Sample preparation for the analysis of volatile organic compounds in air and water matrices

This review summarizes literature data from the past 5 years on new developments and/or applications of sample preparation methods for analysis of volatile organic compounds (VOC), mainly in air and water matrices. Novel trends in the optimization and application of well-established airborne VOC enrichment techniques are discussed, like the implementation of advanced cooling systems in cryogenic trapping and miniaturization in adsorptive enrichment techniques. Next, focus is put on current tendencies in integrated sampling-extraction-sample introduction methods such as solid phase microextraction (SPME) and novel in-needle trapping devices. Particular attention is paid to emerging membrane extraction techniques such as membrane inlet mass spectrometry (MIMS) and membrane extraction with a sorbent interface (MESI). For VOC enrichment out of water, recent evolutions in direct aqueous injection (DAI) and liquid-liquid extraction (LLE) are highlighted, with main focus on miniaturized solvent extraction methods such as single drop microextraction (SDME) and liquid phase microextraction (LPME). Next, solvent-free sorptive enrichment receives major attention, with particular interest for innovative techniques such as stir bar sorptive extraction (SBSE) and solid phase dynamic extraction (SPDE). Finally, recent trends in membrane extraction are reviewed. Applications in both immersion and headspace mode are discussed.     

Advances and developments in membrane extraction for gas chromatography: Techniques and applications

This review article focuses on advances and technical developments of the realm of membrane extraction techniques for the analytes that are (made) amenable to gas chromatographic analysis, and sheds light on the analytical applications to biological and environmental samples. In this review, the state of the art in this growing area of membrane extraction for gas chromatography is presented and several selected examples from our work and that of other groups are discussed. The published articles on the techniques and their applications, found in the scientific literature between the years 2000 and May 2007 and cited in over than 100 references, are perused and commented. A good deal of light will be thrown on the novelty of the techniques, instrumentations and applications. The mentioned techniques are mainly microporous membrane liquid-liquid extraction, extracting syringe, two-phase hollow-fibre-protected liquid-phase microextraction and its modifications, and membrane extraction with sorbent interface and its variants. The merits and demerits of the techniques will be highlighted.     

液膜萃取技术在环境样品前处理中的应用

膜分离技术是利用膜对混合物中各组分的选择渗透性能的差异来实现分离、提纯和浓缩的新型分离技术。近年来,随着人们环保意识的加强,环境中污染物的监测逐渐被重视。因环境样品基体的复杂性,在分析测定前必须进行净化处理。将膜分离技术与液液萃取技术相结合的液膜萃取技术因其     

微液相色谱分离的在线样品预处理技术--固相微萃取和膜萃取

针对近5年内在分析化学领域出现的微量样品预处理新技术(包括纤维管内固相微萃取、中空膜萃取、动态三相微萃取等)，根据分离机理分成两大类，从原理、仪器装置和应用等方面作一综述。     

兽药残留分析中样品前处理技术研究进展

样品前处理是兽药残留分析中的关键步骤,直接影响检测的结果.近年来,出现了一些新的样品前处理技术,如固相萃取、基质固相分散萃取、固相微萃取、搅拌棒吸附萃取、膜萃取、液相微萃取、超临界流体萃取、加速溶剂萃取、分子印迹、微波辅助萃取.这些技术能够有效地减少分析过程中由样品前处理过程带来的误差,具有前处理快速、简便的优点,同时可与分析仪器联用,实现分析的自动化.本文对这些新技术的基本原理、特点及在兽药残留分析中的应用进行了综述,并对样品前处理的前景进行了展望.     

Development and optimisation of a novel three‐way extraction technique based on a combination of Soxhlet extraction,membrane assisted solvent extraction and a molecularly imprinted polymer using sludge polycyclic aromatic hydrocarbons as model compounds

A novel technique that integrates extraction and clean‐up into a single step format is reported as part of the search for new sample preparation techniques in the analysis of persistent organic pollutants from complex samples. This was achieved by combining the extraction efficiency of the Soxhlet extractor, the selectivity of a size exclusion membrane and the specificity of a molecularly imprinted polymer for the extraction of polycyclic aromatic hydrocarbons from wastewater sludge followed by quantitation using gas chromatography with time‐of‐flight mass spectrometry. The approach is described as the Soxhlet extraction membrane‐assisted solvent extraction molecularly imprinted polymer technique. This technique was optimised for various parameters such as extraction solvent, reflux time and membrane acceptor phase. The applicability of the developed technique was optimised using a wastewater sludge certified reference material and then tested on real wastewater sludge samples. The method detection limits ranged from 0.14 to 12.86 ng/g with relative standard deviation values for the extraction of the 16 US‐EPA priority polycyclic aromatic hydrocarbons from wastewater sludge samples ranging from 0.78 to 18%. The extraction process was therefore reproducible and showed remarkable selectivity. The developed technique is a promising prospect that can be applied in the analysis of organic pollutants from complex solid samples.     

