Volatile Metal Species Research Articles

Mechanisms of chemical vapor generation by aqueous boranes for trace element analysis: a rather long and unfinished story

Abstract This paper reports a summary of the studies on the mechanisms that govern the generation of hydrides and other volatile species through reaction with aqueous boranes (CVG). This derivatization reaction has been used since the early 1970s for elemental determination and speciation from the trace level down to the ultratrace level and below. An IUPAC project, concluded in 2011, reported on the mechanisms of hydrogen transfer from borane to the analytical substrate and served to remove erroneous concepts that had dominated CVG until the early 2000s. Following the conclusion of the IUPAC project, many studies have been published on the mechanisms of CVG under conditions approaching those of analyzes of real samples. These studies included the definition of more general reaction models, which valid under non-analytical conditions, the mechanism of action of additives and interferences in CVG of volatile hydrides. In addition to the analytical utility for CVG, the results represent a contribution to the knowledge of the chemistry of aqueous boranes. Other studies will be necessary to clarify still unknown aspects, among them the identity of volatile transition metal species formed by reaction of metal ions with aqueous boranes.

Ultrasonic Nebulization-Accelerated Gas-Phase Enrichment Following In Situ Microplasma Desorption for Analysis of Trace Heavy Metals by Optical Emission Spectrometry.

Despite the great potential of microplasma optical emission spectrometry (OES) for on-site analysis, it remains a challenge to achieve the fast, sensitive, batch, and multielement analysis of trace heavy metals in a complex matrix. Herein, a novel ultrasonic nebulization-accelerated gas-phase enrichment (GPE) following in situ microplasma desorption sampling approach is employed for the determination of trace heavy metals by a miniature dielectric barrier discharge (DBD)-OES device. The volatile heavy metal species obtained by hydride generation (HG) can be quickly separated from the complex matrix under the action of ultrasonic nebulization, adsorbed on the surface of the activated carbon electrode tip for GPE, and then in situ desorbed and excited by DBD microplasma to achieve multielement OES analysis. With an array nebulizer plate, a batch of 10 samples can be handled for GPE in 40 s, and DBD-OES analysis is maintained at a rate of 6 s per sample. Under the optimized conditions, the detection limits for simultaneous determinations of Hg, Cd, Cu, and Sn are 0.005, 0.01, 0.03, and 0.04 μg L-1, respectively, and the detection sensitivities are about 164, 157, 132, and 91-fold improved with respect to those of the conventional HG-DBD-OES mode, respectively. The accuracy and practicability are verified by measuring several certified reference materials. This fast GPE plus in situ DBD-OES analysis strategy possesses the features of simple operation, time-savings, and low cost, contributing to volatile species transport, matrix interference elimination, and device miniaturization for field applications.

Phase Equilibria in the ZnO-“FeO”-SiO2 System in Reducing Atmosphere and in the ZnO-“FeO”-SiO2-“Cu2O” System in Equilibrium with Liquid Copper Metal at 1250 °C (1523 K)

Recent experimental studies in the ZnO-"FeO"-SiO2 system in reducing atmosphere demonstrated significant discrepancies with the current FactSage thermodynamic model developed using previous experimental data in this system in equilibrium with metallic iron and air. The present experimental study on phase equilibria in the ZnO-"FeO"-SiO2-"Cu2O" system in equilibrium with liquid copper at 1250 A degrees C (1523 K) at low copper oxide concentrations in slag was initiated and undertaken to resolve these discrepancies. A high-temperature equilibration-rapid quenching-electron-probe X-ray microanalysis (EPMA) technique using a primary phase substrate support and closed system approach with Cu metal introduced to determine effective equilibrium oxygen partial pressure from the Cu-metal/Cu2Oslag equilibria was applied to provide accurate information on the liquidus and corresponding solid compositions in the spinel, willemite, and tridymite primary phase fields. The present results confirmed the accuracy of the FactSage model, resolved discrepancies, and demonstrated significant uncertainties in the recent studies by other authors on the system in the open reducing atmosphere. The present study shows how this closed system approach can be used to obtain key thermodynamic data on phase equilibria in systems containing volatile metal species, overcoming the limitations and uncertainties encountered in conventional open gas/condensed phase equilibration with these systems. The study highlights the importance of the focus on obtaining accurate experimental data and the risks of misleading information from inadequate experimental control and analysis. The study also demonstrates that continuing in-depth critical review and analysis of the elemental reactions taking place in complex systems is an essential step in phase equilibrium research.

