Ricardo J. Cassella

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

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 2moll(-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 2min of preconcentration time (13.2ml of sample volume), the system achieved a detection limit of 1.1mugl(-1), a R.S.D. 1% at 20muggl(-1) and an analytical throughput of 25h(-1), whereas for 4min of preconcentration time (26.4ml of sample volume), a detection limit of 0.93mugl(-1), a R.S.D. 5.3% at 5mugl(-1) and a sampling frequency of 13h(-1) were reported.

Multivariate technique for optimization of digestion procedure by focussed microwave system for determination of Mn, Zn and Fe in food samples using FAAS

This article describes the development by response surface methodology (RSM) of a procedure for iron, zinc and manganese determination by flame atomic absorption spectrometry (FAAS) in food samples after digestion employing a focussed microwave system. A Doehlert matrix was used to find optimal conditions for the procedure through response surface study. Three variables (irradiation power and time and composition of oxidant solution-HNO(3)+H(2)O(2)) were regarded as factors in the optimization study. The working conditions were established as a compromise between optimum values found for each analyte taking into consideration the robustness of the procedure. These values were 12min, 260W and 42% (v/v) for irradiation time, irradiation power and percent of H(2)O(2) in solution, respectively. The accuracy of the optimized procedure was evaluated by analysis of certified reference materials and by comparison with a well-established closed vessel microwave dissolution methodology.

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.

Flow injection determination of cobalt after its sorption onto polyurethane foam loaded with 2-(2-thiazolylazo)-p-cresol (TAC)

This paper reports the development of a new methodology for determination of cobalt in water samples by using a flow injection system with loaded PUF as solid phase to preconcentrate analytes. Procedure is based on on-line retention of Co(III) ions (generated in alkaline medium by Co(II) oxidation) in a minicolumn packed with a polyether type polyurethane foam loaded with TAC (2-(2-thiazolylazo)-p-cresol) and elution with 2 mol l(-1) HCl directly to the flame atomic absorption spectrometer nebulizer. Several chemical and flow variables that could affect the performance of this system were investigated as well as the possible interferents. For 2 min of preconcentration time (10.0 ml of sample volume) the system achieved a detection limit 3.2 mug l(-1), a R.S.D. 5% at 20 mug l(-1) and an analytical throughput 24 h(-1). Whereas for 3 min of preconcentration time (15.0 ml of sample volume) a detection limit 2.4 mug l(-1), a R.S.D. under 8% at 10 mug l(-1) and a sampling frequency 17 h(-1) were reported.

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

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.

Extraction induced by emulsion breaking: a novel strategy for the trace metals determination in diesel oil samples by electrothermal atomic absorption spectrometry

This present work reports a novel strategy for the extraction of metals (Cu, Fe, Ni and Pb) from diesel oil and their determination by Electrothermal Atomic Absorption Spectrometry (ETAAS). The method is based on the formation of water-in-oil emulsions by vigorous mixing of the samples with a Triton X-114 solution containing HNO3 and posterior breaking of the emulsion by heating. After the emulsion breaking, three well separated phases were obtained: (i) the upper phase, which is an organic phase containing only the diesel oil, (ii) an acidic aqueous phase containing the extracted metals and (iii) the lower phase, which is a surfactant-rich phase. The metals were concentrated in the aqueous phase, as a result of their acidic extraction from diesel oil. Several parameters that could influence the extraction efficiency and the time required to break the emulsions were evaluated such as the concentration and nature of the surfactant (Triton X-100 and Triton X-114), the HNO3 concentration and the temperature. At best conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 7% w/v Triton X-114 and 10% v/v HNO3. Afterwards, the emulsions were broken by heating at 80 °C for 15 min and then, the aqueous phase was collected and the metals were determined by ETAAS using external calibration with aqueous standard solutions. The limits of detection for Cu, Fe, Ni and Pb were equal to 114, 183, 145 and 294 ng L−1 and the limits of quantification were 380, 609, 484 and 980 ng L−1, respectively. These limits were estimated for the original sample taking into account the preconcentration factor obtained due to the Extraction Induced by Emulsion Breaking (EIEB) application. The novel strategy was applied in the analysis of five samples of diesel oil and the obtained results fitted well with those obtained by the reference method. Also, a recovery test was performed by spiking the samples with known amounts of the metals in the form of organometallic standards and thus applying the proposed procedure. The recoveries were in the range of 85.2–109%.

Selectivity enhancement in spectrophotometry: on-line interference suppression using polyurethane foam minicolumn for aluminum determination with Methyl Thymol Blue

A method is proposed for the determination of aluminum by flow injection spectrophotometry with Methyl Thymol Blue after separation of the interferent ions employing a polyurethane foam (PUF) minicolumn. The separation process is based on the retention of the interferents on the PUF minicolumn as thiocyanate complexes. In order to improve the performance of the system the effect of some chemical and flow variables were evaluated and under optimized conditions the system was able to determine aluminum at a concentration of 1.0 µg mL–1 in the presence of Fe(III) at 170 µg mL–1, Zn(II) at 100 µg mL–1 and Cu(II) and Co(II) at 50 µg mL–1, using a PUF minicolumn containing 200 mg of sorbent. The analytical procedure developed was successfully applied to several certified materials, including silicate materials and ores. Very good accuracy and precision was obtained. A limit of detection of 30 ng mL–1 was achieved with RSD of 4.5% at 0.25 µg mL–1. A linear dynamic range from 0.25–2.0 µg mL–1 was observed and a sample frequency of 17 samples per hour was calculated.

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)).

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

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%.