Direct coupling of supported liquid membranes to capillary electrophoresis for analysis of complex samples: A tutorial

This tutorial provides an overview of direct coupling of extraction techniques based on supported liquid membranes (SLMs) to capillary electrophoresis (CE) for treatment and subsequent analysis of complex samples. Pros and cons of using each of the described instrumental arrangement are addressed and where relevant, comments with personal experience of the authors are presented. Solid porous membrane based extraction techniques coupled directly to CE are also presented in this tutorial and a comprehensive discussion is included on their instrumental set-ups and their possible adaptation for use with SLMs.     

Review of online coupling of sample preparation techniques with liquid chromatography

Sample preparation is still considered as the bottleneck of the whole analytical procedure, and efforts has been conducted towards the automation, improvement of sensitivity and accuracy, and low comsuption of organic solvents. Development of online sample preparation techniques (SP) coupled with liquid chromatography (LC) is a promising way to achieve these goals, which has attracted great attention. This article reviews the recent advances on the online SP-LC techniques. Various online SP techniques have been described and summarized, including solid-phase-based extraction, liquid-phase-based extraction assisted with membrane, microwave assisted extraction, ultrasonic assisted extraction, accelerated solvent extraction and supercritical fluids extraction. Specially, the coupling approaches of online SP-LC systems and the corresponding interfaces have been discussed and reviewed in detail, such as online injector, autosampler combined with transport unit, desorption chamber and column switching. Typical applications of the online SP-LC techniques have been summarized. Then the problems and expected trends in this field are attempted to be discussed and proposed in order to encourage the further development of online SP-LC techniques.     

New home-made assembly for hollow-fibre membrane extraction of persistent organic pollutants from real world samples

Nowadays, hollow fibre membrane extraction techniques are widely used but they are usually applied to water or very simple matrices such as water. In this paper, we propose a new assembly that allows the extraction of forty persistent organic pollutants in real world samples, namely orange juice, porcine plasma and tomatoes. The limits of detection obtained are very low even in the analysis of real samples (9-182 ng L(-1)). The relative standard deviations vary from 1 to 18% and the averaged recoveries in the spike experiments are very high (65-120%) in the different types of samples studied. The new assembly allows a very good precision overcoming in one of the most important shortcomings of membrane extraction techniques. A central composite design has been performed to get optimal extraction conditions for the analytes and also the combined response of all the analytes has been obtained to attain the simultaneous optimum.     

Evaluation of two membrane‐based microextraction techniques for the determination of endocrine disruptors in aqueous samples by HPLC with diode array detection

In this study, the viability of two membrane‐based microextraction techniques for the determination of endocrine disruptors by high‐performance liquid chromatography with diode array detection was evaluated: hollow fiber microporous membrane liquid–liquid extraction and hollow‐fiber‐supported dispersive liquid–liquid microextraction. The extraction efficiencies obtained for methylparaben, ethylparaben, bisphenol A, benzophenone, and 2‐ethylhexyl‐4‐methoxycinnamate from aqueous matrices obtained using both approaches were compared and showed that hollow fiber microporous membrane liquid–liquid extraction exhibited higher extraction efficiency for most of the compounds studied. Therefore, a detailed optimization of the extraction procedure was carried out with this technique. The optimization of the extraction conditions and liquid desorption were performed by univariate analysis. The optimal conditions for the method were supported liquid membrane with 1‐octanol for 10 s, sample pH 7, addition of 15% w/v of NaCl, extraction time of 30 min, and liquid desorption in 150 μL of acetonitrile/methanol (50:50 v/v) for 5 min. The linear correlation coefficients were higher than 0.9936. The limits of detection were 0.5–4.6 μg/L and the limits of quantification were 2–16 μg/L. The analyte relative recoveries were 67–116%, and the relative standard deviations were less than 15.5%.     