Speciation and mobility of volatile heavy metals (Cd, Pb, and Tl) in fly ashes.

Speciation of volatile metals Cd, Pb, and Tl in fly ashes (FAs) produced from burning of hard coal in stocker-fired boilers (SFBs) was studied. Two grain fractions of fly ash collected in a multicyclone and battery cyclone of the systems of dust separation from three SFB units operating in various urban heating plants were analyzed. The characteristic feature of speciation of the three metals was a large share of labile fractions: Cd (av. 46.1%), Pb (av. 39.8%), and Tl (av. 21.6%). The fraction which most clearly reflected the different chemical properties of the investigated metals was the oxidizable fraction: F(4)-Cd-0%, F(4)-Pb-av. 10.0%, and F(4)-Tl-av. 30.2%. The importance of condensation of the volatile metal species on FA particles for shaping speciation of these metals was characterized using the normalized enrichment factor (NEF): Pb (2.3±0.8)>Tl (1.8±0.9)≈Cd (1.7±0.6). Speciation of heavy metals may also be important economically, because the level of mobility coefficients (K Cd=0.46, K Pb=0.40, and K Tl=0.22) in the case of fly ashes considerably enriched with toxic metals (Cd 4.8±3.4mg/kg, Pb 293±210mg/kg, and Tl 6.3±4.5mg/kg) may limit their utilization range.

Some speculations on the mechanisms of photochemical vapor generation

Possible mechanisms are advanced to account for a number of observations/phenomena associated with the production of volatile metal species arising from photochemical vapor generation in acetic and formic acid media. These systems include mercury, iodine, selenium, iron and nickel as test cases which generate cold vapor, hydrides, methylated and carbonylated species. A model, based on the photochemical generation of free radicals involving ligand to metal charge transfer reductions and oxidations, is consistent with the majority of experimental data, including the identity of the resultant species and the impact of external parameters. This mechanistic framework will hopefully serve to enhance understanding of the technique so as to elicit enhanced performance through development of improved hardware and minimization/control of interferences.

Method Development for Simultaneous Determination of Transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and Noble (Pd, Pt, Rh) Metal Volatile Species by Microwave-Induced Plasma Spectrometry Using Ultrasonic Micronebulizer Dual Capillary Sample Introduction System

ABSTRACT The commercial ultrasonic nebulizer NOVA-DUO (Optolab, Warsaw, Poland) has been evaluated for the simultaneous determination of transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and noble (Pd, Pt, Rh) volatile metal species by microwave induced plasma–optical emission spectrometry (MIP-OES). Simultaneous mixing and nebulization of the two solutions (acidified sample and reductant) on the piezoelectric transducer, with the possibility of flow rate adjustment, permits a wide variation of sensitivity. The vapor-phase species were rapidly transported via a stream of Ar carrier to an MIP–OES for simultaneous multi-element determination. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the ultrasonic nebulizer/dual capillary system (USN/DCS) observed at 15 µL min−1 flow rate. An improvement in detection limits was achieved compared with pneumatic nebulization. Detection limits are superior to conventional pneumatic nebulization of elements. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of standard deviation of the blank (LOD, 3σblank criterion, peak height), were 2.49, 1.75, 3.39, 2.13, 4.80, 6.21, 4.26, 2.01, 7.65, 3.92, and 4.65 ng mL−1 for Au, Ag, Cd, Cu, Mn, Ni, Pb, Pd, Pt, Rh, and Zn, respectively. The method offers relatively good precision (RSD ranged from 8 to 12%) for liquid analysis and microsampling capability. The accuracy of the method was verified by the use of digested certified reference materials (NRCC TORT-1, NIES CRM-13, NIST SRM 2710, INCT SBF-4) and by aqueous standard calibration technique. The measured elements content in reference materials was in satisfactory agreement with the certified values.

