Francisco Laborda

Selective identification, characterization and determination of dissolved silver(I) and silver nanoparticles based on single particle detection by inductively coupled plasma mass spectrometry

The different behaviours of dissolved silver and silver nanoparticles under ICP-MS single particle detection conditions have been used to differentiate directly between both forms of silver in aqueous samples. Suspensions containing silver nanoparticles at number concentrations below 109 L−1 and/or dissolved Ag(I) are introduced into the ICP-MS by conventional pneumatic nebulization and measured with a time resolution of 5 ms. Each silver nanoparticle is converted in the ICP into a packet of ions, which are detected as a single pulse, whose intensity is proportional to the number of silver atoms in the nanoparticle, whereas dissolved silver produces pulses of averaged constant intensity. The frequency plots with respect to the intensity measured for each pulse show independent distributions for dissolved silver and silver nanoparticles, whose profiles are also different (Poisson and lognormal, respectively). Size limits of detection for pure Ag nanoparticles of 18 nm, equivalent to a silver mass of 32 ag, were obtained. Number concentration limits of detection of 1 × 104 L−1 can be achieved. A methodological approach for identification, characterization and determination of mass and number concentration of dissolved Ag(I) and silver nanoparticles at environmentally relevant concentrations is presented.

Single Particle Inductively Coupled Plasma Mass Spectrometry: A Powerful Tool for Nanoanalysis

Single particle inductively coupled plasma mass spectrometry is an emergent ICPMS method for detecting, characterizing, and quantifying nanoparticles. Although the number of applications reported to date is limited, the relatively simple instrumental requirements, the low number concentration detection levels attainable, and the possibility to detect both the presence of dissolved and particulate forms of an element make this methodology very promising in the nanoscience related areas.

Detection, characterization and quantification of inorganic engineered nanomaterials: A review of techniques and methodological approaches for the analysis of complex samples

The increasing demand of analytical information related to inorganic engineered nanomaterials requires the adaptation of existing techniques and methods, or the development of new ones. The challenge for the analytical sciences has been to consider the nanoparticles as a new sort of analytes, involving both chemical (composition, mass and number concentration) and physical information (e.g. size, shape, aggregation). Moreover, information about the species derived from the nanoparticles themselves and their transformations must also be supplied. Whereas techniques commonly used for nanoparticle characterization, such as light scattering techniques, show serious limitations when applied to complex samples, other well-established techniques, like electron microscopy and atomic spectrometry, can provide useful information in most cases. Furthermore, separation techniques, including flow field flow fractionation, capillary electrophoresis and hydrodynamic chromatography, are moving to the nano domain, mostly hyphenated to inductively coupled plasma mass spectrometry as element specific detector. Emerging techniques based on the detection of single nanoparticles by using ICP-MS, but also coulometry, are in their way to gain a position. Chemical sensors selective to nanoparticles are in their early stages, but they are very promising considering their portability and simplicity. Although the field is in continuous evolution, at this moment it is moving from proofs-of-concept in simple matrices to methods dealing with matrices of higher complexity and relevant analyte concentrations. To achieve this goal, sample preparation methods are essential to manage such complex situations. Apart from size fractionation methods, matrix digestion, extraction and concentration methods capable of preserving the nature of the nanoparticles are being developed. This review presents and discusses the state-of-the-art analytical techniques and sample preparation methods suitable for dealing with complex samples. Single- and multi-method approaches applied to solve the nanometrological challenges posed by a variety of stakeholders are also presented.

