Storage and stability of mercury and methylmercury in sea water

The long-term storage behavior of mercury and methylmercury at ng 1^?1 levels in sea water was studied at pH 4.0, 6.0, 8.0 and 10.0, and with 2% (v/v) hydrochloric or nitric acid added. Partial complexation and disappearance of mercury and methylmercury were observed; some of the lost mercury became detectable (by cold-vapour atomic absorption spectrometry) after prolonged storage.     

Long-term stability of methylmercury standard solutions in distilled,deionized water

The long-term storage behaviour of methylmercury at different concentrations in distilled, deionized water was studied under various storage conditions. The stability is strongly dependent on concentration, the container material and the storage temperature. Container pretreatment also has an influence. Light seems to have no effect on the stability of methylmercury solutions.     

Monitoring inorganic mercury and methylmercury species with liquid chromatography-piezoelectric detection

A piezoelectric detection system coupled with a liquid chromatographic system is developed for the speciation of inorganic mercury(II) and methylmercury. Piezoelectric detection has been demonstrated to be a very sensitive detection system for total mercury determination when a gold-coated piezoelectric quartz crystal was used. The analytical features of this detection unit make it very suitable to be used as a detector coupled with a liquid chromatographic system for monitoring mercury species. After separation by a chromatography column (Spherisorb ODS-2, 5 μm,  mm i.d.), mercury species are liberated and reduced, by using stannous chloride, and are detected as an amalgam on the gold-coated piezoelectric quartz crystal, the sensor subsequently was regenerated by passing a peroxydisulfate solution. This detector exhibits good sensitivity, it allows the determination of mercury at sub-ppb concentration levels (0.30-1.20 μg l⁻¹). The precision, expressed as relative standard deviation, was ±2.7% (n=11) for a 0.5 μg l⁻¹ total mercury concentration. The proposed method is free of interferences and it allowed the determination of inorganic mercury and methylmercury species in natural waters.     

Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters

The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg(2+)) and monomethylmercury compounds (MeHg) in natural water samples at the pg L(-1) level. The method is based on the simultaneous extraction of MeHg and Hg(2+)dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na(2)S, removal of H(2)S by purging with N(2), subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L(-1) for MeHg and 0.06 ng L(-1) for Hg(2+)when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg(2+). Recoveries were 90-110% for both species.     

Critical review of analytical methods for determination of inorganic mercury and methylmercury compounds

This review describes determinations of mercury compounds under three categories: total mercury; separate determinations of inorganic mercury(II) and organomercury compounds by selective reduction; and speciation of inorganic mercury(II), monomethylmercury cation, and dimethylmercury. Topics described for each category include sample treatment, separation, detection, and limit of detection. Finally, we note that most methods would not detect dimethylmercury if it were present.     

Stability of inorganic mercury and methylmercury on yeast-silica gel microcolumns: field sampling capabilities

The stability of methylmercury and inorganic mercury retained on yeast-silica gel microcolumns was established and compared with the stability of these species in solution. Yeast-silica gel columns with the retained analytes were stored for two months at three different temperatures: –20?°C, 4?°C and room temperature. At regular time intervals, both mercury species were eluted and quantified by cold vapor atomic absorption spectrometry (CVAAS). Methylmercury was found stable in the columns over the two-month period at the three different temperatures tested while the concentration of inorganic mercury decreased after one week’s storage even at –20?°C. These results are of great interest since the use of these microcolumns allows the preconcentration and storage of mercury species until analysis, thus saving laboratory space and avoiding the problems associated with maintaining species integrity in aqueous solution.     

A factorial design to determine the effects of some variables in the long-term stability of methylmercury standard solutions in water

A factorial composite design has been employed for a rapid exploration of the effect of some parameters on the stability of spiked methylmercury iodide solutions. The analysis has been performed by capillary gas chromatography with electron-capture detection. The results obtained by the factorial and the univariate methods are in a good agreement. Although, the factorial design does not allow a discrimination of the significance among the same kind of factors, it greatly reduces the number of experiments when the different variables are investigated.     