Room temperature ionic liquids enhanced chemical vapor generation of copper, silver and gold following reduction in acidified aqueous solution with KBH4 for atomic fluorescence spectrometry

Room temperature ionic liquids (RTILs), as novel solvents, have many fascinating properties which make them of fundamental interest to all chemists. Herein, we report the first application of an RTIL in the chemical vapor generation (CVG) of transition and noble metals following reduction of acidified analyte solution with KBH4. Copper, silver and gold were selected as model analytes, and N-butylpyridinium tetrafluoroborate ([N bupy][BF4]) was used as a model RTIL. The RTIL-enhanced CVG of copper, silver and gold was evaluated by flow injection atomic fluorescence spectrometry (FI-AFS). The addition of [N bupy][BF4] leads to a 4.8-, 2.7- and 3.6-times improvement in the CVG efficiencies for copper, silver and gold, respectively. Interference from Zn(II), Fe(III), Co(II), Ni(II), Pb(II), Se(IV) and As(III) was also reduced in the presence of [N bupy][BF4]. The role of the RTIL was supposed to be inhibition of further coalescence of the metal nanoparticles which may constitute the volatile metal species leaving the solution and/or reaching the atomizer, and hence prevention of the loss of volatile metal species. With the consumption of a 0.5 mL sample solution, the detection limits (3s) for Cu, Ag and Au are 19, 15 and 6.3 μg L−1, respectively. The precisions (RSD, n = 11) for eleven replicate measurements of the standard solution containing 50 μg L−1Cu, Ag and Au were 4.4%, 5.2% and 4.7%, respectively. The developed RTIL-enhanced FI-CVG-AFS method was successfully applied to determination of trace Cu, Ag and Au in several certified biological and geological reference materials.

Volatilisation of metals and metalloids by the microbial population of an alluvial soil

In order to assess the microbial contribution to the volatilisation of metal(loid)s by methylation and hydridisation in the environment, we focused on soils of different origin. Here, we describe the biogenic production of volatile metal(loid) species of an alluvial soil with rather low metal(loid) contamination. The production of volatile metal(loid) compounds was monitored in soil suspensions kept under anaerobic conditions over an incubation time of 3 months. In the headspace of the samples, we detected mainly hydrids and methylated derivatives of a broad variety of elements such as arsenic, antimony, bismuth, selenium, tellurium, mercury, tin and lead, with the volatile products of arsenic, antimony and selenium representing the highest portions. Classical cultivation-dependent procedures resulted in the isolation of a strictly anaerobic Gram-positive strain (ASI-1), which shows a high versatility in transforming metal(loid) ions to volatile derivatives. Strain ASI-1 is affiliated to the species Clostridium glycolicum due to its high 16S rDNA sequence similarity with members of that species. As shown by fluorescence in situ hybridisation, strain ASI-1 amounts to approximately 2% of the total microbial flora of the alluvial soil. Since the spectrum of volatile metal(loid) compounds produced by this strain is very similar to that obtained by the whole population regarding both the broad variety of metal(loid)s converted and the preference for volatilising arsenic, antimony and selenium, we suggest that this strain may represent a dominant member of the metal(loid) volatilisating population in this habitat.

A novel approach to the estimation of aqueous solubility of some noble metal vapor species generated by reaction with tetrahydroborate (III)

The solubilities of stable, volatile metal species of Pd, Rh, Cd, Au and elemental Hg in an aqueous medium were estimated. Aqueous solutions were used to trap the species generated by reduction of the aquo ion with tetrahydroborate III. By continuously monitoring the headspace above the trap solution using ICP-MS detection, a saturation condition is readily discerned. Quantitation of the soluble fraction rapidly liberated by sparging the aqueous phase also permits its quantitation. The applicability of this approach was experimentally verified using cold vapour mercury generation to yield a solubility of elemental mercury of 40 ng/ml at 21 °C in a tin chloride reductant medium, in good agreement with a literature value of 44 ng/ml (after correction for salting out). The methodology was then applied to estimation of the solubilities of the gaseous species of Rh, Pd, Cd and Au, yielding values of 0.11, 3, >800 and 1.7 ng/l, respectively.

Partitioning of metal species during an enriched fuel combustion experiment. speciation in the gaseous and particulate phases.

