Dirce Pozebon

Determination of Cu, Mn, Ni and Sn in gasoline by electrothermal vaporization inductively coupled plasma mass spectrometry, and emulsion sample introduction

Trace metals in fuels, except in the case of additives, are usually undesirable and normally they occur in very low concentrations in gasoline, requiring sensitive techniques for their determination. Coupling of electrothermal vaporization with inductively coupled plasma mass spectrometry minimizes the problems related to the introduction of organic solvents into the plasma. Furthermore, sample preparation as oil-in-water emulsions reduces problems related to gasoline analysis. In this work, a method for determination of Cu, Mn, Ni and Sn in gasoline is proposed. Samples were prepared by forming a 10-fold diluted emulsion with a surfactant (Triton X-100), after treatment with concentrated HNO3. The sample emulsion was pre-concentrated in the graphite tube by repeated pipetting and drying. External calibration was used with aqueous standards in a purified gasoline emulsion. Six samples from different gas stations were analyzed, and the analyte concentrations were found to be in the μg l−1 range or below. The limits of detection were 0.22, 0.02, 0.38 and 0.03 μg l−1 for Cu, Mn, Ni and Sn, respectively. The accuracy of the method was estimated using a recovery test.

Review of the applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to the analysis of biological samples

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has received significant attention over the last 10 years and has been widely used for the analysis of biological samples. The technique allows the determination of elements and isotopes in biological tissues and related materials with a spatial resolution typically ranging from 10 to 100 μm. When compared to other techniques usually employed to obtain bioimages, the greater advantage of LA-ICP-MS is its higher sensitivity. The literature survey over the last 10 years concerning the use of LA-ICP-MS for biological tissue analysis is reviewed in this article. Instrumentation, strategies of calibration for quantitative analysis, challenges and recent advances in this field are discussed. Applications of the isotope ratio (IR), including tracer experiments, and isotope dilution (ID), are reviewed for biological samples (briefly for proteins, in order to show the utility of LA-ICP-MS). Bioimaging methods, studies and applications for animal and plants tissues are emphasized, demonstrating the importance of bioimaging of metals and metalloids in biomedical research, bioaccumulation and bioavailability studies for ecological and toxicological risk assessment in humans, animals and plants. The usefulness of the IR associated with bioimaging for predicting geographical origin, habitat, movement of subjects, diet and lifestyle are also demonstrated.

On the use of phosphine-free PdCl2(SEt2)2 complex as catalyst precursor for the Heck reaction

A simple and efficient experimental protocol has been developed for the catalytic arylation of alkenes by the air and water stable, and phosphine-free compound PdCl2(SEt2)2 associated with tetrabutyl ammonium bromide. Using this catalytic protocol, aryl iodides and bromides, and electron-poor aryl chlorides are coupled with n-butylacrylate and styrene under relatively mild reaction conditions with high catalytic activity. Reaction vessel ultra-trace amounts (ppt) of this Pd precursor promotes the coupling of iodo benzene with n-butylacrylate with turnover numbers (mol product/mol Pd) up to 109.

Determination of copper, cadmium, lead, bismuth and selenium(iv) in sea-water by electrothermal vaporization inductively coupled plasma mass spectrometry after on-line separation

A procedure for the determination of Cu, Cd, Pb, Bi and SeIV in sea-water by electrothermal vaporization inductively coupled plasma mass spectrometry, after on-line separation using a flow injection system, is proposed. Matrix separation and analyte preconcentration was accomplished by retention of the analytes complexed with the ammonium salt of O,O-diethyldithiophosphoric acid on C18 immobilized on silica in a minicolumn coupled directly to the autosampler arm of the vaporizer. The methanol used as eluent was vaporized after being automatically injected into the graphite tube, prior to the vaporization of the analytes. The conditions for the on-line complexation and separation as well as the vaporizer temperature program were optimized. The recoveries from sea-water ranged from 90 to 110%. The accuracy of the method was tested by the analysis of two certified sea-waters, CASS-3 and NASS-4, from the National Research Council of Canada. The concentration of Bi in these sea-waters was below the method detection limit. The relative standard deviation was below 10% (n=6). The throughput was 22 samples h–1 and the volume of sample consumed was only 2.3 ml. Tl and AsIII were also separated but their complexation in sea-water was not efficient.

