Direct Fluorescence Monitoring of Coal Organic Matter Released in Seawater

Whenever immersed in seawater after a collier accident, a fossil fuel such as coal could become a source of pollution to the marine environment. To study the effect of such a contamination, four coal samples from different origins were used. A first analysis on those coals enabled us to determine the content of polycylic aromatic hydrocarbons. Seawater was then mixed with coal to study the organic matter released from coal into seawater. Fluorescence was used for its sensitivity to aromatic compounds, with the additional purpose of evaluating the relevance of using an immerse fluorescence probe to monitor water pollution. Excitation–emission matrices were recorded and the excitation–emission wavelength range corresponding to the highest fluorescence intensity was 230 nm/[370 nm; 420 nm]. The samples with coal happened to fluoresce more than the coal-free samples, the difference depending on the coal origin. The fluorescence intensity increased with coal mass, up to some limit. The particle size also influenced the fluorescence intensity, the finest particles releasing more fluorescing substances, due to their higher exchange surface. When seawater percolated through coal, the samples fluoresced highly at the beginning, and then the fluorescence intensity decreased and reached the seawater level. However, even with a 10 ns acquisition time shift, the fluorescence spectra were not specific enough to show the presence of PAHs in the samples, which were too diluted to be detected, whenever released from coal into seawater. The lifetimes of the seawater and of the coal samples were respectively 4.7 and 3.8 ns, indicating that the substances released from coal mainly consisted of short-lived fluorescing substances, such as natural humic or fulvic substances. Consequently, the presence of coal does not seem to be too detrimental to the marine environment, and a direct fluorescence probe could be used to monitor the seawater organic charge increase due to the immersion of coal in seawater.     

Redox-fixable manipulation of planar chirality in late transition metal sandwich compounds; a 1,1'-diphosphacobaltocene/1,1'-diphosphacobaltocenium salt couple

An electrochemically switched face inversion process for η(5)-coordinated ligands in late transition metal sandwich complexes is demonstrated.     

Effects of various salts on the determination of arsenic by graphite furnace atomic absorption spectrometry. Direct determination in seawater

The effect of Na, Mg, Ca and Sr as their nitrate, chloride and sulfate salts and seasalt, with and without the use of palladium, on the determination of arsenic by electrothermal atomic absorption spectrometry was investigated. In the absence of any stabilizing agent, arsenic was partially lost as molecular species at low temperatures. The effect of salts on the shape of the atomization signal, the integrated absorbance and the stabilizing effect were highly dependent both on their nature and mass. By trapping arsenic, oxide species resulting from the decomposition of nitrate salts induced a high stabilization effect depending on their vaporization temperatures: MgO approximately CaO>SrO>Na2O. The stabilization effect of chlorides occurred about 200 degrees C lower and depended on mass, volatility and hydrolytic properties: SrCl2>CaCl2>MgCl2 approximately NaCl. The effect of sulfates was mainly dependent on their decomposition/vaporization mechanisms, and in the presence of Na2SO4 or CaSO4 a strong chemical interference effect was observed. Palladium stabilized arsenic in the presence of nitrates, chlorides or even sulfates, leading to a similar delaying effect, signal shape and integrated absorbance. Seasalt induced also important modifications to the atomization signal of As. Moreover, an interference effect was observed, which could probably be attributed to the simultaneous vaporization of sulfate in seasalt. In seawater, Pd suppressed this interference effect and permitted to use a high pyrolysis temperature up to 1400 C to remove the major part of the seawater matrix before atomization. Under optimized conditions, the detection limit for As obtained in unmodified seawater in the presence of Pd was 0.34 microg L(-1) for a 10 microl sample.     

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L⁻¹ (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L⁻¹ (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L⁻¹) seawater sample were in good agreement with the certified values.     

Methylation sites in tris(μ-thiolato)dimolybdenum(III) complexes

Attempts at methylating cis-[Mo₂Cp₂(μ-SMe)₃L₂](BF₄) [Cp = η⁵-C₅H₅; L = CO (1a) CNxyl (1b), CNBu^t (1c), NCMe (1d)] with methyl triflate gave the corresponding thioether-bridged cations [Mo₂Cp₂(μ-SMe)₂(μ-SMe₂)L₂]²⁺ (4²⁺), except in the case of 1a which did not react at room temperature. The electronic properties of the ancillary ligands L thus have a crucial influence on the course of this reaction. The dimeric compounds [Mo₂Cp₂(μ-SMe)₃(CNBu^t)(CN)] (2) and [Mo₂Cp₂(μ-SMe)₃{μ-η¹-NC(CH₃)CH₂CN}] (3), which potentially offer the alternatives of S- or N-methylation, reacted with methylating agents to give mainly the S-methylated derivatives 5 and 7. Only in the case of the nucleophilic reactant 2 was N-methylation also observed and isomer 6 was obtained as a minor product together with 5. New complexes have been completely characterised by multinuclear NMR, IR and elemental analysis, supplemented for 5 by X-ray diffraction study at 100 K.     

