高效液相色谱-原子荧光光谱法测定海产品中甲基汞

为调查渤海海域海产品中甲基汞的污染情况,建立了高效液相色谱-原子荧光光谱法测定海产品中甲基汞的分析方法。样品中甲基汞经提取剂磁力搅拌提取20min,0.1μm有机系尼龙微孔滤膜过滤,以10%甲醇+0.04mol/L乙酸铵+0.1%L-半胱氨酸为流动相,用HC-C18 0.5um色谱柱分离,原子荧光光谱法进行测定。甲基汞在2-40ng/mL范围内线性关系良好,相关系数r＞0.999,方法检出限为0.02ng/mL,回收率在97.2-99.2%之间,相对标准偏差为3.7%。首次采用0.1%L-半胱氨酸+10%甲醇作为提取剂,该方法操作简单,精密度高,干扰少,可用海产品中甲基汞的测定。     

Effects of sample preparation on methylmercury concentrations in Arctic organisms

The biogeochemical cycling of mercury (Hg) in the marine environment is an issue of global concern, as consumption of marine fish is a major route of human exposure to the toxic specie methylmercury (MeHg). The most widely utilised and accepted technique for preparing biological tissue samples for the analysis of MeHg involves an alkaline digestion of the sample. Recent studies suggest, however, that this technique is inadequate to produce satisfactory recoveries for certain biological samples, including fish, fur, feathers and other ‘indicator’ tissues which contain relatively high levels of MeHg. Thus an improved acidic extraction method has been proven to produce more satisfactory results for a wide range of biological tissues. The present study compares the two methods on real sample material from different organisms of an Arctic marine food chain, and shows how this could lead to misinterpretation of analytical results. Results show significantly (p < 0.05) lower concentrations for alkaline digestion for large parts of the food chain; especially in fish and birds. The mean differences in concentrations found between the two different methods were 28, 31 and 25% for fish (Polar and Atlantic cod), Little Auk and Kittiwake, respectively. For samples lower in the food chain (i.e. zooplankton and krill) no significant differences were found. This leads to a clear underestimation of the levels of MeHg found higher up in these food chains; the ratio of MeHg to Hg in biological samples; and thus potentially erroneous conclusions drawn from these results concerning the biological cycling of mercury species. We hypothesise that the main reasons for these differences are poor extraction efficiency and/or matrix effects on the ethylation step prior to analysis. This is the first study to examine the effects of these artefacts on real environmental samples covering a complete food chain.     

Speciation of mercury by continuous flow liquid-liquid extraction and inductively coupled plasma atomic emission spectrometry detection

An accurate, precise, sensitive and automated non-chromatographic method for methylmercury speciation based on a selective continuous liquid-liquid extraction of methylmercury, into xylene, as bromide and cold mercury vapour generation directly from the organic phase and final ICP-AES mercury detection is proposed. Both separation steps, liquid-liquid and gas-liquid are accomplished in a continuous mode and on line with ICP-AES as detector. The detection limit attained for methylmercury was 4ng·ml^–1 (as mercury). The precision of the determination at a concentration level around 20 times the detection limit was +-5%. The proposed methodology has been applied successfully to the speciation of methylmercury and inorganic mercury in spiked sea water and spiked urine samples.     

Isotope dilution SPME GC/MS for the determination of methylmercury in tuna fish samples

The development of a rapid, precise and accurate analytical method for the determination of methylmercury in tuna fish samples is described. The method is based on the use of isotope dilution GC/MS with electron impact ionization, a widespread technique in routine testing laboratories. A certified spike containing (202)Hg-enriched methylmercury was used for the isotope dilution of the samples. After extraction of the methylmercury from the sample, methylmercury was propylated using sodium tetrapropyl borate in SPME vials and the analytes were sampled from the headspace for 15 min. For isotope measurements, the molecular ion (MePrHg(+)) was used in the SIM mode. Five molecular ions were monitored, corresponding to the (198)Hg, (199)Hg, (200)Hg, (201)Hg and (202)Hg isotopes. The detection at masses corresponding to (198)Hg was used to correct for m + 1 contributions of (13)C from the organic groups attached to the mercury atom on the (199)Hg, (200)Hg, (201)Hg and (202)Hg masses with simple mathematical equations, and the concentration of methylmercury was calculated on the basis of the corrected (200)Hg/(202)Hg isotope ratio. The (202)Hg-enriched methylmercury spike was applied, with satisfactory results, to the determination of methylmercury in the certified reference material BCR 464. The method was successfully applied to the determination of methylmercury in tuna fish samples, and the obtained results were included in the CCQM-P39 interlaboratory exercise, organized by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) with excellent agreement between our results and the average obtained by the other participants.     