Determination of Cd, Hg, Pb and Tl in coal and coal fly ash slurries using electrothermal vaporization inductively coupled plasma mass spectrometry and isotopic dilution

A method has been investigated for the determination of Cd, Hg, Pb and Tl in coal and in coal fly ash, using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry and isotope dilution. The slurry, 25 mg ml−1, was prepared by mixing the powdered sample (≤36–45 µm) with acid solutions (nitric acid for coal and nitric and hydrofluoric acids for coal fly ash) and submitting the mixture to an ultrasonic agitation, letting it stand afterwards in a water bath at 60 °C for 2 h. An ultrasonic probe was used to homogenize the slurry in the autosampler cup just before its introduction into the graphite tube. The best conditions were determined regarding analyte sensitivity, furnace temperature program, amount of modifier, acid concentration, gas flow rate and particle size. For Hg, the pyrolysis stage was omitted and a low vaporization temperature was used (450–1000 °C); the residual matrix was eliminated in the first step of the following cycle. The modifiers used were: Pd for Cd and Tl; Au, Ir or Pd for Hg; Ir or Pd for Pb. The accuracy of the method was checked by analyzing six certified coal reference materials (SARM 20, SARM 19, BCR No. 40, BCR No. 180, BCR No. 181 and NIST 1630a) and one certified coal fly ash (NIST 1633b). With one exception (Hg in BCR No. 180), the found concentrations were typically within 95% confidence interval of the certified values, or close enough to the recommended values, as long as the samples were ground to a small enough particle size. The limits of detection were typically around 0.08 µg g−1, 0.03 µg g−1, 1 µg g−1 and 0.02 µg g−1 for Cd, Hg, Pb and Tl, respectively. The precision was also adequate with relative standard deviations of usually <5%.

Biomonitoring of essential and toxic metals in single hair using on-line solution-based calibration in laser ablation inductively coupled plasma mass spectrometry.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been established as a powerful and sensitive surface analytical technique for the determination of concentration and distribution of trace metals within biological systems at micrometer spatial resolution. LA-ICP-MS allows easy quantification procedures if suitable standard references materials (SRM) are available. In this work a new SRM-free approach of solution-based calibration method in LA-ICP-MS for element quantification in hair is described. A dual argon flow of the carrier gas and nebulizer gas is used. A dry aerosol produced by laser ablation (LA) of biological sample and a desolvated aerosol generated by pneumatic nebulization (PN) of standard solutions are carried by two different flows of argon as carrier or nebulizer gas, respectively and introduced separately in the injector tube of a special ICP torch, through two separated apertures. Both argon flows are mixed directly in the ICP torch. External calibration via defined standard solutions before analysis of single hair was employed as calibration strategy. A correction factor, calculated using hair with known analyte concentration (measured by ICP-MS), is applied to correct the different elemental sensitivities of ICP-MS and LA-ICP-MS. Calibration curves are obtained by plotting the ratio of analyte ion M(+)/(34)S(+) ion intensities measured using LA-ICP-MS in dependence of analyte concentration in calibration solutions. Matrix-matched on-line calibration in LA-ICP-MS is carried out by ablating of human hair strands (mounted on a sticky tape in the LA chamber) using a focused laser beam in parallel with conventional nebulization of calibration solutions. Calibrations curves of Li, Na, Mg, Al, K, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Mo, Ag, Cd, I, Hg, Pb, Tl, Bi and U are presented. The linear correlation coefficients (R) of calibration curves for analytes were typically between 0.97 and 0.999. The limits of detection (LODs) of Li, V, Mn, Ni, Co, Cu, Sr, Mo, Ag, Ba, Cd, I, Hg, Pb, Bi and U in a single hair strand were in the range of 0.001-0.90 μg g(-1), whereas those of Cr and Zn were 3.4 and 5.1 μg g(-1), respectively. The proposed quantification strategy using on-line solution-based calibration in LA-ICP-MS was applied for biomonitoring (the spatial resolved distribution analysis) of essential and toxic metals and iodine in human hair and mouse hair.

Determination of trace elements in biological materials by ETV-ICP-MS after dissolution or slurry formation with tetramethylammonium hydroxide

A method to prepare biological samples to be analysed by electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. A solution or slurry was formed by mixing a sample aliquot, 20–100 mg, with a small volume, 10–200 µL, of a 25% m/v tetramethylammonium hydroxide solution. For animal tissues, complete dissolution was obtained, whereas for the plant and whole egg materials, slurries were obtained. The slurries were stirred manually, every three readings, in the instrument. The pyrolysis and atomization temperatures were optimized, using Pd as a carrier–modifier for As, Se, Te, Ag, Cr, Cu, V, Ni, Mn, Co and Cd. An Ir-coated tube was used for Pb, Sb, Sn and Bi. External calibration was used preferentialy, but in some instances, the analyte additions method was employed. Good results were obtained for four certified reference materials. However, Cr and Cd could not be determined in the bovine muscle sample owing to spectral interferences and matrix effects, respectively.

