Mònica Iglesias

Development of novel and sensitive methods for the determination of sulfide in aqueous samples by hydrogen sulfide generation-inductively coupled plasma-atomic emission spectroscopy

Two new, simple and accurate methods for the determination of sulfide (S(2-)) at low levels (microgL(-1)) in aqueous samples were developed. The generation of hydrogen sulfide (H(2)S) took place in a coil where sulfide reacted with hydrochloric acid. The resulting H(2)S was then introduced as a vapor into an inductively coupled plasma-atomic emission spectrometer (ICP-AES) and sulfur emission intensity was measured at 180.669nm. In comparison to when aqueous sulfide was introduced, the introduction of sulfur as H(2)S enhanced the sulfur signal emission. By setting a gas separator at the end of the reaction coil, reduced sulfur species in the form of H(2)S were removed from the water matrix, thus, interferences could be avoided. Alternatively, the gas separator was replaced by a nebulizer/spray chamber combination to introduce the sample matrix and reagents into the plasma. This methodology allowed the determination of both sulfide and sulfate in aqueous samples. For both methods the linear response was found to range from 5microgL(-1) to 25mgL(-1) of sulfide. Detection limits of 5microgL(-1) and 6microgL(-1) were obtained with and without the gas separator, respectively. These new methods were evaluated by comparison to the standard potentiometric method and were successfully applied to the analysis of reduced sulfur species in environmental waters.

SORPTION OF TRACE HEAVY METALS BY THIOL CONTAINING CHELATING RESINS

ABSTRACT The sorption of copper, cadmium, nickel and zinc ions on thiol (-SH) based chelating polymeric resins (thiomethyl resin and Duolite GT-73) has been investigated. The physical and chemical characterisation of these polymers in the form of scanning electron micrographs (SEM), BET and Langmuir surface area measurements, Fourier transform infra red spectroscopy (FTIR) analysis, X-ray photoelectron spectroscopy (XPS) analysis, atomic composition measurement, sodium capacity determination and zeta potential measurements have been conducted to assess their performance as sorbents for trace toxic metal removal. Density functional theory (DFT) has been used to analyse the pore size distribution data. The adsorption of metal ions from aqueous solution on these sorbents has been studied in batch equilibrium experiments. The influence of pH on metal adsorption capacity has also been examined. The kinetic performance of these polymers has been assessed and the results have been analysed by a pore diffusion model. The resins have been used in mini-columns to study the selectivity towards the desired metal ion. The desorption of metal ions has been studied using hydrochloric acid (1 M and 4 M), sulphuric acid (1 M and 4 M) and acidified thiourea. The present study confirms that these thiol based chelating resins are very effective for selective removal of trace heavy metals from water.

Evaluation of an ICP-collision/reaction cell-MS system for the sensitive determination of spectrally interfered and non-interfered elements using the same gas conditions

Removal of argon-based polyatomics (ArAr and ArO) that interfere with the determination of the main isotopes of selenium and iron was studied using an ICP-MS equipped with a hexapole collision cell. Various gases, including helium, hydrogen, ammonia and N2O, were evaluated to improve detection limits. The behavior of the non-interfered elements was also evaluated using the optimized gas conditions in order to keep the multi-element capability of the ICP-MS. Low detection limits were obtained when a mixture of helium and hydrogen was employed, the values being 2 ng L−1 and 6 ng L−1 for selenium (80Se) and iron (56Fe), respectively. The selected conditions did not degrade the LODs of the non-interfered elements.