Metal associations to microparticles, nanocolloids and macromolecules in compost leachates: Size characterization by asymmetrical flow field-flow fractionation coupled to ICP-MS

A methodological approach based on the size characterization of environmental microparticles (size larger than 1 microm), nanocolloids (1 microm to 15 nm) and macromolecules (lower than 1000 kDa) by asymmetrical flow field-flow fractionation (AsFlFFF), taking advantage of both normal and steric elution modes, is presented. The procedure was optimized to minimize the potential alteration of the size distribution and metal associations of the species characterized. Prior to separation by AsFlFFF, samples are subjected to gravitational settling of the solid suspension, followed by a centrifugation of the settled sample. The comparison between the fractograms of the settled and the centrifuged samples allows the characterization of the microparticles, which are eluted in steric mode in the AsFlFFF system. The characterization of nanocolloids and macromolecules is carried out on the centrifuged sample by applying different operational conditions under normal mode in the AsFlFFF system. A comparison with the conventional frontal filtration through 0.45 microm pore size membranes have shown that filtration removes particles below their nominal pore size, modifying the size distribution of the samples respect to the centrifugation. The methodology proposed has been applied to the size characterization of compost leachates. The contribution of these three differentiated fractions to the mobilization of metals has been determined by coupling the AsFlFFF system to an inductively coupled plasma mass spectrometer (ICP-MS).

Thallium occurrence and partitioning in soils and sediments affected by mining activities in Madrid province (Spain)

Thallium (Tl) and its compounds are toxic to biota even at low concentrations but little is known about Tl concentration and speciation in soils. An understanding of the source, mobility, and dispersion of Tl is necessary to evaluate the environmental impact of Tl pollution cases. In this paper, we examine the Tl source and dispersion in two areas affected by abandoned mine facilities whose residues remain dumped on-site affecting to soils and sediments of natural water courses near Madrid city (Spain). Total Tl contents and partitioning in soil solid phases as determined by means of a sequential extraction procedure were also examined in soils along the riverbeds of an ephemeral and a permanent streams collecting water runoff and drainage from the mines wastes. Lastly, electronic microscopy and cathodoluminescence probe are used as a suitable technique for Tl elemental detection on thallium-bearing phases. Tl was found mainly bound to quartz and alumino-phyllosilicates in both rocks and examined soils. Besides, Tl was also frequently found associated to organic particles and diatom frustules in all samples from both mine scenarios. These biogenic silicates may regulate the transfer of Tl into the soil-water system.

Reduction of polyatomic interferences in inductively coupled plasma mass spectrometry by selection of instrumental parameters and using an argon–nitrogen plasma: effect on multi-element analyses

The effect of instrumental parameters and argon-nitrogen plasmas on polyatomic ion formation has been studied in order to reduce their magnitude in routine multi-element analysis without losing detection capability. Special emphasis was placed on the chlorine based polyatomic interferences on V, Cr, Zn, As and Se. A significant reduction in signals from polyatomic ions was attained by using a high aerosol carrier gas flow rate (0.955 l min–1) instead of the default flow rate (0.755 l min–1), or by adding nitrogen (8%) to the aerosol carrier flow. The ArCl+ interference produced by 0.05% Cl (the maximum concentration expected in digested food stuff samples) was effectively removed by both methods and ClO+ and ClO2+ by addition of nitrogen. Detection limits for elements along the mass range (from Li to U) were, on average, 2–3 times higher with the mixed gas plasma. This slight degradation of detection limits was not judged to be deterimental to multielement determinations in five reference materials when the results from using an argon-only plasma (with low and high aerosol carrier flow rates) were compared with the results from the argon–nitrogen plasma.

Selenium speciation by high-performance liquid chromatography–fraction collection–electrothermal atomic absorption spectrometry: optimization of critical parameters