Determination of thiophanate-methyl and its metabolites at trace level in spiked natural water using the supported liquid membrane extraction and the microporous membrane liquid-liquid extraction techniques combined on-line with high-performance liquid chromatography

On-line supported liquid membrane (SLM) extraction and microporous membrane liquid-liquid extraction (MMLLE) techniques for sample preparation of natural water samples have been developed for the determination of thiophanate-methyl (TM), carbendazim (MBC) and 2-aminobenzimidazole (2-AB) using reversed-phase HPLC. The combination of SLM extraction and MMLLE offers extraction conditions that makes it possible to determine a wide variety of compounds, i.e., permanently charged, ionisable and non-polar at sub ppb level. The detection limits obtained after extraction are about 0.1 microg/l for MBC and 2-AB using SLM, and 0.5 x Lg/l for TM using MMLLE and the precision is better than 5% for both systems. Typical enrichment rates are 0.6 and 2.7 times/min using SLM and MMLLE, respectively.     

样品前处理-色谱分析在线联用技术的研究进展

样品前处理是色谱分析中耗时最多、最容易引起误差的关键环节,因此有关样品前处理技术与色谱分析的在线联用的研究已成为分析化学的前沿课题。本文综述了近年来各种样品前处理技术与色谱分析在线联用的研究进展,包括固相萃取、固相微萃取与液相微萃取、膜辅助萃取、场作用辅助萃取、气相萃取、热解吸以及微芯片分离技术。     

Experimental study on solvent-less sample preparation methods: Membrane extraction with a sorbent interface, thermal membrane desorption application and purge-and-trap

Different solvent-free sample preparation techniques for the enrichment of volatile and semivolatile organic compounds from aqueous samples for subsequent gas chromatographic separation and detection are compared. The methods under study are purge-and-trap, membrane extraction with a sorbent interface in two different configurations, and thermal membrane desorption application. The study has been performed with polar as well as with non-polar compounds in respect to sampling yield, enrichment, repeatability and analysis cycle rate. All experiments have been performed with a mobile GC–MS system.     

Approaches for on-line coupling of extraction and chromatography

This review provides an overview of the approaches available in order to perform on-line coupling of various extraction techniques with liquid and gas chromatography, for the analysis of semivolatile and nonvolatile analytes in liquid and solid samples. The main focus is on the instrumental set-up of these techniques. Selected real applications are described by way of illustration. The extraction methods suitable for on-line coupling covered in this review are: liquid-liquid extraction, solid-phase extraction, membrane-based techniques, pressurised liquid extraction, supercritical fluid extraction, and microwave- and sonication-assisted extractions. The following systems are not covered in this review: on-line coupled solid-phase extraction-liquid chromatography, purge-and-trap-GC, and membrane extraction with a sorbent interface-GC.Abbreviations DMAE Dynamic microwave-assisted extraction - DSAE Dynamic sonication-assisted extraction - FIA Flow injection analysis - FID Flame ionisation detection - GC Gas chromatography - HGAAS Hydride generation atomic absorption spectroscopy - IC Ion chromatography - IPLC Ion pair liquid chromatography - LC Column liquid chromatography - LLE Liquid-liquid extraction - LVI Large-volume injection - MAE Microwave-assisted extraction - MESI Membrane extraction with a sorbent interface - MMLLE Microporous membrane liquid-liquid extraction - MS Mass spectrometry - NP Normal-phase - OTT Open-tubular trapping - OTTTD Open-tubular trapping with thermal desorption - PAH Polycyclic aromatic hydrocarbon - PHWE Pressurised hot water extraction - PCB Polychlorinated biphenyl - PLE Pressurised liquid extraction - PTV Programmed-temperature vaporizer - RP Reversed-phase - RSD Relative standard deviation - SAE Sonication-assisted extraction - SFE Supercritical fluid extraction - SIM Selective ion monitoring - SLM Supported liquid membrane - SPE Solid-phase extraction - SPE-TD Solid-phase extraction-thermal desorption - SVE Solvent vapour exit - TD Thermal desorption     

Sample preparation for gas chromatographic determination of halogenated volatile organic compounds in environmental and biological samples

In this review, the wide spectrum of the techniques of isolation and/or preconcentration and final determination of halogenated volatile organic compounds (HVOCs) in water, air, soil, sediment and biological fluids are presented and discussed. The techniques discussed are solvent microextraction, solid phase extraction, gas extraction (static and dynamic techniques), membrane processes and passive sampling. Also, direct techniques, such as direct aqueous injection into gas chromatography (GC) column and membrane inlet mass spectrometry, are presented. Main attention is paid to the practical application of these techniques during all HVOCs determination.     

