Effect of the interface on separation in multicapillary gas chromatography-based hyphenated techniques for speciation analysis of organometallic compounds

This paper reports the effect of transfer line (TL) internal diameter (i.d.) on gas chromatographic separation characteristics such as efficiency and speed, when a multicapillary (MC) column is used for speciation analysis of mercury. Five different TL consisting of fused-silica capillaries with 0.15, 0.20, 0.25, 0.32, and 0.53 mm i.d. are compared. The separation efficiency and total chromatographic run time are critically affected by the i.d. of the TL. Narrow capillaries (i.d.0.20 mm) produce minimum peak dispersion whereas wide capillaries result in narrow peaks and shorter chromatographic analysis times. A thermodynamic approach is proposed to describe the motion of the analytes through the separation column and TL. The model provides good agreement with the experimental data for high pressures (35 psig) and wide TL (0.25 mm i.d.).Dedicated to the memory of Wilhelm Fresenius     

Coupling techniques in speciation analysis

Summary Direct coupling techniques in speciation analysis lead to reproducible results with lower risks of trace contamination or losses of analytes in a shorter period of time. The direct coupling mode seems to be most promising for liquid chromatographic separation methods — especially gel permeation chromatography — and for some electrophoretic methods — as flow-through and capillary techniques. Promising detection methods are Flame-AAS and ICP-OES but also hydride-generation AAS and chemical reaction detectors in continuous-flow technique.     

Biochemical speciation analysis by hyphenated techniques

The elucidation of mechanisms that govern the essentiality and toxicity of trace elements in living organisms is critically dependent upon the possibility of the identification, characterization and determination of chemical forms of these elements involved in life processes. The recent progress and the state-of-the-art of biochemical species-selective trace element analysis are critically evaluated with particular emphasis on the use of techniques combining the high selectivity of high performance liquid chromatography (HPLC) with the elemental or molecular specificity of mass spectrometry [using inductively coupled plasma (ICP) or electrospray ionization (ESI)]. The potential and limitations of hyphenated techniques as a tool for speciation of metals and metalloids in biological materials is discussed using a number of examples drawn from the latest research in the authors’ laboratory.     

Extraction techniques in speciation analysis of environmental samples

One of the main problems in speciation analysis is that the different species of metals are present in complex matrices at very low concentration levels. Thus it is almost always necessary to separate the analytes of concern from the matrix and to concentrate them up to detectable concentration levels. Special care should be paid during extraction in order to avoid any contamination of samples, losses and changes in speciation of analytes of concern. The most common extraction techniques for speciation analysis of Pb, Sn, Hg, Cr, As, Se and Sb in liquid and solid samples are presented and briefly discussed. Due to the large quantity of material to be covered, speciation of alkyl, aryl, and macromolecular compounds (porphyrines, thioneines, etc.) has not been taken into account.     

Comparison of gas chromatographic hyphenated techniques for mercury speciation analysis

In this study, we evaluate advantages and disadvantages of three hyphenated techniques for mercury speciation analysis in different sample matrices using gas chromatography (GC) with mass spectrometry (GC-MS), inductively coupled plasma mass spectrometry (GC-ICP-MS) and pyrolysis atomic fluorescence (GC-pyro-AFS) detection. Aqueous ethylation with NaBEt(4) was required in all cases. All systems were validated with respect to precision, with repeatability and reproducibility <5% RSD, confirmed by the Snedecor F-test. All methods proved to be robust according to a Plackett-Burnham design for 7 factors and 15 experiments, and calculations were carried out using the procedures described by Youden and Steiner. In order to evaluate accuracy, certified reference materials (DORM-2 and DOLT-3) were analyzed after closed-vessel microwave extraction with tetramethylammonium hydroxide (TMAH). No statistically significant differences were found to the certified values (p=0.05). The suitability for water samples analysis with different organic matter and chloride contents was evaluated by recovery experiments in synthetic spiked waters. Absolute detection and quantification limits were in the range of 2-6 pg for GC-pyro-AFS, 1-4 pg for GC-MS, with 0.05-0.21 pg for GC-ICP-MS showing the best limits of detection for the three systems employed. However, all systems are sufficiently sensitive for mercury speciation in environmental samples, with GC-MS and GC-ICP-MS offering isotope analysis capabilities for the use of species-specific isotope dilution analysis, and GC-pyro-AFS being the most cost effective alternative.     

