Determination of refractory elements in atmospheric particulates using slurry sampling electrothermal vaporization inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry with polyvinylidene fluoride as chemical modifier

Electrothermal vaporization (ETV) inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) with polyvinylidene fluoride (PVDF) as chemical modifier are critically compared for the determination of refractory elements in coal fly ash and airborne particulates. The atmospheric particulates that collected on a PVDF filter were introduced into the graphite furnace in the form of a slurry by dissolving the filter in dimethylformamide, and the dissolved filter PVDF, along with additional added PVDF powder, was used as a chemical modifier for subsequent ETV-ICP-OES and ETV-ICP-MS determination. The vaporization behaviors of analytes (Ti, Zr, V, Mo, Cr, La) in ETV-ICP-OES/MS were studied in detail, and the optimal ETV operating parameters were obtained. Under the optimized operating conditions, the detection limits of target elements were 0.08-2.7 ng m(-3) for ETV-ICP-OES and 0.5-50 pg m(-3) for ETV-ICP-MS, respectively, with analytical precisions of 3.5-7.3% for ETV-ICP-OES and 3.9-9.6% for ETV-ICP-MS, respectively. The tolerable amounts of matrix elements for ETV-ICP-OES are higher than for ETV-ICP-MS. Both ETV-ICP-OES and ETV-ICP-MS were used to directly determine the trace refractory elements in coal fly ash and airborne particulates and the analytical results are comparable.     

Electrothermal vaporization-inductively coupled plasma-mass spectrometry: A versatile tool for tackling challenging samples: A critical review

In this review, the literature on the subject of electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS) published during the last decade is reviewed with a double purpose: an evaluation of the possibilities of this technique for dealing with very challenging analytical applications on the one hand, and the establishment of a reference guide for method development in ETV-ICP-MS on the other. First, a brief introduction, pointing out the milestones in the development of the technique will provide the reader with a better understanding of the present situation of ETV-ICP-MS and its future perspective. After a section on the basic processes occurring in the furnace and during analyte transport, a guide for method development for challenging analytical applications is proposed, based on the existing literature. Next, the latest contributions in the main application areas of the field are reviewed, with special attention to the most challenging ones: i.e. speciation, “thermal” resolution, enabling complex matrixes to be analyzed and spectral overlap to be avoided, and the direct analysis of slurries and solid samples. Finally, the advantages obtained by coupling an ETV unit to newer types of ICP-MS instrumentation, equipped with collision/reaction cells, time-of-flight (TOF) or sector field (SF) spectrometers, are also discussed.     

Electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of trace amount of lanthanides and yttrium in soil with polytetrafluroethylene emulsion as a chemical modifier

A method of electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of trace lanthanides and yttrium in soil samples with a polytetrafluorethylene (PTFE) emulsion as chemical modifier to promote the vaporization of the analytes from the graphite furnace was developed in this paper. The analytical characteristics, spectral interference and matrix effect of the analytical method were evaluated and critically compared with those of pneumatic nebulization inductively coupled plasma mass spectrometry (PN-ICP-MS). Under the optimized operation conditions, the relative detection limits of lanthanides (La-Lu) and yttrium for ETV-ICP-MS and PN-ICP-MS were 0.4-20 ng l⁻¹ and 1.0-21 ng l⁻¹, respectively, the absolute detection limits for ETV-ICP-MS were 4-200 fg, which were improved by 1-2 orders of magnitude compared with PN-ICP-MS. While the analytical precision of ETV-ICP-MS is worse than that of PN-ICP-MS, with the R.S.D.s (%) of 4.1-10% for the former and 2.9-7.8% for the latter. Regarding to the matrix effect, both conventional method and stepwise dilution method were employed to observe the effect of matrix and the very similar results were obtained. It was found that the highest tolerance concentration of the matrix is 1000 mg l⁻¹ and 800 mg l⁻¹ for ETV-ICP-MS and PN-ICP-MS, respectively. To assess the accuracy, the proposed method was applied to the determination of trace lanthanides and yttrium in three different soil standard reference materials and one soil sample, and the determined values are in good agreement with the certified values or reference values.     

