Generation Of Volatile Species Research Articles

A miniaturized microplasma excitation source coupled with photochemically induced volatile species generation as a cost-effective tool for in situ mercury pollution analyses

A portable, miniaturized atmospheric microplasma discharge system coupled with the photochemical vapour generation was developed for the sensitive Hg determination in water samples using OES.

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.

Photochemical vapor generation of Zinc and Gallium

Photochemical vapor generation (PVG) of Zinc (Zn) and Gallium (Ga) was firstly reported in this study. The main parameters influencing PVG of Zn and Ga were investigated with inductively coupled plasma mass spectrometry (ICP-MS), such as the type and concentration of low molecular weight organic acids (LMWOAs), the concentration of transition metal ions and their synergistic effects, the wavelength and time of UV irradiation, and pH of sample solution. Formic acid (FA) and Cu2+ were required for the generation of volatile species of Zn and Ga. In addition, the effects of interfering ions on the PVG of Zn and Ga were investigated. Good precisions with 2.3% and 2.7% were obtained under the selected conditions for replicate measurement of 200 ng mL−1 Zn and Ga standard solution (n = 7), respectively. The limits of detection (LOD, 3σ, n = 11) were calculated to be 8.8 ng mL−1 and 0.77 ng mL−1 for Zn and Ga with PVG-ICP-MS measurement, respectively. Carbonyl compounds were speculated to be formed in this study. Moreover, nanoparticles containing Cu, Zn or Ga were found in liquid solution after UV irradiation, which may be useful for investigating the formation of natural nanoparticles in environment as well as the isotope fractionation of Zn and Ga in photochemical processes.

Volatile Species Generation for Trace Element and Speciation Analysis – Current State and Future Perspectives

Volatile Species Generation for Trace Element and Speciation Analysis – Current State and Future Perspectives

Efficiency of chemical generation of volatile species of zinc from non-acidic conditions

Chemical vapor generation (CVG) producing volatile species of zinc was carried out in a custom made generator with high-resolution continuum-source atomic absorption detection. The influence of composition of the reaction medium and various reaction modifiers was studied. The optimum conditions included neutral to basic pH of the reaction mixture, i.e., 0.1 M HCl and 0.5% (m/v) NaBH4 prepared in 0.1 M NaOH. Substantial improvement of generation efficiency (approx.18-times) was achieved with 8-hydroxyquinoline and a LOD of 4 ng mL−1 was obtained. The overall CVG efficiency of 2.7% was determined by comparison of sensitivity obtained with CVG and conventional solution nebulization (both coupled to inductively coupled plasma mass spectrometry) and 2.5% was determined by employing a radioactive isotope 65Zn. The described method is reasonably resistant to interferences, the greatest interference effect was observed with Bi(III) and Fe(III), other transition and noble metals interfered at a 100-times surplus over Zn and their effects decreased in the order Co(II) > Ni(II) > Cd(II) > Mn(II) > Ag(I) > Cr(III) > Cu(II). The accuracy of the method was verified by determination of zinc in the certified reference materials NIST 1643f (fresh water) and ERM CA713 (waste water).

Speciation analysis of mercury employing volatile species generation: Approaches to reliable determination in blood and hair

