Gold-coated Sand Research Articles

Sampling of atmospheric Hgo using home-made gold-coated sand sorbent prior to analysis by atomic absorption spectrometry

Gold-coated sand for amalgamation was synthesized and applied for the determination of mercury in ambient air using a home-made dual gold trap unit coupled to atomic absorption spectrometer. Gold-coated sand is prepared by chemical reduction of Au(III) solution with hydroxylamine depositing elemental gold on acid-etched sand. A home-made dual gold trap unit which focused time-resolved mercury trapped from the sampling/first trap provided an increase in sensitivity and reliability for the analysis of ultra-trace mercury in air was designed and tested. Instrumental detection and quantitation limits (IDL and IQL) of system were 3.9 and 13pg Hg, respectively. Method detection and quantitation limits (MLOD and MLOQ) of system were 0.04 and 0.13ngHg.m-3 for sampling flow rate of 200mL.min-1 and sampling time of 8 hours. Sampling system for gaseous elemental mercury was set up and cooperated with home-made desorption system were preliminarily applied for analysis of atmospheric mercury in samples collected at Hochiminh city University of Science. The atmospheric mercury concentrations were in range of 2.7 – 8.1ng Hg. m-3 which were comparable to Hg concentration found in other cities in the world.

Development of Fast Sampling and High Recovery Extraction Method for Stable Isotope Measurement of Gaseous Mercury

A method involving fast large-volume sampling and bag extraction of total gaseous mercury (TGM) using a 5 mL acid solution was developed for stable mercury isotope ratio measurements. A big gold-coated sand trap (BAuT)—a 45 (i.d.) × 300 mm (length) quartz tube with 131 times more trapping material than a conventional gold trap—was used for the collection of a large amount of TGM. The collected TGM was extracted using 5 mL inversed aqua regia in a 2 L Tedlar bag followed by isotope measurements using a cold vapor generator coupled with a multicollector inductively coupled plasma mass spectrometer. Sampling tests demonstrated that the collection efficiency of the BAuT was 99.9% or higher during the 1–24 h sampling period under the flow rate of 20–100 L min−1. Recovery tests of 24 h bag extraction using 100 ng NIST SRM 8610 exhibited nearly 100% recovery yields. The five measured stable mercury isotope ratios agreed with reference values within 2σ intervals. The overall methodology tested during the pilot field and laboratory studies demonstrated its successful application in analysis, promising highly precise stable mercury isotopic data with a time resolution of less than 24 h.

Evaluation of passive sampling of gaseous mercury using different sorbing materials.

Atmospheric mercury monitoring is essential because of its potential human health and ecological impacts. Current automated monitoring systems include limitations such as high cost, complicated configuration, and electricity requirements. Passive samplers require no electric power and are more appropriate for screening applications and long-term monitoring. Sampling rate is a major factor to evaluate the performance of a passive sampler. In this study, laboratory experiments were carried out using an exposure chamber to search for high efficiency sorbents for gaseous mercury. Four types of sorbents, including sulfur-impregnated carbon (SIC), chlorine-impregnated carbon (CIC), bromine-impregnated carbon (BIC), and gold-coated sand (GCS) were evaluated under a wide range of meteorological parameters, including temperature, relative humidity, and wind speed. The results showed that the four sorbents all have a high sampling rate above 0.01m3g-1day-1, and wind speed has a positive correlation with the sampling rate. Under different temperature and relative humidity, the sampling rate of SIC keeps stable. The sampling rate of CIC and BIC shows a negative correlation with temperature, and GCS is influenced by all the three meteorological factors. Furthermore, long-term experiments were carried out to investigate the uptake capacity of GCS and SIC. Uptake curves show that the mass amount of sorbent in a passive sampler can influence uptake capacity. In the passive sampler, 0.9g SIC or 0.9g GCS can achieve stable uptake efficiency for at least 110days with gaseous mercury concentration at or below 2ng/m3. For mercury concentration at or below 21ng/m3, 0.9g SIC can maintain stable uptake efficiency for 70days, and 0.9g GCS can maintain stability for 45days.