Mechanism of vaporization of yttrium and rare earth elements in electrothermal vaporization inductively coupled plasma mass spectrometry

The mechanism of vaporization of yttrium and the rare earth elements (REEs) has been studied using graphite furnace atomic absorption spectrometry (GFAAS) and inductively-coupled plasma mass spectrometry (ICP-MS). The appearance temperatures for Y and the REEs obtained by GFAAS were generally identical to the appearance temperatures obtained using ETV-ICP-MS. At lower temperatures, Y and the REEs are predominantly vaporized in atomic form or as oxides, while at temperatures above 2500°C, the elements are vaporized as oxides and/or carbides. This accounts for the very high sensitivity of ETV-ICP-MS compared to GFAAS for the determination of these elements. Absolute limits of detection for Y and all of the REEs using ETV-ICP-MS ranged from 0.002 pg for Tm to 0.2 pg for Ce. The use of freon as a chemical modifier was effective in controlling analyte carbide formation and reducing memory effects.     

Determination of volatile elements in biological materials by isotopic dilution ETV-ICP-MS after dissolution with tetramethylammonium hydroxide or acid digestion

Isotopic dilution for the determination of Ag, Cd, Hg, Pb and Tl in biological materials by ETV-ICP-MS is proposed. The sample was simply dissolved with tetramethylammonium hydroxide (TMAH) or acid digested in a microwave furnace, with an on line matrix separation. When the dissolution was employed, Ir was used as a chemical modifier for Hg and Pb and Pd was used for Cd and Tl. No modifier was used for Ag. The pyrolysis temperatures were taken from pyrolysis temperature curves. The on line preconcentration was performed in a flow injection system with solenoid valves and was based on the analyte complexation with ammonium diethyldithiophosphate and sorption of the complexes on C(18) bonded to silica gel in a minicolumn. For the digested sample submitted to the analyte preconcentration procedure, a modifier, Ir, was only used for Hg. For the other analytes, since a low pyrolysis temperature, 300 degrees C, was employed, no modifier was added. The isotopic dilution calibration was applied to two certified materials, bovine liver and dog fish muscle, dissolved with TMAH or acid digested, and to another two certified materials, corn bran and rice flour, acid digested and submitted to analyte preconcentration. The obtained concentration values agree with the certified ones, showing that this calibration procedure leads to accurate results in the determination of low concentrations of volatile elements. Due to simplicity, the dissolution with TMAH is very attractive.     

Solvent bar microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic arsenic in water samples

A new method of solvent bar microextraction (SBME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the speciation of As(III) and As(V) in water samples was developed. The method is based on the chelation of As(III) and ammonium pyrrolidine dithiocarbamate (APDC) under the selected conditions, and the As(III)-PDC complex could be extracted into the organic phase, while As(V) remained in aqueous solution. The post-extraction organic phase was directly injected into ETV-ICP-MS for determination of As(III) with the use of iridium as permanent chemical modifier. As(V) was reduced to As(III) by L-cysteine and was then subjected to SBME prior to total As determination. The assay of As(V) was based on subtracting As(III) from total As. The factors affecting on the SBME, such as organic solvent, sample pH, chelating reagent concentration, stirring rate and extraction time, and chemical modification of iridium in ETV-ICP-MS have been studied. Under the optimized conditions, the enrichment factor of 220-fold could be achieved in 15 min extraction, the limit of detection (LOD) for As(III) was 0.32 pg mL^− 1, and the relative standard deviation (RSD) was 8.8% (0.1 ng mL^− 1, n = 9). Compared with hollow fiber liquid phase microextraction (HF-LPME), SBME has a higher enrichment factor and faster extraction kinetics. In order to validate the accuracy of the method, a Certified Reference Material of GSBZ50004-88 (No. 200420) water sample was analyzed and the results obtained were in good agreement with the certified values. The developed method was also applied to the speciation of inorganic As in environmental waters with satisfactory results.     

Vaporization and atomization of the platinum group elements in the graphite furnace investigated by electrothermal vaporization-inductively coupled plasma-mass spectrometry

The mechanisms by which the platinum group elements (PGEs) are vaporized in the graphite furnace have been investigated using electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS). The results suggest that live of these elements (Ru, Rh, Pd, Ir and Pt) are reduced to their metallic state in the graphite furnace and then vaporized by direct sublimation of the metal. For Os, the vaporization mechanism is different. In the presence of HNO₃, two distinct vaporization processes are observed. Volatile oxides of Os are released at low temperatures, but some of this oxide is reduced to relatively involatile Os metal which is then vaporized when the temperature is increased above 2000°C. The addition of TeCl₂ chemical modifier was found to have minimal effect on the vaporization mechanism and sensitivity for determination for five of the PGEs. For Os, however, the analytical sensitivity and limit of detection was improved when Te modifier was used in conjunction with a lower vaporization temperature of 1400°C. Optimum conditions for the determination of the PGEs by ETV-ICP-MS are reported, along with their absolute limits of detection; these range from 0.015 pg for Ir to 0.25 pg for Os.     

