ISSN:0267-9477    

DOI:10.1039/b205610k

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

IntroductionInductively coupled plasma mass spectrometry (ICP-MS) is one of the most powerful techniques for trace and ultratrace elemental analysis.1Mass selectivity is commonly achieved by quadrupole-based mass analyzers (ICP-QMS) or double-focusing (DF) sector-field instruments (ICP-DFMS). Except for multicollector (MC)-ICP-MS, the cited mass analyzers are sequential scanning devices.Several advantages are realized in the simultaneous detection of ions, especially for isotopic ratio analyses. The Mattauch-Herzog mass spectrograph arrangement offers simultaneous mass detection,2–7but currently suffers from poorer abundance sensitivity and resolution in comparison with ICP-QMS and ICP-DFMS instrumentation.2A twin-quadrupole ICP-MS provides improved isotopic ratio measurement8–12due to the cancellation of flicker noise from the nebulizer and ICP, but ion signals are attenuated by approximately a factor of 100 compared to single-quadrupole instruments.8A MC-ICP-MS instrument can provide isotope ratio precisions as low as 0.002% and allow for simultaneous monitoring of up to nine isotopes,13–15but the current instrumentation islarge and expensive, and absolute detection efficiencies are inferior to thermal ionization mass spectrometry. Ion traps16–19and Fourier transform ion cyclotron resonance mass analyzers20–22reduce, eliminate, or resolve spectral interferences but their limited ion-storage capabilities and space charge effects hinder the achievable performance when coupled with plasma ion sources.Time-of-flight (TOF) mass spectrometry has been explored for the nearly simultaneous analysis of ion packets in ICP-MS at repetition rates of up to 30,000 Hz.23–30The extracted ions are accelerated to nearly constant kinetic energy into a field-free drift tube where ion flight times, proportional to the square-root of mass, are measured. Because the entire mass spectrum is obtained from each ion packet, analytical performance is largely independent of the number of isotopes monitored, and further, spectral skew is eliminated when analyzing transient signals, such as those encountered with discrete solution introduction, chromatography, laser ablation and electrothermal vaporization sample introduction methods.31The simultaneous extraction of ions is particularly beneficial for isotope ratio measurements of transient samples, because ions of allm/zexperience the same multiplicative noise, thereby correcting for instabilities originating from the ICP source.Recently, an axial ICP-TOFMS instrument was explored using laser ablation32,33and conventional nebulizer-spray chamber arrangements34–40in terms of analytical performance and precision for isotope ratio measurements and speciation analysis.33–41In addition, figures of merit for an ICP-TOFMS based on an orthogonal arrangement were recently reported.42In this present study, we investigate direct liquid sample introduction for ICP-TOFMS for low solution consumption rates (1–100 µL min−1). The absence of the spray chamber coupled with the small dead volume of a direct injection high efficiency nebulizer (DIHEN) provide fast response times, reduced memory effects, no solution waste, and improved chromatographicand capillary electrophoresis separations.43–54In terms of cost, the DIHEN is comparable to most microflow nebulizers equipped with low-volume spray chamber arrangements, but offers the benefits of direct liquid introduction. However, proper care is required in using the DIHEN to prevent solution capillary clogging or melting of the nebulizer tip due to its proximity to the plasma. In this work, we explore the DIHEN-ICP-TOFMS in terms of analytical performance indices under both normal and cool plasma conditions. Further, isotope ratio precision is determined for both steady-state and transient analysis, such as the analysis of microliter volumes of whole human lung fibroblast cells. Based on published literature, this report constitutes the first account of direct liquid introduction into an ICP-TOFMS, documenting improved performance for TOFMS with the DIHEN compared to solution introductionby the traditional nebulizer-spray chamber arrangement.

