Leticia B. Escudero

Determination of inorganic selenium species in water and garlic samples with on-line ionic liquid dispersive microextraction and electrothermal atomic absorption spectrometry.

A non-chromatographic separation and preconcentration method for Se species determination based on the use of an on-line ionic liquid (IL) dispersive microextraction system coupled to electrothermal atomic absorption spectrometry (ETAAS) is proposed. Retention and separation of the IL phase was achieved with a Florisil(®)-packed microcolumn after dispersive liquid-liquid microextraction (DLLME) with tetradecyl(trihexyl)phosphonium chloride IL (CYPHOS(®) IL 101). Selenite [Se(IV)] species was selectively separated by forming Se-ammonium pyrrolidine dithiocarbamate (Se-APDC) complex followed by extraction with CYPHOS(®) IL 101. The methodology was highly selective towards Se(IV), while selenate [Se(VI)] was reduced and then indirectly determined. Several factors influencing the efficiency of the preconcentration technique, such as APDC concentration, sample volume, extractant phase volume, type of eluent, elution flow rate, etc., have been investigated in detail. The limit of detection (LOD) was 15 ng L(-1) and the relative standard deviation (RSD) for 10 replicates at 0.5 μg L(-1) Se concentration was 5.1%, calculated with peak heights. The calibration graph was linear and a correlation coefficient of 0.9993 was achieved. The method was successfully employed for Se speciation studies in garlic extracts and water samples.

Dispersive liquid-liquid microextraction and preconcentration of thallium species in water samples by two ionic liquids applied as ion-pairing reagent and extractant phase.

In the present work, a simple and highly sensitive analytical methodology for determination of Tl(+) and Tl(3+) species, based on the use of modern and non-volatile solvents, such as ionic liquids (ILs), was developed. Initially, Tl(+) was complexed by iodide ion at pH 1 in diluted sulfuric acid solution. Then, tetradecyl(trihexyl)phosphonium chloride ionic liquid (CYPHOS(®) IL 101) was used as ion-pairing reagent and a dispersive liquid-liquid microextraction (DLLME) procedure was developed by dispersing 60 mg of 1-hexyl-3-methylimidazolium hexafluorophosphate [C(6) mim][PF(6)] with 500 μL of ethanol in the aqueous solution. After the microextraction procedure was finished, the final IL phase was solubilized in methanol and directly injected into the graphite furnace of an electrothermal atomic absorption spectrometer (ETAAS). An extraction efficiency of 77% and a sensitivity enhancement factor of 100 were obtained with only 5.00 mL of sample. The limit of detection (LOD) was 3.3 ng L(-1) Tl while the relative standard deviation (RSD) was 5.3% (at 0.4 μg L(-1) Tl and n=10), calculated from the peak height of absorbance signals. The method was finally applied to determine Tl species in tap and river water samples after separation of Tl(3+) species. To the best of our knowledge, this work reports the first application of ILs for Tl extraction and separation in the analytical field.

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.

Liquid-liquid microextraction based on a dispersion of Pd nanoparticles combined with ETAAS for sensitive Hg determination in water samples.

A novel and highly efficient microextraction methodology based on the use of palladium nanoparticles (Pd NPs) was developed for the preconcentration and determination of Hg in water samples. Selective separation of the analyte was achieved by application of dodecanethiolate-coated Pd monolayer-protected clusters (C12S Pd MPCs) in a liquid-liquid microextraction technique (LLME). A volume of 20 μL of toluene phase containing C12S Pd MPCs was used for extraction and final phase was injected in an electrothermal atomic absorption spectrometer (ETAAS) for Hg detection. The effects of different variables, such as sample volume, extraction time, and NPs dispersion volume were carefully studied. A sensitivity enchancement factor of 95 was obtained under optimal experimental conditions. Furthermore, low detection limit (7.5 ng L(-1)) and good precision (relative standard deviation of 4.1% at 0.25 μg L(-1) Hg and n=10) were achieved. The proposed method can be considered as a rapid, cost-effective, and efficient alternative for Hg determination in water samples like river, lake, mineral and tap water.

