膜萃取-气相色谱/微分离子迁移谱检测水中的1,4-二恶烷

利用膜萃取-气相色谱/微分离子迁移谱（ME-GC/DMS）对水中的1,4-二恶烷污染物进行了检测。考察了射频电压、采样流速、膜渗透时间、Trap预富集时间等参数对检测二恶烷的影响规律。结果显示：在优化条件下,二恶烷的定量线性范围为2.0~20.0 μg/L,检出限为0.67 μg/L。实验证明,二恶烷与5种氯代烃的混合物在ME-GC/DMS的二维分离谱图中得到特异性响应,增加了识别的准确性。该研究为发展现场实时监测地下水中污染物的方法提供了重要参考。     

A Comprehensive Review for Groundwater Contamination and Remediation: Occurrence,Migration and Adsorption Modelling

The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people’s lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier’s use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants’ uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.     

Analytical investigations of phenyl arsenicals in groundwater

Phenylic arsenic compounds are the main contaminants in groundwater at abandoned sites with a history of arsenic containing chemical warfare agents (CWA). A fast and sensitive HPLC-ICP-MS method was developed to determine inorganic arsenic compounds like arsenite and arsenate as well as the degradation products of the arsenic containing warfare agents (phenylarsonic acid, phenylarsine oxide, diphenylarsinic acid). Beside these arsenic species the groundwater samples contained also high iron contents (up to 23 mg/l as Fe(II)) which led to precipitates in the samples after coming into contact with the atmosphere. Preservation immediately after sampling by phosphoric acid has shown that a successful avoidance of any losses of any arsenic species between sampling and analysis was possible. The suggested analytical method was applied to groundwater samples taken from different depths at a polluted site. The main contaminant in the water samples was diphenylarsinic acid (up to 2.1 mg/l) identified by ESI-MS, but also elevated concentrations of inorganic arsenic (up to 240 microg/l) were found.     

Nuclear techniques to investigate source and origin of groundwater pollutants and their flow path at Indian Rare Earths Ltd., Cochin,Kerala

Hydrochemical, environmental isotope and injected radiotracer investigations were carried out in order to investigate the possible source of contaminants and their movement in groundwater at Indian Rare Earths (IRE) site. Water samples were collected from piezometers, dug wells and river in and around IRE site for measurement of physical parameters, chemistry and isotopes. Chemical results show high fluoride, nitrate, sulphate and phosphate concentrations in piezometers whereas dug wells and river samples are free from contamination. Isotope data indicate that the contaminated groundwaters are enriched in δ²H and δ¹⁸O compared to dug well and river samples. Radiotracer experiments were carried out using single-well and multi-well techniques (radiotracers: ⁸²Br and ³H) for determining groundwater filtration velocity and flow direction, respectively. Groundwater filtration velocity was found to be about 1.3 cm/day and flow direction is from south to north. Based on the investigations it can be concluded that groundwater is getting contamination from southern part of IRE campus and the possible source for these contaminants could be the Fertilizer and Chemical of Travancore (FACT) industry.     

Critical evaluation of adsorption-based sampling of vaporized metal species in flue gases

Diffusion-controlled sampling techniques, i.e. diffusion screens and diffusion tubes (= denuders), can be used in the collection of several vaporized heavy metal species in clean gases (pure N₂ atmosphere) at elevated temperatures. Collection efficiencies obtained for Hg, HgCl₂, Cd, CdCl₂ and ZnCl₂ were over 90% using adsorption on Au-coated diffusion screens and Ag-coated denuders. However, the collection efficiencies for Zn and PbCl₂ were significantly lower. In field measurements performed at a hazardous waste incineration plant and in a power plant equipped with a circulating fluidized-bed boiler, collection efficiencies seemed to vary noticeably depending on the sampling conditions and metal species to be sampled. Best collection efficiencies were obtained for mercury with both Ag coated denuders and Au coated screens whereas cadmium showed significantly poorer results in field measurements than in the laboratory. Sampling of zinc and lead species seemed to be problematic in all cases. Of the two sampling techniques, the denuder technique is more recommendable than the screen technique for sampling in relatively clean gases. However, neither of these techniques should be used in flue gases without further understanding of the collection mechanisms. Received: 6 November 1996 / Revised: 3 July 1996 / Accepted: 14 July 1996     

