Rodolfo G. Wuilloud

Simple approach based on ultrasound-assisted emulsification-microextraction for determination of polibrominated flame retardants in water samples by gas chromatography–mass spectrometry

A simple, efficient, innovative and environmentally friendly analytical technique was successfully applied for the first time for the extraction and preconcentration of polybrominated diphenyl ethers (PBDEs) from water samples. The PBDEs selected for this work were those most commonly found in the literature in natural water samples: 2,2,4,4-tetraBDE (BDE-47), 2,2,4,4,5-pentaBDE (BDE-99), 2,2,4,4,6-pentaBDE (BDE-100) and 2,2,4,4,5,5-hexaBDE (BDE-153). The extracted PBDEs were separated and determined by gas chromatography-mass spectrometry (GC-MS). The extraction/preconcentration technique is based on ultrasound-assisted emulsification-microextraction (USAEME) of a water-immiscible solvent in an aqueous medium. Several variables including, solvent type, extraction time, extraction temperature and matrix modifiers were studied and optimized over the relative response the target analytes. Chloroform was used as extraction solvent in the USAEME technique. Under optimum conditions, the target analytes were quantitatively extracted achieving enrichment factors (EF) higher than 319. The detection limits (LODs) of the analytes for the preconcentration of 10 mL sample volume were within the range 1-2 pg mL(-1). The relative standard deviations (RSD) for five replicates at 10 pg mL(-1) concentration level were <10.3%. The calibration graphs were linear within the concentration range of 5-5000 pg mL(-1) for BDE-47 and BDE-100; and 5-10,000 pg mL(-1) for BDE-99 and BDE-153, respectively. The coefficients of estimation were > or = 0.9985. Validation of the methodology was performed by standard addition method at two concentration levels (10 and 50 pg mL(-1)). Recovery values were > or = 96%, which showed a successful robustness of the analytical methodology for determination of picogram per milliliter of PBDEs in water samples. Significant quantities of PBDEs were not found in the analyzed samples.

Development of an on-line temperature-assisted ionic liquid dispersive microextraction system for sensitive determination of vanadium in environmental and biological samples

An original flow injection (FI) system was developed for on-line microextraction of Vanadium (V) based on room temperature ionic liquid (RTIL). Vanadium was complexed with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) at pH 4.0. A 40 microL-volume of 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF(6)]) RTIL was mixed with 5 mL of sample solution containing the V-5-Br-PADAP complex. Then, a fully on-line temperature-assisted dispersion procedure was developed, followed by, analyte microextraction; and final on-line separation of the RTIL phase with a florisil-containing microcolumn. Vanadium was removed from the microcolumn with a 10% (v/v) nitric acid (in acetone) solution, and finally measured by electrothermal atomic absorption spectrometry (ETAAS). The detection limit achieved after preconcentration of 5 mL of sample solution, was 4.8 ng L(-1). The relative standard deviation (RSD) for 10 replicate determinations at 5 microg L(-1) of vanadium level was 4.1%, calculated from the obtained peak heights. The calibration graph was linear, with a correlation coefficient of 0.9982 at levels from the detection limits up to 15 microg L(-1). The method was successfully applied for the determination of vanadium in environmental and biological samples.

On-line preconcentration system for bismuth determination in urine by flow injection hydride generation inductively coupled plasma atomic emission spectrometry.

An on-line bismuth preconcentration and determination system implemented with hydride generation inductively coupled plasma atomic emission spectrometry (HG-ICP-AES) associated to flow injection (FI) was studied. Quinolin-8-ol and Amberlite XAD-7 were used for the retention of bismuth, at pH 4.5. The bismuth complex was removed from the micro-column with nitric acid. The detection limit value for the preconcentration of 100 ml of aqueous solution was 0.02 ng ml(-1) with a relative standard deviation (R.S.D.) of 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for bismuth was linear with a correlation coefficient of 0.999 at levels near the detection limits up to at least 100 ng ml(-1). The method was successfully applied to the determination of bismuth in human urine samples.

On-line pre-concentration system for vanadium determination in drinking water using flow injection-inductively coupled plasma atomic emission spectrometry.