Two approaches to Hg speciation analysis, both employing volatile species generation (VSG) were optimized and subsequently applied to biological sample analysis. The first one employs post-column VSG after HPLC separation of Hg species (Hg2+, MeHg+, EtHg+ and PhHg+) prior to their ICP-MS detection (HPLC-VSG-ICP-MS). The optimized post-column VSG step enhances sensitivity 30–40 times and improves limits of detection (LOD) by a factor of five in comparison with the setup without VSG step (HPLC-ICP-MS). LODs between 3 and 6 ng L−1 have been reached by HPLC-VCG-ICP-MS while those reached by HPLC-ICP-MS ranged significantly higher (15–26 ng L−1). Additionally, the VSG step reduces significantly the effect of organic mobile phase on ICP plasma during gradient elution required for PhHg+ determination. Moreover, a simple and short (7 min) two-stage extraction procedure was proposed for simultaneous determination of Hg2+, MeHg+ and EtHg+ in human blood. Acceptable extraction efficiency of Hg species without their inter-conversions was confirmed by Hg speciation analysis in human blood certified reference materials (Seronorm Trace Elements Whole Blood L-1 and L-2) resulting in recoveries better than 90% (Hg2+, MeHg+) and 80% for EtHg+, respectively. The second approach to Hg speciation analysis is based on selective extraction of MeHg+ from hair samples with 2 mol L−1 HCl. Extraction selectivity was verified by HPLC-ICP-MS employing the IAEA-086 certified reference material of human hair. Three spectrometric detectors were compared for subsequent Hg determination in the extracts from hair including single purpose mercury analyzer AMA-254, VSG-AAS and ICP-MS resulting in MeHg+ recovery of 100 ± 10%.

A simple dilute-and-shoot approach using UV photochemical vapor generation for the determination of iodine in alcoholic beverages by ICP-MS

A novel method using photochemical vapour generation (PVG) for the determination of iodine in alcoholic beverages by inductively coupled plasma mass spectrometry (ICP-MS) is presented. The procedure consisted in simply diluting 1.0 mL of an alcoholic beverage (cachaça, vodka, whisky, brandy and gin were analyzed) to a final volume of 15 mL with deionized water prior to introduction in the PVG reactor for the generation of volatile iodine species. The native ethanol content in the samples (approximately 40 % v/v, before dilution) was proven sufficient to produce radicals upon UV irradiation, which ultimately resulted in the release of volatile iodine compounds to the gas phase. The process was systematically evaluated to reach the optimum operating conditions of 1.0 L min-1 Ar as the carrier gas, 1400 W ICP RF power, sample flow rate of 8.08 mL min-1 and 49 s of sample solution exposition to UV photons in the PVG reactor. Two distinct gas-liquid separators (GLS) with internal volumes of 3.1 and 6.5 mL were evaluated. The GLS with an internal volume of 6.5 mL was selected, as it resulted in higher sensitivity for the analyte. Matrix effects required standard addition calibration to be employed to determine the iodine concentrations, which ranged from ca. 21 to 386 μg L-1. Detection and quantification limits were determined as 0.1 and 0.3 μg L-1, respectively. The trueness was verified by comparing the results with those obtained by ICP-MS with pneumatic nebulization, following sample digestion in closed vessels. No significant statistical difference was observed when a paired t-test was applied and the sensitivity achieved from analyte introduction using PVG was 64 % higher when compared to the use of a pneumatic nebulizer. The samples were also spiked with known amounts of the analyte and recoveries ranged from 95 to 105 %, with relative standard deviations better than 9 %.

Mercury volatile species generation from HCl and TRIS buffer media: Quantification of generation efficiency and characterization of severe changes in speciation information due to de-alkylation

Severe changes in speciation information were observed during volatile species generation (VSG) due to de-alkylation of generated Hg species as proven by cryogenic trapping with inductively coupled plasma mass spectrometric detection (CT-ICP-MS). Methyl mercury hydride is de-methylated to Hg0 by 45% and 6%, respectively, in HCl and TRIS buffer media. Ethylmercury hydride is de-ethylated to Hg0 by 71% and 28%, respectively in HCl and TRIS buffer media. Only Hg0 as a volatile product was observed when generating from phenylmercury regardless of the reaction medium employed. These findings limit significantly the application of VSG to Hg speciation analysis, especially the possibility of generation of alkyl-substituted mercury hydrides for cryogenic trapping/separation or gas chromatography. On the contrary, post-column VSG of Hg species prior to spectrometric detection can be employed to enhance sensitivity without any negative effects on accuracy and precision of the results.