Sample treatment in chromatography-based speciation of organometallic pollutants.

Speciation analysis is nowadays performed routinely in many laboratories to control the quality of the environment, food and health. Chemical speciation analyses generally include the study of different oxidation state of elements or individual organometallic compounds. The determination of the different chemical forms of elements is still an analytical challenge, since they are often unstable and concentrations in different matrices of interest are in the microg l(-1) or even in the ng l(-1) range (e.g., estuarine waters) or ng g(-1) in sediments and biological tissues. For this reason, sensitive and selective analytical atomic techniques are being used as available detectors for speciation, generally coupled with chromatography for the time-resolved introduction of analytes into the atomic spectrometer. The complexity of these instrumental couplings has a straightforward consequence on the duration of the analysis, but sample preparation to separate and transfer the chemical species present in the sample into a solution to be accepted readily by a chromatographic column is the more critical step of total analysis, and demands considerable operator skills and time cost. Traditionally, liquid-liquid extraction has been employed for sample treatment with serious disadvantages, such as consumption, disposal and long-term exposure to organic solvent. In addition, they are usually cumbersome and time-consuming. Therefore, the introduction of new reagents such as sodium tetraethylborate for the simultaneous derivatization of several elements has been proposed. Other possibilities are based in the implementation of techniques for efficient and accelerated isolation of species from the sample matrix. This is the case for microwave-assisted extraction, solid-phase extraction and microextraction, supercritical fluid extraction or pressurized liquid extraction, which offer new possibilities in species treatment, and the advantages of a drastic reduction of the extraction time and the embodiment into on-line flow analysis systems. This new generation of treatment techniques constitutes a good choice as fast extraction methods for feasible species-selective analysis of organometallic compounds under the picogram level, that can be used for national regulatory agencies, governmental and industrial quality control laboratories, and consequently, for manufacturers of analytical instrumentation.     

Development of sensitive GC-AAS instrumentation for analysis of organometallic species in the environment

Abstract

Atomic absorption spectrometry provides a highly sensitive element-specific detection system for organometallic species preseparated by gas chromatography. Both flame and flameless atomisation systems have been used and high sensitivity attained with elements such as Sn, Pb and As. Non-ionic alkyl or hydride species which are G.C.-volatile may be analysed directly, whilst ionic species generally require conversion to a hydride or a butylated form prior to analysis.

The development of a G.C.-A.A.S. interface will be described, together with the optimisation of an A.A.S. detector based upon a hydrogen diffusion flame, which is sensitive to picogram levels of organometallic compounds. The G.C.-A.A.S. equipment has been further interfaced with a two-stage thermal desorption system for analysis of vapours collected on polymeric absorbents. The application of the system to the analysis of organometallic species of Pb in a variety of environmental media will also be described.     

Advances in arsenic speciation techniques

The present review describes the speciation techniques of arsenic. The principal advanced techniques discussed are gas chromatography, reversed-phase liquid chromatography, ion chromatography, capillary electrophoresis. Some other techniques are also mentioned. The extraction procedures of arsenic species from unknown samples are also discussed. Arsenic speciation is summarized in tabular form and optimizing parameters are also discussed.     