Abstract An on-line vanadium preconcentration and determination system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) associated to flow injection (FI) was studied. For the retention of vanadium, 2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and Amberlite XAD-7 were used, at pH 3.7. The vanadium was removed from the microcolumn in countercurrent with nitric acid. An enrichment factor (EF) of 75 was obtained. The detection limit value for the preconcentration of 50xa0ml of aqueous solution of vanadium was 0.04xa0μgxa0l −1 . The precision for 10 replicate determinations at the 5xa0μgxa0l −1 vanadium levels was 2.5% relative standard deviation (R.S.D.), calculated with the peak heights obtained. The calibration graph using the preconcentration system for vanadium was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 50xa0μgxa0l −1 . The accuracy of the method was demonstrated by analysing a standard reference material NIST SRM 1640 trace elements in natural water. The method was successfully applied to the determination of vanadium in drinking water samples.

On-line ionic liquid-based preconcentration system coupled to flame atomic absorption spectrometry for trace cadmium determination in plastic food packaging materials.

A novel on-line preconcentration method based on liquid-liquid (L-L) extraction with room temperature ionic liquids (RTILs) coupled to flame atomic absorption spectrometry (FAAS) was developed for cadmium determination in plastic food packaging materials. The methodology is based on the complexation of Cd with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) reagent after sample digestion followed by extraction of the complex with the RTIL 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim][PF(6)]). The mixture was loaded into a flow injection analysis (FIA) manifold and the RTIL rich-phase was retained in a microcolumn filled with silica gel. The RTIL rich-phase was then eluted directly into FAAS. A enhancement factor of 35 was achieved with 20 mL of sample. The limit of detection (LOD), obtained as IUPAC recommendation, was 6 ng g(-1) and the relative standard deviation (R.S.D.) for 10 replicates at 10 microg L(-1) Cd concentration level was 3.9%, calculated at the peak heights. The calibration graph was linear and a correlation coefficient of 0.9998 was achieved. The accuracy of the method was evaluated by both a recovery study and comparison of results with direct determination by electrothermal atomic absorption spectrometry (ETAAS). The method was successfully applied for Cd determination in plastic food packaging materials and Cd concentrations found were in the range of 0.04-10.4 microg g(-1).

Water deficit and exogenous ABA significantly affect grape and wine phenolic composition under in field and in-vitro conditions

Phenolic compounds are components responsible of the sensorial characteristics of red wine. Indeed, they present important properties for human health. In the present work, the effects of combined in field treatments (water-stress and exogenous ABA) on phenolic accumulation were evaluated for berries and wine. The responses were assessed by UV–Vis and CZE. A differential phenolic regulation was observed under the same conditions and good correlations were achieved for grape and wine. ABA appears to regulate the content of each phenols under study depending on plant water-status. Although the effects of water-stress and exogenous ABA were similar in magnitude, our results support evidence suggesting that both affect different metabolic pathways. ABA supply increased catechin and malvidin synthesis for both water statuses while the resveratrol was enhanced only for water-stress. Indeed, ABA reduced the quercetin content for both water statuses. In vitro assays were carried out to estimate the effects of combined treatments (temperature-exogenous ABA) on anthocyanin accumulation in berries and pulp. These tests demonstrated that the effect of ABA was dependent on the hormonal level (207% for 0.5xa0gxa0L−1 and 307% for 1xa0gxa0L−1 of ABA). Effect of temperature varied according to the phenological state. In pulps, we detected an increase of anthocyanin after ABA treatments.

Ionic liquid-assisted separation and determination of selenium species in food and beverage samples by liquid chromatography coupled to hydride generation atomic fluorescence spectrometry

Different ionic liquids (ILs) were assayed as mobile phase modifiers for the separation and determination of selenite [Se(IV)], selenate [Se(VI)], selenomethionine (SeMet) and Se-methylselenocysteine (SeMeSeCys) by reversed-phase high-performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry (RP-HPLC-HG-AFS). The use of several ILs: 1-butyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl), 1-octyl-3-methylimidazolium chloride, 1-dodecyl-3-methylimidazolium bromide, 1-hexadecyl-3-methylimidazolium bromide and tributyl(methyl)phosphonium methylsulphate was evaluated. Also, the effect of pH, buffer type and IL concentration on the separation of Se species was studied. Complete separation was attained within 12min using a C8 column and a gradient performed with a mobile phase containing 0.1% (v/v) [C6mim]Cl at pH 6.0. The proposed method allows the separation of inorganic and organic Se species in a single chromatographic run, adding further benefits over already reported methods based on RP-HPLC. In addition, the influence of ILs on the AFS signals of each Se species was evaluated and a multivariate methodology was used for optimization of AFS sensitivity. The limits of detection were 0.92, 0.86, 1.41 and 1.19μgL-1 for Se(IV), Se(VI), SeMet and SeMeSeCys, respectively. The method was successfully applied for speciation analysis of Se in complex samples, such as wine, beer, yeast and garlic.

