Membrane-based sample preparation coupled on-line to chromatography or electrophoresis

Reversed-phase chromatomembrane extraction as a novel approach for automated sample pretreatment: Anions determination in biodiesel by ion chromatography with conductivity detection

In this study, a reversed-phase chromatomembrane extraction (RP-CME) method as a novel approach for automated sample pretreatment was suggested for the first time. The RP-CME was applied to automated separation of anions (formate, chloride, nitrate, phosphate and sulfate) from biodiesel samples as a proof-of-concept example. The novel design of chromatomembrane cell was developed for on-line RP-CME. The RP-CME procedure assumed mass-transfer of water-soluble analytes from organic sample phase (biodiesel sample) to aqueous phase supported in a porous composite mass-transfer block. The composite mass-transfer block based on microporous hydrophobic poly (tetrafluoroethylene) and hydrophilic glass fiber was developed for the RP-CME implementation. The block provided the effective retention of aqueous phase into the cell and simultaneous penetration of organic phase. The hydrophilic membrane-based sheet was used for the on-line separation of hydrophilic emulsion (biodiesel in water) containing target analytes obtained during analytes elution by aqueous phase from the mass-transfer block. The RP-CME was successfully coupled with an ion chromatography with conductivity detection. The limits of detection, calculated from a blank test based on 3σ, were 5 μg kg^-1 for sulfate, 6 μg kg^-1 for nitrate, 3 μg kg^-1 for chloride, 5 μg kg^-1 for phosphate and 1 μg kg^-1 for formate.

Investigation of retention of undesirable organic matter from aqueous samples in stopped-flow dialysis procedures for inorganic anions

Sample preparation is a key issue in the analysis of many real samples using ion chromatography (IC). One of the many means of sample preparation that has received considerable attention in recent years is the stopped-flow in-line dialysis approach hyphenated to IC. Using appropriate dialysis membranes undesirable high-molecular weight compounds, colloids and dispersed particulate matter are retained whereas the analyte ions pass through the membrane and are separated and quantified by IC. However, in the many papers about analytical use of in-line dialysis (not only in connection with IC) the retention of undesirable compounds has never been quantified. This study is a first attempt to fil this gap. The breakthrough (BT) of humic acids (HA) and lignin as model compounds often contained in natural water samples was investigated in the stopped-flow dialysis procedure using different dialysis membranes. BT was measured and quantified by UV-absorption in the receiver solution leaving the dialysis cell. The most important factor for retention of undesired compounds is the pore size or the molecular weight cut-off (MWCO) of the dialysis membrane. In addition, the recovery of analytes in acceptable time needs to be considered. The optimized system addresses these two aspects and permits using the proper membrane almost quantitative recovery of several inorganic ions and at the same time almost complete retention of the model interferents. Artificial natural water samples were prepared and analyzed containing a mixture of HA, lignin and a surfactant and a number of anions. In long-term operation no alterations of the dialysis process occurred and no adverse effects in IC separations were observed.

Automated sample preparation for CE-SDS

Traditionally, CE with SDS (CE-SDS) places many restrictions on sample composition. Requirements include low salt content, known initial sample concentration, and a narrow window of final sample concentration. As these restrictions require buffer exchange for many sample types, sample preparation is often tedious and yields poor sample recoveries. To improve capacity and streamline sample preparation, an automated robotic platform was developed using the PhyNexus Micro-Extractor Automated Instrument (MEA) for both the reduced and nonreduced CE-SDS assays. This automated sample preparation normalizes sample concentration, removes salts and other contaminants, and adds the required CE-SDS reagents, essentially eliminating manual steps during sample preparation. Fc-fusion proteins and monoclonal antibodies were used in this work to demonstrate benefits of this approach when compared to the manual method. With optimized conditions, this application has demonstrated decreased analyst "hands on" time and reduced total assay time. Sample recovery greater than 90% can be achieved, regardless of initial composition and concentration of analyte.