Preparation of gold-coated sand for ultratrace mercury analysis

In this study, the gold-coated sand was prepared to make gold-trap for mercury analysis at ultra-trace levels. The preparation process was conducted with the etching of sand surface to form silanol groups using a mixture of H2O2/H2SO4 followed by the replacement of the silanol groups by amino groups with aminopropyltriethylsilane. The amino-modified surface is embedded with Au atoms by soaking the amino modified sand in nano gold solution then the Au film is thickened with a mixture of Au(III)+NH2OH.HCl. The gold-coated sand can capture up to 21 μg Hg per 1 g of sorbent. The interferences for the efficiency of mercury sorption such as HNO3, HCl, H2SO4 and temperatureare were investigated. The goldcoated sand was successfully applied for mercury analysis in certified reference materials (DORM-4) by CV-AAS and combustion/thermal decompostion methods.

Analytical performances of nanostructured gold supported on metal oxide sorbents for the determination of gaseous mercury.

Nanostructured gold supported TiO2, ZnO, and Al2O3 materials (1% w/w Au) were tested as sorbents for gaseous mercury (Hg) trapping and preconcentration. Their analytical performances were first compared with the one of traditional gold wool trap for the quantification of Hg standards injected into the argon flow followed by thermal desorption at 600°C and CVAFS detection. Good linearity and reproducibility were obtained, especially for Au/TiO2 material (R 2 = 0.995; slope: 1.39) in the volume range of 10 to 60 µL (132–778 pg Hg). This latter even showed a better performance compared to pure Au in the volume range of 10 to 100 µL (132–1329 pg Hg) when the carrier gas flow was increased from 60 to 100 mL min−1. The method detection limit (MDL) obtained with Au/TiO2 trap (0.10 pg Hg0 L−1) was suitable for total gaseous mercury (TGM) determination. Au/TiO2 was, therefore, used in trapping and determining TGM in collected air samples. TGM values in the samples ranged from 6 to 10 ng m−3. Similar results were obtained with the commercial gold-coated sand trap which showed an average TGM concentration of 7.8 ± 0.9 ng m−3.

Evaluation of Potential for Mercury Volatilization from Natural and FGD Gypsum Products Using Flux-Chamber Tests

Synthetic gypsum produced by flue-gas desulfurization (FGD) in coal-fired power plants (FGD gypsum) is put to productive use in manufacturing wallboard. FGD gypsum wallboard is widely used, accounting for nearly 30% of wallboard sold in the United States. Mercury is captured in flue gas and thus is one of the trace metals present in FGD gypsum; raising questions about the potential for mercury exposure from wallboard. Mercury is also one of the trace metals present in "natural" mined gypsum used to make wall board. Data available in the literature were not adequate to assess whether mercury in wallboard from either FGD or natural gypsum could volatilize into indoor air. In this study, mercury volatilization was evaluated using small-scale (5 L) glass and Teflon flux chambers, with samples collected using both iodated carbon and gold-coated sand traps. Mercury flux measurements made using iodated carbon traps (n=6) were below the detection limit of 11.5 ng/m2-day for all natural and synthetic gypsum wallboard samples. Mercury flux measurements made using gold-coated sand traps (n=6) were 0.92 +/- 0.11 ng/m2-day for natural gypsum wallboard and 5.9 +/- 2.4 ng/m2-day for synthetic gypsum wallboard. Room air mercury concentrations between 0.028 and 0.28 ng/m3 and between 0.13 and 2.2 ng/m3 were estimated based on the flux-rate data for natural and synthetic gypsum wallboard samples, respectively, and were calculated assuming a 3 m x 4 m x 5 m room, and 10th and 90th percentile air exchange rates of 0.18/hour and 1.26/hour. The resulting concentration estimates are well below the U.S. Environmental Protection Agency (EPA) reference concentration for indoor air elemental mercury of 300 ng/m3 and the Agency for Toxic Substances and Disease Registry minimal risk level (MRL) of 200 ng/m3. Further, these estimates are below background mercury concentrations in indoor air and within or below the range of typical background mercury concentrations in outdoor air.

