Chun-Mao Tseng

Rapid Determination of Inorganic Mercury and Methylmercury in Biological Reference Materials by Hydride Generation, Cryofocusing, Atomic Absorption Spectrometry After Open Focused Microwave-assisted Alkaline Digestion

A rapid and simple microwave-assisted digestion method with alkaline solution (tetramethylammonium hydroxide or methanolic KOH solution) for speciation analysis of inorganic mercury and methylmercury (MeHg + ) in biological tissues was developed. Extracts with quantitative recoveries of mercury species after microwave-assisted alkaline dissolution of the sample were directly analysed by an automated on-line hyphenated system incorporating aqueous hydride generation, cryogenic trapping, gas chromatography and detection by atomic absorption spectrometry. Optimum conditions allow sample throughput to be controlled by the instrumental analysis time (≈10 min per sample) and not by the sample preparation step. At a power of 40–60 W, sample preparation time is only 2–4 min, which is much faster than previous literature methods. The proposed method was validated by the analysis of three biological certified reference materials, CRM 463, DORM-1 and TORT-1, and one BCR sample from an interlaboratory study, Tuna Fish 2. The detection limit of the overall procedure was found to be 3 ng per gram of pulverised dried biological tissue, for both labile Hg 2+ and MeHg + . After alkaline extraction, a mean recovery of 102% with a relative standard deviation of 7% was obtained for methylmercury concentrations ranging from 0.128 to 3.464 µg g -1 as Hg in the four reference fish tissues mentioned above. Total mercury, calculated as the sum of determined inorganic mercury and methylmercury, was also in agreement with the certified values. The methylmercury extraction efficiency of five extractants, viz. , nitric, hydrochloric and acetic acid, and tetramethylammonium hydroxide and methanolic KOH solution, the temperature profile of these extractants under microwave irradiation and the behaviour and stability of methylmercury in a focused microwave field were also investigated.

A unique seasonal pattern in phytoplankton biomass in low‐latitude waters in the South China Sea

elevated to 0.3 mg/m 3 , 35 mg/m 2 and 300 mg-C/m 2 /d, respectively, in the winter but stayed low, at 0.1 mg/m 3 , 15 mg/m 2 and 110 mg-C/m 2 /d as commonly found in other low latitude waters, in the rest of the year. Concomitantly, soluble reactive phosphate and nitrate+nitrite in the mixed layer also became readily detectable in the winter. The elevationofphytoplanktonbiomasscoincidedapproximately with the lowest sea surface temperature and the highest wind speed in the year. Only the combined effect of convective overturn by surface cooling and wind-induced mixing could have enhanced vertical mixing sufficiently to make the nutrients in the upper nutricline available for photosynthetic activities and accounted for the higher biomass in the winter. Citation: Tseng, C.-M., G. T. F. Wong, I.-I. Lin, C.-R. Wu, and K.-K. Liu (2005), A unique seasonal pattern in phytoplankton biomass in low-latitude waters in the South China Sea, Geophys. Res. Lett., 32, L08608, doi:10.1029/2004GL022111.

Rapid and Quantitative Microwave-assisted Recovery of Methylmercury From Standard Reference Sediments

A simple and rapid method has been developed to determine methylmercury in sediments. The procedure is based on the quantitative microwave-assisted leaching of methylmercury from sediments with an acidic extractant. Sample preparation is achieved in an open focused microwave field by heating about 1 g of dry sediment suspended into 10 ml of 2 mol l -1 HNO 3 during 3–4 min at a power of 40–60 W. The extracted mercury compounds are ethylated, cryogenically trapped in a chromatographic phase, successively eluted and detected in an electrothermally heated quartz furnace by CV AAS. The method has been validated by the analysis of the certified IAEA-356 and CRM 580 reference materials and one sediment sample, BCR S19, from an intercomparison study within the framework of a certification exercise sponsored by the Community Bureau of Reference (BCR) of the European Commission. The detection limit of the procedure is 0.5 ng of methylmercury per gram of dry sediment. After analysis of the sediments mentioned above (methylmercury ranging from 5 to 80 ng g -1 ), a mean methylmercury recovery of 97% and an RSD of 7% were obtained. Under optimum conditions, sample throughput is restricted by the instrumental analysis time (about 20 min per sample), rather than by the sample preparation step. In addition, the methylmercury extraction efficiency of four different acids, nitric, hydrochloric, sulfuric and acetic acid, has been investigated for comparison. Results on the behaviour and stability of methylmercury in a microwave field are also provided.