An eco-friendly cellular phase microextraction technique based on the use of green microalgal cells for trace thallium species determination in natural water samples

A simple and environmentally friendly technique named cellular phase microextraction (Cell-PME) was developed for thallium (Tl) species determination. Basically, Tl(III) species were mixed with a solution containing Chlorella vulgaris microalgal cells (480 mg L−1) at pH 7 and the resulting system was stirred with a vortex for 8 min. After a centrifugation process, the sediment phase was directly injected into the graphite furnace of an electrothermal atomic absorption spectrometer. In contrast to Tl(III), Tl(I) species were not retained by the biomass. Optimization of variables influencing the biosorption process, including sample pH, microalgal mass and sample volume, was performed. A biosorption efficiency of 65% and an enrichment factor of 50 were obtained with only 5.00 mL of sample. The limit of detection (LOD) was 8.3 ng L−1 Tl, while the relative standard deviation (RSD) was 5.1% (at 1 μg L−1 Tl and n = 10), calculated from the peak height of absorbance signals (Gaussian-shape and reproducible peaks). The proposed method was successfully applied to determine Tl species in environmental samples, including drinking and natural water. To the best of our knowledge, a biosorption process is applied for the first time for Tl species separation and determination in the analytical field.

Stability of iron-quercetin complexes in synthetic wine under in vitro digestion conditions.

UNLABELLED Wine is a dietary source of polyphenolic compounds with reported health benefits when moderately consumed. Several of these compounds can associate with metals forming complexes. Therefore, this work was conducted to reach a better understanding of the nature and chemical stability of wine-derived Fe(3+)-quercetin complexes in a digestion model. The stability of the complexes in a synthetic (simulated) wine was studied before and after in vitro gastric and intestinal digestions by high-performance liquid chromatography (HPLC) with UV-Vis detection. Metal determination was performed by atomic absorption spectrometry (ETAAS) to evaluate possible dissociation of complexes. During HPLC analysis all peaks eluted from the chromatographic column were collected, acidified, and analyzed by ETAAS. The results showed that complexes remain substantially stable after gastric digestion conditions, with recoveries of 84% to 90%. Although metal complexes were partially degraded during intestinal digestion, 41% to 45% of the Fe(3+)-quercetin complexes was recovered. PRACTICAL APPLICATION This work reveals the chemical stability of Fe3+–quercetin complexes in synthetic wines after an in vitro gastrointestinal digestion. The knowledge of this process would be useful to understand the bioavailability of these compounds.

Macroalgae of Iridaea cordata as an efficient biosorbent to remove hazardous cationic dyes from aqueous solutions

In the present work, Iridaea cordata (IC), a red marine macroalgae, was used as an efficient biosorbent for the removal of crystal violet (CV) and methylene blue (MB) dyes from aqueous solutions. The effects of pH (5, 7, and 9) and IC concentration (1, 3, and 5 g L-1) on the biosorption were studied through a 32 full factorial design. Under the optimal conditions (pH: 7, biosorbent concentration: 1 g L-1), biosorption kinetic studies were developed and the obtained experimental data were evaluated by pseudo-first order and pseudo-second order models. The results showed that the pseudo-second order model was in agreement with the experimental kinetic data for both dyes. Equilibrium studies were also carried out, and results exhibited good concordance with the Brunauer-Emmett-Teller isotherm. The biosorption capacities were 36.5 and 45.0 mg g-1 for CV and MB dyes, respectively. The dye removal percentages were around 75% for CV and 90% for MB. Thermodynamically, the biosorption process proved to be exothermic, spontaneous, and favorable. These results showed that IC biomass is a promising biosorbent for removal of CV and MB dyes from aqueous solutions.