Two-photon excitation of mercury atoms by photodissociation of mercury halides

Photodissociation of HgCl₂, HgBr₂, and Hgl₂ with an ArF laser at 193 nm produces strong fluorescence from highly excited Hg atoms. The experiments indicate that single photon dissociation of the mercuric halide, HgX₂, is followed by the two-photon dissociation of HgX (X² Σ) molecules to produce electronically excited Hg atoms.     

Chalcogenophilicity of mercury

Density-functional theory (DFT) calculations have been carried out to investigate the chalcogenophilicity of mercury (Hg) reported recently [J. Am. Chem. Soc. 2010, 132, 647-655]. Molecules of different sizes have been studied including ME, [M(EH)(4)](n), M(SH)(3)EH (M = Cd, Hg; E = S, Se, Te; n = 0, 2+) and [Tm(Y)]MEZ complexes (Tm = tris(2-mercapto-1-R-imidzolyl)hydroborato; Y = H, Me, Bu(t); M = Zn, Cd, Hg; E = S, Se, Te; Z = H, Ph). The bonding of Cd and Hg in their complexes depends on the oxidation state of the metal and nature of the ligands. More electronegative ligands form bonds of ionic type with Cd and Hg while less electronegative ligands form bonds that are more covalent. The Cd-ligand bond distances are shorter for the ionic type of bonding and longer for the covalent type of bonding than those of the corresponding Hg-ligand bonds. The variation of this Cd/Hg bonding is in accordance with the ionic and covalent radii of Cd and Hg. The experimentally observed (shorter) Hg-Se and Hg-Te bond distances in [Tm(Bu(t))]HgEPh (E = S, Se, Te) are due to the lower electronegativity of Se and Te, crystal packing, and the presence of a very bulky group. The bond dissociation energy (BDE) for Hg is the highest for Hg-S followed by Hg-Se and Hg-Te regardless of complex type.     

Determination of mercury and organic mercury contents in Malaysian seafood

The contents of mercury and organic mercury in various types of seafood from various location in Malaysia were determined by neutron activation analysis. Total mercury was determined by instrumental neutron activation analysis (INAA) whilst organic mercury was determined by INAA after chemical separation. Samples were digested in acid media and into the solution was added copper ion and KBr to release organic mercury compound from sulphur component of the tissue. The organic mercury was then extracted into toluene and then treated with cysteine paper to convert the compound into sub-organo-mercury from. The paper was then transferred into polyethylene vials and irradiated in the MINT TRIGA Reactor. Analytical results of organic mercury in Indian mackerel (Rastrelliger kanagurta), Spanish mackerel (Scomberomurus commersoni), shrimp (Peneaus sp.), squid (Loligo sp.) and cockle (Anadara granosa) is in the range of 45%–94% of the total mercury.     

Catalytic microdetermination of mercury

An automatic spectrophotometric reaction-rate method is described for the microdetermination of mercury. The method is based on the catalytic effect of mercury on the reaction of ferrocyanide with nitrosobenzene. The time required for production of a small fixed amount of the violet product as given by a preselected change in the output voltage of a photoconductive circuit, is measured automatically and related directly to the mercury concentration. The possibility of masking interfering ions with EDTA was examined. Amounts of mercury in the range 0.25–2.5 /smg, were determined with relative errors of 1–2% in measurement times of only 15–120 sec. Results obtained with mercurial compounds, treated with bromine water, were within 1–2% of the theoretical values and results obtained with pharmaceutical preparations were within the range assigned to those preparations.     

Simultaneous determination of oxygen and mercury in inorganic and organic mercury compounds

Oxygen and mercury in inorganic and organic mercury compounds are determined simultaneously by a modification of the Schütze-Unterzaucher method. The determination of mercury is not influenced by the presence of sulphur and nitrogen in the samples. In 13 inorganic and organic mercury compounds, oxygen has been determined with an error of less than 0.4% and mercury with an error of less than 0.5%.     

Revision of the dissociation energies of mercury chalcogenides--unusual types of mercury bonding.