Stability of inorganic mercury and methylmercury on yeast-silica gel microcolumns: field sampling capabilities

The stability of methylmercury and inorganic mercury retained on yeast-silica gel microcolumns was established and compared with the stability of these species in solution. Yeast-silica gel columns with the retained analytes were stored for two months at three different temperatures: -20 degrees C, 4 degrees C and room temperature. At regular time intervals, both mercury species were eluted and quantified by cold vapor atomic absorption spectrometry (CVAAS). Methylmercury was found stable in the columns over the two-month period at the three different temperatures tested while the concentration of inorganic mercury decreased after one week's storage even at -20 degrees C. These results are of great interest since the use of these microcolumns allows the preconcentration and storage of mercury species until analysis, thus saving laboratory space and avoiding the problems associated with maintaining species integrity in aqueous solution.     

A factorial design to determine the effects of some variables in the long-term stability of methylmercury standard solutions in water

A factorial composite design has been employed for a rapid exploration of the effect of some parameters on the stability of spiked methylmercury iodide solutions. The analysis has been performed by capillary gas chromatography with electron-capture detection. The results obtained by the factorial and the univariate methods are in a good agreement. Although, the factorial design does not allow a discrimination of the significance among the same kind of factors, it greatly reduces the number of experiments when the different variables are investigated.     

Determination of methylmercury in the presence of inorganic mercury by anodic stripping voltammetry

Methylmercury is determined in a non-complexing nitrate medium by differential pulse anodic stripping voltammetry at a gold film electrode, with a detection limit of 2 × 10^-8 mol l^-1 for 5-min plating times. A method of double standard additions is proposed for determining methylmercury in the presence of mercury(II) ions.     

On-line high-performance liquid-chromatographic separation and cold vapor atomic absorption spectrometric determination of methylmercury and inorganic mercury

A reversed-phase high-performance liquid chromatography (HPLC) method with cold vapor atomic absorption spectrometry (CV-AAS) detection is developed for mercury speciation. In this paper, the efficiency of tetrabutylammonium bromide reagent and sodium chloride in a methanol-water mixture as mobile phase is evaluated for HPLC separation of methylmercury and inorganic mercury coupled with on-line CV-AAS determination. Both mercury species are separated on a reversed-phase C(18) column. Several parameters (e.g. composition and flow-rate of mobile phase) are investigated for the optimization of HPLC separations. CV-AAS technique parameters are also studied for their effect on sensitivity (sodium borohydride and sodium hydroxide concentrations in the reducing agent, reducing agent flow-rate, length of the reduction coil and nitrogen flow-rate). Quantitative recoveries for both inorganic mercury and methylmercury are obtained from a spiked natural water sample.     

Short-term bioconcentration and distribution of methylmercury,tributyltin and corresponding inorganic species in the starfish leptasterias polaris

Starfish, Leptasterias polaris, were exposed between 30 min and 48 h to seawater containing 0.25 nmol dm^?3 of radiolabelled methylmercury (Me²⁰³HgCI), tributyltin [(C₄H₉)₃¹¹³SnCI], and inorganic ²⁰³HgCI₂ and ¹¹³SnCI⁴, with the objectives of comparing the uptake and distribution kinetics of these metal species in organs and tissues of treated organisms. Some starfish exposed to metals for 48 h were allowed to depurate for 24 h in clean seawater. Whole-body autoradiography was used to locate radiotracers very precisely within starfish tissues. The total amount of methylmercury (MeHg) accumulated in the whole animal after 48 h reached 0.53 nmol compared with 0.09 nmol for inorganic mercury, while tributyltin (TBT) reached 0.72 nmol compared with 0.017 nmol for inorganic tin. No significant reduction of body burdens occurred during the depuration period. The first-order rate constant characterizing the uptake of metals by whole animals, k₁, ranged from 0.102 h^?1 for MeHg to 3.6 × 10^?3h^?1 for inorganic mercury(II) and to 8.4 × 10^?4 h^?1 for inorganic tin(IV). The first-order rate constant characterizing the translocation of metals from seawater-exposed tissues toward internal organs, k₃, was available for inorganic Hg and Sn and had values similar to k₁. Concentration ratios between external tissues and internal organs after a 48 h exposure were 11.5 and 25.4 for MeHg and TBT, respectively, and 2.1 and 6.1 for inorganic mercury and tin. Furthermore, autoradiograms showed that MeHg and TBT were accumulated only on the external surface of the body wall and podia. This finding indicates a much slower translocation process for organometallic species than inorganic species, a process which seems to be related to the binding mode of MeHg and TBT to the organic matrix of external tissues of starfish.     