Microfabricated valveless devices for thermal bioreactions based on diffusion-limited evaporation

Microfluidic devices that reduce evaporative loss during thermal bioreactions such as PCR without microvalves have been developed by relying on the principle of diffusion-limited evaporation. Both theoretical and experimental results demonstrate that the sample evaporative loss can be reduced by more than 20 times using long narrow diffusion channels on both sides of the reaction region. In order to further suppress the evaporation, the driving force for liquid evaporation is reduced by two additional techniques: decreasing the interfacial temperature using thermal isolation and reducing the vapor concentration gradient by replenishing water vapor in the diffusion channels. Both thermal isolation and vapor replenishment techniques can limit the sample evaporative loss to approximately 1% of the reaction content.     

Continuous analysis of δ18O and δD values of water by diffusion sampling cavity ring‐down spectrometry: a novel sampling device for unattended field monitoring of precipitation,ground and surface waters

A novel sampling device suitable for continuous, unattended field monitoring of rapid isotopic changes in environmental waters is described. The device utilises diffusion through porous PTFE tubing to deliver water vapour continuously from a liquid water source for analysis of δ¹⁸O and δD values by Cavity Ring‐Down Spectrometry (CRDS). Separation of the analysed water vapour from non‐volatile dissolved and particulate contaminants in the liquid sample minimises spectral interferences associated with CRDS analyses of many aqueous samples. Comparison of isotopic data for a range of water samples analysed by Diffusion Sampling‐CRDS (DS‐CRDS) and Isotope Ratio Mass Spectrometry (IRMS) shows significant linear correlations between the two methods allowing for accurate standardisation of DS‐CRDS data. The internal precision for an integration period of 3 min (standard deviation (SD) = 0.1 ‰ and 0.3 ‰ for δ¹⁸O and δD values, respectively) is similar to analysis of water by CRDS using an autosampler to inject and evaporate discrete water samples. The isotopic effects of variable air temperature, water vapour concentration, water pumping rate and dissolved organic content were found to be either negligible or correctable by analysis of water standards. The DS‐CRDS system was used to analyse the O and H isotope composition in short‐lived rain events. Other applications where finely time resolved water isotope data may be of benefit include recharge/discharge in groundwater/river systems and infiltration‐related changes in cave drip water. Copyright © 2011 John Wiley & Sons, Ltd.     

Designing a contaminated soil sampling strategy for human health risk assessment

Human health risk assessment is a site-based approach used to identify the potential health hazards which are induced by an old site contamination. For a proper evaluation of the daily doses of contaminants to which people will be exposed given the future occupation of the site, both a characterization and a quantification of soil pollution are needed. Such information can be provided by soil sampling. Thus the choice of the location, the number, depth and type of soil samples is very important and ought to follow a well-defined strategy. A review of contaminated site sampling practices in Europe and North America could not identify any completely formalized sampling strategy for human health risk assessment. On the contrary there are several approaches which can be roughly classified into two categories: a systematic sampling scheme over the whole site, on the one hand, and a sampling design driven by an initial knowledge of the contamination sources and fitted to the suspected pollution pattern, on the other. The first approach provides a complete coverage of the site but it may be rather expensive and entail useless sampling. The performance of the second depends on the quality of prior information. Actually both methods can be combined as explained hereafter. In view of the specificity of each site, the requirements of health risk assessment and the time and cost constraints, it seems difficult to work out a typical soil sampling strategy suitable for all sites. However, some recommendations can be made according to the site dimensions, the nature, degree and heterogeneity of contamination, and the (future) use of the site. The scientist should thus rely on a thorough examination of all available information (site history, geology and hydrogeology, soil properties, contaminants behaviour , etc.) to delimit contaminated areas as homogeneous as possible and then distribute the sampling points (e.g.using a sampling grid). They should also take the potential exposure paths into account in order to define the areas and soil strata to be sampled as a priority. Statistical and geostatistical tools can be helpful for formulating a sampling strategy as well as for interpreting the collected data. Received: 7 December 2001 Accepted: 24 February 2002     

