The effects of oxygen on the detection of mercury using laser-induced breakdown spectroscopy

A systematic study of the processes associated with mercury atomic emission in a laser-induced plasma and the interactions of mercury with oxygen species is presented. At early plasma decay times, on the order of 5–10 μs, no significant variation in mercury atomic emission was observed with the addition of oxygen-containing species. At intermediate and long decay times (10–100 μs), a significant reduction in the 253.7-nm mercury emission intensity was recorded with the introduction of oxygen-containing species. The decrease in mercury emission was temporally coincident with the recombination of atomic oxygen, as measured by the O(I) emission. The decreased mercury emission was not due to thermal effects, based on plasma temperature measurements, and was independent of the molecular source of oxygen, for similar concentrations of oxygen as air, carbon dioxide, and carbon monoxide. Analysis of additional mercury atomic emission lines revealed that the reduction in mercury emission in the presence of oxygen species is limited primarily to the 253.7-nm transition. In concert, the data lead to the conclusion that the 253.7-nm mercury emission line is selectively quenched by oxygen species, primarily O₂ and NO, that are formed during the plasma recombination process. Implications for laser-induced breakdown spectroscopy-based emissions monitoring of mercury species are discussed.     

The influence of mercury contact angle, surface tension, and retraction mechanism on the interpretation of mercury porosimetry data

The use of a semi-empirical alternative to the standard Washburn equation for the interpretation of raw mercury porosimetry data has been advocated. The alternative expression takes account of variations in both mercury contact angle and surface tension with pore size, for both advancing and retreating mercury meniscii. The semi-empirical equation presented was ultimately derived from electron microscopy data, obtained for controlled pore glasses by previous workers. It has been found that this equation is also suitable for the interpretation of raw data for sol-gel silica spheres. Interpretation of mercury porosimetry data using the alternative to the standard Washburn equation was found to give rise to pore sizes similar to those obtained from corresponding SAXS data. The interpretation of porosimetry data, for both whole and finely powdered silica spheres, using the alternative expression has demonstrated that the hysteresis and mercury entrapment observed for whole samples does not occur for fragmented samples. Therefore, for these materials, the structural hysteresis and overall level of mercury entrapment is caused by the macroscopic (> approximately 30 microm), and not the microscopic (< approximately 30 microm), properties of the porous medium. This finding suggested that mercury porosimetry may be used to obtain a statistical characterization of sample macroscopic structure similar to that obtained using MRI. In addition, from a comparison of the pore size distribution from porosimetry with that obtained using complementary nitrogen sorption data, it was found that, even in the absence of hysteresis and mercury entrapment, pore shielding effects were still present. This observation suggested that the mercury extrusion process does not occur by a piston-type retraction mechanism and, therefore, the usual method for the application of percolation concepts to mercury retraction is flawed.     

Calibrated nanoinjections of mercury vapor

A simple technique for the calibration of mercury vapor chemosensors is described. It is based on a reductive deposition of a well-defined quantity of mercury (0) onto gold wire followed by thermal evaporation of the mercury into the sensor cell. The quantity of mercury on the gold wire was measured electrochemically by oxidation before and after heating, as well as after storage under different conditions. It is shown that the technique can be used for calibrated injections of nanogram quantities of mercury. The approach was applied to test the performance of ultrasensitive mercury chemoresistors.     

Calibrated nanoinjections of mercury vapor

A simple technique for the calibration of mercury vapor chemosensors is described. It is based on a reductive deposition of a well-defined quantity of mercury (0) onto gold wire followed by thermal evaporation of the mercury into the sensor cell. The quantity of mercury on the gold wire was measured electrochemically by oxidation before and after heating, as well as after storage under different conditions. It is shown that the technique can be used for calibrated injections of nanogram quantities of mercury. The approach was applied to test the performance of ultrasensitive mercury chemoresistors.     

Direct measurement of the mercury content of exhaled air: a new approach for determination of the mercury dose received

A new rapid technique is presented for determination of the dose of mercury inhaled; it is based on direct measurement of the concentration of mercury in exhaled air by use of a Zeeman mercury spectrometer RA-915+. It has been demonstrated experimentally that the dose received during short-term exposure to mercury vapor is determined more reliably by this method rather than by conventional techniques based on measurement of the mercury content in blood or urine.     