Fabrication of macroporous polymeric membranes through binary convective deposition

Binary convective deposition of silica/polystyrene under a number of different operating conditions is used to form nanoporous polymeric membranes with uniform and repeatable pore size throughout and across the membrane. One micrometer silica microspheres and 100 nm PS nanoparticles are codeposited from suspension under conditions where respective constituent fluxes are matched. Membrane thickness is controlled through single and consecutive monolayer and multilayer depositions. Consecutive monolayer depositions result in thin films with highest order and packing. Polymeric membranes were successfully fabricated from a continuous thin film by etching the SiO(2) microspheres with HF or KOH. Etching proceeds radially inward from the polymer-oxide interface suggesting that etchant/thin film interfacial energies help create the initial etching profile and drastically increase the overall etching rate. These membranes, of tunable pore size and functionality, will be ideal for targeted bioseparations specifically in the partition of pathogen particles out of blood suspensions.

Simultaneous determination of some food additives in soft drinks and other liquid foods by flow injection on-line dialysis coupled to high performance liquid chromatography

Flow injection on-line dialysis was developed for sample pretreatment prior to the simultaneous determination of some food additives by high performance liquid chromatography (FID-HPLC). A liquid sample or mixed standard solution (900 μL) was injected into a donor stream (5%, w/v, sucrose) of FID system and was pushed further through a dialysis cell, while an acceptor solution (0.025 mol L(-1) phosphate buffer, pH 3.75) was held in the opposite side of the dialysis membrane. The dialysate was then flowed to an injection loop of the HPLC valve, where it was further injected into the HPLC system and analyzed under isocratic reverse-phase HPLC conditions and UV detection (230 nm). The order of elution of five food additives was acesulfame-K, saccharin, caffeine, benzoic acid and sorbic acid, respectively, with the analysis time of 14 min. On-line dialysis and HPLC analysis could be performed in parallel, providing sample throughput of 4.3h(-1). Dialysis efficiencies of five food additives were in ranges of 5-11%. Linear calibration graphs were in ranges of 10-100 mg L(-1) for acesulfame-K and saccharin, 10-250 mg L(-1) for benzoic acid and 10-500 mg L(-1) for caffeine and sorbic acid. Good precisions (RSD<5%) for all the additives were obtained. The proposed system was applied to soft drink and other liquid food samples. Acceptable percentage recoveries could be obtained by appropriate dilution of the sample before injecting into the system. The developed system has advantages of high degrees of automation for sample pretreatment, i.e., on-line sample separation and dilution and low consumption of chemicals and materials.

Decomposition of 3'-azido-2',3'-dideoxythymidine 5'-monophosphate (AZTMP) prodrugs in biological media studied by on-line solid-phase extraction coupled to liquid chromatography mass spectrometry

Using a column-switching HPLC method previously described, we studied the behavior of some mononucleotide prodrugs (pronucleotides) of 3'-azido-2',3'-dideoxythymidine in various biological media. From UV data, this method allowed quantification of transient metabolites resulting from prodrug bioconversion. The kinetic data related to the successive steps were calculated according to pseudo-first-order kinetic models and optimized using mono- or poly-exponential regressions. Various metabolites were identified by co-injection with authentic samples and/or ESI-MS coupling. The results led us to propose, for each considered pronucleotide, a global decomposition pathway ending in the selective delivery of the corresponding mononucleotide. Associated to the determination of other parameters (lipophilicity, aqueous solubility), the present study contributes to the search of suitable pharmacological properties for further in vivo evaluations.