Environmental application of elemental speciation analysis based on liquid or gas chromatography hyphenated to inductively coupled plasma mass spectrometry—A review

In recent years the number of environmental applications of elemental speciation analysis using inductively coupled plasma mass spectrometry (ICP-MS) as detector has increased significantly. The analytical characteristics, such as extremely low detection limits (LOD) for almost all elements, the wide linear range, the possibility for multi-elemental analysis and the possibility to apply isotope dilution mass spectrometry (IDMS) make ICP-MS an attractive tool for elemental speciation analysis. Two methodological approaches, i.e. the combination of ICP-MS with high performance liquid chromatography (HPLC) and gas chromatography (GC), dominate the field. Besides the investigation of metals and metalloids and their species (e.g. Sn, Hg, As), representing “classic” elements in environmental science, more recently other elements (e.g. P, S, Br, I) amenable to ICP-MS determination were addressed. In addition, the introduction of isotope dilution analysis and the development of isotopically labeled species-specific standards have contributed to the success of ICP-MS in the field. The aim of this review is to summarize these developments and to highlight recent trends in the environmental application of ICP-MS coupled to GC and HPLC.     

Exploiting the κ2-Fashioned Coordination of [Se2]-Donor Ligand L3Se for Facile Hg−C Bond Cleavage of Mercury Alkyls and Cytoprotection against Methylmercury-Induced Toxicity

The Hg−C bond of MeHgCl, a ubiquitous environmental toxicant, is notoriously inert and exceedingly difficult to cleave. The cleavage of the Hg−C bond of MeHgCl at low temperature, therefore, is of significant importance for human health. Among various bis(imidazole)-2-selones L_nSe (n=1–4, or 6), the three-spacer L₃Se shows extraordinarily high reactivity in the degradation of various mercury alkyls including MeHgCl because of its unique ability to coordinate through κ²-fashion, in which both the Se atoms simultaneously attack the Hg center of mercury alkyls for facile Hg−C bond cleavage. It has the highest softness (σ) parameter and the lowest HOMO(L_nSe)-LUMO(MeHgX) energy gap and, thus, L₃Se is the most reactive among L_nSe towards MeHgX (X=Cl or I). L₃Se is highly efficient, more than L₁Se, in restoring the activity of antioxidant enzyme glutathione reductase (GR) that is completely inhibited by MeHgCl; 80 % GR activity is recovered by L₃Se relative to 50 % by L₁Se. It shows an excellent cytoprotective effect in liver cells against MeHgCl-induced oxidative stress by protecting vital antioxidant enzymes from inhibition caused by MeHgCl and, thus, does not allow to increase the intracellular reactive oxygen species (ROS) levels. Furthermore, it protects the mitochondrial membrane potential (ΔΨ_m) from perturbation by MeHgCl. Major Hg-responsive genes analyses demonstrate that L₃Se plays a significant role in MeHg⁺ detoxification in liver cells.     

A new procedure for the speciation of mercury in water based on the transformation of mercury (II) and methylmercury (II) into stable acetylides followed by HPLC analysis

Conversion of mercury(II) and methylmercury(II) species dissolved in water into di(phenylethynyl)mercury and methyl(phenylethynyl) mercury takes place in satisfactory yield under alkaline conditions by stirring the aqueous solution with phenylacetylene at room temperature. Mercury speciation is simply obtained by HPLC analysis of the two organometallic species. The presence of heavy metals such as copper(II), zinc(II), cadmium(II) and lead(II) in concentrations 10000 times higher than mercury is tolerated, while little interference is displayed by humic acids and cysteine. Seawater samples can also be analysed following a properly adapted procedure.     

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.     

Studies on organo-mercury compounds speciation

Four studies on organo-mercury compounds speciation carried out in the analytical chemistry laboratory of the University of Santiago are briefly described and discussed. Search for new methods of separation based on liquid chromatography as well as quality control and application studies have been started and the results obtained up to the end of 1990 are presented.