Combustion processes are the most important source of metal in the atmosphere and need to be better understood to improve flue gas treatment and health impact studies. This combustion experiment was designed to study metal partitioning and metal speciation in the gaseous and particulate phases. A light fuel oil was enriched with 15 organometallic compounds of the following elements: Pb, Hg, As, Cu, Zn, Cd, Se, Sn, Mn, V, Tl, Ni, Co, Cr, and Sb. The resulting mixture was burnt in a pilot-scale fuel combustion boiler under controlled conditions. After filtration of the particles, the gaseous species were sampled in the stack through a heated sampling tube simultaneously by standardized washing bottles-based sampling techniques and cryogenically. The cryogenic samples were collected at -80 degrees C for further speciation analysis by LT/GC-ICPMS. Three species of selenium and two of mercury were evidenced as volatile species in the flue gas. Thermodynamic predictions and experiments suggest the following volatile metal species to be present in the flue gas: H2Se, CSSe, CSe2, SeCl2, Hg(0), and HgCl2. Quantification of volatile metal species in comparison between cryogenic techniques and the washing bottles-based sampling method is also discussed. Concerning metal partitioning, the results indicated that under these conditions, at least 60% (by weight) of the elements Pb, Sn, Cu, Co, Tl, Mn, V, Cr, Ni, Zn, Cd, and Sb mixed to the fuel were found in the particulate matter. For As and Se, 37 and 17%, respectively, were detected in the particles, and no particulate mercury was found. Direct metal speciation in particles was performed by XPS allowing the determination of the oxidation state of the following elements: Sb(V), Tl(III), Mn(IV), Cd(II), Zn(II), Cr(III), Ni(II), Co(II), V(V), and Cu(II). Water soluble species of inorganic Cr, As, and Se in particulate matter were determined by HPLC/ICP-MS and identified in the oxidation state Cr(III), As(V), and Se(IV).

Surfactant assisted chemical vapour generation of silver for AAS and ICP-OES: a mechanistic study

A chemical vapour generation (CVG) procedure for the production of volatile species of Ag was developed and studied using AAS and ICP-OES detection. A characteristic mass of 0.12 ng was achieved using a miniature diffusion flame atomizer-AAS system, whereas a 38-fold higher sensitivity (as cps per ng of introduced analyte) compared with conventional liquid nebulization was obtained with ICP-OES. The overall efficiency of introduction of Ag to the plasma was verified to be over 20%. More than one order of magnitude enhancement of efficiency was obtained by the addition of a surfactant (Triton X-100 in combination with an antifoaming agent), the effect of which, however, cannot be ascribed to the formation of organized media. Experiments concerning the mechanism of the CVG, transport and memory effect are discussed: Ag CVG is not a simple one-step process as is the case for CVG of selenium, but rather a two-step procedure. Transport properties of the volatile Ag species resemble more the transport of the liquid aerosol than a simple gaseous species such as H2Se. Possible alternatives concerning the identity of the volatile metal species are presented.

Volatile metal species in coal combustion flue gas.

Metals are released in effluents of most of combustion processes and are under intensive regulations. To improve our knowledge of combustion process and their resulting emission of metal to the atmosphere, we have developed an approach allowing usto distinguish between gaseous and particulate state of the elements emitted. This study was conducted on the emission of volatile metallic species emitted from a coal combustion plant where low/medium volatile coal (high-grade ash) was burnt. The occurrence of volatile metal species emission was investigated by cryofocusing sampling procedure and detection using low-temperature packed-column gas chromatography coupled with inductively coupled plasma-mass spectrometry as multielement detector (LT-GC/ICP-MS). Samples were collected in the stack through the routine heated sampling line of the plant downstream from the electrostatic precipitator. The gaseous samples were trapped with a cryogenic device and analyzed by LT-GC/ICP-MS. During the combustion process, seven volatile metal species were detected: three for Se, one for Sn, two for Hg, and one for Cu. Thermodynamic calculations and experimental metal species spiking experiments suggest that the following volatile metal species are present in the flue gas during the combustion process: COSe, CSSe, CSe2, SeCl2, Hg0, HgCl2, CuO-CuSO4 or CuSO4 x H2O, and SnO2 or SnCl2. The quantification of volatile species was compared to results traditionally obtained by standardized impinger-based sampling and analysis techniques recommended for flue gas combustion characterization. Results showed that concentrations obtained with the standard impinger approach are at least 10 times higher than obtained with cryogenic sampling, suggesting the trapping microaerosols in the traditional methods. Total metal concentrations in particles are also reported and discussed.