Solvent extraction of yttrium from chloride media by di (2- ethylhexyl) phosphoric acid in kerosene. Speciation studies and gel formation

Abstract The distribution of yttrium(III) between acidic aqueous chloride solutions and organic solutions of di(2-ethylhexyl) phosphoric acid, D2EHPA, in kerosene has been examined as a function of various chemical parameters at constant aqueous ionic strength 2.0 M and different ranges of metal concentration. For low and middle metal concentration, 1.5 × 10−4 − 2.587 × 10−2 M (13–2300mg l−1), the distribution of yttrium has been examined as a function of the extractant concentration and at fixed [H+] of 1.0M. The distribution data has been analyzed by both graphical and numerical methods. The results for the low metal concentration may be explained by the formation of two organic metal species, YA3.2HA and YA3.HA (HA refers to D2EHPA). Equilibrium constants have been determined and they are compared with corresponding constants in nitrate media and with results reported in the literature. Possible mixed extracted complexes containing chloride were rejected by the numerical calculations. Such prediction was confirmed by separate analysis of the chloride content in the organic phase. When the metal concentration is increased, the system shows a major complexity which is attributed to the formation of aggregates in the organic phase. For the highest metal concentration, a gel is observed to form under some of the experimental conditions. These results are discussed in terms of polymeric metal complexes.

On-line determination of trace levels of palladium by flame atomic absorption spectrometry

A preconcentration method is developed for the on-line determination of palladium in complex matrices with flame atomic absorption spectrometry (FAAS). The flow system comprised of a minicolumn filled with polyamine Metalfix-Chelamine resin which is highly selective for Pt(IV), Au(III) and Pd(II). Best preconcentration conditions are established by testing different resin quantities, sample and eluent solution volumes, and adsorption and elution steps flow rates. Sample volumes of 4.7 ml of palladium solutions resulted in an enrichment factor of twenty at the optimum hydrodynamic conditions. This value can be increased by injecting larger volumes of sample solution. The method is sensitive, easy to operate and permitted the determination of sub-mg l(-1) levels of palladium with a detection limit of 0.009 mg l(-1). The resin was used up to 60 times in consecutive retention-elution cycles without any appreciable deterioration in its performance. The applicability of this method was tested by determining the palladium content in synthetic geological samples as well as in the pellet-type used car catalyst reference material.

Arsenic mobilization in the aquifers of three physiographic settings of West Bengal, India: understanding geogenic and anthropogenic influences.

A comparative hydrogeochemical study was carried out in West Bengal, India covering three physiographic regions, Debagram and Chakdaha located in the Bhagirathi-Hooghly alluvial plain and Baruipur in the delta front, to demonstrate the control of geogenic and anthropogenic influences on groundwater arsenic (As) mobilization. Groundwater samples (n = 90) from tube wells were analyzed for different physico-chemical parameters. The low redox potential (Eh = -185 to -86 mV) and dominant As(III) and Fe(II) concentrations are indicative of anoxic nature of the aquifer. The shallow (<100 m) and deeper (>100 m) aquifers of Bhagirathi-Hooghly alluvial plains as well as shallow aquifers of delta front are characterized by Ca(2+)HCO3(-) type water, whereas Na(+) and Cl(-) enrichment is found in the deeper aquifer of delta front. The equilibrium of groundwater with respect to carbonate minerals and their precipitation/dissolution seems to be controlling the overall groundwater chemistry. The low SO4(2-) and high DOC, PO4(3-) and HCO3(-) concentrations in groundwater signify ongoing microbial mediated redox processes favoring As mobilization in the aquifer. The As release is influenced by both geogenic (i.e. geomorphology) and anthropogenic (i.e. unsewered sanitation) processes. Multiple geochemical processes, e.g., Fe-oxyhydroxides reduction and carbonate dissolution, are responsible for high As occurrence in groundwaters.

Adsorption Behavior of Platinum Group Metals (Pd, Pt, Rh) onNonylthiourea-Coated Fe3O4 Nanoparticles

Abstract Magnetite nanoparticles coated with nonylthiourea (NTH) were synthesized and analyzed for the separation and recovery of platinum group metals (PGMs) from diluted aqueous chloride solutions. Physical characterizations of the coated nanoparticles were performed by Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and FT‐IR Spectrometry. Separation efficiency of the coated nanoparticles and the equilibrium adsorption isotherm of PGMs were investigated. The maximum adsorption was attained in less than 30 minutes, and the maximum loading capacity of NTH‐coated Fe3O4 nanoparticles for Pt(IV) and Pd(II) was determined to be 10.7 and 8.1 mg g−1, respectively. The recovery of PGMs from the loaded nanoparticles was examined using different eluting solutions, including HNO3, thiourea, and NaClO4.