Optimization of experimental parameters for the determination of mercury by MIP/AES

A system using a microwave induced plasma, as an emission source was optimized for total mercury determinations. The system contains a flow injection section in which mercury is reduced and deposited on a gold/platinum collector, and carried to the emission source. The microwave was generated in a Surfatron cavity. An experimental design was applied to optimize parameters concerning plasma conditions, amalgamation, desorption and mercury vapor generation. The limit of detection of the method was 14 pg ml(-1) of mercury, using peak area mode while LDs was 1.3 pg ml(-1) using peak height mode, with a 2% RSD and a linear dynamic range of almost three orders of magnitude. The accuracy was assessed using a certified reference material of atmospheric particulate National Institute of Standards and Technology (NIST) 2704. No significant difference at 95% confidence level was observed between the certified value and our result.     

固体进样直接测定法测定铜精矿中汞

建立了固体进样直接测定法测定铜精矿中汞含量的方法。铜精矿样品在测汞仪的分解炉中经300℃干燥和750℃高温热分解后,汞被催化分解为汞原子,于850℃齐化成金汞齐。汞蒸气被氧气流带入单波长光学吸收池,在波长253.7 nm处测量汞的吸光度,采用标准曲线法计算汞量。方法的线性范围分别为0~1.00,0~100μg/mL,线性相关系数为0.9999,检出限分别为0.10,0.04 ng/g。5个汞含量不同的铜精矿样品测定结果的相对标准偏差为2.14%~4.35%(n=11),样品加标回收率为92.00%~104.02%。采用该方法分别对2个铜精矿样品和铜精矿国际标准物质进行测定,测定结果与标准分析方法测定值和标准物质标示值基本一致。该方法简便、快速、准确,可以作为标准方法推广使用。     

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.     

The effect of humic acid on mercury solubility and complexation

Utilization of mercury in gold mining in the tropics has contributed to large inputs of the metal into the aquatic environment. Although in this activity mercury is utilized in its elemental state, which is relatively immobile and inert, transformations to methylmercury occurring in natural systems lead to mercury contamination of aquatic organisms and the food chain. We investigated the effectiveness and mechanisms involved in the solubilization of mercury in the presence of humic acid, which is an important component of dark river waters in the tropics. Results showed that the solubility of elemental mercury was enhanced due to the presence of humic acid through a solubilization–complexation mechanism, which was attributed to the presence of acid sites on the humic acid molecule, mainly the carboxyl group. Calcium ions in solution prevent humic‐acid‐induced elemental mercury solubility. Although it was demonstrated that the mercury complex formed is more mobile in the presence of humic acid, preliminary results indicated that this mercury complex seem absorbed by fish. Copyright © 2000 John Wiley & Sons, Ltd.     

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.     

Ultrasensitive determination of mercury by ICP-OES coupled with a vapor generation approach based on solution cathode glow discharge

We herein proposed a sample introduction technique based on solution cathode glow discharge（SCGD）of a portable design for inductively coupled plasma-optical emission spectrometry（ICP-OES） and its application in sensitive determination of mercury. The products from SCGD containing mercury vapor, were transported by an Ar flow to ICP spectrometer for detection. A gas liquid separator（GLS） and a dryer were used to condense and remove most of the accompanying moisture, which greatly improved both th...     

Possible interferences of mercury sulfur compounds with ethylated and methylated mercury species using HPLC-ICP-MS

The HPLC-ICP-MS coupling technique is able to separate and detect methyl, ethyl and inorganic mercury isotopes specifically. An identification of ethyl mercury(+) is not possible when the widely used sodium tetraethylborate derivatisation method in combination with GC-AFS/AAS or ICP-MS techniques is performed because it contains ethyl groups.An unidentified compound with the same retention time as ethyl mercury was found in the HPLC chromatograms of industrial sewage samples and humic-rich soils of microcosm experiments after applying water vapour distillation. We also observed such unidentified peaks in samples of heavily contaminated sites in Eastern Germany, separated by HPLC fractionation only. In the experiments described, different mercury sulfur adducts were synthesised and tested for their retention times in the HPLC-ICP-MS system. It was found that the compound CH₃–S–Hg⁺ showed the same retention time as the ethyl mercury standard. It is therefore possible that ethyl mercury detected in chromatography by comparison of the retention time could also be due to an adduct of a sulfur compound and a mercury species. CH₃–S–Hg⁺ should be tested in other chromatographic mercury speciation methods for this effect.This work can also be regarded as a contribution to the discussion of artificially occurring methyl mercury in sediments during sample preparation.     