Gas-Phase Mercury Reduction to Measure Total Mercury in the Flue Gas of a Coal-Fired Boiler

Gaseous elemental and total (elemental + oxidized) mercury (Hg) in the flue gas from a coal-fired boiler was measured by a modified ultraviolet (UV) spectrometer. Challenges to Hg measurement were the spectral interferences from other flue gas components and that UV measures only elemental Hg. To eliminate interference from flue gas components, a cartridge filled with gold-coated sand removed elemental Hg from a flue gas sample. The Hg-free flue gas was the reference gas, eliminating the spectral interferences. To measure total Hg by UV, oxidized Hg underwent a gas-phase, thermal-reduction in a quartz cell heated to 750°C. Simultaneously, hydrogen was added to flash react with the oxygen present forming water vapor and preventing Hg re-oxidation as it exits the cell. Hg concentration results are in parts per billion by volume Hg at the flue gas oxygen concentration. The modified Hg analyzer and the Ontario Hydro method concurrently measured Hg at a field test site. Measurements were made at a 700-MW steam turbine plant with scrubber units and selective catalytic reduction. The flue gas sampled downstream of the selective catalytic reduction contained 2100 ppm SO2 and 75 ppm NOx. Total Hg measured by the Hg analyzer was within 20% of the Ontario Hydro results.

Potential atmospheric transport pathways for mercury measured in the Canadian High Arctic.

Large-scale transport pathways for atmospheric gaseous mercury emitted from surrounding source regions to reach the Alert sampling site located at the Northwest Territories of Canada between August 1992 and August 1993 were investigated. The 12-month atmospheric mercury data set comprises blank-corrected total gaseous mercury (TGM) concentrations collected on gold-coated sand traps during one-week long sampling intervals. For TGM concentrations above the 12-month mean TGM level, the analysis reveals regions in Eastern Europe (close to East Germany and Poland), areas on Northeastern America in Canada (Northwest Territories), and central Siberia of the former U.S.S.R. Identification of the physical locations of the emission sources was limited by the temporal resolution of weekly averaged data; however, major atmospheric pathways of mercury transport to the Arctic were successfully resolved. The objective of this note is to demonstrate that the potential source contribution function could be applied to resolve the sources and recover transport pathways of atmospheric mercury over a large scale.

Mercury content of Antarctic surface snow: Initial results

Surface snow from Windless Bight, Ross Ice Shelf, Antarctica has been analyzed for its Hg content. Ultra-clean techniques were used for field extraction of Hg onto gold-coated sand, followed by photo-acoustic analysis within 24 h. Results yield a mean mercury content of 2.7 pg g −1. However, the true level is probably < 1 pg g −1, as measured amounts decreased throughout the period of sampling, indicating that the first samples were probably contaminated and that later results are likely to be more accurate. Our results suggest that previous studies of Antarctic snow have suffered from major contamination problems. Refinement of techniques should allow historical trends in atmospheric Hg levels to be identified from a snow pit at a suitable remote site.

Determination of Mercury in Surface Waters Using an Optimized Cold Vapor Spectrophotometric Technique

Abstract An analytical method to measure mercury in environmental samples was optimized based upon amalgamation of mercury on gold-coated sand and subsequent ultraviolet absorption measurement of the mercury vapor driven off the sand upon heating. Sample handling and storage methods were employed that were virtually free from mercury loss or contamination. Analytical procedures were tested on standard reference materials obtained from the USEPA and USGS and at concentration levels in the range anticipated for the environmental samples. Stream samples, collected over a seven-month period, were filtered (0.45 μm) in the field, and the mercury in dissolved and particulate fractions was determined. Dissolved mercury concentrations ranged from 24.1 ng/1 to 116.9ng/1 (N = 120) while particulate mercury concentrations ranged from 0.2 μg/g to 33.4 μg/g (N = 120). The method has been found useful for analyzing environmental samples and has been shown to be very sensitive and free of interferences.

Determination of mercury emissions from a municipal incinerator

A cold-vapor atomic absorption system is described for the determination of volatile mercury in the stack gases of a municipal solid-waste incinerator. The gases are washed in a K/sub 2/CR/sub 2/O/sub 7//HNO/sub 3/ solution. By oxidation of the mercury in the washing bottle, a 99% collection efficiency is obtained. Total collection is guaranteed by adding a gold-coated sand absorber to the sampling train. After sampling, aliquots of the diluted absorbing solution are analyzed according to the reduction-aeration method with SnC/sub 12/. The released mercury is concentrated on a gold absorber. After thermal desorption from the gold, the mercury is measured in a modified atomic absorption spectrometer. The detection limit of the combined method is 1 ng. Calibration is achieved by injection of elemental mercury onto the gold. Generally, the reproducibility is better than 3%. The mercury concentrations found vary from 121 to 163 mu g of Hg per cubic metre of flue gas.

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.

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.