Detection of volatile organometal chloride species in model atmosphere above seawater and sediment.

The principal route for release of organometallic species into the atmosphere is currently considered to be the biological or chemical formation of saturated volatile compounds such as dimethylmercury, metal hydrides, etc. Model experiments conducted in our laboratory pointto the release of extremely toxic, volatile organotin, -lead, -mercury, and -arsenic species that have been detected as the chlorides in the gas phase above seawater and sediment mixtures. As the sediment was sterilized prior to the analytical study, any bioformation of volatile metal species was excluded. The most probable account of these observations is the naturally occurring formation of metal chlorides, fueled by the abundance of chloride ion (or other halides) present in seawater and many other natural environments. This raises the suggestion that the release of toxic trace elements to the atmosphere by environmental processes may be seriously underestimated. A conservative projection, based on laboratory data, suggests that the emission of butyltin into the atmosphere may reach as high as 150 ng/m2 of water/yr from a polluted marine environment, suggesting a very significant level of release of butyltin from seawater at the global level. For the sampling and determination of volatile metal species, solid-phase microextraction combined with inductively coupled plasma time-of-flight mass spectrometry has been used. This new analytical system is capable of detection of semivolatile, thermally unstable compounds such as the class encompassing metal halide species.

Expanding the scope of chemical vapor generation for noble and transition metals.

A modified Bergener parallel path nebulizer was used for the generation of volatile metal species of Pt, Co, Ag, Cu, Rh, Pd, Au, Ni, Ir, Ti and Mn through reaction with tetrahydroborate (III). Several physicochemical factors were identified which impact on their yield which, at present, is estimated to range from 0.02-2% absolute.

Separation methods for environmental technologies

AbstractMuch of the environmental damage in air, soil, sediment, surface and groundwater can be repaired, and further damage prevented through the use of efficient separation technologies. Such technologies should typically achieve higher degrees of species separation. Environmental contamination requires remediation separation technologies especially suited for very low concentrations. This paper highlights the separation and recovery of volatile organic compounds and toxic metal species. Conventional separation technologies are currently inefficient and costly. In this paper, the scope of separation science and technologies in environmental areas will be outlined, and several promising emerging ideas in the areas of sorption and membranes are discussed. The authors view high surface area membrane‐based sorption as a common approach that shows significant promise for tackling these difficult problems by improving technical capability, operability, and process economics.

Adsorption Mechanism of Heavy Metals on Sorbents during Incineration

This study investigated the adsorption mechanism of heavy metals Cr, Cu, Pb, and Cd on the sorbent during incineration by the following technologies: (1) thermal desorption of heavy metals from the sorbent; (2) identification of heavy metal species in the adsorbed sorbent by x-ray diffraction technique; (3) thermodynamic equilibrium simulation of heavy metals and sorbent; and (4) micrography of the sorbent by scanning electron microscopy. Experimental results indicated that adsorption mechanism of heavy metals on sorbent is related to the volatility of heavy metal species formed at high temperatures and the chemical reactivity with the sorbent. For less volatile heavy metals Cr and Cu, chemical reaction is the major adsorption mechanism, and particle growth due to condensation, coagulation, and sedimentation will become important as the reacting time is increased. For highly volatile metal Cd and most metal chlorides, physical molecular adsorption and particle growth processes are the major mechanisms. Most volatile metal species are adsorbed/distributed on the surface of the sorbent. For Pb (which has been classified as medium to high volatility), chemical and physical adsorption mechanisms are all-important depending on the reacting environment.

