Comparative study of magnesium nitrate,palladium nitrate and reduced palladium for the direct determination of mercury in sea water by electrothermal atomization atomic absorption spectrometry

A comparative study of different chemical modifiers in graphite furnace atomic absorption spectrometry for the direct determination of mercury in sea water samples, in synthetic sea water sample of high (72.8%) and low 34.2%) salinity and in aqueous solutions, was carried out. The use of reduced palladium produces better results. The mixture of palladium nitrate and ascorbic acid, gives the best limit of detection (1.9 gl^–1). The use of reduced palladium and magnesium nitrate produced excellent recoveries (close to 100%) in the whole salinity range for all mercury concentration tested. The use of palladium nitrate alone or combined with magnesium nitrate gave good recoveries with respect to a real sea water sample for low salinities. The interference from the major components of sea water were completely removed by using reduced palladium and magnesium nitrate modifiers. Thus, a single calibration curve with synthetic sea water may be applied to the analysis of sea water samples of widely differing salinities.     

Comparison of different chemical modifiers for the direct determination of arsenic in sea water by electrothermal atomic absorption spectrometry

A comparative study of different chemical modifiers for the direct determination of arsenic in real and in synthetic sea water samples of high (72.8 per thousand ) and low (34.2 per thousand ) salinity was carried out. The use of lanthanum chloride and magnesium nitrate (LOD=3.0 microg l(-1)) offers good recoveries for low salinities, while for high salinities an enhancement higher than 200% was obtained, rendering this method unsuitable for sea water samples. The use of silver nitrate (LOD=2.0 microg l(-1)) produces unfavourable analytical recoveries, around 150 and 300% for synthetic sea water of low and high salinity. Zirconium oxychloride (LOD=1.8 microg l(-1)) and palladium nitrate alone or combined with magnesium nitrate and reducing agents (LOD=1.1-1.3 microg l(-1)) produce analytical recoveries close to 100% for all arsenic concentration tried over all salinities; thus, a single calibration curve using aqueous standard solutions may be applied to the analysis of sea water samples over all salinities. Finally, the addition of reducing agents and magnesium nitrate to palladium does not improve the sensitivity.     

The Polyphenols α-Mangostin and Nordihydroguaiaretic Acid Induce Oxidative Stress,Cell Cycle Arrest,and Apoptosis in a Cellular Model of Medulloblastoma

Medulloblastoma is a common malignant brain tumor in the pediatric age. The current therapeutics present serious collateral effects. Polyphenols α-mangostin and nordihydroguaiaretic acid (NDGA) exert potent antitumoral activity in different cancer models, although their antitumoral effects have not been described in medulloblastoma cells yet. This study aimed to examine the proapoptotic effects of these polyphenols on human medulloblastoma cells. Medulloblastoma cell line Daoy was incubated with increasing concentrations of α-mangostin or NDGA for 24 h. The cell viability was analyzed using crystal violet and trypan blue dyes. Determination of the glutathione (GSH)/glutathione disulfide (GSSG) ratio and levels of carbonylated proteins was performed to evaluate the oxidative stress. Cell cycle progression and induction of cell death by fluorochrome-couple and TUNEL assays were evaluated using flow cytometry assays. Individual treatments with α-mangostin or NDGA decreased the viability of Daoy cells in a dose-dependent manner, inducing G2/M and S-G2/M cell cycle arrest, respectively. Both polyphenols induced cell death and increased oxidative stress. Very interestingly, α-mangostin showed more potent effects than NDGA. Our results indicate that α-mangostin and NDGA exert important cytostatic and cytotoxic effects in the Daoy cell line. These data highlight the potential usefulness of these compounds as an alternative strategy in medulloblastoma treatment.     

Contribution to the Development of Indirect Atomic Absorption Methods: Application of the Ion Pair 1,10-phenanthroline-mercury(II)-iodide to Iodide Determination in Water and Infant Formulae Samples

A method to determine iodide is developed, based on the formation of an ion pair between 1, 10-phenanthroline, mercury(II) and iodide that can be selectively extracted into IBMK. When the IBMK layer is analyzed by electrothermal atomic absorption spectrometry (ETAAS) for mercury, iodide can be quantified too. Parameters related to the preparation of the ion pair and to the measuring process are studied. Thus, 7.2–7.4 reveals to be the best pH interval to carry out the extraction, and 250 and 1000?°C, respectively, the mineralization and atomization temperatures for mercury determination by ETAAS. The procedure is applied to drinking tap water and commercial infant formulae milk samples. The accuracy of the method has been investigated by means of the analytical recovery for water samples (mean analytical recovery obtained at different concentration levels 98.1%) and by using the certified reference material BCR CRM No 151 Skim Milk Powder (Spiked) for the infant formulae (results within certification interval). The repeatability of the measurements at different concentration levels gave a RSD lower than 10% for both types of samples and the repeatability of the whole procedure for infant formulae shows a RSD of 1.33%. In addition, the limits of detection and quantification were 2.5?μg/L and 8.5?μg/L, respectively, for drinking water and 1.1?μg/g and 3.8?μg/g, respectively, for infant formulae.     

