摘要:

Dr. Spiros A. PergantisSchool of Biological and Chemical Sciences, Birkbeck College, University of London, Gordon House, 29 Gordon Square, London, UK WC1H 0PPJAASEditorial Board.

ISSN:0267-9477    

DOI:10.1039/b207639j

出版商:RSC    

年代:2002

数据来源: RSC

ISSN:0267-9477    

DOI:10.1039/b206607f

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

1IntroductionRecently, there has been increasing interest in the effect of small amounts of hydrogen on the analytical results of argon glow discharges.1–7It appears that the relative sensitivity factors (RSF) of different elements in glow discharge mass spectrometry (GDMS) are influenced by the addition of hydrogen.1,2More specifically, a better correlation can be obtained between measured RSF and values predicted with simple empirical equilibrium models,1,2which opens up possibilities for quantitative analysis with GDMS even when suitable standard reference materials are not available. Moreover, in glow discharge optical emission spectrometry (GD-OES) it has been demonstrated that some optical emission line intensities increase while others decrease when hydrogen is added.3–6This has some very important implications for the analysis of “real samples”. Indeed, many applications exist where hydrogen is a major component of the sample itself, such as organic residues after rolling and degreasing, corrosion products and polymer coatings.3Additionally, some traces of hydrogen are always detected in a glow discharge, arising from residual moisture in the source and on the sample surface, gaseous hydrocarbons coming from the pre-vacuum oil-pumps, leakage of water vapor through porous samples,etc.4Because of the effects of hydrogen on the optical emission line intensities,3–6a good understanding of the role of hydrogen in a glow discharge plasma is important in order to include corrections of the hydrogen effect in quantification algorithms, especially for the analysis of thin films and other surface layers containing hydrogen.Other investigations in analytical glow discharges have included the effect of hydrogen on the ion intensities in a fast flowing glow discharge, with gas mixing close to the ion exit in order not to disturb the discharge.7Finally, hydrogen Balmer lines have been investigated in argon–hydrogen mixtures in a Grimm-type glow discharge8–10to obtain information on reactions in the plasma,8on the electron density9and on the electric field distribution.10Argon–hydrogen mixtures have also been studied in other kinds of discharges.11–32The effect of hydrogen was to cause a drop in ionization in the discharge, and in the argon ion and electron concentration.11–13Moreover, it has been recognized that the addition of hydrogen affects the sputter rates in glow discharges.14,15A number of papers have also reported the measurement of ion energy distributions in argon–hydrogen discharges.16–18Finally, a vast number of chemical reactions between argon and hydrogen species has been studied for conditions typically used in discharge plasmas,19–32providing useful information, such as cross sections and rate coefficients, for numerical investigations of argon–hydrogen discharges.In a recent paper, we gave an overview of all possible reactions that might take place in an argon–hydrogen glow discharge in order to make qualitative predictions of the effect of hydrogen on the discharge behavior and on the analytical characteristics.33Based on these reactions, we have recently developed a comprehensive modeling network describing the behavior in an argon glow discharge with 1% hydrogen added.34Ten different species were taken into account in that model, including electrons, Ar+, ArH+, H+, H2+and H3+ions, fast argon atoms, H atoms and H2molecules, as well as argon metastable (Arm*) atoms. These species were found to interact with each other by using a large number of processes. More than 60 reactions were taken into account, including ionization, excitation,charge transfer, proton transfer, H-atom transfer, collision-induced dissociation and elastic collisions between different species.In the present paper, the model developed inref. 34is extended by adding two more species,i.e., the sputtered Cu atoms and the corresponding Cu+ions. The different species are described by a number of fluid models and Monte Carlo simulations, which form a large modeling network. The models are briefly described and the results,i.e., the effect of different H2concentrations on the discharge behavior, are presented.

ISSN:0267-9477    

DOI:10.1039/b200025c

出版商:RSC    

年代:2002

数据来源: RSC

摘要:

IntroductionMetallospecies play a unique and important role in many essential life processes of which the mechanisms are still poorly understood at the molecular level. Therefore, the detection, identification and determination of trace element compounds in biological systems—bioinorganic speciation analysis—has been enjoying a lot of interest in recent years, becoming an emerging field of analytical chemistry.1–4In this context, particular attention has been given to hyphenated techniques that combine the high separation efficiency of high-performance liquid chromatography (HPLC) or capillary zone electrophoresis (CZE) with the elemental or molecular specificity of inductively coupled plasma (ICP) or electrospray (ES) mass spectrometry (MS), respectively.5The characterization of metal complexes with metallothionein, a low molecular mass (6–7 kDa) metal-binding protein, synthesized by mammals in response to heavy metal stress,6,7has been one of the most popular topics investigated by hyphenated techniques. Liquid chromatography followed by metal-specific detection by ICP-MS was widely applied to the detection and determination of MT and its isoforms in animal tissues.8–16The high separation efficiency of CZE for metal-binding peptides17–19has made many researchers choose rabbit liver metallothionein (MT), preparation available from Sigma–Aldrich, as the favourite test sample to demonstrate the performance of newly developed CZE-ICP-MS interface designs.20–23The recombinant mouseliver MT-1 was recently used for a study of metal complexation equilibria by CZE-ICP-MS.24However, no applications of CZE-ICP-MS to the characterization of metal complexes in animal tissues cytosols have been developed so far.The to-date studies of bioinduction of MTs in rat by hyphenated techniques were limited to Zn-induced proteins, which allowed an easy demetallation of MTs prior to their characterization as apo-forms by CZE-MS.25,26The acidic buffer conditions employed for the separation did not allow the investigation of the complexes present since the link between the metal and the ligand in the complex had been destroyed.25–27Our attempts to use this approach for the characterization of Cd-induced MTs turned out to be unsuccessful because of the impossibility of efficient demetallation of Cd–MT with CZE acidic buffers.28In another approach, signals of major MT-1 and MT-2 isoforms could be obtained for rat tissues but the signal to noise ratio was poor.29Most of information acquired on MT by hyphenated techniques so far has been qualitative. It was usually limited to the number of peaks present in the chromatogram or electropherogram and sometimes included identification data from mass spectrometry. The quantitative aspect was usually neglected. In the best case, the quantification was carried out on the basis of a tentatively assigned complex stoichiometry. Recently, Schaumlöffelet al.proposed determination of MT based on the on-line determination of sulfur in CZE peaks by ICP-SF-DF-isotope dilution-MS.30The objective of this study was the evaluation of ICP-sector field-MS and isotope dilution quantification for the characterization of metal complexes with MT induced in the liver of a rat exposed to Cd stress. Our particular attention was focused on the MT quantification, the determination of the stoichiometry of the complex, and on the complementarity of electrospray MS for the identification of the MT isoforms present.

ISSN:0267-9477    

DOI:10.1039/b110579p

出版商:RSC    

年代:2001

数据来源: RSC