Importance sampling for quantum Monte Carlo in manifolds: addressing the time scale problem in simulations of molecular aggregates

Several importance sampling strategies are developed and tested for stereographic projection diffusion Monte Carlo in manifolds. We test a family of one parameter trial wavefunctions for variational Monte Carlo in stereographically projected manifolds which can be used to produce importance sampling. We use the double well potential in one dimensional Euclidean space to study systematically sampling issues for diffusion Monte Carlo. We find that diffusion Monte Carlo with importance sampling in manifolds is orders of magnitude more efficient compared to unguided diffusion Monte Carlo. Additionally, diffusion Monte Carlo with importance sampling in manifolds can overcome problems with nonconfining potentials and can suppress quasiergodicity effectively. We obtain the ground state energy and the wavefunction for the Stokmayer trimer.     

Transport modeling of membrane extraction of chlorinated hydrocarbon from water for ion mobility spectrometry

Membrane-extraction Ion Mobility Spectrometry (ME-IMS) is a feasible technique for the continuous monitoring of chlorinated hydrocarbons in water. This work studies theoretically the time-dependent characteristics of sampling and detection of trichloroethylene (TCE). The sampling is configured so that aqueous contaminants permeate through a hollow polydimethylsiloxane (PDMS) membrane and are carried away by a transport gas flowing through the membrane tube into IMS analyzer. The theoretical study is based on a two-dimensional transient fluid flow and mass transport model. The model describes the TCE mixing in the water, permeation through the membrane layer, and convective diffusion in the air flow inside membrane tube. The effect of various transport gas flow rates on temporal profiles of IMS signal intensity is investigated. The results show that fast time response and high transport yield can be achieved for ME-IMS by controlling the flow rate in the extraction membrane tube. These modeled time-response profiles are important for determining duty cycles of field-deployable sensors for monitoring chlorinated hydrocarbons in water.     

Kinetically controlled catalytic formation of zinc oxide thin films at low temperature

We developed a unique method to produce ZnO thin films by kinetically controlled catalytic hydrolysis of a molecular precursor at low temperature, operating in conjunction with the vectorial control of crystal growth. Using a system in which the diffusion of a volatile catalyst into a solution of molecular precursor of the metal oxide limits the rate of hydrolysis and establishes a gradient of catalyst concentration, we investigated the nucleation of textured nanoparticles at the gas-liquid interface and characterized their subsequent growth. Use of this slow diffusion method combined with prediction of molecular species using a partial charge model enables a higher level of organizational control than obtained in other low-temperature synthesis methods, without the use of organic molecules. Various metal oxides and their morphologies and chemical compositions can be tailored for specific applications using this relatively simple approach.     

Trace analysis of BTEX compounds in water with a membrane interfaced ion mobility spectrometer

A tubular silicone membrane interface has been developed for trace detection of benzene, toluene, ethyl benzene, and xylene (BTEX) compounds in water with a portable ion mobility spectrometer. Effects of flow rate, membrane length and stirring conditions on the IMS signals have been systematically investigated. Besides conventional dynamic mode operation, static mode sampling has been demonstrated for the first time and high sensitivities were achieved by sampling of BTEX contaminated water with static mode operation. A toluene concentration of 0.101 mg l(-1) in purified water, corresponding to a headspace concentration of 2.75 (mug m(-3)), was determined by static mode sampling. Headspace sampling without the membrane interface could not detect toluene at this concentration. This method has high sensitivity for trace concentrations of gasoline components in river water with a response time of several seconds. The apparatus developed is portable and can be used for sensitive detection of organic contaminants in water, with improved performance compared to conventional modes of IMS sampling.     