磁性离子印迹技术用于元素形态分离分析

元素的形态决定了其在环境和生物过程中的不同行为,形态分析正在被分析化学、环境化学、地球化学、生态学、农学和生物医学等众多学科所关注。环境和生物样品基质复杂、化学形态多样、含量低且易转化是元素形态分析面临的挑战,因此对元素形态的甄别、定量、生态毒性评价和生理功能研究需要对原生形态进行高选择性识别和高效率分离。固相萃取是一种有效应对以上难题的方法,但现有材料和方法远不能满足要求。离子印迹聚合物可与印迹金属离子特异性结合,具有准确、灵敏、可靠的特点,近年来在元素形态分离富集和分析检测方面得到了较为广泛的应用。鉴于非磁性吸附剂在固相萃取操作时,需要将分散在样品溶液中的吸附材料经过离心或过滤分离,操作比较繁琐费时,而磁性材料易被外部磁场快速分离,因此操作简便快速的磁固相萃取正成为元素形态分离富集中一种极具潜力的方法。这篇综述系统总结了离子印迹技术的最新进展,包括离子印迹技术的原理、离子印迹聚合物的制备方法,并根据元素形态分析中离子印迹磁固相萃取的发展现状,分析了离子印迹技术所面临的挑战,最后对元素形态分析中离子印迹技术的未来发展方向和策略提出了建议,提出开发基于有机-无机杂化聚合的多功能磁性离子印迹纳米复合物用于样品的前处理是建立识别选择性高、分离能力强、吸附容量大、形态稳定性好的形态分析方法的一种重要举措。     

Hydride-trapping techniques for the speciation of arsenic

The determination of arsenic species by the trapping of volatile hydrides prior to atomization in the light path of an atomic absorption spectrometer is described and its operation in the measurement of arsenic species in the marine environment are discussed. Examples are drawn from the analysis of Tamar estuary water and sediment interstitial (pore) waters and from studies of the temporal variation of dimethylarsenic in coastal waters. Improvements in both the design and operation of the technique have resulted in enhanced performance. Baseline resolution of inorganic arsenic, monomethylarsenic and dimethylarsenic is now possible and trimethylarsine is resolved. Ultraviolet photolysis of arsenobetaine and arsenocholine gives partial conversion to trimethylarsine oxide. This can be employed in the qualitative appraisal of the presence of trimethylarsenic species. Current detection limits (3 sigma) for inorganic, mono- and di-methylarsenic lie in the range 19 to 61 pg absolute, giving 19–61 ng/1 concentration detection limits for 1 ml samples. This can be improved even further by using larger sample volumes. The properties of the analysis system when presented with various arsenic species are described. A ca. 10% loss of arsenite occurs in samples stored at —20 °C and immediate freezing of samples in liquid nitrogen is recommended.     

Separation techniques for the analysis of artists' acrylic emulsion paints

Emulsion paints are complex chemical systems. The main problems in their characterization are related to the similarities in polymer composition and to the presence of many different types of additives. Thus high resolution separations, sensitivity, and response specificity are required to identify simultaneously the polymer matrix and the minor components. Especially surfactants and pigments are thought to affect significantly the properties of the paint layers during ageing and their identification is the first step in evaluating the behaviour of these products in working conditions. Representative samples of acrylic emulsion paints for artists have been investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and size exclusion chromatography-Fourier transform infrared spectroscopy (SEC-FTIR), and the results have been compared. All the analysed samples were bound in ethyl acrylate-methyl methacrylate, poly(EA-co-MMA), or n-butyl acrylate-methyl methacrylate, poly(nBA-co-MMA), copolymers. Two types of nonionic surfactants, ethoxylated fatty alcohols and alkylaryl polyethoxylates, commonly used as emulsifiers and dispersive agents have been identified, together with a number of organic pigments.     

Separation of arsenic species by capillary electrophoresis with sample-stacking techniques

A simple capillary zone electrophoresis procedure was developed for the separation of arsenic species (AsO(2)(2-), AsO(4)(2-), and dimethylarsinic acid, DMA). Both counter-electroosmotic and co-electroosmotic (EOF) modes were investigated for the separation of arsenic species with direct UV detection at 185 nm using 20 mmol L(-1) sodium phosphate as the electrolyte. The separation selectivity mainly depends on the separation modes and electrolyte pH. Inorganic anions (Cl(-), NO(2)(-), NO(3)(-) and SO(4)(2-)) presented in real samples did not interfere with arsenic speciation in either separation mode. To improve the detection limits, sample-stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were investigated for the preconcentration of As species in co-CZE mode. Less than 1 micromol L(-1) of detection limits for As species were achieved using FASI. The proposed method was demonstrated for the separation and detection of As species in water.     

