M.R. Fernández de la Campa

Generation of volatile cadmium species with sodium tetrahydroborate from organized media: application to cadmium determination by inductively coupled plasma atomic emission spectrometry

Continuous flow generation of volatile cadmium species (assumed to be the hydride) as a means of gaseous sample introduction into an inductively coupled plasma atomic emission spectrometer has been investigated in detail. Different ‘organized molecular assemblies’(micelles and vesicles) have been tried in order to improve the generation of such cadmium species using NaBH4 as the reducing agent. Didodecyldimethylammonium bromide (DDAB) vesicles were found to be the most appropriate for the purpose. The advantages of this ‘assumed’ cadmium hydride generation from vesicular media are discussed and critically compared in terms of sensitivity, selectivity and accuracy, with the determination of low levels of cadmium by inductively coupled plasma atomic emission spectrometry (ICP-AES). The proposed method for the determination of cadmium by ICP-AES using DDAB and NaBH4 provided 5-fold lower detection limits (1 ng ml–1) as compared with conventional nebulization ICP-AES. A precision of 2% at the 50 ng ml–1 level of the metal was achieved and selectivity studies were carried out. The proposed method was applied to the determination of low levels of cadmium in tea infusion. Validation of the method was performed by analysis of the same samples by electrothermal atomic absorption spectrometry with satisfactory results.

Determination of arsenic by inductively-coupled plasma atomic emission spectrometry enhanced by hydride generation from organized media

A method is described for the determination of arsenic, which combines a continuous flow hydride generation technique with an inductively coupled plasma atomic emission detection system. Some atomic absorption preliminary studies are described as well. Arsine is generated with NaBH(4) from a didodecyldimethylammonium bromide (DDBA) vesicular medium. The analytical performance of this vesicles-enhanced method is superior to the generation of the hydride from aqueous media: the detection limit (0.6 ppb) is improved by a factor of 2 and greater tolerance to interferences is observed for arsine generation from DDBA vesicles. Precision of As determinations is also improved. The proposed method has been validated for low As levels determinations in two Certified Reference Materials (CRM) sediments with satisfactory results. The potential of organized media to improve hydride generation is addressed.

Effects of organised media on the generation of volatile species for atomic spectrometry

Abstract The use of surfactant-based organised assemblies, such as micelles and vesicles, to improve the characteristics of room temperature chemical generation of volatile species of metals and semi-metals (e.g. hydride generation, cold mercury vapour or alkylcompound generation), as a means to further enhance sample introduction efficiency/kinetics for atomic techniques, is reviewed. The complex influence of different organised media (including cationic, anionic, non-ionic and zwitter-ionic micelles and cationic and anionic vesicles) on the hydride generation of the elements As, Pb and Cd and on Hg 0 cold vapour generation have been revised and compared with organised media effects on alkylmetals generation of Se, Pb, Cd and Sn. Enhancements in efficiency/transport of volatile species formed in the surfactant-based media, increases in the reaction kinetics, stabilization of some room temperature unstable species and also changes in the observed selectivity of reactions taking place in conventional aqueous media are some of the discussed effects. Possible mechanisms and analytical potential and usefulness of this enhancement by surfactants of the generation of volatile species for atomic detection methodologies are summarized and illustrated with the determination of low levels of arsenic, lead, cadmium, tin, selenium and mercury.

Room-temperature liquid phosphorimetry of the aluminium-ferron chelate in micellar media : Determination of aluminium☆

Abstract Aluminium reacts with 7-iodo-8-quinolinol-5-sulphonic acid (Ferron) in cetyltrimethylammonium bromide (CTAB) micelles to form a highly phosphorescent complex at room temperature. Suitable experimental conditions and the phosphorescent characteristics of the complex are described. Comparison with the results obtained for the phosphorescent niobium-Ferron complex in CTAB micelles helps to elucidate the mechanism of this type of phosphorescence. For aluminium the detection limit is 5.4 ng ml−1; the relative standard deviation is 4.5% for 20 μg Al. The method is applied to aluminium determination in waters and dialysis fluids.