Capabilities of several phosphonium ionic liquids for arsenic species determination in water by liquid–liquid microextraction and electrothermal atomic absorption spectrometry

The capabilities of several phosphonium-ionic liquids (PILs) to form ion-pairs with a complex obtained by reaction of arsenate species with molybdate were evaluated. Phosphonium-ILs containing the tetradecyl(trihexyl)phosphonium cation but different anions (dicyanamide and decanoate) and tributyl(methyl)phosphonium methylsulphate IL were studied. The size, polarity and localization of charges in PIL cations were shown to influence their capability to form ion-pairs with the arsenomolybdate (AsMo12O403−) complex and to extract As(V). The performance of PILs was compared with that of a widely used ion-pairing reagent, cetyltrimethylammonium bromide (CTAB). Finally, the IL tetradecyl(trihexyl)phosphonium dicyanamide was chosen to develop a liquid–liquid microextraction (LLME) procedure using only 80 μL of tetrachloroethylene as the extractant. The organic phase was directly injected into the graphite furnace of an electrothermal atomic absorption spectrometer (ETAAS) for As determination. An extraction efficiency of 100% and a sensitivity enhancement factor of 130 were obtained with 5 mL of sample. The detection limit was 1.9 ng L−1 and the relative standard deviation for six replicate measurements of 1.0 μg L−1 for As was 4.9%, 5.0% and 5.1% for As(V), As(III) and organic As species, respectively.

Gain of local structure in an amphipathic peptide does not require a specific tertiary framework

In this work, we studied how an amphipathic peptide of the surface of the globular protein thioredoxin, TRX94‐108, acquires a native‐like structure when it becomes involved in an apolar interaction network. We designed peptide variants where the tendency to form α‐helical conformation is modulated by replacing each of the leucine amino acid residues by an alanine. The induction of structure caused by sodium dodecyl sulfate (SDS) binding was studied by capillary zone electrophoresis, circular dichroism, DOSY‐NMR, and molecular dynamics simulations (MDS). In addition, we analyzed the strength of the interaction between a C18 RP‐HPLC matrix and the peptides. The results presented here reveal that (a) critical elements in the sequence of the wild‐type peptide stabilize a SDS/peptide supramolecular cluster; (b) the hydrophobic nature of the interaction between SDS molecules and the peptide constrains the ensemble of conformations; (c) nonspecific apolar surfaces are sufficient to stabilize peptide secondary structure. Remarkably, MDS shed light on a contact network formed by a limited number of SDS molecules that serves as a structural scaffold preserving the helical conformation of this module. This mechanism might prevail when a peptide with low helical propensity is involved in structure consolidation. We suggest that folding of peptides sharing this feature does not require a preformed tightly‐packed protein core. Thus, the formation of specific tertiary interactions would be the consequence of peptide folding and not its cause. In this scenario, folding might be thought of as a process that includes unspecific rounds of structure stabilization guiding the protein to the native state. Proteins 2010.

A comparative evaluation of different ionic liquids for arsenic species separation and determination in wine varietals by liquid chromatography – hydride generation atomic fluorescence spectrometry

The application of different ionic liquids (ILs) as modifiers for chromatographic separation and determination of arsenite [As(III)], arsenate [As(V)], dimethylarsonic acid (DMA) and monomethylarsonic acid (MMA) species in wine samples, by reversed-phase high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry detection (RP-HPLC-HG-AFS) was studied in this work. Several factors influencing the chromatographic separation of the As species, such as pH of the mobile phase, buffer solution concentration, buffer type, IL concentration and length of alkyl groups in ILs were evaluated. The complete separation of As species was achieved using a C18 column in isocratic mode with a mobile phase composed of 0.5% (v/v) 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) and 5% (v/v) methanol at pH 8.5. A multivariate methodology was used to optimize the variables involved in AFS detection of As species after they were separated by HPLC. The ILs showed remarkable performance for the separation of As species, which was obtained within 18min with a resolution higher than 0.83. The limits of detection for As(III), As(V), MMA and DMA were 0.81, 0.89, 0.62 and 1.00μg As L(-1). The proposed method was applied for As speciation analysis in white and red wine samples originated from different grape varieties.