Recent developments in speciation and determination of organometallic compounds in environmental samples

Summary Recent developments in the techniques of speciation and determination of organometallic compounds in the environment are reviewed. There is an increasing trend in the use of high performance liquid chromatography as separation tool, and in the use of plasma-excited atomic emission spectrometry as detector. New techniques have been reported to overcome the historically difficult interface of HPLC to furnace AAS. There are also new techniques in the derivatization of ionic organometallic species for gas chromatography. Tandem analytical systems are getting more and more sophisticated, so are the sensitivity and specificity.     

Hyphenated techniques as tools for speciation analysis of metal-based pharmaceuticals: developments and applications

Method development and applications of hyphenated techniques as tools for speciation analysis of metal-based pharmaceuticals are summarized within this review. Advantages and limitations of the separation modes-high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), and gas chromatography (GC)-as well as the detection modes-inductively coupled plasma-mass spectrometry (ICP-MS) and electrospray ionization-mass spectrometry (ESI-MS)-are discussed. ICP-MS detection is found to be advantageous for the quantification of drugs containing metals and other heteroatoms. The species-independent sensitivity and multielement capabilities of ICP-MS allow it to be used for quantification even when species-specific standards are not available, as well as to determine the stoichiometry in metallodrug-biomolecule interactions. Molecular information that is totally destroyed when ICP is applied as ionization source and is therefore not obtainable via ICP-MS detection can be accessed by the complementary technique of ESI-MS. Speciation analysis combining both elemental and molecular information is therefore a powerful tool for the analysis of metal-based pharmaceuticals and their metabolites in body fluids and other relevant matrices.     

Enrichment procedures for small quantities of metals by organometallic and other coprecipitation techniques for X-ray fluorescence analysis

Summary Enrichment procedures for small quantities of metals by organometallic and other coprecipitation techniques for X-ray fluorescence analysis were studied. In order to obtain a higher X-ray intensity and good reproducibility in the measurements, five requirements were considered for the precipitants and for the precipitate. Favourable organic precipitants are mainly alizarine blue, phenyl fluorone, and cupferron, good inorganic precipitates were fluorides and reduced metals. Other precipitation procedures can be applied to some metal elements, if the precipitation reaction is selective and a higher X-ray intensity is obtained.

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Anreicherungsverfahren für Spurenelemente durch Mitfällung in Form organischer Komplexe und anderer Verbindungen für die röntgenspektroskopische Analyse

Zusammenfassung Verschiedene Anforderungen werden beschrieben, die an ein verbessertes Anreicherungsverfahren gestellt werden. Als ausgezeichnete Fällungsmittel erwiesen sich Alizarinblau, Phenylfluoron und Kupferron. Zweckmäßige anorganische Niederschläge sind Fluoride und reduzierte Metalle. Andere Fällungsverfahren werden für einige Elemente benutzt, wenn die Reaktionen selektiv sind und die Röntgenintensität höher ist.

     

Evaluation of DGT techniques for measuring inorganic uranium species in natural waters: Interferences,deployment time and speciation