Metallomics, elementomics, and analytical techniques

Metallomics is an emerging and promising research field which has attracted more and more attention. However, the term itself might be restrictive. Therefore, the term "elementomics" is suggested to encompass the study of nonmetals as well. In this paper, the application of state-of-the-art analytical techniques with the capabilities of high-throughput quantification, distribution, speciation, identification, and structural characterization for metallomics and elementomics is critically reviewed. High-throughput quantification of multielements can be achieved by inductively coupled plasma-mass spectrometry (ICP-MS) and neutron activation analysis (NAA). High-throughput multielement distribution mapping can be performed by fluorescence-detecting techniques such as synchrotron radiation X-ray fluorescence (SR-XRF), XRF tomography, energy-dispersive X-ray (EDX), proton-induced X-ray emission (PIXE), laser ablation (LA)-ICP-MS, and ion-detecting-based, secondary-ion mass spectrometry (SIMS), while Fourier transform-infrared (FT-IR) and Raman microspectroscopy are excellent tools for molecular mapping. All the techniques for metallome and elementome structural characterization are generally low-throughput, such as X-ray absorption spectroscopy (XAS), NMR, and small-angle X-ray spectroscopy (SAXS). If automation of arraying small samples, rapid data collection of multiple low-volume and -concentration samples together with data reduction and analysis are developed, high-throughput techniques will be available and in fact have partially been achieved.

Extracting syringe for extraction of phthalate esters in aqueous environmental samples

The use of the extracting syringe (ESy), a fully automated membrane-based extraction technique, for analysis of phthalate esters in complex aqueous samples has been investigated. The ESy, working as an autosampler that combines the extraction process and injection into the gas chromatograph (GC) in one single step, is placed on top of the GC equipped with a flame ionisation detector. The aqueous samples are loaded in a tray and automatically extracted by employing microporous membrane liquid-liquid extraction principle. After the extraction, the extract is directly injected into the GC's programmable temperature vaporisation injector. Six different phthalate esters were used as model compounds. Four extraction solvents were tested and the addition of sample organic modifier was examined. Toluene was the optimal solvent to use for extraction. Due to the large variation in polarity of phthalate esters, 50% methanol as organic modifier had to be added to the samples so as to extract the most nonpolar phthalate esters; di-2-ethylhexylphthalate and di-n-octylphthalate, whereas the other four relatively polar phthalate esters were extracted from unmodified samples. No significant difference between extraction of river water, leachate water from a landfill and reagent water was noted, except for minor deviations. The extraction time was 20 min for extraction of a 1-mL sample, resulting in a good linearity for all aqueous media investigated, good enrichment factors (54-110 folds) and low LOD values (0.2-10 ng mL(-1)) and relative standard deviation (%R.S.D.; 0.9-3.7%).

Principles, developments and applications of on-line coupling of extraction with chromatography

On-line coupling of extraction and chromatographic separation allows the whole analysis to be performed in a closed system. On-line systems are particularly useful when the analytes are labile, the amount of sample is limited, or very high sensitivity is required. Many on-line systems have been developed both for liquid and for solid samples. This review discusses the different instruments that have been constructed and the factors that need to be considered in the coupling. Selected illustrative applications are described to illustrate the potential of the on-line systems.

Sample preparation techniques for the determination of trace residues and contaminants in foods

The determination of trace residues and contaminants in complex matrices, such as food, often requires extensive sample extraction and preparation prior to instrumental analysis. Sample preparation is often the bottleneck in analysis and there is a need to minimise the number of steps to reduce both time and sources of error. There is also a move towards more environmentally friendly techniques, which use less solvent and smaller sample sizes. Smaller sample size becomes important when dealing with real life problems, such as consumer complaints and alleged chemical contamination. Optimal sample preparation can reduce analysis time, sources of error, enhance sensitivity and enable unequivocal identification, confirmation and quantification. This review considers all aspects of sample preparation, covering general extraction techniques, such as Soxhlet and pressurised liquid extraction, microextraction techniques such as liquid phase microextraction (LPME) and more selective techniques, such as solid phase extraction (SPE), solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE). The applicability of each technique in food analysis, particularly for the determination of trace organic contaminants in foods is discussed.

