Nicolle F. Robaina

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

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.

Application of the extraction induced by emulsion breaking for the determination of chromium and manganese in edible oils by electrothermal atomic absorption spectrometry.

This work reports the optimization of a method, based on the extraction induced by emulsion breaking, for the determination of trace concentrations of Cr and Mn in edible oils by electrothermal atomic absorption spectrometry (ETAAS). In the method, a water-in-oil emulsion was prepared by mixing the oil sample with an acid solution (HNO(3)) of Triton X-114 to allow the intense contact between the sample and the extractant acid solution. Afterwards, the emulsion was broken by heating and the acid aqueous phase deposited in the bottom of the flask was collected for the determination of the metals of interest. The method was optimized by studying the influence of several parameters such as the concentration of HNO(3) and the emulsifier agent (Triton X-100 and Triton X-114) in the extractant solution. The best results were verified when the procedure was performed with 5 mL of the sample and 1 mL of the extractant solution containing 15%m/v of Triton X-114 and 2.8 mol L(-1) of HNO(3). Also, the fastest emulsion breaking was verified when the emulsions were heated at 90°C. In these conditions, the emulsions were broken in approximately 10 min. The quantification of Cr and Mn in the extracts was carried out by external calibration with aqueous standard solutions, which simplified the procedure. The limits of detection for the determination of Cr and Mn in the oil samples were 66 and 36 ng L(-1), respectively, and the limits of quantification were 219 and 120 ng L(-1), respectively. The developed method was applied in the determination of Cr and Mn in twelve samples of edible oils produced with different oleaginous. Recovery tests were performed to attest the accuracy of the method, being observed recovery percentages in the range of 86-115%.

Polyurethane foam loaded with SDS for the adsorption of cationic dyes from aqueous medium: multivariate optimization of the loading process.

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 200mg 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 x 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 x 10(-5) and 1.0 x 10(-4)mol L(-1)).

Extraction induced by emulsion breaking for metals determination in diesel oil by ICP-MS

This present work proposes a new approach for diesel oil preparation for metals determination by ICP-MS. The proposed methodology is based on the extraction of the elements of interest into an aqueous phase employing the extraction induced by emulsion breaking procedure. In this approach, the diesel oil was emulsified with an acid surfactant (Triton X-114) solution in order to form a stable water-in-oil emulsion. Further, the emulsion was broken by centrifugation for 60 min at 3200 rpm, yielding two separated phases: (i) the upper organic phase, containing the diesel oil mixed with the surfactant and (ii) the lower acidic aqueous phase, containing the elements of interest that were extracted from oil. Then, the lower phase was collected, diluted and the analytes were determined by ICP-MS using the internal standardization method. The optimization of the methodology was carried out by analyzing the effect of several parameters that could affect the extraction efficiency such as the concentrations of HNO3 and Triton X-114 in the solution used for emulsification (and extraction), the extraction and collection times and the calibration strategy. The limits of detection and quantification for the elements of interest (Al, Cu, Mn, Ni, Sn and V) were in the range of 26–88 ng L−1 and 86–295 ng L−1, respectively. The accuracy of the methodology was tested by the analysis of spiked samples, since there are no certified samples of diesel oil available in the market. The recovery percentages were in the range of 84–113%. The developed methodology was successfully applied in the metals determination in five commercial diesel oils of different brands.

Study of Rhodamine B Retention by Polyurethane Foam from Aqueous Medium in Presence of Sodium Dodecylsulfate

Abstract This work reports a study about the adsorption of Rhodamine B (RB) by unloaded polyether type polyurethane foam (PUF) in a medium containing sodium dodecylsulfate (SDS). The adsorption process was based on the formation of an ionic-pair between RB and SDS, which presented high affinity by PUF. Adsorption was characterized in relation to equilibrium, kinetic, and thermodynamic aspects and the results obtained showed that the ratio between the SDS and RB concentrations played an important role on the adsorption efficiency. A maximum adsorption capacity of 6.85 × 10−6 mol RB g−1 was observed at established experimental conditions. The adsorption process was spontaneous (negative ΔG) and presented an endothermic characteristic (positive ΔH). Also, its rate was regulated by an intraparticle diffusion process. Sequential extraction experiments were carried out by changing PUF plugs in 30 and 60 min time intervals, resulting in removal rates higher than 95%.

Diffuse reflectance determination of Malachite Green using polyurethane foam as solid support and sodium dodecylsulfate as counter ion

This paper reports the use of polyurethane foam (PUF) as solid support for diffuse reflectance spectrophotometric determination of Malachite Green (MG), a well known cationic dye used as biocide in the aquaculture industry, using sodium dodecylsulfate (SDS) as a counter ion. The method was based on the formation of an ionic-pair between the dye and the anionic surfactant SDS, which was sorbed onto PUF surface, where the diffuse reflectance was measured at 635 nm. Several parameters that could affect the performance of the system were evaluated. As expected, the SDS concentration presented strong influence on the analytical signal because the PUF was able to retain only the ionic-pair. The pH influenced the analytical signal, which was more intense in the acidic/neutral range, while the ionic strength only influenced the kinetic of the MG (as MG-SDS ionic-pair) sorption. The methodology was employed in the determination of MG in river waters and a recovery test was performed to test the accuracy of the procedure. Recovery percentages between 98.7 and 107% were observed when 60 or 80 μg L(-1) of MG were added to the samples.

Determination of chloride in brazilian crude oils by ion chromatography after extraction induced by emulsion breaking

The present paper reports on the development of a novel extraction induced by emulsion breaking (EIEB) method for the determination of chloride in crude oils. The proposed method was based on the formation and breaking of oil-in-water emulsions with the samples and the consequential transference of the highly water-soluble chloride to the aqueous phase during emulsion breaking, which was achieved by centrifugation. The determination of chloride in the extracts was performed by ion chromatography (IC) with conductivity detection. Several parameters (oil phase:aqueous phase ratio, crude oil:mineral oil ratio, shaking time and type and concentration of surfactant) that could affect the performance of the method were evaluated. Total extraction of chloride from samples could be achieved when 1.0g of oil phase (0.5g of sample+0.5g of mineral oil) was emulsified in 5mL of a 2.5% (m/v) solution of Triton X-114. The obtained emulsion was shaken for 60min and broken by centrifugation for 5min at 5000rpm. The separated aqueous phase was collected, filtered and diluted before analysis by IC. Under these conditions, the limit of detection was 0.5μgg(-1) NaCl and the limit of quantification was 1.6μgg(-1) NaCl. We applied the method to the determination of chloride in six Brazilian crude oils and the results did not differ statistically from those obtained by the ASTM D6470 method when the paired Student-t-test, at 95% confidence level, was applied.