Derivative techniques in activation analysis

Derivative activation analysis is a technique in which the element or chemical entity to be determined is either replaced or complexed in a preirradiation chemical procedure with another element for which neutron activation analysis has an intrinsically higher sensitivity. Although the technique has many potential applications, the literature of the field is very limited. Examples of recent applications in our laboratory include: determination of P in natural waters, biological reference standards, brain tissue, rocks and coal; determination of Ni in a stony meteorite; determination of T1 in solutions; and speciation of oxygen (e.g., hydroxyl and carbonyl moieties) in coal via 14 MeV neutron activation.     

Coupling of inductively coupled plasma mass spectrometry (ICP-MS) with electrothermal vaporisation (ETV)

An inductively coupled plasma mass spectrometer (ICP-MS) was coupled on-line with an electrothermal vaporisation (ETV). The influence of aerosol gas flow as well as the variation of the coupling distance on the signal intensity was investigated and compared with the results of hydraulic high-pressure nebulizer (HHPN) measurements. Furthermore, temperature programs known from graphite furnace atomic absorption spectroscopy (GFAAS) were applied to ETV-ICP-MS. After optimisation of temperature programs, calibration series based on mono-element and multi-element solutions were carried out. The dynamic range and the detection limits of the method were determined. By use of internal standardisation it was tried to improve linearity and reproducibility. According to the results, internal standardisation does not have a great impact on linearity, but may be a useful tool to improve reproducibility. However, the latter is still low.     

Recent trends in nanomaterial-based microanalytical systems for the speciation of trace elements: A critical review

Trace element speciation in biomedical and environmental science has gained increasing attention over the past decade as researchers have begun to realize its importance in toxicological studies. Several nanomaterials, including titanium dioxide nanoparticles (nano-TiO₂), carbon nanotubes (CNTs), and magnetic nanoparticles (MNPs), have been used as sorbents to separate and preconcentrate trace element species prior to detection through mass spectrometry or optical spectroscopy. Recently, these nanomaterial-based speciation techniques have been integrated with microfluidics to minimize sample and reagent consumption and simplify analyses. This review provides a critical look into the present state and recent applications of nanomaterial-based microanalytical systems in the speciation of trace elements. The adsorption and preconcentration efficiencies, sample volume requirements, and detection limits of these nanomaterial-based speciation techniques are detailed, and their applications in environmental and biological analyses are discussed. Current perspectives and future trends into the increasing use of nanomaterial-based microfluidic techniques for trace element speciation are highlighted.     

The role of element speciation in environmental and occupational medicine

In order to evaluate the interaction with the environment or to assess absorption, binding mechanisms, reactivity and excretion of elements in humans, element speciation can provide more information than the analysis of element as a whole. Some examples that confirm the importance of speciation depend on the choice of the most appropriate indicator or representative matrix. The determination of As(III), As(V), monomethylarsonic and dimethylarsinic acids can be used to evaluate occupational exposure to As. Exposure to inorganic Hg should be measured by its content in urine, whereas in the case of exposure to alkyl Hg, blood and hair should be considered. Speciation may also be useful in studying element toxicokinetics, since it is well known that hexavalent Cr is taken up more than the trivalent form, and that species of the same metal are differently partitioned in blood. Pentavalent forms of As are absorbed more than trivalent forms, and the organic species of elements are excreted faster than inorganic species. In addition, speciation can play an important role in assessing element toxicodynamics. The toxicity of the three oxidation states of Hg differs considerably; for As a decreasing toxicity from arsenite to dimethylarsinic acid is proposed; for organotin compounds, higher toxicity for ethyl groups than for phenyl groups is reported. However, speciation in biological media is difficult when applied to other elements because of the lack of information on the existence and significance of species whose determination could be valuable. Furthermore, there may be no analytical methods that allow an accurate measurement of the species. The feasibility of speciation in occupational and environmental medicine depends mainly on our capability to solve some problems related to the identification and determination of species and on the demonstration that species measurement represents a clear improvement compared to total element determination.     