Photoredox Properties of Iron(III) Fluoro Complexes Containing Tetradentate Open-Chain N2O2Ligands

Tetradentate open-chain Schiff base N₂O₂-ligands of acacen, benacen or salen type and fluoride anions F^? coordinate to the iron(III) central atom in methanol forming the complexes [Fe(N₂O₂)(CH₃OH)F]. The complexes do not undergo spontaneous redox changes when kept in the dark. Their irradiation into intraligand or ligand-to-metal charge transfer bands causes the photoreduction of Fe(III) to Fe(II) associated with oxidation of metanol to its radical CH₂OH. The final products of the primary photoredox and secondary dark redox processes, Fe(II) and CH₂O, are formed in a 2:1 molar ratio. The efficiency of the axial methanol ligand photooxidation is strongly wavelength dependent and influenced by the peripheral groups R of the tetradentate ligands     

Determination of total sulfite in wine. Zone electrophoresis-isotachophoresis quantitation of sulfate on a chip after an in-sample oxidation of total sulfite

This work deals with the determination of total sulfite in wine. The determination combines an in-sample hydrogen peroxide oxidation of total sulfite in alkalized wine to sulfate with the separation and quantitation of the latter anion by zone electrophoresis (ZE) on-line coupled with isotachophoresis (ITP) on a column-coupling chip. Sample clean up, integrated into the ITP-ZE separation, eliminated wine matrix in an extent comparable to that provided by a highly selective distillation isolation of sulfite. At the same time, conductivity detection, employed to the detection of sulfate in the ZE stage of the ITP-ZE combination, provided for sulfate the concentration limit of detection corresponding to a 90 microg/l concentration of sulfite in the loaded sample (0.9 microl). Such a detectability allowed a reproducible quantitation of total sulfite when its concentration in wine was 15 mg/l. Formaldehyde binding of free sulfite in wine, included into the pre-column sample preparation, prevented an uncontrolled oxidation of this sulfite form. This step contributed to an unbiased determination of sulfate present in the original wine sample (this determination corrected for the concentration of sulfate determined in the sample after the peroxide oxidation of sulfite to the value equivalent to the total sulfite). The 99-101% recoveries of sulfite, determined for appropriately spiked wine samples, indicate a very good accuracy of the present method. Such a statement also supports excellent agreements of the results of quantitation based on the in-sample peroxide oxidation of the total sulfite (bound sulfite released at a high pH) with those in which this analyte was isolated from wine by distillation (bound sulfite released at a very low pH).     

Poly (acrylic acid) microchannel modification for the enhanced resolution of catecholamines microchip electrophoresis with electrochemical detection

A new modification of glass electrophoresis microchips based on poly (acrylic) acid immobilization has been performed. It is based on the reaction of PAA with an amine functionalized surface, obtained through the bifunctional reagent 3-aminopropyl triethoxysilane. Parameters affecting all the three steps involved: surface activation, silanization and polymer immobilization were optimized employing soda-lime glass plates. Characterization by SEM and XPS was carried out. Application of the modified microchips to the separation of a model system: dopamine (D), epinephrine (E) and norepinephrine (NE), that on the other hand are of high clinical relevance was performed employing amperometric detection. Modification is necessary for obtaining partial resolution of all the three analytes in a microchip with an effective separation length of 30 mm. Situation changes from no resolution (Rs) at all (only one peak was achieved for the mixture) to a partial resolution (Rs D–NE and Rs NE–E are 0.25 and 0.24 respectively). Microchips with 60 mm of separation channel were also modified, implying this procedure a resolution enhancement (Rs of 0.49 and 0.28 for D–NE and NE–E respectively), even when methanol is employed as organic modifier (Rs values of 0.70 (D–NE) and 0.66 (NE–E) for a 3% MeOH).     

Fatty acid composition of lipids in pot marigold (Calendula officinalis L.) seed genotypes

Background

The process of thermal decomposition of dichloromethane (DCM) and chlorobenzene (MCB) during the combustion in an inert, bubbling fluidized bed, supported by LPG as auxiliary fuel, have been studied. The concentration profiles of C₆H₅CI, CH₂Cl₂, CO₂, CO, NO_x, COCl₂, CHCl₃, CH₃Cl, C₂H₂, C₆H₆, CH₄ in the flue gases were specified versus mean bed temperature.

Results

The role of preheating of gaseous mixture in fluidized bed prior to its ignition inside bubbles was identified as important factor for increase the degree of conversion of DCM and MCB in low bed temperature, in comparison to similar process in the tubular reactor.

Conclusions

Taking into account possible combustion mechanisms, it was identified that autoignition in bubbles rather than flame propagation between bubbles is needed to achieve complete destruction of DCM and MCB. These condition occurs above 900°C causing the degree of conversion of chlorine compounds of 92-100%.