic anions (chloride, sulfate and phosphate) in vegetable oils. The analytes were extracted from samples prior to injection into the chromatographic system, employing a simple two-step procedure. In the first step, 4.5 g of the sample was vigorously mixed with 15 mL of deionized water and then mixed for 15 min on a horizontal roller. Afterwards, the mixture was sonicated for 15 min in an ultrasonic bath. Then, the mixture was centrifuged for 15 min at 5000 rpm and, after filtration through a 0.22 μm membrane, the aqueous phase was used for the determination of the analytes. A clean-up step was introduced in the analysis of olive oils in order to correct an increase of the baseline of the chromatograms. The limits of detection and quantification of the proposed method were, respectively, 0.005 and 0.02 μg g^-1 for chloride, 0.02 and 0.06 μg g^-1 for phosphate and 0.008 and 0.03 μg g^-1 for sulfate. Vegetable oils from corn, canola, soybean, sunflower and olive were analyzed and recovery tests (94.8 ± 10.1% mean recovery) were performed to attest the accuracy of the proposed method.

A batch and fixed bed column study for fluorescein removal using chitosan modified by epichlorohydrin

This study evaluates the feasibility of commercial chitosan (CQ) and modified chitosan (MQ) by epichlorohydrin to be used as a solid phase to remove fluorescein (FSC) from aqueous solutions by two different approaches: in batch and on a fixed column bed. For the batch study, all parameters that influence sorption capacity were evaluated, such as: pH, mass, ionic strength, temperature and time of contact. In the optimized condition, 75% removal was obtained for FSC using CQ, while the modification allowed an increase up to 99%, as well as an increase in the stability of the polymer. In the fixed column bed study, the influence of all the parameters was evaluated through breakthrough curves, and the thermodynamics parameters of each approach were obtained. The results of these studies demonstrate that the modification with epichlorohydrin enhanced the sorptive properties (from 35% to 95% in fixed bed experiments) and the polymer stability (making it insoluble), making it suitable to be used in wastewater treatment.

Adsorption of the herbicides diquat and difenzoquat on polyurethane foam: Kinetic, equilibrium and computational studies

This work reports a study about the adsorption of the herbicides diquat and difenzoquat from aqueous medium employing polyurethane foam (PUF) as the adsorbent and sodium dodecylsulfate (SDS) as the counter ion. The adsorption efficiency was shown to be dependent on the concentration of SDS in solution, since the formation of an ion-associate between cationic herbicides (diquat and difenzoquat) and anionic dodecylsulfate is a fundamental step of the process. A computational study was carried out to identify the possible structure of the ion-associates that are formed in solution. They are probably formed by three units of dodecylsulfate bound to one unit of diquat, and two units of dodecylsulfate bound to one unit of difenzoquat. The results obtained also showed that 95% of both herbicides present in 45mL of a solution containing 5.5mgL^-1 could be retained by 300mg of PUF. The experimental data were well adjusted to the Freundlich isotherm (r² ≥ 0.95) and to the pseudo-second-order kinetic equation. Also, the application of Morris-Weber and Reichenberg equations indicated that an intraparticle diffusion process is active in the control of adsorption kinetics.

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

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 cycles of a scan, the specificity and performance remained robust. The new immunosensor successfully detected humIgE antibodies reactive against hoIgG3, which could allow the diagnosis of potential allergenic patients needing therapeutic antivenom preparations from a horse.

Polyurethane foam loaded with sodium dodecylsulfate for the extraction of 'quat' pesticides from aqueous medium: Optimization of loading conditions

The cationic herbicides paraquat, diquat and difenzoquat are largely used in different cultures worldwide. With this, there is an intrinsic risk of environmental contamination when these herbicides achieve natural waters. The goal of this work was to propose a novel and low-cost sorbent for the removal of the cited herbicides from aqueous medium. The proposed sorbent was prepared by loading polyurethane foam with sodium dodecylsulfate. The influence of several parameters (SDS concentration, HCl concentration and shaking time) on the loading process was investigated. The results obtained in this work demonstrated that all studied variables influenced the loading process, having significant effect on the extraction efficiency of the resulted PUF-SDS. At optimized conditions, the PUF was loaded by shaking 200mg of crushed foam with 200mL of a solution containing 5.0×10(-3)molL(-1) SDS and 0.25molL(-1) HCl, for 30min. The obtained PUF-SDS was efficient for removing the three herbicides from aqueous medium, achieving extraction percentages higher than 90%. The sorption process followed a pseudo second-order kinetics, which presented excellent predictive capacity of the amount of herbicide retained with time.