ISSN:0267-9477    

DOI:10.1039/b200771c

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

IntroductionCigarette smoke is composed of approximately 4000 gas and particulate constituents,1,2and its chemical composition is complex and rich in organic materials. Smoke released from the combustion of tobacco can be classified into mainstream and sidestream smoke. Mainstream smoke is the smoke coming out of the butt end of a cigarette during smoking; smoke coming from the lit end between puffs is defined as sidestream smoke. Trace metals comprise a very low percentage of cigarette smoke and mercury represents a small fraction of the trace metals present. Air deposition and soil uptake are the two most probable sources of mercury in tobacco, and it is estimated that 10% of this mercury content will be transferred to the mainstream smoke during cigarette smoking.3Because of its unique characteristics of low boiling point and high volatility, the majority of mercury is exclusively present in the gas phase of mainstreamcigarette smoke and a negligible amount exists in the particulate phase.4The dominance of mercury in the gas phase has also been found in ambient air5,6and natural gas.7Due to the extremely low concentration of mercury in the mainstream cigarette smoke, a highly sensitive and selective analytical technique is absolutely required in order to avoid smoking large numbers of cigarettes for sample preparation. An efficient and appropriate method for gaseous mercury collection without dilution is also essential. Historically, the whole cigarette smoke is delivered to a liquid impinger trap containing acidic potassium permanganate or iodine monochloride solution to absorb all mercury compounds, followed by vigorous sample digestion and then analysis by cold vapor atomic absorption spectrometry (CVAAS). Dilution is significant such that tens or hundreds of cigarettes need to be smoked in order to collect sufficient amounts of sample for analysis.Several types of sampling apparatus have been designed and applied to collect mercury in ambient air and atmosphere as a consequence of natural and anthropogenic activities. Filtration, inertial impaction, electrostatic precipitation, cryogenic collection, liquid and solid absorption/adsorption and amalgamation are examples of techniques used to collect mercury through physical or chemical processes.8Filtration, impaction, and electrostatic precipitation, normally applied for collection of the particulate phase mercury, are not suitable for the collection of gaseous mercury. However, the gaseous mercury can be selectively trapped if filter media are pretreated or impregnated with chemicals, for example, KI–I2, CdS, Se, or cuprous iodide.8,9Cryogenic collection is infrequently used because the water vapor in the sample matrix must be removed first to avoid clogging of traps. A liquid sorbent containingacidic potassium permanganate or iodine monochloride solution is capable of collecting mercury by chemical oxidation or complexation. However, excessive organic matter in the sample matrix can deplete the chemical reagents prematurely and hence decrease their collection efficiency.4Solid sorbents, including activated carbon, alumina, bauxite, lime, silicate and zeolite, have been applied as denuders to remove mercury compounds from flue gas. Similar to filters with chemical pretreatment, sulfur-impregnated solid absorbers can improve the mercury collection efficiency dramatically.5,10–12Solid sorbents in various forms have been recognized as capable of collecting gaseous mercury efficiently under a variety of conditions; however, their adsorption or absorption property is not selective. Interfering substances can be trapped simultaneously with mercury during sampling. Chlorine, nitrogen dioxide and volatileorganic substances are examples of these interfering species. Furthermore, with solid sorbents, a significant amount of mercury can remain even after long periods of thermal desorption. This memory effect requires acid digestion for complete recovery of mercury. In general, mercury can be effectively collected by using these items of trapping apparatus; subsequent sample preparation, however, is usually tedious and time-consuming.Instrumental neutron activation analysis (INAA) is capable of analyzing solid matrix absorbents without prior digestion, but irradiation sources and laboratory equipment are not easily accessible except in academic research laboratories. It is not practical to use INAA in routine mercury analysis. A pretreated graphite tube, similar to the chemical pretreatment of filter and solid absorbents, has also been applied to trap gaseous mercury directly onto the inner surface of the graphite tube and subsequently analyze it by graphite furnace atomic absorption spectrometry (GFAAS) without the necessity of further sample preparation.13,14Moreover, volatile mercury compounds can be preferentially amalgamated with a few metals such as copper, gold, silver and tin, and then released from the amalgam by thermal desorption for direct measurement. Silver and gold are two common metals used for mercury amalgamation. Silver provides desorptionefficiency equivalent to gold but can only trap elemental mercury and, to some extent, methylmercury. Sulfur compounds poison silver easily, thus reducing the adsorption efficiency after extended use. Gold is capable of collecting a wide range of volatile organic and inorganic mercury compounds, including Hg, HgCl2, (CH3)2Hg, CH3HgCl, (C2H5)2Hg and C2H5HgCl.8Its desorption temperature starts at a temperature of 350 °C, depending on the mercury species. Gold is the most preferred for its high collection and desorption efficiencies resulting in low memory effect, and has been extensively applied to the determination of mercury in ambient air and atmosphere.8,15–18In contrast to solid and liquid adsorbers, most interference species that absorb the same wavelength as mercury canbe separated from mercury prior to analysis. Even lower detection limits at the sub-nanogram level can be achieved through pre-concentration onto the amalgam for a longer period of sampling time. Simplicity without lengthy sample preparation has made gold amalgamation the method of choice for mercury collection in gas sampling.No two gold amalgam traps can be fabricated exactly the same in terms of carrier gas flow restriction and thermal desorption characteristics. Thermal desorption of several gold amalgam traps for introducing mercury to the detector could result in slightly different responses, even though they contain equal amounts of mercury. To avoid the necessity of calibration of each amalgam trap individually, the two-stage gold amalgamation technique uses a single amalgam trap, namely the analytical trap, to re-collect mercury released from the sampling amalgam traps at the first stage of thermal desorption. At the second stage, the mercury analyte is then liberated from the analytical trap and introduced to the detector for analysis. In this manner, only the analytical trap needs to be calibrated and any differences between sampling amalgam traps become irrelevant. Numerous amalgam traps can be utilized to collect gaseous mercury in the sampling field and then transported to the laboratory for lateranalysis. Two-stage gold amalgamation has been successfully applied for the determination of mercury at atmosphere and ambient air.15,16The main challenge in applying the two-stage gold amalgamation technique for mercury analysis in mainstream cigarette smoke is the separation of the complex organic matrix in cigarette smoke from the gaseous mercury before amalgamation. The organic compounds condense or are adsorbed onto the amalgam, hence reducing the surface area available for mercury amalgamation, and can interfere with mercury during detection. In this study, the particulate phase of cigarette smoke was removed by either an electrostatic precipitator or a Cambridge filter, followed by a second Cambridge filter to further adsorb gaseous organic and inorganic components. The gas phase mercury was collected onto a gold–platinum gauze and then analyzed by the two-stage amalgamation CVAAS.