A ruler for determining the position of proteins in membranes

Both the oxygen diffusion rate and the oxygen solubility vary with depth into the interior of biological membranes. The product of these two gradients generates a single gradient, a permeability gradient, which is a smooth continuous function of the distance from the center of the membrane. Using electron paramagnetic resonance and the spin-probe method, the relaxation gradient of oxygen, which is directly proportional to the permeability gradient, is the quantity that can be directly measured in membranes under physiological conditions. The gradient obtained provides a calibrated ruler for determining the membrane depth of residues either from loop regions of membrane-binding proteins or from the membrane-exposed residues of transmembrane proteins. We have determined the relaxation gradient of oxygen in zwitterionic and anionic phospholipid membranes by attaching a single nitroxide probe to a transmembrane alpha-helical polypeptide at specific residues. The peptide ruler was used to determine the depth of penetration of the calcium-binding loops of the C2 domain of cytosolic phospholipase A(2). The positions of selected residues of this membrane-binding protein that penetrate into the membrane, determined using this ruler, compared favorably with previous determinations using more complex methods. The relaxation gradient constrains the possible values of the membrane-dependent oxygen concentration and the oxygen diffusion gradients. The average oxygen diffusion coefficient is estimated to be at least 2-fold smaller in the membrane than that in water.     

Determination of Organic Contaminants in Landfill Leachates: A Review

Leachates derived from landfills constitute a potential risk of groundwater pollution because a variety of contaminants can be released by leaking from the contention system. Therefore, the leachate composition is of interest of their appropriate management. Although the leachate characterisation is usually carried out by global parameters (i.e. DOC, BOD, COD, AOX, etc), its characterisation at molecular level is of increasing interest and will be reviewed in the present article. Sample handling and determination techniques for a variety of organic contaminants is discussed and pitfalls as well as limitations of each analytical technique will be highlighted.     

Fingerprint identification of volatile organic compounds in gasoline contaminated groundwater using gas chromatography differential ion mobility spectrometry

Groundwater can be contaminated when e.g. gasoline tanks leak. Due to sampling and lab analysis, groundwater monitoring is time consuming and expensive. The technologies developed for rapid on-site analysis of gasoline contaminated groundwater face the technical limitation to distinguish the gasoline from complex matrices. In the present study the fingerprint identification of volatile organic components (VOCs) in gasoline contaminated groundwater using gas chromatography (GC) differential ion mobility spectrometry (DMS) is investigated. Groundwater was spiked with five sorts of gasoline (one reformulated gasoline, gasoline without additives and three different brand gasoline collected on petrol stations) and analyzed by GC-DMS. Seven VOCs (benzene, toluene, ethyl benzene, m-xylene, p-xylene, o-xylene, 1,2,4-trimethylbenzene) were identified by GC mass spectrometry (GC-MS) as well as by GC-DMS and selected as markers. The semi-quantitative determination of the selected compounds was achieved. The limits of detection of the GC-DMS are 46.42?ng for benzene, 1.13?ng for toluene, 1.80?ng for ethylbenzene, 0.22?ng for m-xylene, 1.13?ng for p-xylene, 0.61?ng for o-xylene and 0.37?ng for 1,2,4-trimethylbenzene, respectively. These results reveal the feasibility of GC-DMS for on-site monitoring of contaminated groundwater.     

Discrimination of ionic pollutants except condensation nuclei of acid fog using an ultrasonic humidifier.

Fog droplets in the atmosphere are first produced by the activation of cloud condensation nuclei (CCN), which are originally some ionic compound. Subsequently, the nuclei grow by vapor diffusion. Fog droplets are polluted through the activation process and successive diffusion growth and residence (post activation). We cannot distinguish the effects of the two pollution processes of natural fog water samples. We found that fog droplets can be produced artificially without CCN using an ultrasonic humidifier. Because the artificial fog droplets are not polluted by CCN, the movement of the fog droplets in natural air will take up some pollutants in the air. Consequently, the two pollution processes of fog (the activation of CCN and the post activation process) can be discriminated using data from field experiments. This sampling analytical method is extremely important for further research regarding fog, clouds and environmental chemistry.     

