Semi-automated hollow-fibre membrane extraction, a novel enrichment technique for the determination of biologically active compounds in water samples

Kinetic Calibration for Automated Hollow Fiber-Protected Liquid-Phase Microextraction

Recently, a kinetic calibration method was developed for the quantification of microextraction. In this study, we proved that the sample volume and sampling time do not affect the feasibility of the calibration method, theoretically. The new theoretical considerations of the kinetic calibration method were validated through the investigation of the kinetics of the absorption and desorption processes of hollow fiber-protected liquid-phase microextractrion (HF-LPME). The kinetic calibration method for HF-LPME was successfully used to correct the matrix effects in the carbaryl analysis of a red wine sample. This research extends the kinetic calibration approach to fast sampling and some in-vial analyses, whereby the sample volume is not much larger than the product of the distribution coefficient and the volume of the extraction phase. HF-LPME technique was successfully automated with a CTC CombiPal autosampler, and a new device was designed for the automation of HF-LPME in this study. All steps of the HF-LPME technique, including the filling of the extraction solvent, sample transfer and agitation, withdrawing the solvent to a syringe, and introducing the extraction phase into the injector, were automated by a CTC autosampler. The fully automated HF-LPME technique is more convenient and more accurate. The good reproducibility of the fully automated HF-LPME technique eliminates the need for an internal standard to improve the analytical precision. The automated HF-LPME technique can be also used to obtain the distribution coefficient between the sample matrix and the extraction phase. The distribution coefficients of carbaryl and (13)C-carbaryl between 1-octanol and red wine, at 25 degrees C, were obtained with this technique.

Extraction of hydroxyaromatic compounds in river water by liquid–liquid–liquid microextraction with automated movement of the acceptor and the donor phase

Liquid-liquid-liquid microextraction with automated movement of the acceptor and the donor phase technique is described for the extraction of six hydroxyaromatic compounds in river water using a disposable and ready to use hollow fiber. Separation and quantitative analyses were performed using LC with UV detection at 254 nm. Analytes were extracted from the acidified sample solution (donor phase) into the organic solvent impregnated in the pores of the hollow fiber and then back extracted into the alkaline solution (acceptor phase) inside the lumen of the hollow fiber. The fiber was held by a conventional 10 microL LC syringe. The acceptor phase was sandwitched between the plunger and a small volume of the organic solvent (microcap). The acceptor solution was repeatedly moved in and out of the hollow fiber using a syringe pump. This movement provides a fresh acceptor phase to come in contact with the organic phase and thus enhancing extraction kinetics thereby leading to the improvement in enrichment of the analytes. The microcap separates the acceptor phase and the donor phase in addition to being partially responsible for mass transfer of the analytes from the donor solution to the acceptor solution. Under stirring, a fresh donor phase will enter through the open end of the fiber that will also contribute to the mass transfer. Various parameters affecting the extraction efficiency viz type of organic solvent, extraction time, stirring speed, effect of sodium chloride, and concentration of donor and acceptor phases were studied. RSD (3.9-5.6%), correlation coefficient (0.995-0.997), detection limit (2.0-51.2 ng/mL), enrichment factor (339-630), relative recovery (93.2-97.9%), and absolute recovery (33.9-63.0%) have also been investigated. The developed method was applied for the analysis of river water.

Strategies for the microextraction of polar organic contaminants in water samples

In this paper the most recent developments in the microextraction of polar analytes from aqueous environmental samples are critically reviewed. The particularities of different microextraction approaches, mainly solid-phase microextraction (SPME), stir-bar-sorptive extraction (SBSE), and liquid-phase microextraction (LPME), and their suitability for use in combination with chromatographic or electrically driven separation techniques for determination of polar species are discussed. The compatibility of microextraction techniques, especially SPME, with different derivatisation strategies enabling GC determination of polar analytes and improving their extractability is revised. In addition to the use of derivatisation reactions, the possibility of enhancing the yield of solid-phase microextraction methods for polar analytes by using new coatings and/or larger amounts of sorbent is also considered. Finally, attention is also focussed on describing the versatility of LPME in its different possible formats and its ability to improve selectivity in the extraction of polar analytes with acid-base properties by using separation membranes and buffer solutions, instead of organic solvents, as the acceptor solution.

Adsorptive cathodic stripping voltammetric assay of the estrogen drug ethinylestradiol in pharmaceutical formulation and human plasma at a mercury electrode

The electroreduction of ethinylestradiol at the hanging mercury drop electrode in the Britton-Robinson universal buffer of pH 2-11 was studied and its interfacial adsorptive character onto the mercury electrode surface was identified. A validated simple, rapid, sensitive, specific, precise and inexpensive square-wave voltammetric procedure is described for the determination of ethinylestradiol following its accumulation onto a hanging mercury drop electrode in a Britton-Robinson universal buffer of pH 7. The optimal procedural conditions were: accumulation potential E(acc)=-0.7 V versus Ag/AgCl/KCl(s), accumulation duration=60s, pulse-amplitude=70 mV, scan increment=10 mV and frequency=120 Hz. Limits of detection (LOD) and quantification (LOQ) of 5.9x10(-10)M and 1.9x10(-9)M bulk ethinylestradiol, respectively, were achieved. The proposed procedure was successfully applied to the quantification of ethinylestradiol in pharmaceutical formulation (Ethinyl-oestradiol tablets) and in human serum and plasma without the necessity for sample pretreatments and/or time-consuming extraction or evaporation steps prior to the analysis. LOD of 8.7x10(-10)M and 3x10(-9)M and LOQ of 2.9x10(-9)M and 1x10(-8)M of ethinylestradiol were achieved in human serum and plasma, respectively.

