Analysis of PCBs in soils and sediments by microwave-assisted extraction,headspace-SPME and high resolution gas chromatography with ion-trap tandem mass spectrometry

A procedure for the determination of seven indicator PCBs in soils and sediments using microwave-assisted extraction (MAE) and headspace solid-phase microextraction (HS-SPME) prior to GC-MS/MS is described. Optimization of the HS-SPME was carried out for the most important parameters such as extraction time, sample volume and temperature. The adopted methodology has reduced consumption of organic solvents and analysis runtime. Under the optimized conditions, the method detection limit ranged from 0.6 to 1?ng/g when 5?g of sample was extracted, the precision on real samples ranged from 4 to 21% and the recovery from 69 to 104%. The proposed method, which included the analysis of a certified reference material in its validation procedure, can be extended to several other PCBs and used in the monitoring of soil or sediments for the presence of PCBs.     

ICP-MS研究太湖表层沉积物对Cd2+和Zn2+的吸附-解吸特性

前期研究发现太湖过滤水和表层沉积物中Zn含量最高,且表层沉积物中Cd存在强生态危害。因此,在优化实验条件下,以电感耦合等离子体质谱(ICP-MS)为分析手段研究了太湖苏州湾大桥东表层沉积物(标记为SES)对Cd2+和Zn2+的吸附-解吸特性。吸附动力学结果表明：SES对Cd2+和Zn2+的吸附能力相差不大,在吸附时间t<120 min时,吸附是一个快速阶段,而当t≥120 min时则相反,吸附趋于动态平衡;Cd2+和Zn2+的吸附更符合伪二级动力学模型。吸附热力学实验表明,沉积物对Cd2+的吸附更符合Freundlich模型,而对Cd2+的吸附更符合Langmuir模型。沉积物中Cd2+和Zn2+的解吸动力学研究发现,二者均更符合Elovich方程,为非均相扩散过程。且当pH值增大时,沉积物中Cd2+和Zn2+的解吸量逐渐减小,并在pH=9时趋于稳定。结合Cd2+和Zn2+的吸附-解吸特性发现,SES对Cd2+和Zn2+的吸附速率远远大于其解吸速率,与作者前期研究结果一致。揭示了太湖表层沉积物对Cd2+和Zn2+的吸附-解吸作用机理及不同因素对吸附-解吸行为的影响。对研究太湖固-液两相界面重金属的分配和污染水体修复具有重要指导意义。     

气相色谱和原子荧光联用测定生物和沉积物样品中甲基汞

提出了一种气相色谱和原子荧光在线联用测定甲基汞的方法。对气相色谱和原子荧光的在线联用进行了设计,优化了进样口温度、载气流速、尾吹气流量及氩气流量等实验条件。在最佳仪器条件下,甲基汞(MMC)和乙基汞(EMC)的绝对检出限(3σ)可达0.005 ng。对于10 ng·mL-1 MMC和EMC标准溶液,连续5次进样测得精密度(RSD)分别为2.5％和1.3％。对标准参考物(DORM-2)的分析结果与标准值一致。两个沉积物中甲基汞的加标回收率分别为70％和77％。方法准确、灵敏,可应用于生物和沉积物样品中甲基汞的分析。     

A new procedure, based on combustion to sulphate and ion chromatography for the analysis of elemental sulphur in sediments

Summary A procedure exploiting the bomb preparation method for the analysis of total sulphur in organic materials has been developed for the determination of zero-valent sulphur (S^o) in sediments. Sediment samples were dried over magnesium oxide and sonicated in the presence of toluene to extract S^o. Toluene solutions were directly oxidized by combustion in a bomb containing sodium carbonate-bicarbonate buffer, which trapped sulphur species generated from S^o as sulphate ions. These were in turn analysed by suppressed anion chromatography with ion-conductivity detection. The method was used to determine the distribution of S^o in saltmarsh sediment cores.     

Fractionation studies of mercury in soils and sediments: A review of the chemical reagents used for mercury extraction

Mercury in contaminated soils and sediments could be extracted by various chemical reagents in order to determine the different mercury species and partitions, providing useful information of toxicology, bioavailability and biogeochemical reactivity. Unfortunately, at present, neither specific extractants nor standard protocols exist for the isolation of particular mercury species. Although there has been considerable research focused on reagents for extracting mercury species, there is still little consensus. Thus, workers are advised to select the most appropriate reagent based on the nature of their sample, and to take all possible steps to validate the analyses performed. Therefore, the aim of this paper is to review the current reagents used for determining total mercury and its speciation as well as fractionation such as methylmercury, ethylmercury, elemental mercury, mercury sulphide and organically bound mercury by supposed selective (one reagent) and sequential (several reagents) extractions. The gathering information presented here bring to light the need for standard protocol for which the used chemical reagents should take into account the particular chemistry of mercury associated with specific properties of soil and sediment. Beside this required scheme, appropriate reference materials are also demanded.     