Cryofocusing coupled to atomic absorption spectrometry for rapid and simple mercury speciation in environmental matrices

A fully automated on-line hyphenated system for mercury speciation analysis in environmental samples is presented. It provides derivatization by hydride generation or ethylation, preconcentration by cryotrapping, separation by packed column gas chromatography and detection by quartz furnace atomic absorption spectrometry. Automation of the hyphenation results in improved reproducibility of the analysis. The system has been specifically optimised for analysis of mercury compounds, but it is also potentially operative for other hydride- or ethylated derivative-forming elements, after the corresponding optimisation. Main advantages and potential limitations of the system are discussed. General procedures for the analysis of both solid (sediments, biotissues, suspended particulate matter) and liquid (sea and fresh water) samples are proposed and validated by analysis of certified reference materials. The obtained methylmercury and inorganic mercury concentrations are in agreement with the certified values. Detection limits of the method have been estimated as 0.5 ng g–1 , 3 ng g–1 , 0.1 ng l–1 for both mercury species in dry sediments, biological tissues and aqueous samples, respectively. Analysis of one sample only requires 10 min (hydride generation) or 20 min (ethylation), so that a sample throughout of 6 or 3 samples h–1, respectively, may be achieved. Results from the analysis of real samples collected in the Gironde and Scheldt estuaries (sediments, suspended particulate matter, water and biological tissues) are also provided.

Interferences generated by organic and inorganic compounds during organotin speciation using hydride generation coupled with cryogenic trapping, gas chromatographic separation and detection by atomic absorption spectrometry

Abstract Hydride generation reactions are frequently used for the speciation analysis of organotin compounds in a wide variety of matrices. However, the organotin determination procedure may be altered by different interferences mechanisms. This work evaluates the interferences likely to occur in the determination of tributyltin in a harbour sediment candidate reference material for the EEC Community Bureau of Reference with the method of hydride generation combined on-line with cryogenic trapping, gas chromatographic separation and detection by atomic absorption spectrometry. First, a full geochemical characterization of the sediment and of its acetic acid leachate was achieved to evaluate interfering compounds that may inhibit the determination of TBT by hydride generation in this sediment. Second, interference studies on various organic and inorganic compounds likely to alter the overall organotin determination were carried out with simple model solutions. These model solutions were spiked successively with different possible interfering compounds mixed with the organotins under study, i.e., monomethyltin (MMT), monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in a mixed solution at concentrations of 5 ng as Sn of each compound in 50 ml of water. Organic interferents studied were organic pollutants (organic solvents, polychlorinated biphenyls, pesticides, n -alkanes), humic substances and a complexing agent, EDTA. The inorganic interferents were represented by a mixture of fourteen inorganic metals. The addition of organic compounds to the hydride generation reaction had little effect on the signal suppression for all organotin species. Reproducibility was significantly affected only by the presence of humic substances in solution. Signal suppression was observed only for the monoalkyltins (MMT and MBT) in the presence of EDTA. Solutions of mixed inorganic metals were found to be highly efficient in inducing severe signal suppression for all organotin compounds at a level of 100 μg of each element. Interference mechanisms during the speciation determination step are outlined and discussed.

Interferences during mercury speciation determination by volatilization, cryofocusing, gas chromatography and atomic absorption spectroscopy: comparative study between hydride generation and ethylation techniques

The interfering effects of sodium chloride and a mixture of metal ions on the speciation determination of mercury by derivatization (hydride generation or ethylation), preconcentration by cryotrapping, gas chromatographic separation and detection by quartz furnace atomic absorption spectroscopy were investigated. The potential of the masking agent EDTA to overcome the interference was also studied. The experiments were arranged according to a 2n+1 factorial experimental design, so the possibility of synergistic effects among the variables considered was also taken into account. NaCl interferes in the determination of methylmercury (MeHg+) by ethylation, but causes fewer problems in the case of inorganic mercury (Hg2+) or if the analysis is carried out by hydride generation. The presence of metal ions strongly decreases the sensitivity in the determination of both compounds by hydride generation, but has no effect if ethylation is used as the derivatization technique. EDTA only partially eliminates the interfering effect of metals in the determination of MeHg+ by hydride generation. It also avoids decomposition of MeHg+ to Hg0 , promoted by NaCl, after derivatization of the compounds by hydride generation. The results obtained are discussed in terms of a comparison between the two derivatization techniques used, i.e., hydride generation and ethylation. Potential chemical pathways and reaction mechanisms for the observed interferences are also given.

Potential interferences generated during mercury species determination using acid leaching, aqueous ethylation, cryogenic gas chromatography and atomic spectrometry detection techniques

A careful search for formation of methylmercury (MeHg+) as an artefact and for potential interferences has been carried out using an analytical procedure involving aqueous phase ethylation, cryogenic trapping, low temperature gas chromatography and quartz furnace atomic absorption spectrometry (Eth-CT-GC-QFAAS) for mercury speciation, after open-focused microwave extraction. The results show that spurious MeHg+ formation from Hg2+ can occur mainly in the chromatographic column during the determination step rather than during the extraction step. The silanizing agent, dimethyldisilazane, acting as a methyl donor, appears to be responsible for the EtMeHg formation when high concentrations of Hg2+ (>1 ppm) are present in the solution during the analysis. On the other hand, the production of several unknown peaks, closely corresponding to Me2Hg, Et2Hg etc. in the chromatogram, is the result of impurities in the derivatizing agent, NaBEt4. The magnitude of these interferences varies with different lots of reagent. The derivatization and determination steps must always be checked following standard QA/QC procedures. Once interference problems are taken into account, reliable understanding of Hg cycling and behaviour in aquatic environments will be achieved.