ISSN:0267-9477    

DOI:10.1039/b200715k

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

IntroductionMetallothioneins (MT) are involved in multiple biological processes. Some examples are the homeostasis of essential metals and the detoxication of toxic metals like cadmium. After absorption, Cd is mostly non-specifically bound to albumin before clearance from circulation, primarily by the liver. Once inside the cell, however, Cd induces transcription of the metallothionein gene and subsequently becomes bound tightly to the protein. Cd metallothioneins (Cd-MT) are the subject of a vast literature.1–5Classical techniques for the determination of total MT include metal-saturation assays, based on the competitive displacement and the subsequent determination of the initially MT-bound metal (usually Cd and Zn) by a metal with higher affinity to MT such as Ag,6and immunological assays7among others. Recent studies on the measurements of MT and their isoforms have been reviewed.8,9In most cases, quantification of the metal in the fraction containing the MT have been performed by atomic absorption spectrometry either using flame (FAAS) or electrothermal (ETAAS) systems. Total MT in animal tissues have been determined by ETAAS after saturation with Cd because of its higher affinity for MT.10,11FAAS or ETAAS, combined with liquid chromatography, has also been used for the separation and quantification of MT isoforms aftersaturation with Cd;12–15critical steps in sample preparation, such as MT-extraction from liver, MT saturation with Cd and protein separation are involved. Cadmium bound to metallothioneins has been determined by affinity chromatography with FAAS detection in physiological fluids,16by capillary electrophoresis with UV and ICP-MS detection in mussel hepatopancreas cytosols17and by supercritical fluid extraction also with FAAS detection in rabbit liver,18with a detection limit of 7.7 ng ml−1. The determination of trace cadmium and cadmium metallothioneins in biological materials has been carried out with flow injection (FI) and LC-FAAS; the system was optimised for the detection of Cd (total and bound soluble) in mussels and animal tissues by FI-FAAS or for the determination of MT-Cd (isoforms Iand II) in horse kidney using LC-FAAS, with a thermospray micro-atomizer interface.19An overview of the impact of fullerenes in analytical chemistry in the framework of the general applications of these materials has recently been published.20The analytical potential of C60fullerene as a sorbent material for the preconcentration of various species has seemingly been developed only by the authors' group. FI systems, in which a column of C60was intercalated, coupled to FAAS have been employed for metal preconcentration; C60exhibits the highest preconcentration factor, lowest detection limits and highest selectivity in comparison with conventional sorbent materials.20Thus, ultratrace levels of inorganic Cd were quantitatively sorbed onto a C60fullerene column as neutral chelates, using APDC or 8-hydroxyquinoline as chelating reagents and isobutyl methyl ketone as eluent.21This paper is the first to discuss the analytical potential of C60fullerenes for preconcentration of metal-MT complexes. Indirect quantification of MT based on their cation content offers the advantage of a high sensitivity intrinsic to elemental detection systems. However, in biological materials containing very low MT levels, preconcentration steps are required prior to analysis. A simple FI system in which metal-MT complexes are preconcentrated onto a C60column and then passed to a FAAS instrument for metal determination is described. For this purpose, cadmium was the selected metal because it forms stable complexes with MT. In addition, after mineralization of the biological materials, total cadmium can be determined by using Na-DDC as chelating reagent and a flow system similar to one described elsewhere.21Discrimination between inorganic cadmium and cadmium bound to MT is obtained by the difference between both determinations.