Direct laser photo-induced fluorescence determination of bisphenol A

Classical photo-induced fluorescence methods are conducted in two steps: a UV irradiation step in order to form a photo-induced compound followed by its fluorimetric determination. Automated flow injection methods are frequently used for these analyses. In this work, we propose a new method of direct laser photo-induced fluorescence analysis. This new method is based on direct irradiation of the analyte in a fluorimetric cell in order to form a photo-induced fluorescent compound and its direct fluorimetric detection during a short irradiation time. Irradiation is performed with a tuneable Nd:YAG laser to select the optimal excitation wavelength and to improve the specificity. It has been applied to the determination of bisphenol A, an endocrine disrupter compound that may be a potential contaminant for food. Irradiation of bisphenol A at 230 nm produces a photo-induced compound with a much higher fluorescence quantum yield and specific excitation/emission wavelengths. In tap water, the fluorescence of bisphenol A increases linearly versus its concentration and, its determination by direct laser photo-induced fluorescence permits to obtain a low limit of detection of 17 μg L⁻¹.     

Intramolecularly Stabilised Group 10 Metal Stannyl and Stannylene Complexes: Multi‐pathway Synthesis and Observation of Platinum‐to‐Tin Alkyl Transfer

Reaction of [PdClMe(P^N)₂] with SnCl₂ followed by Cl‐abstraction leads to apparent Pd?C bond activation, resulting in methylstannylene species trans‐[PdCl{(P^N)₂SnClMe}][BF₄] (P^N=diaryl phosphino‐N‐heterocycle). In contrast, reaction of Pt analogues with SnCl₂ leads to Pt?Cl bond activation, resulting in methylplatinum species trans‐[PtMe{(P^N)₂SnCl₂}][BF₄]. Over time, they isomerise to methylstannylene species, indicating that both kinetic and thermodynamic products can be isolated for Pt, whereas for Pd only methylstannylene complexes are isolated. Oxidative addition of RSnCl₃ (R=Me, Bu, Ph) to M⁰ precursors (M=Pd or Pt) in the presence of P^N ligands results in diphosphinostannylene pincer complexes trans‐[MCl{(P^N)₂SnCl(R)}][SnCl₄R], which are structurally similar to the products from SnCl₂ insertion. This showed that addition of RSnCl₃ to M⁰ results in formal Sn?Cl bond oxidative addition. A probable pathway of activation of the tin reagents and formation of different products is proposed and the relevancy of the findings for Pd and Pt catalysed processes that use SnCl₂ as a co‐catalyst is discussed.     

Determination of 1 ng/l. Levels of mercury in water by electrothermal atomization atomic-absorption spectrometry after solvent extraction

Optimization of the furnace parameters for electrothermal atomization of mercury leads to a characteristic mass of 20 pg in aqueous solution and 30 pg in chloroform extracts (with Zeeman correction). With a single-step solvent extraction from 100 ml of sample, performed in the sampling vessel, and direct injection of 400 μl of the extract into the furnace, a characteristic concentration of 0.8 ng/l. is reached.     

Palladium-catalyzed dehydrostannylation of n-alkyltin trichlorides

[Pd(PPh(3))(4)] catalyzes the dehydrostannylation of n-alkyltin trichlorides into HSnCl(3)(THF)(n) and isomers of the corresponding alkene. The reaction mechanism involves oxidative addition of the Sn-C bond followed by β-H elimination from the resulting n-alkylpalladium trichlorostannyl species. Rate-determining reductive elimination of HSnCl(3) from cis-[PdH(SnCl(3))(PPh(3))(2)] completes the catalytic cycle. Organotin trichlorides without β-H atoms either do not react or undergo thermal disproportionation. These results are relevant to understand some of the problems associated with the use of monoalkyltin compounds as coupling partner in Stille-type cross-coupling reactions as well as with the catalytic hydrostannylation of 1-alkenes to monoalkyltin trichlorides.     

Speciation of major arsenic species in seawater by flow injection hydride generation atomic absorption spectrometry

Arsenic present at 1 microg L(-1) concentrations in seawater can exist as the following species: As(III), As(V), monomethylarsenic, dimethylarsenic and unknown organic compounds. The potential of the continuous flow injection hydride generation technique coupled to atomic absorption spectrometry (AAS) was investigated for the speciation of these major arsenic species in seawater. Two different techniques were used. After hydride generation and collection in a graphite tube coated with iridium, arsenic was determined by AAS. By selecting different experimental hydride generation conditions, it was possible to determine As(III), total arsenic, hydride reactive arsenic and by difference non-hydride reactive arsenic. On the other hand, by cryogenically trapping hydride reactive species on a chromatographic phase, followed by their sequential release and AAS in a heated quartz cell, inorganic As, MMA and DMA could be determined. By combining these two techniques, an experimental protocol for the speciation of As(III), As(V), MMA, DMA and nonhydride reactive arsenic species in seawater was proposed. The method was applied to seawater sampled at a Mediterranean site and at an Atlantic coastal site. Evidence for the biotransformation of arsenic in seawater was clearly shown.