Field cryofocussing hydride generation appliedto the simultaneous multi-elemental determination of alkyl-metal(loid)species in natural waters using ICP-MS detection

Two hydride generation manifold systems, utilizing flow injection and cryotrapping techniques for alkyl-metal(loid) speciation analysis in natural waters, are described in this paper. They provide shipboard capacity for simultaneous derivatization of analytes with NaBH4 and cryotrapping of the generated products in a field packed column at -196 degrees C. The first system is a large-volume hydride generator, using a reagent-injection flow technique as a flow batch type, that has been fully optimized and applied to the simultaneous detection of alkylated species in estuarine waters. The technique permits the analysis of a large volume sample (0.5-11) at a sampling rate of 3 h-1. The second is an online continuous flow hydride generator. A sampling rate of 3-12 h-1 can be achieved with samples of 0.1-0.51. In addition, shipboard operation eliminates major problems related to sample pretreatment, transport and storage. Ultra-trace multi-element determination is finally performed in the laboratory by cryogenic GC hyphenated with ICP-MS. Routine detection limits of 0.5-10 pg (as metal) for 0.51 water samples were achieved for the selected alkyl-metal(loid) species of arsenic, germanium, mercury and tin. Concentrations of various species, obtained from water samples taken from the Rhine estuary, are also presented. These species include alkylated arsenic compounds, other than methyl derivatives, that have been tentatively identified and are reported here for the first time.

Tungsten and other heavy metal contamination in aquatic environments receiving wastewater from semiconductor manufacturing

Through analyses of water and sediments, we investigate tungsten and 14 other heavy metals in a stream receiving treated effluents from a semiconductor manufacturer-clustered science park in Taiwan. Treated effluents account for ∼ 50% of total annual river discharge and <1% of total sediment discharge. Dissolved tungsten concentrations in the effluents abnormally reach 400 μg/L, as compared to the world river average concentration of <0.1 μg/L. Particulate tungsten concentrations are up to 300 μg/g in suspended and deposited sediments, and the corresponding enrichment factors are three orders of magnitude higher than average crust composition. Surprisingly, the estimated amount of tungsten exported to the adjacent ocean is 23.5 t/yr, which can approximate the amount from the Yangtze River should it be unpolluted. This study highlights the urgency of investigating the biological effect of such contamination.

Prokaryotic assemblages and metagenomes in pelagic zones of the South China Sea

BackgroundProkaryotic microbes, the most abundant organisms in the ocean, are remarkably diverse. Despite numerous studies of marine prokaryotes, the zonation of their communities in pelagic zones has been poorly delineated. By exploiting the persistent stratification of the South China Sea (SCS), we performed a 2-year, large spatial scale (10, 100, 1000, and 3000 m) survey, which included a pilot study in 2006 and comprehensive sampling in 2007, to investigate the biological zonation of bacteria and archaea using 16S rRNA tag and shotgun metagenome sequencing.ResultsAlphaproteobacteria dominated the bacterial community in the surface SCS, where the abundance of Betaproteobacteria was seemingly associated with climatic activity. Gammaproteobacteria thrived in the deep SCS, where a noticeable amount of Cyanobacteria were also detected. Marine Groups II and III Euryarchaeota were predominant in the archaeal communities in the surface and deep SCS, respectively. Bacterial diversity was higher than archaeal diversity at all sampling depths in the SCS, and peaked at mid-depths, agreeing with the diversity pattern found in global water columns. Metagenomic analysis not only showed differential %GC values and genome sizes between the surface and deep SCS, but also demonstrated depth-dependent metabolic potentials, such as cobalamin biosynthesis at 10 m, osmoregulation at 100 m, signal transduction at 1000 m, and plasmid and phage replication at 3000 m. When compared with other oceans, urease at 10 m and both exonuclease and permease at 3000 m were more abundant in the SCS. Finally, enriched genes associated with nutrient assimilation in the sea surface and transposase in the deep-sea metagenomes exemplified the functional zonation in global oceans.ConclusionsProkaryotic communities in the SCS stratified with depth, with maximal bacterial diversity at mid-depth, in accordance with global water columns. The SCS had functional zonation among depths and endemically enriched metabolic potentials at the study site, in contrast to other oceans.