Rapid Wet Synthesis of Nano-Sized β-TCP by Using Dialysis

Nano-sized β-tricalcium phosphate (nano-sized β-TCP) was synthesized by dialysis process using Ca(NO3)2·4H2O and (NH4)2HPO4 as starting materials. The time needed for the whole process is much shorter than other reported methods. In this new synthesis, dialysis was used to remove the unwanted ions, and the removal efficiency of impurity ion was evaluated by comparing the representative ion NH4 + between the original slurries and deionized water outside of the dialysis tube. The resulting powders were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), and chemical analysis. Results showed the final products are pure β-TCP. The pictures of high resolution-transmission electron microscope (HR-TEM) further indicated that β-TCP crystals are around 100nm in diameter.

Dialysis Efficiency in Rapid Synthesis of Nano-Hydroxyapatite

In our previous work the nano-sized hydroxyapatite (nano-HAP) with uniform morphology has been firstly synthesized by a wet chemical method based on dialysis, but the dialysis efficiency was not investigated in detail. In this paper, the removal efficiency of impurity ions such as NH4 + and NO3 - was respectively evaluated by calculating the concentration of the representative irons between the inner slurry and outer distilled water. Results showed that 99% NO3 - ions and 96.9% NH4 + - ions in the slurry has been eliminated. In the first dialysis time, the NH4 + ions diffuse faster than the NO3 - ions due to their smaller size. In the following dialysis times, the dialysis efficiency of NO3 - ions is higher than that of the NH4 + ions because of the presence of higher NO3 - ions concentration gradient. The final nano-HAP is also characterized by XRD, TEM, and FT-IR. It is revealed that the products are stick-like with a length of about 150nm and a diameter of about 20-50 nm. Current work suggests that dialysis is an efficient purified method for nano-HAP production and especially can be applied to industrial preparation of fine nano-sized HAP powders.

Combining high-performance liquid chromatography with on-line microdialysis sampling for the simultaneous determination of ascorbyl glucoside, kojic acid, and niacinamide in bleaching cosmetics

We have used on-line microdialysis sampling coupled with high-performance liquid chromatography and UV-vis detection to simultaneously determine the contents of ascorbyl glucoside (AA-2G), kojic acid (KA), and niacinamide (VitB(3)) in commercial bleaching cosmetics. Our results indicate that AA-2G, KA, and VitB(3) separated well within 4.5 min on a reverse-phase Hypersil Fluophase PFP column when eluting with 0.020 M phosphate buffer solution in 40% (v/v) methanol at pH 5.5. The calibration curves were linear over the ranges 0.068-304, 0.071-284, and 0.024-488 microg mL(-1) for AA-2G, KA, and VitB(3), respectively, with correlation coefficients for the linear regression analyses falling within the range 0.9982-0.9999. The detection limits for AA-2G, KA, and VitB(3) were 0.01, 0.01, and 0.007 microg mL(-1), respectively. The detection wavelength was robust when the levels of the analytes in the samples were high (0.1-2%). The analytes were all detected using ultraviolet light (254 nm). The compounds diffuse through the membrane more readily when KA and VitB(3) are in their molecular forms and AA-2G is ionized. The recoveries were in the range 92-106% with good reproducibility (R.S.D.=3.9-8.7%). We used this procedure to assay six commercially available bleaching cosmetics; our results confirmed not only the precision of the method but also the claims made on the labels of the cosmetics. This approach provides a very simple means to determine the contents of AA-2G, KA, and VitB(3) in various dosages in bleaching cosmetics.