Sampling and sampling strategies for environmental analysis

Sampling errors are generally believed to dominate the errors of analytical measurement during the entire environmental data acquisition process. Unfortunately, environmental sampling errors are hardly quantified and documented even though analytical errors are frequently yet improperly reported to the third decimal point in environmental analysis. There is a significant discrepancy in directly applying traditional sampling theories (such as those developed for the binary particle systems) to trace levels of contaminants in complex environmental matrices with various spatial and temporal heterogeneities. The purpose of this critical review is to address several key issues in the development of an optimal sampling strategy with a primary goal of sample representativeness while minimizing the total number of samples and sampling frequencies, hence the cost for sampling and analysis. Several biased and statistically based sampling approaches commonly employed in environmental sampling (e.g. judgmental sampling and haphazard sampling vs. statistically based approaches such as simple random, systematic random, and stratified random sampling) are examined with respect to their pros and cons for the acquisition of scientifically reliable and legally defensible data. The effects of sample size, sample frequency and the use of compositing are addressed to illustrate the strategies for a cost reduction as well as an improved representativeness of sampling from spatially and temporally varied environmental systems. The discussions are accompanied with some recent advances and examples in the formulation of sampling strategies for the chemical or biological analysis of air, surface water, drinking water, groundwater, soil, and hazardous waste sites.     

Strategies for monitoring the emerging polar organic contaminants in water with emphasis on integrative passive sampling

Although polar organic contaminants (POCs) such as pharmaceuticals are considered as some of today's most emerging contaminants few of them are regulated or included in on-going monitoring programs. However, the growing concern among the public and researchers together with the new legislature within the European Union, the registration, evaluation and authorisation of chemicals (REACH) system will increase the future need of simple, low cost strategies for monitoring and risk assessment of POCs in aquatic environments. In this article, we overview the advantages and shortcomings of traditional and novel sampling techniques available for monitoring the emerging POCs in water. The benefits and drawbacks of using active and biological sampling were discussed and the principles of organic passive samplers (PS) presented. A detailed overview of type of polar organic PS available, and their classes of target compounds and field of applications were given, and the considerations involved in using them such as environmental effects and quality control were discussed. The usefulness of biological sampling of POCs in water was found to be limited. Polar organic PS was considered to be the only available, but nevertheless, an efficient alternative to active water sampling due to its simplicity, low cost, no need of power supply or maintenance, and the ability of collecting time-integrative samples with one sample collection. However, the polar organic PS need to be further developed before they can be used as standard in water quality monitoring programs.     

Estimation of Self‐Diffusion Coefficients of Small Penetrants in Semicrystalline Polymers Using Single‐Sided NMR

A simple and fast way to measure proton self‐diffusion coefficients of small penetrant molecules in semicrystalline polymers is introduced. The approach takes advantage of the strong static gradient of a mobile single‐sided NMR sensor and it is demonstrated on PE samples with varying degrees of crystallinity fully saturated in either toluene or n‐hexane. The self‐diffusion coefficients were measured using the gradient stimulated echo sequence appended with a CPMG. It is also shown for the first time, with demonstration on PE plates several millimeter thick with different aging histories, that one‐dimensional profiles of self‐diffusion coefficients as a function of depth can be easily obtained.     

Development of the performance reference compound approach for the calibration of “polar organic chemical integrative sampler” (POCIS)

The purpose of the Water Framework Directive is to ensure the quality of the natural water across Europe. In this context, passive samplers have shown interesting capacities for the monitoring of contaminants in aqueous ecosystems. They allow the measurement of time-weighted average concentrations, overcoming many drawbacks of the spot-sampling techniques known to be expensive and time consuming. However, application of passive samplers such as polar organic chemical integrative samplers (POCIS) for the monitoring of hydrophilic contaminants requires calibration to define compound sampling rates; key parameters to deduce the pollutant water concentrations from the amounts of pollutants accumulated by the device. Unfortunately, sampling rates are influenced by a range of environmental factors; in that respect, a question remains: is it not evident to know to what extent the sampling rates obtained in laboratory experiments can be used in field conditions? The problem can be solved for hydrophobic samplers by using performance reference compounds (PRCs), and an ongoing challenge for POCIS is focused on the improvement of the quantitative aspect of this family of samplers. In this study, potential PRCs have been selected during a specific experiment and their performance was tested in the laboratory under two hydrodynamic conditions. Results revealed a good proportionality between elimination rates of PRCs and sampling rates of chemicals. Afterwards, the application of the approach under environmental conditions was assessed by deploying POCIS in the Arcachon Bay (France) where POCIS–PRC-derived water concentrations appear to be close to the simultaneous grab-sampling results.