Study of the influence of ordered media on the determination of lead by hydride generation inductively coupled plasma atomic emission spectrometry

Abstract Continuous-flow generation of plumbane from different media for sample introduction into an inductively coupled plasma (ICP) for the determination of lead by atomic emission spectrometry (AES) was investigated in detail. Different “organized molecular assemblies” (micelles and vesicles) were tried for plumbane generation using the ammonium peroxodisulphate-nitric acid system as oxidant and sodium tetrahydroborate as the reducing agent. Cetyltrimethylammonium bromide (CTAB) or, alternatively, didodecyltrimethylammonium bromide was found to accelerate plumbane generation in the oxidant mixture. The advantages of hydride generation using aqueous, micellar or vesicular media are discussed and critically compared in terms of sensitivity, selectivity and accuracy of the corresponding ICP-AES determination of low levels of lead. The method using ammonium peroxodisulphate-nitric acid-CTAB proved to be superior (detection limit 9 ng ml−1 and precision 1.4% at the 50 mg ml−1 level) to conventional hydride generation, and was applied to the determination of low levels of lead in soft drinks by ICP-AES. Validation of the results was carried out successfully by graphite furnace atomic absorption spectrometry.

Induced lead binding phytochelatins in Brassica juncea and Sesuvium portulacastrum investigated by orthogonal chromatography inductively coupled plasma-mass spectrometry and matrix assisted laser desorption ionization-time of flight-mass spectrometry

The accumulation and transport of lead in Brassica juncea and Sesuvium portulacastrum plants and the possible formation of complexes of this element with bioligands such as phytochelatins was studied in roots and shoots of plants exposed to different amounts of Pb(NO(3))(2). Speciation studies on the plant extracts were conducted using size exclusion liquid chromatography and ion pair liquid chromatography coupled to UV and ICP-MS to monitor lead and sulphur. The identification of the species separated by chromatography was performed by MALDI-TOF-MS. In both types of exposed plants it was possible to identify the presence of the phytochelatin isoform PC(3). The results obtained suggest that both types of plants can be useful in studies of phytoremediation but the ability of S. portulacastrum to accumulate and redistribute Pb from root to shoot is more effective than B. juncea.

Comparison of two CE-ICP-MS interfaces based on microflow nebulizers: application to cadmium speciation in metallothioneins using quadrupole and double focusing mass analyzers

Two different interfaces, based on microflow nebulizers, were investigated in detail and compared for metal speciation studies by CZE-ICP-(Q)MS and CZE-ICP-(DF)MS. The model species selected were rabbit liver metallothioneins (MTs). Small differences among MT sub-isoforms determine the need for an adequate interface, which is critical if the resolution achieved (e.g., by UV) is to be maintained with ICP-MS detection. HEN and MicroMist nebulizers were compared to interface the flows emerging from the CE capillary with the ICP-MS instrument. The observed analytical characteristics of the hybrid systems were compared in terms of calibration graphs, resolution, repeatability and detection limits (DLs). The separation profiles matched perfectly those obtained with UV detection for both interfaces under scrutiny. Similar performances were observed by CE-ICP-(Q)MS in terms of resolution and DLs achieved. The MicroMist interface proved to offer better performance than the HEN-based one using the ICP-(DF)MS instrument, because the introduction of an additional Ar “make-up” gas into the spray chamber is not required (very important if the HEN-based interface is used). In general terms, the MicroMist interface was easier to operate, providing the best DLs for Cd (about 2 pg in each isoform by CE-ICP-(DF)MS, a value 6 times lower than that obtained in a quadrupole system).