Chromatographic effluents were analysed by electrothermal atomic absorption spectrometry (ETAAS) using a sampling procedure based on fraction collection and hot injection onto a graphite furnace. In order to reduce analyte dilution and to attain the maximum sensitivity of the combined system, special attention was paid to the volume of fraction collected and the volume of each fraction injected onto the furnace. Total volumes of 60 µl (50 µl of sample + 10 µl of modifier) were introduced into the graphite furnace by hot injection, using a pre-heating temperature of 120 °C and an injection rate of 3.3 µl s–1. Under these conditions, the detection limit for determination of selenium was 1.21 µg l–1 and the repeatability 2.4% for 40 µg l–1. When effluent fractions were analysed with the hot injection programme, the use of fraction volumes of 0.50 ml or lower provided a detection limit below 1 ng of selenium with respect to the sample injected into the chromatograph. This procedure was applied to the speciation of selenium. The separation of trimethylselenonium, selenite and selenate was performed by anion-exchange chromatography using 0.01 mol l–1 ammonium citrate at pH 3.0 and 7.0 as eluent. The presence of such a concentration of citrate produced a negative interference on selenium determination and this signal suppression was reduced by 17% on increasing the amount of nickel (200 µg) and also adding magnesium nitrate (50 µg) and overcome by using matrix-matched standards. Detection limits were 1.67, 1.27 and 0.76 ng of Se for trimethylselenonium, selenite and selenate, respectively.

Interferences in electrochemical hydride generation of hydrogen selenide

Abstract Interferences from Cu(II), Zn(II), Pt(IV), As(III) and nitrate on electrochemical hydride generation of hydrogen selenide were studied using a tubular flow-through generator, flow injection sample introduction and quartz tube atomic absorption spectrometry. Comparison with conventional chemical generation using tetrahydroborate was also performed. Lead and reticulated vitreous carbon (RVC), both in particulate form, were used as cathode materials. Signal supressions up to 60–75%, depending on the cathode material, were obtained in the presence of up to 200 mg l−1 of nitrate due to the competitive reduction of the anion. Interference from As(III) was similar in electrochemical and chemical generation, being related to the quartz tube atomization process. Zinc did not interfere up to Se/Zn ratios 1:100, whereas copper and platinum showed suppression levels up to 50% for Se/interferent ratios 1:100. Total signal suppression was observed in presence of Se/Cu ratios 1:100 when RVC cathodes were used. No memory effects were observed in any case. Scanning electron microscopy and squared wave voltametry studies supported the interference mechanism based on the decomposition of the hydride on the dispersed particles of the reduced metal.

Suitability of analytical methods to measure solubility for the purpose of nanoregulation

Abstract Solubility is an important physicochemical parameter in nanoregulation. If nanomaterial is completely soluble, then from a risk assessment point of view, its disposal can be treated much in the same way as “ordinary” chemicals, which will simplify testing and characterisation regimes. This review assesses potential techniques for the measurement of nanomaterial solubility and evaluates the performance against a set of analytical criteria (based on satisfying the requirements as governed by the cosmetic regulation as well as the need to quantify the concentration of free (hydrated) ions). Our findings show that no universal method exists. A complementary approach is thus recommended, to comprise an atomic spectrometry-based method in conjunction with an electrochemical (or colorimetric) method. This article shows that although some techniques are more commonly used than others, a huge research gap remains, related with the need to ensure data reliability.

Effect of nickel and palladium as chemical modifiers and influence of urine matrix on different chemical species of selenium in electrothermal atomic absorption spectrometry

The effect of nickel and palladium nitrates on the main selenium species in human urine, selenite and trimethylselenonium, was studied with respect to thermal stabilization in the graphite furnace. Special attention was also paid to the use of reduced palladium, either thermally or chemically. In all instances, maximum charring temperatures of 1200–1300 °C were attained for both species in aqueous solution. Trimethylselenonium was partially stabilized by reduced palladium, showing a similar behaviour to that using typical reducing agents that are found in urine, such as urea. The influence of the urine matrix on the selenium signal, using nickel as chemical modifier, was studied and minimized by optimization of the amount of modifier and charring and atomization steps. A selenium response independent of the urine matrix (selenium recoveries of 96%) was obtained for urine samples diluted 1+4 with water by adding 100 µl of nickel, using 900 and 2300 °C as charring and atomization temperatures, respectively, and including a cool-down step between charring and atomization.