Application of hollow fiber liquid phase microextraction for the determination of insecticides in water

In the present work, a novel sample pre-treatment technique for the determination of trace concentrations of some insecticide compounds in aqueous samples has been developed and applied to the determination of the selected analytes in environmental water samples. The extraction procedure is based on coupling polypropylene hollow fiber liquid phase microextraction (HF-LPME) with gas chromatography by flame thermionic detection (GC-FTD). For the development of the method, seven organophosphorous insecticides (dichlorvos, mevinphos-cis, ethoprophos, chlorpyrifos methyl, phenthoate, methidathion and carbofenothion) and one carbamate (carbofuran) were considered as target analytes. Several factors that influence the efficiency of HF-LPME were investigated and optimized including agitation, organic solvent, sample volume, exposure time, salt additives and pH. The optimized methodology exhibited good linearity with correlation coefficient = 0.990. The analytical precision for the target analytes ranged from 4.3 to 11.1 for within-day variation and 4.6 to 12.0% for between-day variation. The detection limits for all analytes were found in the range from 0.001 to 0.072 microg/L, well below the limits established by the EC Drinking Water Directive (EEC 80/778). Relative recoveries obtained by the proposed method from drinking and river water samples ranged from 80 to 104% with coefficient of variations ranging from 4.5 to 10.7%. The present methodology is easy, rapid, sensitive and requires small sample volumes to screen environmental water samples for insecticide residues.

Performance optimisation of a passive sampler for monitoring hydrophobic organic pollutants in water

The performance of an integrative passive sampler that consists of a C18 Empore disk sorbent receiving phase fitted with low density polyethylene membrane was optimised for the measurement of time-weighted average concentrations of hydrophobic micropollutants in water. A substantial improvement of sampling characteristics including the rate of sampling and the sampling precision was achieved by decreasing the internal sampler resistance to mass transfer of hydrophobic organic chemicals. This was achieved by adding a small volume of n-octanol, a solvent with high permeability (solubility [times] diffusivity) for target analytes, to the interstial space between the receiving sorbent phase and the polyethylene diffusion-limiting membrane.

Suitability of hollow fibre liquid-phase microextraction for the determination of acidic pharmaceuticals in wastewater by liquid chromatography–electrospray tandem mass spectrometry without matrix effects

The applicability of hollow fibre liquid-phase microextraction (LPME), as an alternative to solid-phase extraction (SPE), for the extraction/enrichment of acidic drugs (e.g. ibuprofen, clofibric acid, bezafibrate, etc.) from water samples prior to the determination by LC-ESI-MS-MS has been evaluated. After LPME method optimisation, it was found that this technique can provide very clean extracts, which do not lead to signal suppression during LC-ESI-MS-MS analysis of the analytes. The limits of quantification (0.5-42 ng/L) are suitable for the analysis of these drugs in wastewater. However repeatability needs to been improved (intra-day R.S.D. = 3.4-32%), which may be expected by automation and the development of commercially available devices and fibres specially prepared for analytical purposes. The method was finally applied to wastewater samples (treated and untreated) and results comparable to SPE were obtained.

Enhanced extraction capacity and chemical noise reduction in solid-phase microextraction

Solid-phase microextraction fibres with different lengths, coatings (polydimethylsiloxane, polyacrylate, Carbowax/divinylbenzene), film thicknesses, and mounting techniques were examined in combination with GC-MS with regard to their enhanced extraction capacities and fibre 'bleeding'. A series of phenols and halogenated aromatics with diverse physicochemical properties were investigated to characterize the effects of the enhanced extraction capacities of solid-phase microextraction fibres. Fibre extension was found to be effective for the microextraction of compounds with high log Kow values, whereas increasing both coating thickness and fibre length is most effective for the microextraction of more polar compounds such as phenols. Almost no bisphenol A was released when custom-made polydimethylsiloxane fibres were used, finally eliminating a drawback of endocrine disrupter analysis by solid-phase microextraction.

Sensitive trace enrichment of environmental andiandrogen vinclozolin from natural waters and sediment samples using hollow-fiber liquid-phase microextraction

The presence of vinclozolin in the environment as far as the endocrine disruption effects in biota are concerned has raised interest in the environmental fate of this compound. In this respect, the present study attempts to investigate the feasibility of applying a novel quantitative method, liquid-phase microextraction (LPME), so as to determine this environmental andiandrogen in environmental samples such as water and sediment samples. The technique involved the use of a small amount (3 microL) of organic solvent impregnated in a hollow fiber membrane, which was attached to the needle of a conventional GC syringe. The extracted samples were analyzed by gas chromatography coupled with electron-capture detection. Experimental LPME conditions such as extraction solvent, stirring rate, content of NaCl and pH were tested. Once LPME was optimized, the performance of the proposed technique was evaluated for the determination of vinclozolin in different types of natural water samples. The recovery of spiked water samples was from 80 to 99%. The procedure was adequate for quantification of vinclozolin in waters at levels of 0.010 to 50 microg/L (r> 0.994) with a detection limit of 0.001 microg/L (S/N= 3). Natural sediment samples from the Aliakmonas River area (Macedonia, Greece) spiked with the target andiandrogen compound were liquid-liquid extracted and analyzed by the methodology developed in this work. No significant interferences from the samples matrix were noticed, indicating that the reported methodology is an innovative tactic for sample preparation in sediment analysis, with a considerable improvement in the achieved detection limits. The results demonstrated that apart from analyte enrichment, the proposed LPME procedure also serves as clean-up method and could be successfully performed to determine trace amounts of vinclozolin in water and sediment samples.