ISSN:0267-9477    

DOI:10.1039/b202535n

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

IntroductionSelenium (Se) is an essential trace element at low levels of intake and produces toxic symptoms when it is ingested at levels higher than those required for adequate nutrition.1Selenium deficiency has been associated with several diseases,e.g., heart diseases and cancer.2Recently, it was reported that sufficient selenium supplement can protect against cancer.3A variety of Se-enriched materials, such as garlic, yeast, and lactic acid bacteria, have been studied for the purpose of selenium supplementation. With the increased use of Se for dietary supplementation in animals and humans, the chemical forms and quantities of Se in urine are of interest because urinary excretion is the main route of Se elimination and more than 50% is excreted this way. Moreover, the urinary Se speciation may provide information about the Se status of the body, either as a detoxified formor as the metabolite of an essential chemical form.4To date, besides the inorganic Se compounds, the only organic Se compound identified conclusively in human urine has been TMSe+.5,6Evidence for the presence of selenourea (SeUr) has also been reported.7Selenoamino acids, such as selenomethione (SeMet) and selenocystine (SeCys) have been hypothesized as metabolites in the biological pathways of Se.8,9Due to the complex urine matrix and low concentration of Se (normally less than 100 ng mL−1), analytical methods for urinary speciation of Se are very scarce. Earlier methods often required a large volume of urine samples (1–2 l) and employed a series of chemical pretreatment steps, such as precipitation/coprecipitation,10thermal decomposition and derivatization of selenoamino acids.11,12Such sample treatments may have changed the original Se species present in urine, thus resulting in erroneous results. In recent years, the development of analytical chemistry methods based on the hyphenation of HPLC with ICP-MS have been reported in the literature. In order to separate Se species, different separation modes, such as ion-exchange,4,13–15reversed-phase,16–19ion-pair reversed-phase20and vesicle-mediated chromatography,19,21have been examined. Some difficulties, however, have been encountered when the different HPLC methods were applied to urine samples,e.g., the inability to separate inorganic Se species together with organic ones. Some reported methods can only separate two or three Se compounds, either inorganic or organic species, and, in some methods, the conclusively identified metabolite TMSe+was not considered at all in the separation system.18,19,21On the other hand, many reported methods are not robust enough to maintain their separation performance in urine samples. Furthermore, due to the lack of sensitivity, some methods can only work with spiked urine samples.21,22In order to minimize urine matrix interference in both the chromatographic separationand the ICP-MS detection steps, solid-phase extraction,18ethanolic precipitation5and dilution14–16,19,20,23sample pretreatment steps have been carried out. However, there is a strong chance that these sample preparations alter the composition of the original sample24or cause loss of the analytes of interest. Therefore, analytical methods that are sensitive and highly robust for direct urinary Se speciation analysis are urgently required.In this paper, we report a sensitive and robust HPLC-ICP-MS method for urinary Se speciation analysis. This method was developed to meet the demand of our ongoing research project on the study of Se metabolism of Se–yeast supplements. By using a unique reversed-phase chromatographic separation system with mixed ion-pair reagents,25,26in which both anionic (sodium 1-butanesulfonate) and cationic (tetramethylammonium hydroxide) ion-pairing reagents were added simultaneously into an aqueous solution, five Se species, Se(vi), SeUr, TMSe+, SeMet, SeCM, and SeEt, could be directly analyzed in human urine samples. Due to its remarkable analytical characteristics, such as low detection limits and highly matrix tolerance, this method provides a powerful tool for the study of Se metabolism and for the dose control of ingested Se nutritional supplements.