The use of surfactants to obtain cadmium atoms at room temperature and its application for the cold vapour AAS determination of the metal

So far, mercury is the only metal that has been proved to be able to form a monoatomic vapour at room temperature. This property has been widely used in analytical techniques, particularly in atomic spectroscopy, where cold vapour atomic absorption spectrometry (CV–AAS) has become the most common method for the determination of low levels of Hg.In this communication we will show evidence that cadmium appears also to be able to form ‘cold atomic vapour’ in appropriate conditions. Experimental results show that by reduction of Cd2+ with sodium tetrahydroborate in vesicles of didodecyldimethylammonium bromide (DDAB), some volatile cadmium species (probably hydrides) can be produced that transport the metal to the atomic absorption measurement cell, where atomic cadmium vapour has been proved to be present in measurable concentrations.Based on these facts, a new determination of traces of cadmium by cold vapour atomic absorption spectrometry is proposed. Such CV–AAS determination of the metal is very sensitive in normal conditions (detection limit of 0.08 ng ml–1) and the sensitivity can be improved further by working at lower temperatures for generation of the volatile species.

Metal speciation of metallothionein in white sea catfish, Netuma barba, and pearl cichlid, Geophagus brasiliensis, by orthogonal liquid chromatography coupled to ICP-MS detection

Metal speciation analysis in MTs was carried out in two tropical fish species of Brazil, the freshwater fish pearl cichlid (Geophagus brasiliensis) and the marine fish white sea catfish (Netuma barba), that are presently used to monitor the effects of heavy metal pollution in aquatic ecosystems in Brazil. In order to obtain the MT fraction, liver cytosols from both fish species where subjected to size exclusion fractionation, monitoring on-line the metal signal (Cd, Cu and Zn) by ICP-MS while protein elution was followed by on-line UV detection. That MT fraction was then separated by anion-exchange (AE)-FPLC, whose optimal chromatographic conditions were optimized for the separation of the different hepatic MT isoforms existing in both fish species. Specific detection of separated metalloforms was carried out again by the hyphenation of the AE chromatographic system with the ICP-MS instrument. The analytical results showed that MTs of these fish species, unknown so far, exhibited unique characteristics in comparison with standard MTs and other fish liver MTs. In fact, MT isoforms of N. barba turned out to be very anionic, as indicated by their high retention in the Mono Q column and the strong ionic strength required to separate them. As for G. brasiliensis, cadmium was exclusively present in only one of the peaks of the MT isoforms showing a unique metal-binding behavior for MT in this fish species. The differences between the MTs among these species and the different association of metals in particular MT isoforms display the importance of the metal speciation analysis in these proteins prior to its use as bioindicators.

Improvement in mercury cold vapour atomic techniques by resorting to organized assemblies and on-line membrane drying of vapour

The most commonly used technique for mercury determination today is cold vapour (CV) generation with atomic absorption spectrometry (AAS), although inductively coupled plasma atomic emission spectrometry (ICP-AES) has also been used for final detection in several continuous CV-ICP-AES methodologies. In this paper improvements in Hg CV generation for both ICP-AES and AAS detection have been tried. The metal transport/excitation in the ICP-AES was improved by incorporating on-line with the ICP, a commercially available ‘membrane drier tube’. The ability of such a membrane to eliminate water vapour from the gaseous sample stream enhanced Hg signals in ICP-AES and decreased baseline drift in flames. On the other hand, earlier work on the use of organized media in atomic spectrometry has shown the ability of micelles and vesicles to improve the kinetics of volatile species generation with sodium tetrahydroborate. In this vein the effect of different organized media on Hg CV generation has been studied. Micelles studied include: cationic hexadecyltrimethyl-ammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS) and non-ionic Triton X-100. Cationic vesicles studied were didodecyldimethylammonium bromide (DDAB). The best detection limits were obtained using DDAB vesicles. The detection limits obtained when the Hg vapour was generated from conventional aqueous techniques were 0.6 and 1 ppb using ICP-AES and AAS detection, respectively. When both vesicles of DDAB and drying membrane tube were used in the CV generation system, the detection limits obtained were 0.2 ppb both for ICP-AES and AAS techniques, showing the beneficial effect of using a drier tube on-line with the plasma in ICP-AES. The proposed CVAAS method has been applied to the determination of Hg in sulfuric acid and sea-water samples.