Preconcentration of phenlymercury,methylmercury and inorganic mercury from natural waters with diethylammonium diethyldithiocarbamate-loaded polyurethane foam

The percentage extraction of organomercurials and inorganic mercury on polyurethane foam loaded with diethylammonium diethyldithiocarbamate is high over a wide pH range, particularly when a plasticizer is added to the foam. Flow rates up to 120 ml min^-1 give quantitative extraction of inorganic mercury. Mercury(II), methylmercury and phenylmercury ions at 1 μg l^-1 levels can be almost quantitatively preconcentrated from tap and saline water, and eluted from the foam with acetone.     

Photoelectrochemical determination of inorganic mercury in aqueous solutions

An analytical method using an optical probe in a photoelectrochemical cell for the sensitive and selective determination of aqueous Hg²⁺ is presented. A previously synthesized Hg²⁺ selective chemosensor, proven to be Hg²⁺ sensitive up to 2 μg L⁻¹, has been immobilized onto indium tin oxide (ITO) electrodes in a composite form with polyaniline. The coated ITO electrode was placed in a photoelectrochemical cell under closed circuit conditions in which the optical recognition of the chemosensor was converted to a measurable signal. A composite of the fluorescent chemosensor, Rhodamine 6G derivative (RS), and polyaniline (PANI) was immobilized on ITO glass plates and subjected to photovoltage measurements in the absence and presence of Hg²⁺. The optical responses of the coated electrode were used to determine the sensitivity and selectivity of the immobilized sensor to Hg²⁺ in the presence of background ions. The optical response of the PANI-dye coated electrode increased linearly with increasing Hg²⁺ concentration in the range 10-150 μg L⁻¹, with a detection limit of 6 μg L⁻¹.     

Demethylation of methylmercury during inorganic mercury determination by the magos cold vapor atomic absorption technique

Previous animal experiments suggested that the Magos cold vapor atomic absorption spectroscopic (CVAAS) method might overestimate the concentrations of inorganic mercury (I-Hg) in the presence of methylmercury (MeHg). In the present study it is shown that this error is due to a fast degradation of MeHg during the formation of the analytical signal. For brain samples, about 5% of the total amount of MeHg in the reaction vessel is degraded to I-Hg. Speciation of Hg in aqueous solution of MeHg chloride, after purification with ionexchange chromatography using the Magos method, showed that about 9% was I-Hg. Analysis by NMR of MeHg chloride and MeHg hydroxide showed that less than 1% was in the form of I-Hg. The absolute magnitude of the error in the CVAAS method is dependent on the amounts of SnCl₂ and MeHg in the reaction vessel; however, the ratio of I-Hg to total (T-Hg) is shown to be independent of the amount of MeHg (25.5–255 ng as Hg) in the reaction vessel. A procedure for corrections is proposed, based on the results from these studies and empirical data from speciation analyses of brain tissue from MeHg-exposed rats and rabbits.     

Storage stability of reactive phenolic dispersions

Storage stability of an aqueous phenolic dispersion resin has been studied by accelerated methods with chemical kinetics and centrifugation. The activation energy of the resin advancement reaction was 25.6 kcal/g mole. Results indicate that the chemical and physical properties of the dispersion resin do not change significantly in a storage period of 4.5 months under normal conditions (25°C). Under refrigeration (4°C) the product is stable indefinitely for all practical purposes.