UV photochemical vapor generation of Cd from a formic acid based medium: optimization, efficiency and interferences

UV-photochemical generation of cadmium volatile species was carried out from formic acid medium containing ferrous ions resulting in improved reproducibility.

Transition metal ion Co(II)-assisted photochemical vapor generation of thallium for its sensitive determination by inductively coupled plasma mass spectrometry

Herein, a sensitive method for the determination of trace thallium (Tl) in water samples was established using photochemical vapor generation (PVG) for gaseous sample introduction into an inductively coupled plasma mass spectrometer (ICP-MS) for quantitation. Various transition metal ions were spiked and studied as enhancement reagents to assist the photochemical generation of volatile thallium species in the medium of formic acid. An impressive limit of detection (LOD) of 11 ng L−1 was obtained with 20% formic acid solution containing 5 mg L−1 of cobalt ions, 210 s for UV irradiation and 50 mL min−1 carrier gas flow rate. The accuracy and reliability of the present method was validated by analysis of a water certified reference material, BWB2198-2016, as well as two types of real water samples (tap water and bottled drinking water), with spike recoveries between 102% and 109% achieved.

In-situ generation of Ag, Cd, Hg, In, Pb, Tl and Zn volatile species by flowing liquid anode atmospheric pressure glow discharge operated in gaseous jet mode – Evaluation of excitation processes and analytical performance

The use of flowing liquid anode atmospheric pressure glow discharge (FLA-APGD) operated with the aid of a gaseous jet as an efficient and novel excitation source for optical emission spectrometry (OES) was evaluated in details. Although about 50 elements have been tested by introducing respective standard solutions into a discharge system, only emission lines of Ag, Cd, Hg, In, Pb, Tl and Zn have been identified. In this arrangement, the surface of solution was bombarded by electrons resulting in generation of volatile species of mentioned elements. After penetrating the plasma, they were excited and extraordinary atomic emission was observed for these elements. It was found that the use of the Ar or He jet provided beneficial excitation conditions, while reduction of the discharge gap led to suppression of the intensity of interfering diatomic molecular bands like NO, OH and N2. Under optimal operating conditions of the discharge system, detection limits (DLs) assessed for Ag, Cd, Hg, In, Pb, Tl and Zn were respectively 0.001, 0.006, 0.16, 0.093, 0.076, 0.007 and 0.018 µg L−1, and they were on average by 10-times better as referred to earlier FLA-APGD constructions operated without the gaseous jet. In addition, the discharge was characterized by greater stability and precision of measurements (< 2%). Dynamic ranges of calibration curves covered between 3.5 (Cd, In, Zn) and over 5 orders of magnitude (Ag, Tl). The biggest weakness of the developed system turned out to be high susceptibility to matrix interferences. It was found that presence of foreign ions (at concentrations of 1–10 mg L−1) suppressed emission from studied elements on average by 20–60%. To clarify the reason for extremely high sensitivity of emission lines of Ag, Cd, Hg In, Pb, Tl and Zn, efficiency of transport of these elements from the liquid phase to the plasma was determined. It was established that from 5% to 70% of analytes presented in sample solutions were released, whereas evaporation of water was merely 5–15%. Since the FLA-APGD plasma was enriched with analytes atoms, it was concluded that such processes like electrospray formation or solution evaporation do not make a major contribution to transport of analytes from the liquid phase to the discharge, and that it was mainly due to plasma-induced volatile species generation processes.

Electrochemical generation of palladium volatile species enhanced with Sn(ii): application for detection of Pd(ii) by pyrolytic graphite-coated furnace atomic absorption spectrometry

Electrochemical generation of palladium volatile species is performed using the tungsten-inert gas welding electrode enhanced with Sn(ii).