Determination of erbium and neodymium dopants in bismuth tellurite optical crystals by graphite furnace atomic spectrometry techniques

Application of concentrated HCl as a solvent and triammonium citrate (TAC) as a chemical modifier is advantageous for the determination of Er and Nd dopants in bismuth tellurite (Bi₂TeO₅) single crystals by graphite furnace atomic absorption spectrometry (GFAAS). The use of mini-flow of the internal gas, instead of gas stop, results in better precision at a price of a relatively small decrease in sensitivity. By evaluating integrated absorbance (A_int) signals for the GFAAS measurements (in the presence of matrix and TAC additive), characteristic mass values of 42 and 320 pg, and a limit of detection (LOD) of 4.9 and 131 μg l⁻¹ are found for Er and Nd, respectively. These LOD data correspond to 0.78 μg g⁻¹ Er and 21 μg g⁻¹ Nd in the solid samples. The calibration curves are linear up to 0.33 and 2.9 mg l⁻¹ concentrations in the solutions of Er and Nd, respectively. The ratio of the A_int signals of Er and Nd under gas stop and mini-flow were found near constant (1.34) with and without the matrix plus TAC. According to the vaporisation studies by graphite furnace electrothermal vaporisation inductively coupled plasma atomic emission spectrometry (GF-ETV-ICP-AES), the vaporisation of Bi and Te components of the solid Bi₂TeO₅ can be completed at 1200°C in a relatively short time, ensuring a preconcentration for the Er and Nd dopants, which do not vaporise below 2200°C in an argon atmosphere. On the other hand, fast vaporisation can be performed for the analytes at 2200°C with the use of CCl₄ vapour (∼0.5 v/v%) in the internal furnace gas (Ar). It was estimated for the Er analyte that by applying 10 mg of solid sample in the GF-ETV device (dispensed into a graphite sample boat) and using a two-step heating procedure (prevaporisation of the matrix in argon and vaporisation of the analyte in a chlorinating atmosphere), the lower limit of the quantitative determination with the ICP-AES method would be approximately one order of magnitude better than attainable with the GFAAS method based on dissolution.     

Separate vaporisation of boric acid and inorganic boron from tungsten sample cuvette-tungsten boat furnace followed by the detection of boron species by inductively coupled plasma mass spectrometry and atomic emission spectrometry (ICP-MS and ICP-AES)

Utilising extremely different vaporisation properties of boron compounds, the determination procedures of volatile boric acid and total boron using tungsten boat furnace (TBF) ICP-MS and TBF-ICP-AES have been investigated. For the determination of volatile boric acid by TBF-ICP-MS, tetramethylammonium hydroxide (TMAH, Me₄NOH) was used as a chemical modifier to retain it during drying and ashing stages. As for the total boron, not only non-volatile inorganic boron such as boron nitride (BN), boron carbide (B₄C), etc. but also boric acid (B(OH)₃) was decomposed by a furnace-fusion digestion with NaOH to produce sodium salt of boron, a suitable species for the electrothermal vaporisation (ETV) procedure. The proposed method was applied to the analysis of various standard reference materials. The analytical results for various biological and steel samples are described.     

Photochemical vapor generation of selenium: Mechanisms and applications

Selenium was the first reported element that could be converted into its volatile compounds via photochemical vapor generation (photo-CVG) process before its atomic spectrometric detection. Photo-CVG is a newly emerging vapor generation technique, offering its inherent advantages of matrix interferences eliminated and high vapor efficiency etc., photo-CVG has been combined with various methods for selenium determination and mechanism exploration. Herein, we summarize the development of selenium in photo-CVG from the first report in 2003, the mechanisms of selenium with or without TiO₂ were discussed and its applications for selenium determination, speciation analysis and prereduction were summarized.     

Determination of phosphorus and arsenic in trichlorosilane by electrothermal vaporization-inductively coupled plasma mass spectrometry with prior concentration by cuprous chloride

A method for the determination of trace impurities of phosphorus and arsenic in trichlorosilane with prior separation followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) has been developed. The preconcentration of the analytes from the sample matrix was made by adding cuprous chloride to a 10 mL trichlorosilane sample for the formation of non-volatile compounds with the elements of interest. Upon evaporation of trichlorosilane, the analytes retained in the residue were then determined in the presence of copper as modifier by ETV-ICP-MS. The dual role of cuprous chloride both in the preconcentration and instrumental determination was investigated and discussed. By meticulous control of experimental conditions, limits of detection for these two elements as low as sub-ng/g can be achieved. The method was applied to the determination of phosphorus and arsenic in a commercially available trichlorosilane sample.     