Speciation analysis for mercury in gas condensates by capillary gas chromatography with inductively coupled plasma mass spectrometric detection

A method allowing species-selective determination of atomic mercury, non-polar dialkylated mercury compounds,polar monoalkylated species and inorganic mercury complexes in natural gas condensates was developed. Inductively coupled plasma mass spectrometry was employed as a detection method for capillary gas chromatography and compared with microwave induced plasma atomic emission detection for the analysis of hydrocarbon-rich matrices. The method was based on two consecutive injections allowing comprehensive speciation analysis. First a sample aliquot was diluted with toluene and analysed for Hg0 and individual dialkylmercury compounds. Then, another aliquot was butylated with a Grignard reagent for the species specific determination of Hg(II) and monoalkylated mercury species. The detection limits were down to 0.08 pg level.     

Accurate calibration of mercury vapour measurements

Almost all measurements of mercury vapour, for example those to determine mass concentration in air, are currently ultimately traceable to the vapour pressure of mercury, usually via a bell-jar calibration apparatus. This allows a saturated concentration of mercury vapour in air to develop in a confined space in equilibrium with ambient conditions, from which a known mass of mercury can be removed for calibration purposes. Setting aside the uncertainty in the vapour pressure of mercury at a given temperature, the accuracy of vapour phase mercury determinations depends critically on fully understanding the operation and sensitivities of the mercury bell-jar apparatus. This paper discusses the thermodynamic and kinetic considerations that must be taken into account when using the bell-jar apparatus, provides the theoretical basis for understanding the operation of the bell-jar, and presents experimental data demonstrating the systematic biases which may be obtained if the bell-jar is used incorrectly. These biases depend on the temperature difference between the mercury vapour in the bell-jar and the syringe used to remove the mercury vapour from the bell-jar, but they may be well in excess of 10% under some operating conditions. The results from this study have been used to propose best practice solutions for mercury vapour calibrations using the bell-jar.     

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.     

A radiochemical neutron activation analysis method for the determination of total mercury in coal

A radiochemical neutron activation analysis method has been developed based on pyrolysis followed by double gold amalgamation for the determination of mercury in solid samples. Accurate results were obtained for mercury in six standard reference materials of varying matrices, including coal. Linearity was demonstrated up to mercury concentrations of 10,000 ng/g. The method is capable of yielding precise, reproducible values with a detection limit of 5 ng/g for mercury in coal.     

Voltammetry of osmium-modified DNA at a mercury film electrode: application in detecting DNA hybridization

Mercury film electrodes (MFE) have recently been used in nucleic acid electrochemical analysis as alternatives to the classical mercury drop ones. DNA modified with osmium tetroxide, 2,2'-bipyridine (Os,bipy) can be detected with a high sensitivity at mercury electrodes via measurements of a catalytic osmium signal. In this paper we show that mercury film on a glassy carbon electrode can be used in voltammetric analysis of Os,bipy-modified DNA. Application of the MFE as a detection electrode in double-surface electrochemical DNA hybridization assay involving osmium labeling of target DNA is demonstrated.     

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.     

The liquid membrane process for the separation of mercury from waste water

The separation of mercury from waste water by means of the liquid membrane process (LMP) was investigated. The mercury was transferred from the external continuous phase across the liquid membrane to the internal phase. Dibutylbenzoylthiourea was used as a carrier in the liquid membrane, and Rofetan OM as a surfactant. The mercury reacts with thiourea in the internal phase to give a mercury—urea complex. The chemical system used for LMP is very efficient in the transfer of mercury. Laboratory experiments were primarily concerned with the influence of different volume ratios and initial concentrations of mercury. In the majority of cases more than 95% of the mercury in the external phase is transferred across the liquid membrane within three minutes. The experimental values could be quantitatively represented by an empirical model.     

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.