Arsenic determination by ICP-QMS with octopole collision/reaction cell. Overcome of matrix effects under vented and pressurized cell conditions.

The determination of arsenic by inductively coupled plasma mass spectrometry (ICP-MS) in natural waters with high sodium and chloride content has been investigated. The instrument used is equipped with an octopole collision/reaction cell to overcome spectroscopic interferences. Thus, the optimization of collision/reaction gas flow rates is required when using a pressurized cell. A mixture of 2.9 mL min(-1) of H(2) and 0.5 mL min(-1) of He has been found to be suitable for the removal of (40)Ar(35)Cl(+) interference. The effect of the introduction of small amounts of alcohol has also been studied in this work under both vented and pressurized cell conditions. It has been observed that the presence of 4% (v/v) of ethanol or methanol results in an increase in arsenic sensitivity. Moreover, under vented cell conditions the addition of alcohol also decreases the formation of polyatomic interference. However, this decrease is not observed under pressurized cell conditions. Different elements have been studied as possible internal standards for arsenic determination in presence of high amounts of sodium. Good results have been obtained for rhodium and yttrium under both vented and pressurized cell conditions. Although the presence of alcohol in the sample matrix also affects their behaviour, rhodium and yttrium are still the most suitable elements to correct for these matrix effects. Different experimental conditions have been compared for arsenic determination in spiked, certified and natural waters with high sodium and chloride content. The best results have been obtained under pressurized cell conditions, in the presence of ethanol and using rhodium as internal standard.

Precise and accurate determination of lead isotope ratios in mining wastes by ICP-QMS as a tool to identify their source

A methodology for a precise and accurate determination of lead isotope ratios in mining wastes by inductively coupled plasma quadrupole-based mass spectrometry (ICP-QMS) has been developed. The study of instrumental bias factors led to the conclusion that internal correction to compensate mass discrimination is required as well as an interference equation correction when Hg is present. The proposed method has been applied to determine lead isotope ratios in several mining wastes, soils and sediments collected at three mining areas in Spain (Aran Valley, Cartagena and Osor). Statistical analysis highlights that (206)Pb/(207)Pb and (208)Pb/(207)Pb lead isotope ratios can be used as a fingerprint of mining waste origin which is related to the geological age of the lead ore. On the other hand, no statistically significant isotopic differences between original ore samples (galena) and processing wastes within a mining district were found, corroborating a unique lead source. Moreover, the lead isotopic composition of soil and sediment samples collected at the studied mining areas is close to that determined in the mining tailings from the same areas, suggesting that the unusual high content of lead in these samples is derived from mining activities rather than from other lead sources.

Sulfide and sulfate determination in water samples by means of hydrogen sulfide generation-inductively coupled plasma-atomic emission spectrometry

When sulfur is measured in natural water samples by means of inductively coupled plasma-atomic emission spectrometry (ICP-AES), its emission intensity is mainly due to sulfate. Because of its low concentration, the sulfur emission coming from sulfide can be considered negligible. In the present work, it is shown that H2S generated by previous acidification of the sample enhances the sulfur signal emission as compared to the signal that is found when the water sample is analyzed in the absence of acid. The generation of hydrogen sulfide (H2S) takes place in a coil in which sulfide reacts with a hydrochloric acid solution. When this procedure is used, sulfur emission intensity is due to both sulfate and sulfide. The contribution of sulfide is obtained by subtracting the emission intensity measured straight from the water sample from that measured in the acidic medium.