Bioimaging of metals in thin mouse brain section by laser ablation inductively coupled plasma mass spectrometry: novel online quantification strategy using aqueous standards

A novel solution-based calibration method for quantitative spatial resolved distribution analysis (imaging) of elements in thin biological tissue sections by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) is described. A dual flow of the carrier and nebulizer gas is used to transport the aerosol of the laser ablated solid sample (brain tissue) and that of the nebulized aqueous standard into inductively coupled plasma (ICP) source, respectively. Both aerosols are introduced separately in the injector tube inside a special ICP torch and then mixed in the inductively coupled plasma. Calibration curves were obtained via two different calibration strategies: (i) solution based calibration and (ii) with a set of well characterized homogeneous brain laboratory standards. In the first approach matrix matching is performed by solution nebulization of a series of aqueous standards with defined analyte concentrations and simultaneous laser ablation of brain homogenate followed by nebulization of 2% (v/v) HNO3 and laser ablation of a whole brain slice (line by line). In the second approach of calibration a set of brain homogenates with defined analyte concentrations is analyzed by LA-ICP-MS followed by the imaging of brain tissue under the same experimental conditions (dry plasma). Calibration curves of elements of interest (e.g., Li, Na, Al, K, Ca, Ti, V, Mn, Ni, Co, Cr, Cu, Zn, As, Se, Rb, Sr, Y, Cd, Ba, La, Ce, Nd, Gd, Hg, Pb, Bi and U) were obtained using (i) aqueous standards or (ii) the set of synthetic laboratory standards prepared from a mouse brain homogenate doped with elements at defined concentrations. The ratio of the slope of the calibration curves (obtained by using aqueous standards and solid standards) was applied to correct the differences of sensitivity among ICP-MS and LA-ICP-MS. Quantitative images of Li, Mn, Fe, Cu, Zn and Rb in mouse brain were obtained under wet plasma condition (nebulization of HNO3 solution in parallel with ablation of solid brain sample).

Determination of Ag, Te, U and Au in waters and in biological samples by FI–ICP-MS following on-line preconcentration

An on-line preconcentration system for Au, Ag, Te and U, using solenoid valves, a mini-column filled with C 18 immobilized on silica to retain the complexes formed with the ammonium salt of O,O-diethyl dithiophosphoric acid and elution with methanol is proposed. All parameters of the preconcentration, such as sample flow rate, concentration of the complexing agent, acid nature and concentration and elution were optimized. Due to the difficulty of finding compromising conditions for all analytes, they were determined individually. Detections limits ranged from 0.05 to 2.24 pg ml -1 for U and Te, respectively, while the preconcentration factors ranged from 2.6 to 180 for U and Te, respectively. The precision was adequate for the low measured concentrations, with R.S.D. below 10%. Accuracy was assured by the analysis of standard reference enriched water, sea and riverine waters, milk powder, apple leaves and urine, after microwave-assisted digestion of the last three materials. The relatively small volume of methanol, diluted to 1 + 1, introduced into a conventional nebulizer, minimizes the problems associated with the introduction of organic solvent in the plasma.

Potentiometric determination of fluoride in geological and biological samples following pyrohydrolytic decomposition

A method for the determination of fluoride in coal, coal fly ash, phosphate rock, limestone, mineral clay, fossilised materials, oyster tissue and vegetation using pyrohydrolysis for sample decomposition is proposed. A specific apparatus was constructed and the influence of vanadium pentoxide (V 2O5) as a catalyst for the pyrohydrolysis reaction was investigated. It was verified that V2O5 does not influence the release of fluoride from the vegetation, oyster tissue, coal and coal fly ash matrices analysed. However, the catalyst was necessary for the phosphate rock, fossil bone, mineral clay and limestone samples. Certified and noncertified samples were analysed using an ion selective electrode (ISE) for the analyte detection. Precise (relative standard deviation—R.S.D .< 7%) and accurate (recovery in accordance to certified values) results were obtained. The limit of quantification (LOQ) of the method was 5.0 gg −1 of fluoride using 20 mg of sample and a final dilution to 10 ml. The sample frequency was five samples per hour.