Sorption of the herbicides diquat and difenzoquat from aqueous medium by polymeric resins in the presence of sodium dodecylsulfate: Kinetic and mechanistic study

The goal of this work was to propose a novel method for the solid-phase extraction of the herbicides diquat (DQT(2+)) and difenzoquat (DFQT(+)) from aqueous medium using polymeric Amberlite XAD-2 and XAD-4 resins in the presence of sodium dodecylsulfate (SDS). The addition of SDS to the medium was of fundamental importance in order to allow the formation of a negatively charged surface able to sorb the cationic solutes. Several factors that could influence the sorption process, such as SDS concentration in the medium, sorbent mass, pH, ionic strength, and initial concentration of the solutes were investigated. Kinetic studies were also performed to model the system and to identify the mechanisms that operate the sorption process of the herbicides. SDS concentration in the medium presented remarkable influence on the extraction efficiency, achieving maximum values when the ratios [SDS]/[herbicide] were approximately 90, for XAD-2, and 22 and 11 for DQT(2+) and DFQT(+), respectively, for XAD-4. The sorption process followed a pseudo second-order kinetic in all cases studied. It was also found that an intraparticle diffusion process controlled exclusively the sorption of the herbicides by the Amberlite XAD-2 and XAD-4 resins in the first 15 min, becoming less active with time.

Modeling, kinetic, and equilibrium characterization of paraquat adsorption onto polyurethane foam using the ion-pairing technique

We studied the adsorption of paraquat onto polyurethane foam (PUF) when it was in a medium containing sodium dodecylsulfate (SDS). The adsorption efficiency was dependent on the concentration of SDS in solution, because the formation of an ion-associate between the cationic paraquat and the dodecylsulfate anion was found to be a fundamental step in the process. A computational study was carried out to identify the possible structure of the ion-associate in aqueous medium. The obtained data demonstrated that the structure is probably formed from four units of dodecylsulfate bonded to one paraquat moiety. The results showed that 94% of the paraquat present in 45 mL of a solution containing 3.90 × 10(-5) mol L(-1) could be retained by 300 mg of PUF, resulting in the removal of 2.20 mg of paraquat. The experimental data were reasonably adjusted to the Freundlich isotherm and to the pseudo-second-order kinetic model. Also, the application of Morris-Weber and Reichenberg models indicated that both film-diffusion and intraparticle-diffusion processes were active during the control of the adsorption kinetics.

Development of a method for total Hg determination in oil samples by cold vapor atomic absorption spectrometry after its extraction induced by emulsion breaking

This work reports the development of a novel extraction method for total Hg determination in oil samples. After extracting Hg from samples it was quantified in the extracts by cold vapor atomic absorption spectrometry (CV-AAS), employing a laboratory-made gas-liquid separator (GLS) and NaBH4 as reducing agent. The extraction of Hg from samples was carried out by extraction induced by emulsion breaking (EIEB), which is based on the formation and breaking of water-in-oil emulsion between the oil samples and an extractant solution containing an emulsifying agent (surfactant) and nitric acid. Operational parameters of the GLS were evaluated in order to set the best performance of the measurement system. In these studies it was proven that the volume of sample and the concentration of HCl added to the sample extracts had significant influence on Hg response. The best conditions were achieved by adding 0.5 mL of a 0.3 mol L(-1) HCl solution on 1 mL of sample extract. The extraction conditions were also optimized. The highest efficiency was observed when 4 mL of a solution containing 2.5% triton X-100 and 15% v/v HNO3 were employed for the extraction of Hg contained in 20 mL of sample. Emulsion breaking was performed by heating at 80 °C and took approximately 20 min. The limit of quantification of the method was 1.9 µg L(-1) and recovery percentages between 80% and 103% were observed when spiked samples (2 and 10 µg L(-1)) of diesel oil, biodiesel and mineral oil were analyzed.

Direct determination of sitagliptin in pharmaceutical formulations and its determination in urine after solid-phase extraction by spectrofluorimetry

The fluorescence characteristics of sitagliptin phosphate were used to develop a methodology that allowed its determination in pharmaceutical formulations and urine samples; under the studied conditions, limits of determination and quantification of 0.25 and, respectively, 0.85 mg/L were achieved. Linear correlation between fluorescence analytical signal and sitagliptin concentration was achieved up to 10.0 mg/L. The method was considered selective for sitagliptin determination in pharmaceutical formulations because no interferences due to excipients present in considered matrix were observed (as demonstrated by recovery tests comparing analytical and addition curves). When the method was applied to urine samples, Interferences related to the matrix were observed, which made a solid-phase extraction system necessary. The use of calibration was possible only by applying the standard addition method.

Novel spectrophotometric method for the determination of aluminum in soda drinks packed in cans and plastic bottles

In the present work, a new spectrophotometric method was developed for the determination of aluminum in soda drinks packed in different materials. Reaction among Al(III), phenylfluorone (PF) and cetylpyridinium chloride (CPC) in slightly alkaline medium was explored for this purpose. The method was optimized regarding to its chemical parameters in order to establish better conditions in terms of sensitivity and selectivity. The results obtained showed that the concentration of CPC presented remarkable influence on the sensitivity and acted as a sensitizer for the studied system. The possible interferences of some metallic cations were evaluated and the cations Cu(II), Mn(II), and Zn(II) presented noticed interference on the Al(III) signal. So, their interference was eliminated by using EDTA with minimum loss of sensitivity. The results obtained in the determination of total aluminum in soda drinks by the developed methodology were not statistically different from those obtained by electrothermal atomic absorption spectrometry. In the optimized conditions the method presented a linear range of 5-100 microg L(-1). The limits of detection and quantification were 0.81 and 2.7 microg L(-1), respectively. The methodology was successfully applied in the determination of aluminum in 10 samples of soda drinks packed in cans and plastic bottles.