The fabrication and evaluation of inline coupling of microdialysis with capillary electrophoresis and its application in the determination of blood glucose

A novel method of inline coupling of microdialysis (MD) with CE has been investigated. A polysulfone MD membrane was in situ prepared at the inlet end of the separation capillary, which endued the capillary with an additional function of clean-up sampling and made the pretreatment of complex matrices simple. The properties of the membrane and its influence on electrophoresis were evaluated. The membrane cut off macromolecules and particles efficiently and persistently, and changing the components of membrane-casting solution could control the molecular weight cutoff of the membrane. Using the capillary having the MD membrane in electrophoresis, column efficiency with little reduction was achieved. The mixture of chlorpheniramine (CPA) and BSA was used to verify the analytical characteristics. Only the peak of CPA appears in the electropherograms and the RSDs of migration times and peak areas of CPA were 0.8 and 4.6%, respectively. The method was applied for the determination of glucose in human blood using an electrochemical detector. Whole blood containing glucose and macromolecules was electrokinetically injected directly into the capillary without pretreatment, and the concentration of glucose in human blood was 5.5 mmol/L. Equilibrium dialysis injection is also investigated in this paper. The results show that the method may be further used for in vivo sampling to monitor the endogenous or exogenous small molecules and their metabolites.

Fermentation reactor coupled with capillary electrophoresis for on-line bioprocess monitoring

In this paper, a filter probe integrated into a computerized pneumatic sampler for capillary electroseparations was developed for an on-line monitoring of bioprocesses. The optimization of the performance of the coupled system was done by using a response surface modeling and three-level two-factor design. The resolution was found to be the most important parameter influencing the performance of an on-line analysis of the microbial metabolism. For the on-line analysis the migration time and detection limit were also found to be important parameters. Different parameters were combined by using an overall desirability function to find optimum conditions for all parameters. The equipment with an optimized separation protocol was used to monitor the bioaccumulation of Cu, Zn, Co and Cd (with detection limits 0.46, 0.37, 1.2, 0.84 mM correspondingly) by the Rhodococcus sp. bacteria isolated from the highly polluted technogenic soil of northeastern Estonia during a 2-week experiment.

A Novel Synthesis of Nano-Fluoride-Substituted Hydroxyapatite Through Dialysis

A novel synthesis of nano-fluoride-substituted hydroxyapatite (nano-F-HAP) was successfully realized through dialysis process within 4 h, which required much shorter time than the methods reported so far. In new preparation, a dialysis was employed to purify unwanted ions. The removal efficiency of impurity ions in dialysis was evaluated by calculating the concentration of the representative irons NH4 + between the inner slurry and outer distilled water. Results showed that total dialysis efficiency came to 94.5%. The final products were characterized by XRD, HR-TEM, and FT-IR. The XRD and FT-IR results strongly supported substitution of F- for OH-, and the TEM pictures further indicated that the final crystals are about 100nm in length and about 20 nm in diameter without obvious aggregation. Therefore, comparing with traditional purifying processing, such a new synthesis provides a promising application for scale preparation of fine nano-F-HAP crystals.

Miniaturized membrane-assisted solvent extraction combined with gas chromatography/electron-capture detection applied to the analysis of volatile organic compounds

A new module of membrane-assisted solvent extraction (MASE) with miniaturized membrane bags was applied to the determination of seven volatile organic compounds (VOCs): chloroform, 1,1,1-trichloroethane, trichloroethylene, 1,1,2-trichloroethane, tetrachloroethene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane with boiling points between 61 and 147 degrees C in aqueous samples. Different from the known procedure the new, shortened membrane bags were filled with 100 microl of an organic solvent. The membrane bags were placed in a 20 ml headspace vial and filled with 15 ml of the aqueous sample. The vial was transferred into an autosampler where it was stirred for a definite time at elevated temperature. After the extraction, 1 microl of the organic extract was transferred into the spilt/splitless injector of a GC system equipped with an electron-capture detector. This work included optimization of the membrane device, the determination of the optimized extraction conditions such as stirring rate, extraction time and the impact of salt addition. The validation of the method involved repeatability, recovery and detection limit studies, followed of its application towards real water samples. The repeatability, expressed as the relative standard deviation of the peak areas of six extractions was below 10%. The detection limits (LODs) were between 5 ng/l (tetrachloroethene) and 50 ng/l (chloroform). Calibration was performed in a range from 5 ng/l to 150 microg/l, since the concentration in the aqueous samples was expected quite various in this concentration range. Five river water samples of Bitterfeld, Saxony-Anhalt, Germany were analyzed with miniaturized-MASE and the results were compared with those obtained with Headspace-Analysis. The method can be fully automated and moreover, it allows the simultaneous determination of volatile and semi volatile compounds.