Determination of Polybrominated Diphenyl Ethers in Coastal and River Sediments by Pressurized Liquid Extraction Coupled with Gas Chromatography‐Mass Spectrometry

This study presents a time‐ and solvent‐saving method, pressurized liquid extraction (PLE), to extract polybrominated diphenyl ethers (PBDEs) in sediment samples. The effects of various operating parameters (i.e., extraction solution, temperature, pressure, static/dynamic extraction times) for the quantitative extraction of PBDEs by home‐made PLE were systematically investigated and optimized. The analytes were then identified and quantitated by gas chromatography‐mass spectrometry (GC‐MS) in selected ion monitoring (SIM) mode. The 16 PBDE congeners (from tri‐ to deca‐BDE) can be completely extracted by dichloromethane: n‐hexane (3/2, v/v) at 100 °C and 100 atm combined with 15 min static and then 15 min dynamic extraction steps. Recovery of PBDEs in spiked sediment samples ranged from 52 to 104% with 2‐16% RSD, except for BDE‐206. Limits of quantitation (LOQ) were established between 4 and 400 pg/g (dry weight) in 10 g of sediment sample. The extraction efficiency of the PLE was also compared with the traditional Soxhlet extraction method. The total contents of PBDEs ranged from 8.0 to 37.9 ng/g (dry weight) in various river and coastal sediment samples in Taiwan. Deca‐BDE (BDE‐209) was the major PBDE detected in these sediment samples.     

Sediment dating by luminescence: a review

In the present article we review applications of luminescence methods for the determination of the age of sediments for Quaternary Earth science. “Sediment” is taken to include any mineral particles transported by wind, water and/or ice and subsequently deposited. Methodology is not discussed per se but appears in context. The emphasis is on recent work and is illustrative rather than exhaustive. Applications in archaeology are mentioned only briefly. Successful dating requires that the luminescence signal has been zeroed by sunlight at the time the sediment was laid down. Dune sands and loess transported in full daylight usually satisfy this condition and have been dated by both traditional thermoluminescence and by optical methods. Optical dating is advantageous for less well-bleached sediments, such as are found in colder climates and those laid down by fluvial and glacial processes, although the prospects for dating the latter are shown to be poor. Among less common contexts are volcanic eruptions, earthquake faults and tsunami deposits. The dating of very young sediments, less than 2 ka, is demonstrated and the factors limiting the dating of very old sediments, 500 ka to 1 Ma, are discussed. Validation of any dating method by comparison with other methods is necessary; luminescence ages have been successfully compared with ages obtained by, for example, ¹⁴C, U–Th series and δ¹⁸O isotope ratios. The most difficult problems encountered in dating quartz, feldspars and undifferentiated fine grain mixtures include: anomalous fading (which leads to underestimates of age), incomplete zeroing (which gives overestimates) and sample inhomogeneity. Methods devised to minimise these effects include preheating regimes, selection of observing wavelengths and of stimulating wavelengths for optical dating, the use of single aliquot and single grain measurements. The use of appropriate data analysis procedures is also important. Advice on current best practice on procedures for obtaining reliable ages is offered and, in all applications, there are suggestions as to where further research might be directed.     

Organic Compounds in Nature: Limits of Our Knowledge

Current geochemical and environmental research reveals the presence in soils and sediments of extremely complex assemblages of organic compounds. Their recognition has long been delayed by both conceptual and analytical limitations. Even today the best techniques cannot fully resolve these mixtures into their individual components. Yet, the knowledge of their structures and abundances is needed in geochemistry, and especially for the assessment of their potential biological effect and ecological impact. The classical “natural products approach” is unlikely to provide this information; therefore, I foresee the need for a more realistic assessment of nature, that acknowledges the limitations of our present analytical powers and of our knowledge.     

Simplified procedures for the analysis of polycyclic aromatic hydrocarbons in water, sediments and mussels

We describe in this paper simple and robust analytical protocols to determine the 16 polycyclic aromatic hydrocarbons (PAHs) of the US Environmental Protection Agency priority list in water, sediment and mussels. For water samples, eight different solid-phase extraction (SPE) sorbents have been compared and among them, C18 provided highest recoveries and limits of detection of 0.3-15 ng/L. For lyophilized sediments, Soxhlet and ultrasonic extraction were compared, and the last one permitted to recover all analytes with highest repetitivity and was validated by analysing a certified reference material. Finally, the analysis of mussels was undertaken using Soxhlet, ultrasonic and pressurized liquid extraction (PLE) and the performance of several clean-up steps are compared. Whereas for the former two, incomplete recovery or losses of some analytes were evidenced, PLE permitted a more efficient extraction and although alkaline digestion was necessary to remove coextracted compounds, the method gave acceptable recoveries and limits of detection of 0.5-7.7 microg/kg dry mass, as for sediments. In all cases, analysis was performed by gas chromatography coupled to mass spectrometry and internal standard quantification was performed using five deuterated PAHs. Each method performance is discussed for the three matrices analysed and the paper reports advantages and disadvantages of each for their routine application in monitoring programs.     

Biogenic substances in sediments and fossils

Most sedimentary rocks contain small concentrations of finely divided organic material. With the aid of modern analytical methods, samples of such rocks can be examined in detail, and conclusions can be drawn concerning the origin of the organic substances. Intact or modified biogenic compounds such as paraffins, isoprenoids, alcohols, ketones, carboxylic acids, steroids, triterpenes, and porphyrins have been isolated from the soluble fractions of the organic material of many sediments and from identified fossils of various geological ages. Even Precambrian rocks contain biogenic substances, so that life forms must have existed more than three billion years ago. The main component of the organic material is “kerogen”, the complicated polymeric structure of which has not yet been established.