Mercury chalcogenides HgE (E=O, S, Se, etc.) are described in the literature to possess rather stable bonds with bond dissociation energies between 53 and 30 kcal mol(-1), which is actually difficult to understand in view of the closed-shell electron configuration of the Hg atom in its ground state (...4f(14)5d(10)6s(2)). Based on relativistically corrected many body perturbation theory and coupled-cluster theory [IORAmm/MP4, Feenberg-scaled IORAmm/MP4, IORAmm/CCSD(T)] in connection with IORAmm/B3LYP theory and a [17s14p9d5f]/aug-cc-pVTZ basis set, it is shown that the covalent HgE bond is rather weak (2-7 kcal mol(-1)), the ground state of HgE is a triplet rather than a singlet state, and that the experimental bond dissociation energies have been obtained for dimers (or mixtures of monomers, dimers, and even trimers) Hg2E2 rather than true monomers. The dimers possess association energies of more than 100 kcal mol(-1) due to electrostatic forces between the monomer units. The covalent bond between Hg and E is in so far peculiar as it requires a charge transfer from Hg to E (depending on the electronegativity of E) for the creation of a single bond, which is supported by electrostatic forces. However, a bonding between Hg and E is reduced by strong lone pair-lone pair repulsion to a couple of kcal mol(-1). Since a triplet configuration possesses somewhat lower destabilizing lone pair energies, the triplet state is more stable. In the dimer, there is a Hg-Hg pi bond of bond order 0.66 without any a support. Weak covalent Hg-O interactions are supported by electrostatic bonding. The results for the mercury chalcogenides suggests that all experimental dissociation energies for group-12 chalcogenides have to be revised because of erroneous measurements.     

Determination of mercury and mercury compounds in air and other non-corrosive gases

Summary Mercury is adsorbed on cellulose powder and activated charcoal. The contents of the adsorber are burnt in the oxy-hydrogen flame, and the mercury determined by the flameless atomic absorption procedure. The method is applicable to mercury present as metallic vapour, organo mercurical compounds and particulate matter containing adsorbed mercury compounds. The combustion step eliminates all possible non-atomic absorption interferences in the measuring procedure and ensures quantitative recovery of the mercury from the adsorption material.Quantitative adsorption recovery over a wide range of flow rate from 2–200 l/h allows the use of small battery operated pumps for personal monitoring, or vacuum pumps for high speed and large volume sampling. The range of flow rate makes isokinetic sampling conditions possible.

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Bestimmung von Quecksilber und Quecksilberverbindungen in Luft und anderen nicht korrodierenden Gasen

Zusammenfassung Quecksilber wird an Cellulosepulver und Aktivkohle adsorbiert. Der Inhalt des Adsorbers wird in der Wasserstoff-Sauerstoff-Flamme verbrannt und das Quecksilber durch flammenlose Atomabsorption bestimmt. Die Methode erfa\t Quecksilber als Metalldampf, in Form von Organo-Quecksilberverbindungen sowie Quecksilberverbindungen, die an Staubpartikel adsorbiert sind. Die Verbrennung in der Wasserstoff-Sauerstoff-Flamme eliminiert Störungen durch nicht-atomare Absorption bei der AAS-Messung und garantiert die quantitative Erfassung des adsorbierten Quecksilbers.Die quantitative Adsorption über einen gro\en Bereich der Durchflu\geschwindigkeit von 2–200 l/h erlaubt batteriebetriebene Pumpen für die Quecksilbermessung am Mann, oder den Einsatz von Vakuumpumpen für die Probenahme bei hoher Durchflu\rate und gro\em Probenvolumen. Der gro\e Bereich der Durchflu\rate gestattet isokinetische Bedingungen für die Probenahme.

     

Concentration of mercury in wheat samples stored with mercury tablets as preservative

Tablets consisting of mercury in the form of a dull grey powder made by triturating mercury with chalk and sugar are used in Indian household for storing food-grains. The contamination of wheat samples by mercury, when stored with mercury tablets for period of upto four years has been assessed by using non-destructive neutron activation analysis. The details of the analytical procedure used have also been briefly described.     

Titrimetric analysis of total mercury ions including mercury(I) ions

A systematic analytical method is proposed and applied to directly determine the total concentration of Hg(II) and Hg(I) ions in water. Experimental results demonstrate that this method provides a low detection limit of 0.05 mM and small relative error within 1.5% in an ion concentration range of 0.2–50 mM. The technique is especially applicable for sample solutions that the traditional titration method like Volhard and EDTA complexation titrimetry could not analyze directly. This method could be employed to analyze solutions in any ratio of Hg(II) and Hg(I) ions including pure Hg(II) or pure Hg(I) ions, exhibiting several advantages, such as simple operation, good reproducibility, and low cost. Correspondence: Xin-Gui Li, Key Laboratory of Advanced Civil Engineering Materials, Institute of Materials Chemistry, College of Materials Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.     

