Role of octanol–water partition coefficients in extraction of ionisable organic compounds in a supported liquid membrane with a stagnant acceptor

Behaviour of nonsteroidal anti-inflammatory drugs and eight of their metabolites during wastewater treatment studied by hollow fibre liquid phase microextraction and liquid chromatography mass spectrometry

In this work hollow fibre liquid phase microextraction combined with liquid chromatography mass spectrometry was applied for the determination of the nonsteroidal anti-inflammatory drugs (NSAIDs) ketoprofen, naproxen, diclofenac and ibuprofen as well as eight of their known human metabolites in wastewater samples. Extraction time and addition of tri-n-octylphosphine oxide (TOPO) to the liquid membrane were evaluated resulting in a method with an optimal extraction time of 5h and 5% (w/V) TOPO addition to the membrane liquid (di-n-hexyl ether). With the optimized method, enrichment factors ranged between 778 and 4830. The method was applied for analysis of samples collected from Källby wastewater treatment plant in the city of Lund, Sweden. Samples were collected from the influent, water entering as well as exiting the conventional activated sludge treatment and the effluent to study the behaviour of these compounds during the treatment process. All twelve substances were found in the influent and for all four drugs, higher concentrations were detected of the metabolites than the parent compounds. Highest concentrations were detected of o-desmethylnaproxen, 2-hydroxyibuprofen and carboxyibuprofen (average influent concentrations of 45, 35 and 63 μg/L respectively). The study showed only partial removal during the primary treatment whereas both parent compounds and metabolites were efficiently removed during the activated sludge process. In the effluent all analytes were detected in concentrations below 1 μg/L thus showing that either the investigated metabolites do not belong to the NSAID transformation products formed during the activated sludge treatment or they are also quickly further transformed within the treatment.

Prediction of extraction efficiency in supported liquid membrane with a stagnant acceptor phase by means of artificial neural network

An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol-water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back-propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol-water partition coefficients logP, acid dissociation constant pK(a), water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters.

Continuous flow hollow fiber liquid-phase microextraction and monitoring of pharmaceuticals in a sewage treatment plant effluent

A method for simultaneous extraction and quantification of four non-steroidal anti-inflammatory drugs (NSAIDs) based on continuous flow hollow fiber liquid-phase microextraction (CFHF-LPME) was developed. The effect of sample flow rate, acceptor flow rate, type of acceptor flow (continuous, semi-continuous or forward-backward), type of supported liquid membrane and sample volume was studied. The extraction of the final method was linear over an environmentally relevant concentration range and yielded high enrichment factors (720-940 times) in reagent water and (270-800 times) in sewage water for all analytes within 45 min. Repeatability was best (RSD 6-15%) during the first 30 min of extraction. The optimised method was used to monitor the occurrence and fate of the four NSAIDs in a Swedish sewage treatment plant (STP) effluent, which is discharged into a system of ponds before release into a river, during the period May-September 2008. All four analytes were detected at concentrations up to 0.92 µg L-1 ketoprofen, 0.08 µg L-1 naproxen, 0.43 µg L-1 diclofenac and 0.25 µg L-1 ibuprofen. A concentration drop during the summer was observed. For diclofenac and ketoprofen significant removal in the primary recipient pond system was observed. The presence of the studied pharmaceuticals in STP effluent together with concern about their environmental effects makes monitoring of their occurrence and knowledge of their environmental fate important. The proposed method provides a basis for automation of extraction towards on-site extraction using CFHF-LPME.

Speciation of alkyllead in aqueous samples with application of liquid membrane probe for extraction and preconcentration

Lead is known to be toxic, especially in its organic forms (organolead, OL). In the environment tetraalkyllead species are rapidly degraded by sunlight and atmospheric constituents like ozone or hydroxyl radicals. Such breakdown yields the soluble forms such as trialkyllead and dialkyllead and finally ionic lead species. The liquid membrane extraction probe (LMP) device has been developed and used as an extraction and preconcentration tool for the speciation analysis of organolead compounds by GC/MS. It allows analysis of OL species at low concentrations in complicated matrices of environmental samples. The effect of pH, stirring rate, and time that influence the extraction efficiency of OL extraction by the LMP method were optimized. The transformation of tetramethyllead in aqueous media at different concentrations of major ions K(+), Na(+), Ca(2+), Mg(2+), Cl(-), SO(4)(2-) and the application of LMP to environmental samples are presented. It was found that degradation of tetramethyllead takes between 24 and 37 days. The detection limit (LOD) of the method for all organolead species investigated is around 4.7 microg/L, with a limit of quantitation of 15 microg/L.