Competitive transport of alkali metal ions from aqueous media into toluene solutions of 2-(sym-dibenzo-16-crown-5-oxy)-decanoic acid. A comparative study

Competitive permeation of alkali metal ions from an alkaline source phase into or through a toluene phase facilitated by the lipophilic crown ether carboxylic acid 2-(symdibenzo-16-crown-5-oxy)-decanoic acid is studied in liquid—liquid extraction, bulk liquid membrane transport, and emulsion liquid membrane transport. Most rapid transport was obtained in emulsion liquid membrane experiments. Some differences in selectivity orders for alkali metal permeation were observed for the three separation techniques.     

Porous metal membranes for solid-phase extraction of polycyclic aromatic hydrocarbons

Solid-phase extraction (SPE) is one of the most important techniques for sample preparation, purification, concentration and cleanup. Membranes made from synthetic organic polymers, cellulose, or glass fibers are used for sample pretreatment. In this work, we report that a porous metal membrane, the metal filter in HPLC, was used as a novel kind of solid-phase extraction adsorbent material. To evaluate the performance of the porous metal membrane for the SPE, naphthalene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, perylene and benzo(a)pyrene were selected as analytes. Several parameters that affected the extraction efficiency such as the extraction time, the concentration of NaCl, the extraction temperature and the agitation speed were optimized. The experimental result indicates that the porous metal membrane possesses high adsorption ability to the tested polycyclic aromatic hydrocarbons (PAHs). Under the optimum conditions, the detection limits of the developed method were in the range of 0.03-0.082 μg L(-1) (S/N = 5), and excellent linear correlations between peak area and concentration of PAHs were found over the range of 0.1-60 μg L(-1). The precisions (RSD) for five replicate extractions of the PAHs from sample solutions were in the range of 2.6-5.0%. The recoveries of the PAHs from tap water and river water samples spiked with 9 PAHs (20 μg L(-1) of each individual PAH) ranged from 83.0% to 112.5%. The porous metal membrane is durable, simple, inexpensive, reproducible and has a high adsorption ability for use in SPE of PAHs.     

Application of hollow fiber supported liquid membrane extraction to the simultaneous determination of pesticide residues in vegetables by liquid chromatography/mass spectrometry

A new analytical procedure using a hollow fiber supported liquid membrane (HFSLM) has been developed for the simultaneous determination of pesticide residues in vegetables by liquid chromatography (LC) coupled with electrospray mass spectrometry (MS). The extraction technique requires minimal sample preparation and solvent consumption. Optimum extraction conditions have been evaluated with respect to sample pH, ionic strength, liquid membrane composition, extraction time, stirring rate and acceptor composition. The extraction method has been validated for matrices such as cucumber, tomato and pepper, indicating that cucumber can be selected as representative matrix for routine analysis of these food commodities. Linear ranges of pesticides in vegetable samples were 10 to 200 microg/kg, and the repeatability of the method was less than 20% for the lowest calibration point. The limits of detection ranged from 0.06 to 2.7 microg/kg and the limits of quantification from 0.2 to 9.0 microg/kg, which were low enough to determine the pesticide residues at concentrations below or equal to the maximum residue levels (MRLs) specified by European Union. The method was finally applied to the determination of more than 20 pesticides in market vegetable samples and the concentrations found in these samples were always lower than the MRLs. This new approach can be considered as a powerful alternative to the traditional extraction techniques.     

Development and application of polymer-coated hollow fiber membrane microextraction to the determination of organochlorine pesticides in water

A novel extraction procedure coupled with gas chromatography-mass spectrometric detection for quantification of organochlorine pesticides (OCPs) in water is described. Amphiphilic polyhydroxylated polyparaphenylene (PH-PPP) was synthesized and coated on the surfaces of a porous polypropylene hollow fiber membrane (HFM). Due to the high porosity of the HFM, maximum active surface area to achieve high extraction efficiency is expected. The polymer-coated HFM was used for the extraction of 15 OCPs from water. The extraction efficiency was compared with emerging and established methods such as liquid-phase microextraction (LPME), solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) techniques. We term the current procedure as polymer-coated hollow fiber microextraction (PC-HFME). PC-HFME showed good selectivity and sensitivity. Detection limits for OCPs were in the range of 0.001-0.008 microg l(-1). The sensitivity and selectivity of the coated HFM could be adjusted by changing the characteristics of the coated PH-PPP film.