Determination of methylmercury by solid-phase microextraction inductively coupled plasma mass spectrometry: a new sample introduction method for volatile metal species

Direct coupling of solid-phase microextraction (SPME) with inductively coupled plasma mass spectrometry (ICP-MS) is described for methylmercury speciation. A thermal desorption interface, consisting of a heated, glass-lined splitless-type GC injector, was placed directly at the base of the torch to minimize the length of transfer line. This arrangement provides for fast desorption and high sample introduction efficiency. Direct liquid immersion and headspace extraction of methylmercury was studied, including the effect of temperature and time on the extraction efficiency. For clean solutions, immersion sampling SPME provided good sensitivity that was linear over two orders of magnitude whereas headspace sampling showed 15% lower sensitivity, but a linear range of more than three orders of magnitude. The detection limit for headspace methylmercury sampling was 0.2 ng ml−1. Calibration by the method of additions using direct extraction revealed a severe matrix effect with biological tissue samples, diminishing the methylmercury response 70-fold, whereas that obtained by headspace extraction was statistically indistinguishable from signals generated using matrix free standards. Analytical results showed good agreement between certified and measured values for analysis of NRCC DORM-2, (Dogfish muscle) and DOLT-2 (Dogfish liver) reference materials.

Volatile Metal and Metalloid Species (Pb, Hg, Se) in a European Urban Atmosphere (Bordeaux, France)

Ambient air measurements of volatile metal and metalloid compounds were conducted in a European urban environment (Bordeaux, France). Air samples were collected with a cryogenic trap and analyzed by low-temperature gas chromatography with ICP/MS detection. Indoor and outdoor sites were studied. Tetraalkyllead compounds (Me4-nEtnPb, n = 0−4) and elemental mercury were found to be the major volatile metal species. Average concentrations of 15.5 and 2.7 ng/m3 as metal have been reported respectively for total alkyllead species and elemental mercury in open area. These results illustrate the general phasing out of atmospheric lead initiated in the past decade. Accumulation of dimethyl selenide has been recorded in a building probably originating from human breath. Volatile metal species distribution in the different sites is discussed with regards to meteorological conditions and automotive traffic parameters. Occurrence of unknown volatile metal and metalloid species likely to occur in urban environment is also reported and discussed.

Sampling and probing volatile metal(loid) species in natural waters by in-situ purge and cryogenic trapping followed by gas chromatography and inductively coupled plasma mass spectrometry (P-CT–GC–ICP/MS)

An in situ purge and cryogenic trapping method for the pre-concentration of volatile metal and metalloid compounds dissolved in natural waters was developed. The analytes were collected in cryogenic trap stored at −196°C until analysis in the laboratory. Cryogenic traps were then introduced into a flash desorption, cryofocusing gas chromatography system hyphenated to an inductively coupled plasma mass spectrometer (ICP/MS). This multi-element detection technique allowed to determine volatile compounds of selected elements in aqueous solution simultaneously by scanning their corresponding stable isotopes. Blanks and recoveries for the whole analytical procedure of several volatile compounds of selected elements (Me 2Se, Me 2Se 2, Me 2Hg, Et 2Hg, Me 4Sn, Et 4Sn, Me 4Pb, Et 4Pb) were determined and are discussed. Method detection limits for 1 l water sample were estimated for Se, Hg, Sn and Pb volatile species to be as low as 10.0 (0.8), 1.0 (0.2), 0.4 (0.05) and 0.4 (0.08) fmol/l (pg/l), respectively. The occurrence of volatile compounds of selenium, tin, mercury and lead was evidenced and investigated in three major European estuaries such as the Gironde (F), the Rhine (NL) and the Scheldt (B/NL). The presence of these volatile species in natural waters seems to be related to both exchanges between environmental compartments and anthropogenic inputs.

Organometal(loid) species in geochemical exploration: preliminary qualitative results

Organic and other volatile metal(loid) species (e.g. hydrides) in environmental gases can be determined with high sensitivity and selectivity by low-temperature gas chromatography coupled on-line to plasma mass spectrometry (LTGC/ICP–MS). A standard reference solution is analysed simultaneously for calibration of the results as well as for monitoring the excitation conditions in the plasma. This highly sensitive analytical method was applied in field screening tests at Cu and Hg deposits in Germany. In some of the soil gas and soil samples investigated, organic compounds of several elements (e.g. As, Hg) could clearly be identified. The implications of these results with respect to potential use of organometal(loid) species in geochemical exploration are discussed.