Increasing the sensitivity of electrochemical generation of volatile Te species

Vapor generation is a very sensitive sample introduction technique for the determination of hydride forming elements by atomic spectrometry. However, the drawback of Te determination using vapor generation methods lies in the low stability of the volatilized Te species. We report a sensitive method for the determination of Te(IV) based on electrochemical vapor generation and atomic fluorescence spectrometry. Transport losses were reduced and sensitivity of the method was improved by cooling the gas-liquid separator and by using a mix of Ar and H2 as the stripping and carrier gas. The limit of detection, repeatability and generation efficiency are 0.14 ng mL−1, 2.1% and 79%, respectively.

Comparison of interference in chemical, electrochemical and UV-photochemical generation methods of volatile Se species

We present a comparison of interference in three methods of generation of volatile Se species to compare their performance with regard to matrix effects.

Diethyldithiocarbamate enhanced chemical generation of volatile palladium species, their characterization by AAS, ICP-MS, TEM and DART-MS and proposed mechanism of action

Comprehensive investigation of chemical generation of volatile species (VSG) of palladium for detection by analytical atomic and mass spectrometry and, specifically, the mechanistic aspects of their formation and tentative identification are presented. VSG was achieved in a flow injection mode using a generator that permitted rapid mixing of acidified sample with NaBH4 reductant. Atomization in a diffusion flame with detection by atomic absorption spectrometry was exclusively used for optimization of generation conditions while inductively coupled plasma mass spectrometry was utilized to investigate overall system efficiency and analytical metrics of the VSG system for potential ultratrace analysis. Sodium diethyldithiocarbamate (DDTC) served as a crucial reaction modifier, enhancing overall system efficiency 9-fold. Combinations of modifiers, Triton X-100 and Antifoam B surfactants provided a synergistic effect to yield a further 2-fold enhancement of VSG. The overall system efficiency was in the range 16–22%, with higher efficiencies correlating with higher Pd concentrations. The contribution of co-generated aerosol to the overall system efficiency, determined by means of concurrent measurement of added Cs, was negligible – less than 0.1%. The nature of the volatile species was investigated using several approaches, but principally by transmission electron microscopy (TEM) after their collection on a grid, and by direct analysis in real time (DART) using high resolution orbitrap mass spectrometry. These experiments suggest a parallel but dual-route mechanism of VSG of Pd, one attributed to generation of a volatile DDTC chelate of Pd and a second to nanoparticle formation.

Flow injection determination of Se in dietary supplements using TiO2 mediated ultraviolet-photochemical volatile species generation

This paper proposes a method for determination of selenium content in samples of dietary supplements using TiO2 mediated UV-photochemical vapor generation with quartz furnace atomic spectrometric detection. The flow-injection method was optimized for determination of selenium in the form of selenite or selenate ions. The limits of detection of the proposed method are 0.89ngmL−1 and 0.68ngmL−1 for selenite and selenate, respectively. Extraction in neutral medium was used for the leaching of selenate and NaOH solution was used for the leaching of selenite. The methods accuracy was verified against the declared amounts of Se in five different samples of over-the-counter dietary supplements and on NIST SRM 3280. The method was also compared to results achieved with determination by electrothermal atomization atomic absorption spectrometry following microwave decomposition. The recovery of selenium during sample preparation was tested by spiking the tablets prior to extraction and estimated to be approximately 100%. An interference study has been carried out to estimate the effect of concomitant elements on the methods accuracy.

Large-eddy Simulation of Pilot-assisted Pulverized-coal Combustion in a Weakly Turbulent Jet

Large-eddy simulation has been performed to investigate pilot-assisted pulverized-coal combustion in a weakly turbulent air jet. An advanced pyrolysis model, the chemical percolation devolatilization (CPD) model, has been incorporated into the LES framework to predict the local, instantaneous pyrolysis kinetics of coal particles during the simulation. Prediction on volatile species generation is thus improved, which provides an important initial condition for gas-phase volatile and solid-phase char combustion. For gas-phase combustion, the partially stirred reactor (PaSR) model is employed to model the combustion of volatile species, taking into account subgrid turbulence-chemistry interactions. For heterogeneous solid-phase char combustion, both the intrinsic chemical reaction on the internal surface of a char particle and the diffusion of gaseous oxidant through the film layer around the particle have been incorporated by using a kinetic/diffusion surface reaction model. The LES results show overall good agreements with experimental data. Sensitivity analysis has been performed to better understand the impact of parameter uncertainties on the LES results.