Membrane-assisted solvent extraction of seven phenols combined with large volume injection-gas chromatography-mass spectrometric detection

Membrane-assisted solvent extraction (MASE) was applied for the determination of seven phenols (phenol, 2-chlorophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) with log Kow (octanol-water-partition-coefficient) between 1.46 (phenol) and 5.12 (pentachlorophenol) in water. The extraction solvents cyclohexane, ethyl acetate and chloroform were tested and ethyl acetate proved to be the best choice. The optimisation of extraction conditions showed the necessity of adding 5 g of sodium chloride to each aqueous sample to give a saturated solution (333 g/L). The pH-value of the sample was adjusted to 2 in order to convert all compounds into their neutral form. An extraction time of 60 min was found to be optimal. Under these conditions the recovery of phenol, the most polar compound, was 11%. The recoveries of the other analytes ranged between 42% (2-chlorophenol) and 98% (2,4-dichlorophenol). Calibration was performed using large volume injection (100 microL injection volume). At optimised conditions the limits of detection were between 0.01 and 0.6 microg/L and the relative standard deviation (n = 3) was on average about 10%. After the method optimisation with reagent water membrane-assisted solvent extraction was applied to two contaminated ground water samples from the region of Bitterfeld in Saxony-Anhalt, Germany. The results demonstrate the good applicability of membrane-assisted solvent extraction for polar analytes like phenols, without the necessity of derivatisation or a difficult and time-consuming sample preparation.

Strategies for continuous on-line high performance liquid chromatography coupled with diode array detection and electrospray tandem mass spectrometry for process monitoring of sulphonated azo dyes and their intermediates in anaerobic–aerobic bioreactors

On-line HPLC with diode array detection (DAD) coupled to electrospray tandem mass spectrometry (ESI-MS/MS) is presented as an integrated quality control and process integrated optimisation tool for the continuous monitoring of sulphonated azo dyes (SADs) and their intermediates in anaerobic and aerobic bioprocesses. Ion-pair RP-HPLC is found out to be more suitable for simultaneous monitoring of aromatic amines (AAs), sulphonated aromatic amines (SAAs) and sulphonated azo dyes in comparison to RP-HPLC with polar embedded phases. Monitoring of the anaerobic degradation of the diazo Reactive Black 5 displays the dependency of a two stage azo group reduction mechanism on the redox potential of the bioreactor. An autoxidation sensitive intermediate released from the anaerobic reduction is characterised by ESI-MS/MS for the first time. The functionality of the method is demonstrated by the control and evaluation of selective adaptation of bacteria to certain pollutants and the identification of unknown intermediates causing re-gaining colour released from azo dye treatment.

Determination of organophosphorus pesticides using membrane-assisted solvent extraction combined with large volume injection-gas chromatography-mass spectrometric detection

Eight organophosphorus pesticides (parathion-methyl, fenitrothion, malathion, fenthion, bromophos, bromophos-ethyl, fenamiphos and ethion) in aqueous samples were analysed by means of membrane-assisted solvent extraction. First a 20 ml extraction vial was filled with 15 ml of aqueous sample. Then the membrane bag consisting of nonporous polypropylene was put into the vial and filled with 800 microl of organic solvent. The analytes were separated from the aqueous layer by transporting them through the membrane material into the small amount of solvent. The technique was fully automated and successfully combinable with large volume extraction and GC-MS. To achieve an optimum performance several extraction conditions were investigated. Cyclohexane was chosen as acceptor phase. Then the impact of salt, methanol, pH value, as well as working parameters like stirring rate of the agitator and extraction time, were studied. Moreover, the influence of matrix effects was examined by adding different concentrations of humic acid sodium salt. Detection limits in the ng/l level were achieved using large volume injection with the injecting volume of 100 microl. The recovery values ranged from 47 to 100% and the relative standard deviation for three standard measurements was between 4 and 12% (except for bromophos-ethyl: 22%). The linear dynamic range was between 0.001 and 70 microg/l. The applicability of the method to real samples was tested by spiking the eight organophosphorus pesticides to red wine, white wine and apple juice samples.