ISSN:0267-9477    

DOI:10.1039/b202531k

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

IntroductionIt is known that such elements as arsenic, cadmium, and copper are potential risks in the environment even in very low concentrations.1Various assessments of the ecotoxicological hazards of heavy metal concentrations in contaminated soils, including sequential extraction procedures, have been made.2,3However, the acid-leachable toxic metal content is one of the most powerful measures of the hazardous nature of a soil sample. Thus, it is important to test the validity of and further develop the analytical methods used in the determination of acid-leachable elements with toxic effects in environmental matrices.There are only a few widely used methods for metal extraction in contaminated soil and sediment samples.4,5The methods of microwave-assisted acid leaching6and ultrasound-assisted extraction7can be used for this purpose as well as reflux with either nitric acid oraqua regia, which is the ISO 11466 standard method.4,8All the commonly available atomic absorption and emission spectroscopic techniques can be used in environmental analytical work including the analysis of contaminated soil samples.9Inductively coupled plasma atomic emission spectrometry (ICP-AES) has the possibility of simultaneous multi-element analysis with detection limits low enough for most trace metal analyses.10Inductively coupled plasma mass spectrometry (ICP-MS) has the same features but with significantly lower detection limits.11When low detection limits are required for metal analysis without multi-element capability, electrothermal atomic absorption spectrometry (ETAAS) is a useful technique.12,13Hydride generation atomic absorption (HG-AAS) is an effective technique for the determination of hydride-forming elements such as arsenic, antimony, selenium,and tin.14One disadvantage of the HG-AAS technique is that high salt concentrations, specially chloride, may cause interferences with respect to the analyte elements.15The ETAAS technique has been successful in cadmium determination in different kinds of samples with Pd16and other matrix modifiers such as W or a mixture of NH4H2PO4and Mg(NO3)2.17The determination of arsenic and copper can be performed with a mixture of Pd and Mg(NO3)2as a matrix modifier.18In the case of complicated sample matrices the determination of arsenic can be subject to dramatic interference by the matrix elements and by high chloride or sulfate concentrations.12,18However, in the determination of arsenic in a complicated sample matrix by ETAAS a solution of 0.2% m/v NaNO3was evaluated and found to be a useful matrix modifier.12The aim of this study was to demonstrate the efficiency of the ultrasound-assisted extraction method compared with the methods universally used in the determination of acid-leachable toxic metal concentrations in soil samples by ETAAS. The matrix interference caused by chloride was also studied by the analysis of SRM samples with different hydrochloric acid concentrations. The determination of arsenic was subject to dramatic interference by chloride, even in low concentrations, but in the case of cadmium and copper no interferences were found. The analysis of arsenic in samples with low chloride concentrations can effectively be performed by matrix modification with a solution of 0.2% m/v NaNO3.

ISSN:0267-9477    

DOI:10.1039/b202534p

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

IntroductionVery recently, the number of elements that may potentially be converted into volatile species by hydride generation technique has been enlarged. In the light of the latest publications,1–8some transition and noble metals are capable of forming volatile species in the reaction performed by NaBH4in the acidic medium. So far, transition metals such as Co,5,6Cd,9,10Cu,1–3,5,6Cr,5Fe,5Mn,6Ni,4-6Zn,3,6Ti6and Tl,2along with the following noble metals: Ag,2,3,6,8Au,2,3,6,7Ir,6Pd,2,6,7Pt6,7and Rh2,6have been found to form volatile compounds under the conditions of the hydride generation reaction. No information on Os and Ru volatile species generation in the reaction with sodium tetrahydroborate has been reported so far accordingly to our knowledge. The majority of novel species of the transition and noble metals have been generated at relatively low concentrations of HCl or HNO3.1,3-7According to the former research works, it was concluded that these species are very unstable.1,3,4It was also observed that experimental parameters, especially the sample acidity and the type of acid, affect significantly the efficiency of the volatile species generation and response of the metals.In the present contribution, the reaction of Ir, Os, Rh and Ru ions with NaBH4in the acid medium was studied. Experimental conditions influencing generation of Os, Rh and Ru volatile species, among them the type of acid and its concentration in the sample, sample flow rate and flow rate of the reductant, were examined. The efficiency of the noble metal volatile species generation reaction was evaluated. An investigation on analytical performance,i.e.detection limits and linearity ranges of Rh and Ru analytical lines, was also performed.

ISSN:0267-9477    

DOI:10.1039/b202313j

出版商:RSC    

年代:2002

数据来源: RSC