Titrimetric analysis of total mercury ions including mercury(I) ions

A systematic analytical method is proposed and applied to directly determine the total concentration of Hg(II) and Hg(I) ions in water. Experimental results demonstrate that this method provides a low detection limit of 0.05 mM and small relative error within 1.5% in an ion concentration range of 0.2–50 mM. The technique is especially applicable for sample solutions that the traditional titration method like Volhard and EDTA complexation titrimetry could not analyze directly. This method could be employed to analyze solutions in any ratio of Hg(II) and Hg(I) ions including pure Hg(II) or pure Hg(I) ions, exhibiting several advantages, such as simple operation, good reproducibility, and low cost.     

Further studies of the formation of mercury barbiturate films at a mercury anode

Potential sweep and step experiments have been used to reinvestigate the electrochemistry of 5,5′-disubstituted barbituric acids at a mercury electrode and it is confirmed that while all such compounds form a monolayer of an insoluble mercury barbiturate, the mechanism and kinetics of these oxidations depend on the detailed structure of the barbiturates. The experiments have been extended to barbituric acid and 5-ethylbarbituric acid and these would suggest that when the barbiturate is not fully substituted in the 5-position, more than a monolayer of the mercury salt is formed.     

Electrodeposition of mercury on gold from very dilute mercury(II) solution

Flameless atomic absorption spectrometry (flameless a.a.s.) was applied to study the state of mercury deposited on a gold plate electrode from very dilute mercury(II) solution by controlled-potential electrolysis. A stable monolayer is formed on the gold electrode by the electrolysis at a potential about 200 mV more positive than the reversible Nernst potential for the reduction of mercury(II) to mercury(0). After the monolayer formation, bulk mercury is deposited on the monolayer at the reversible potential and an adatom layer is also found. The difference of activation free energies between the evaporation of mercury from the monolayer and that from bulk mercury corresponds to the underpotential shift for the electrodeposition of mercury on the gold electrode.     

Determination of total particulate mercury in air with the coleman mercury analyzer system

A simple and rapid cold-vapour atomic absorption system is described for the simultaneous determination of low ambient levels of particulate mercury and volatile mercury compounds. Of the different filters checked for particle collection, quartz fibre filters have the best properties. Sampling characteristics were considered with respect to efficiency, reproducibility and duration of sampling. The homogeneity of the solid mercury deposit on the filter was tested. Possible enrichment during sampling by absorption of volatile mercury compounds and possible mercury losses by volatilization of solid compounds were examined. After sampling the mercury is released by pyrolysis and collected on a gold-coated sand absorber. In order to avoid deactivation of the absorber by condensation of pyrolysis products or interference during the subsequent dcsorption and atomic absorption measurement of the collected mercury, a heated catalytic convertor and two specific absorbers for organic substances are inserted in the analysis line.     

Electrophoresis of concentrated mercury drops

The electrophoretic behavior of concentrated monodispersed, positively charged mercury drops is investigated theoretically. The present study extends previous analyses by considering arbitrary surface potentials, double-layer polarization, and the interaction between adjacent double layers. The coupled equations describing the spatial variations in the flow field, the electric field, and the concentration field are solved by a pseudo-spectral method. For a low surface potential phi(r), the mobility increases monotonically with kappaalpha; kappa and alpha are respectively the reciprocal Debye length and the radius of a mercury drop. For medium and high phi(r), the mobility curve has a reflection point, which arises from the interaction of adjacent double layers, for kappaalpha. Also, if phi(r) is high, the mobility curve may exhibit a local minimum as kappaalpha varies. This phenomenon is pronounced if the concentration of the dispersed phase is high. If the double layer is thick, the mobility increases with phi(r), and the reverse is true if it is thin. We show that the higher the concentration of the dispersed phase the smaller the mobility, and as kappaalpha becomes large the mobility approaches a constant value, which is independent of the concentration of the dispersed phase. The mobility of mercury drops is larger than that of the corresponding rigid particles.     

Determination of volatile mercury compounds in air with the coleman mercury analyzer system

A simple but very selective cold-vapour atomic absorption system is described for the determination of volatile mercury compounds at very low levels in ambient air. Three different absorbers are compared: activated charcoal, silver-coated sea sand and gold-coated sea sand. To eliminate interferences, a two-step desorption unit is used. After thermal desorption, the mercury is measured by using a modified MAS-50 spectrophotometer. The effects of flow rate and desorption temperature are discussed. The detection limit is 0.1 ng. Above 1 ng, the reproducibility is about 1%. Calibration is done by injection of elemental mercury vapour. The method with gold-coated sand absorbers is most satisfactory and is suitable for the analysis of ambient outdoor and indoor air. All likely volatile mercury compounds are absorbed, and a wide range of mercury concentrations can be determined. In routine application, one analysis takes about 3 min.