Miniaturized and Automated Sample Pretreatment for Determination of PCBs in Environmental Aqueous Samples Using an On-Line Microporous Membrane Liquid−Liquid Extraction-Gas Chromatography System

A new, fast, and automated sample pretreatment technique for determination of lipophilic organic compounds in aqueous samples has been developed and applied to the determination of polychlorinated biphenyls (PCBs) in environmental river water. It is based on miniaturized microporous membrane liquid-liquid extraction coupled on-line to gas chromatography (GC) with electron capture detection. The heart of the system that simultaneously connects the sample pretreatment step to the final GC analysis has been named the extracting syringe (ESy). The ESy carries a miniaturized membrane extraction card attached to an electrically and mechanically designed installment and is mounted directly over a GC injector for fully automated injection of the extract. A method was developed to extract 10 PCB congeners from 1-mL water samples (after addition of 40% acetonitrile) with an extraction time of 10 min. The optimized methodology showed good linearity (in the dynamic concentration range of 5 ng L(-)(1)-1 microg L(-)(1)), enrichment factors of 33-40 times, repeatable extractions (RSD 2-5%, n = 4), and low detection limits (2-3 ng L(-)(1)). Acetonitrile had to be added to the samples in order to overcome the influence of PCB adsorption on the repeatability of extraction and enrichment and to minimize the overall memory effect (OME). OME and carryover depended not only on the concentration of the organic solvent added to the sample and that used in the washing procedure but also on whether the extracting card was changed or not. When an optimized washing procedure was applied, the OME was approximately 0.2% at high concentrations (i.e., 1 microg L(-)(1)). When each extraction took place in a new extraction card, no OME was detected. Additionally, no significant adsorption onto glass surfaces or a matrix effect on extraction was noticed. The main features of this methodology are good extraction repeatability, low detection limits at short extraction time, and the unsurpassed characteristic of no detectable OME in the entire system when each sample is processed in a new card. The total consumption of organic (nonchlorinated) solvents is less than 5 mL per sample.

Comparison of different trapping methods for pressurised hot water extraction

Four trapping methods for pressurised hot water extraction were compared in terms of recovery and selectivity. Also, robustness, repeatability and solvent consumption of the trapping systems were investigated. The trapping methods were collection into solvent following liquid-liquid extraction, solid-phase trapping into Tenax TA (SPE), flat sheet microporous membrane liquid-liquid extraction and hollow fibre microporous membrane liquid-liquid extraction. Polycyclic aromatic hydrocarbons were extracted with these systems from four soil and sediment matrices and the extracts were analysed by GC-MS and size-exclusion chromatography. Clear differences were observed in the selectivity and extraction efficiencies of the trapping systems.

Before the injection--modern methods of sample preparation for separation techniques

The importance of sample preparation methods as the first stage in an analytical procedure is emphasised and examined. Examples are given of the extraction and concentration of analytes from solid, liquid and gas phase matrices, including solvent phase extractions, such as supercritical fluids and superheated water extraction, solid-phase extraction and solid-phase microextraction, headspace analysis and vapour trapping. The potential role of selective extraction methods, including molecular imprinted phases and affinity columns, are considered. For problem samples alternative approaches, such as derivatisation are discussed, and potential new approaches minimising sample preparation are noted.