Determination of phosphorus and arsenic in trichlorosilane by electrothermal vaporization-inductively coupled plasma mass spectrometry with prior concentration by cuprous chloride

A method for the determination of trace impurities of phosphorus and arsenic in trichlorosilane with prior separation followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) has been developed. The preconcentration of the analytes from the sample matrix was made by adding cuprous chloride to a 10 mL trichlorosilane sample for the formation of non-volatile compounds with the elements of interest. Upon evaporation of trichlorosilane, the analytes retained in the residue were then determined in the presence of copper as modifier by ETV-ICP-MS. The dual role of cuprous chloride both in the preconcentration and instrumental determination was investigated and discussed. By meticulous control of experimental conditions, limits of detection for these two elements as low as sub-ng/g can be achieved. The method was applied to the determination of phosphorus and arsenic in a commercially available trichlorosilane sample.     

Solid phase extraction for the speciation and preconcentration of inorganic selenium in water samples: A review

Selenium is an essential element for the normal cellular function of living organisms. However, selenium is toxic at concentrations of only three to five times higher than the essential concentration. The inorganic forms (mainly selenite and selenate) present in environmental water generally exhibit higher toxicity (up to 40 times) than organic forms. Therefore, the determination of low levels of different inorganic selenium species in water is an analytical challenge. Solid-phase extraction has been used as a separation and/or preconcentration technique prior to the determination of selenium species due to the need for accurate measurements for Se species in water at extremely low levels. The present paper provides a critical review of the published methods for inorganic selenium speciation in water samples using solid phase extraction as a preconcentration procedure. On the basis of more than 75 references, the different speciation strategies used for this task have been highlighted and classified. The solid-phase extraction sorbents and the performance and analytical characteristics of the developed methods for Se speciation are also discussed.     

Evaluation of pyrolysis curves for volatile elements in aqueous standards and carbon-containing matrices in electrothermal vaporization inductively coupled plasma mass spectrometry

Pyrolysis curves in electrothermal atomic absorption spectrometry (ET AAS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) have been compared for As, Se and Pb in lobster hepatopancreas certified reference material using Pd/Mg as the modifier. The ET AAS pyrolysis curves confirm that the analytes are not lost from the graphite furnace up to a pyrolysis temperature of 800 °C. Nevertheless, a downward slope of the pyrolysis curve was observed for these elements in the biological material using ETV-ICP-MS. This could be related to a gain of sensitivity at low pyrolysis temperatures due to the matrix, which can act as carrier and/or promote changes in the plasma ionization equilibrium. Experiments with the addition of ascorbic acid to the aqueous standards confirmed that the higher intensities obtained in ETV-ICP-MS are related to the presence of organic compounds in the slurry. Pyrolysis curves for As, Se and Pb in coal and coal fly ash were also investigated using the same Pd/Mg modifier. Carbon intensities were measured in all samples using different pyrolysis temperatures. It was observed that pyrolysis curves for the three analytes in all slurry samples were similar to the corresponding graphs that show the carbon intensity for the same slurries for pyrolysis temperatures from 200 °C up to 1000 °C.     

Optimization of ETV-ICP-MS conditions for the determination of multi-elements in semiconductor grade acids

The performance of an electro thermal vaporization (ETV) unit as a sample introduction device for an inductively coupled plasma mass spectrometer (quadrupole-ICP-MS) was evaluated. The technique was found to have several advantages over the conventional nebulization method. Some features of ETV-ICP-MS for single element determination have been investigated. Attempts were made to optimize the experimental parameters such as vaporization temperature, vaporization interval and carrier gas flow rate. The study highlights on the determination of Cr, Mn, Al and Na. A compromise condition for multi-element determination was suggested and tested from single-element optimum conditions obtained. 25 L solution was used for the analysis. Results obtained for the analysis of conc. HCl samples are also reported.     

毛细管电泳在形态分析中的应用

对近年来毛细管电泳（ＣＥ）与紫外检测器（ＵＶｄｅｔｅｃｔｏｒ）和ＣＥ与感应耦合等离子体质谱（ＩＣＰ－ＭＳ）联用在形态分析中的应用及其存在的一些问题加以评述。