Chemical generation of volatile species of copper – Optimization, efficiency and investigation of volatile species nature

This work is a comprehensive study on chemical generation of volatile species (VSG) of copper for analytical atomic spectrometry. VSG was carried out in a flow injection mode in a special arrangement of the generator. Atomization in a diffusion flame atomizer (DF) with atomic absorption spectrometry detection was mostly used for VSG optimization. Inductively coupled plasma mass spectrometry (ICP-MS) was utilized to investigate generation efficiencies and feasibility of VSG system for ultratrace analysis. Concentration of individual reagents, namely of nitric acid, sodium tetrahydroborate and various reaction modifiers, was optimized with respect to generation efficiency. Triton X-100 and Antifoam B were chosen as the best combination of the modifiers owing to sixfold increase in sensitivity, decrease of tailing of measured signals and long-term repeatability. The addition of 500 μg L−1 of Ag was found crucial to maintain identical generation efficiency at low concentrations of Cu. This phenomenon was ascribed to the change in the size of generated species. The release and generation efficiency were accurately determined as 56–58 and 31–32%, respectively. The contribution of co-generated aerosol to release and generation efficiency measured by means of Cs and Ba was found negligible, only 0.40 and 0.13%, respectively, which underlines highly efficient VSG of Cu. The nature of volatile species was investigated by various approaches. The results cannot provide the decisive evidence. However, experiments with the DF, ICP-MS and transmission electron microscopy (TEM) indicate that the generated species are not volatile in the true sense but that they are strongly associated with fine aerosol co-generated during VSG. Cu clusters or nanoparticles of very small size (< 10 nm) are presumed but the formation of metastable copper hydride cannot be conclusively excluded.

Development of on-line UV-induced volatile species generation for selenium speciation [Se(iv) and SeCN−] by ion chromatography-inductively coupled plasma mass spectrometry in petroleum refinery wastewater

UV-irradiation of selenocyanate in the presence of formic and nitric acids gives improved vapor generation at room temperature, over hydride generation. Using this, a rapid and sensitive method has been developed for selenium speciation.

On-line UV photochemical generation of volatile copper species and its analytical application

Volatile Cu species were on-line generated by photochemical reduction in a formic acid medium utilizing a unique flow-through photochemical reactor. Digests of biological samples in 18% formic were introduced to the photochemical vapor generation (PVG) reactor under conditions wherein copper-containing species were initially retained on the reactor wall following a purge of the line with air and desorbed in the presence of a plug of 60% formic acid to yield volatile species which were transported to a gas–liquid separator and introduced to multi-collector inductively coupled plasma spectrometry (MC-ICPMS). Sensitivity of the proposed method could be further improved if a sample solution is repeatedly introduced using several cycles comprising loading and drying steps. However, the unstable volatile Cu species generated by PVG together with the early release of Cu during drying step resulted in a poor measurement precision of near 30% (n=4, RSD) and a non-linear correlation between the signal intensity and the Cu2+ concentration. Despite the above shortcomings, the accurate and precise determination of Cu concentrations in biological samples was achieved by applying isotope dilution (ID) calibration. A method detection limit of 8ngg−1 normalized to a nominal test mass of 0.25g of sample was obtained based on ID quantification. Method validation was demonstrated by analysis of three biological certified reference materials of TORT-3, SRM 1566b and DOLT-5 with satisfying results. Concentrations of 490.8±0.6, 71.88±0.06 and 34.95±0.04μgg−1 (1SD, n=4) with precisions of 0.12, 0.08 and 0.13% RSD for Cu were obtained in TORT-3, SRM 1566b and DOLT-5, respectively, in good agreement with certified values.