Three adsorbents (Chelex-100, manganese dioxide [MnO₂] and Metsorb), used as binding layers with the diffusive gradient in thin film (DGT) technique, were evaluated for the measurement of inorganic uranium species in synthetic and natural waters. Uranium (U) was found to be quantitatively accumulated in solution (10–100 μg L⁻¹) by all three adsorbents (uptake efficiencies of 80–99%) with elution efficiencies of 80% (Chelex-100), 84% (MnO₂) and 83% (Metsorb). Consistent uptake occurred over pH (5–9), with only MnO₂ affected by pH < 5, and ionic strength (0.001–1 mol L⁻¹ NaNO₃) ranges typical of natural waters, including seawater. DGT validation experiments (5 days) gave linear mass uptake over time (R² ≥ 0.97) for all three adsorbents in low ionic strength solution (0.01 M NaNO₃). Validation experiments in artificial sea water gave linear mass uptake for Metsorb (R² ≥ 0.9954) up to 12 h and MnO₂ (R² ≥ 0.9259) up to 24 h. Chelex-100 demonstrated no linear mass uptake in artificial sea water after 8 h. Possible interferences were investigated with SO₄²⁻ (0.02–200 mg L⁻¹) having little affect on any of the three DGT binding layers. PO₄³⁻ additions (5 μg L⁻¹–5 mg L⁻¹) interfered by forming anionic uranyl phosphate complexes that Chelex-100 was unable to accumulate, or by directly competing with the uranyl species for binding sites, as with MnO₂ and the Metsorb. HCO₃⁻ (0.1–500 mg L⁻¹) additions formed anionic species which interfered with the performance of the Chelex-100 and the MnO₂, and the Ca²⁺ (0.1–500 mg L⁻¹) had the affect of forming labile calcium uranyl species which aided uptake of U by all three resins. DGT field deployments in sea water (Southampton Water, UK) gave a linear mass uptake of U over time with Metsorb and MnO₂ (4 days). Field deployments in fresh water (River Lambourn, UK) gave linear uptake for up to 7 and 4 days for Metsorb and MnO₂ respectively. Field deployment of the Metsorb-DGT samplers with various diffusive layer thicknesses (0.015–0.175 cm) allowed accurate measurements of the diffusive boundary layer (DBL) and allowed DBL corrected concentrations to be determined. This DBL-corrected U concentration was half that determined when the effect of the DBL was not considered. The ability of the DGT devices to measure U isotopic ratios with no isotopic fractionation was shown by all three resins, thereby proving the usefulness of the technique for environmental monitoring purposes.     

Size fractionation techniques combined with INAA for speciation purposes

In natural waters trace elements, especially trace metals may be present in a variety of physicochemical forms. They may be associated with forms ranging from simple ions and molecules via hydrolysis products and colloids, pseudocolloids and organic or inorganic particles. The transition between categories is gradual. The presence of species differing in size, charge and density will influence on the transport, mobility and bioavailability of the trace element in question. Fractionation techniques which do not influence the distribution patterns are therefore required for speciation purposes. In the present work dialysis in situ and large membrane (hollow fibers) ultrafiltration are used for fractionation of low molecular weight species, colloids, pseudocolloids and particles. Due to the presence of foreign components transformation processes influence the distribution patterns of trace elements of interest. Sorption to foreign surfaces, complexation with agents present and aggregation of colloids (e.g., increasing ionic strength) result in a shift towards higher dimensions while desorption and dispersion processes mobilize the trace elements. Information on several components is therefore needed in speciation studies and a multielemental method of analysis having low determination limits must be applied. Instrumental neutron activation is appropriate to this kind of study because of its high sensitivity for simultaneous determination of a great-number of elements. Size fractionation techniques combined with INAA for the characterization of trace element species in natural waters will be discussed.     

Electrophoretic techniques in element species analysis. Comparison between flow-through and flat-bed techniques

A comparison of electrophoretic techniques for the separation of metal-protein complexes from food extracts is described. A preparative flow-through electrophoresis system with continuous elution of the fractionated substances and an analytical flat-bed gel electrophoresis technique with off-line electro-elution are optimized with regard to this separation problem. The metal-protein complexes are extracted from four flour samples using Tris-glycine buffer (pH 8.3). For the separation, polyacrylamide gels of 14% T and 3% C are prepared and Tris-HCl (pH 8.9) is used as an electrophoresis buffer. For a soy bean flour, not only the separation of protein fractions is achieved but also the metal distribution patterns that are determined by flame atomic absorption spectrometry are given. The results show that the use of the flow-through technique is limited to special fields of application, whereas the flat-bed electrophoresis with subsequent electro-elution of metal-protein complexes is a useful technique in element species analysis.