Solvent-extraction and Langmuir-adsorption-based transport in chemically functionalized nanopore membranes

We have investigated the transport properties of nanopore alumina membranes that were rendered hydrophobic by functionalization with octadecyltrimethoxysilane (ODS). The pores in these ODS-modified membranes are so hydrophobic that they are not wetted by water. Nevertheless, nonionic molecules can be transported from an aqueous feed solution on one side of the membrane, through the dry nanopores, and into an aqueous receiver solution on the other side. The transport mechanism involves Langmuir-type adsorption of the permeating molecule onto the ODS layers lining the pore walls, followed by solid-state diffusion along these ODS layers; we have measured the diffusion coefficients associated with this transport process. We have also investigated the transport properties of membranes prepared by filling the ODS-modified pores with the water-immiscible (hydrophobic) liquid mineral oil. In this case the transport mechanism involves solvent extraction of the permeating molecule into the mineral oil subphase confined with the pores, followed by solution-based diffusion through this liquid subphase. Because of this different transport mechanism, the supported-liquid membranes show substantially better transport selectivity than the ODS-modified membranes that contain no liquid subphase.

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.

Measurement of nitrophenols in air samples by impinger sampling and supported liquid membrane micro-extraction

A sensitive analytical technique for the detection of trace nitrophenols in air has been developed. The steps in this process are impinger sampling to capture the nitrophenols in an aqueous phase, which is then followed by supported liquid membrane micro-extraction (SLMME) and analytical detection. The nitrophenols were analyzed by reverse-phase high performance liquid chromatography (HPLC) and did not require any derivatization. Method detection limits (MDL) of 0.5-1.0 ng L(-1) from aqueous solutions and 3.1-46.7 ppbV from air extractions were observed. The high enrichment of nitrophenol in SLMME allowed low detection limits even with HPLC-UV detection. SLMME is an inexpensive, easy to use procedure that employs disposable membrane fibers.

Evaluation of progesterone content in saliva using magnetic particle-based immuno supported liquid membrane assay (m-ISLMA)

Progesterone in saliva was monitored using a new method called magnetic particle-based immuno supported liquid membrane assay (m-ISLMA) in a sequential injection (SI) setup, allowing automatic sample cleanup, analyte enrichment, and detection in a single analysis unit. Progesterone (Ag) diffuses from a continuous flowing sample - the donor - into a supported organic liquid membrane (SLM), based on analyte partitioning (solubility) between the aqueous donor and the organic phase. The Ag is re-extracted from the SLM into a second stagnant aqueous acceptor, containing antibodies (Ab) immobilized on magnetic beads, held at the bottom of the acceptor by a magnet. Due to the formation of strong Ag-Ab-bead complexes and a large excess of Ab-beads, the Ag is accumulated and selectively enriched in the acceptor. The extracted progesterone was quantified by injecting into the acceptor a horseradish peroxidase (HRP) labeled analyte tracer, the substrate (luminol, H(2)O(2), and p-iodophenol), and finally detection of the generated chemiluminescence by a photomultiplier tube. After optimization of experimental parameters (e.g., sample flow rate, extraction time, type of organic solvent and antibody-bead concentration in the acceptor), a detection limit of 8.50+/-0.17 fgL(-1) and a dynamic range between 35 fgL(-1) and 10 pgL(-1) was reached. The progesterone level of saliva for three subjects (women in different period of ovarian cycle) was investigated, and the corresponding progesterone concentrations detected with m-ISLMA coincided well with the expected values.

Urine sample preparation of tricyclic antidepressants by means of a supported liquid membrane technique for high-performance liquid chromatographic analysis

Supported liquid membrane (SLM) technique for sample work-up and enrichment was used for determination of tricyclic antidepressant drugs in urine by high-performance liquid chromatography (HPLC) with UV detection. The studied antidepressant drugs were amitriptyline, opipramol, noxiptyline and additionally diethazine was used as possible internal standard. Alkaline phosphoric buffer with urine sample, as the donor solution, was passed over the liquid membrane into which investigated substances were extracted. On the other side of the membrane, analyzed compounds were trapped due to creating non-extractable form in acidic acceptor solution. Enriched and cleaned up drugs were then injected into a HPLC system with ultraviolet detection to analyze of their concentration in acceptor solution. Optimum extraction efficiency was determined by changing acceptor and donor solutions pH, application of different flow rates of donor solution and by using different solvents in the membrane. Also, donor solution volume, extraction time and concentration of analytes were varied to check the linearity of extraction process. The highest extraction efficiency: 43% for opipramol, 56% for noxiptyline, 43% for amitriptyline and 42% for diethazine (R.S.D. values were <6% and n=3) was achieved when 0.05 M phosphate buffer pH 4.0 and 9.5 were used as donor and acceptor solutions, respectively, n-undecane with 5% tri-n-octylphosphine oxide (TOPO) was used as liquid membrane. Limit of quantification (LOQ) for tricyclic antidepressants after enrichment of 100ml of urine sample was about 1 ng/ml.

Separation of drug traces from water with particular membrane systems

The purpose of the present project is to examine the applicability of certain natural biological and liquid membranes for the separation of drugs of environmental concern such as ibuprofen, diclofenac, carbamazepine, and sulfamethoxazol from dilute aqueous solutions. Different types of intestine parts of cattle, sheep, and pig were applied as biological flat sheet membranes after different modes of pretreatment. Best results were obtained with special parts of cattle appendix. The concentration of each drug in the aqueous feed phase was in the range of 0.1-10 mg (cm3)(-1), the pH-values adjusted between 8 and 10. Pure water was used as the permeation phase. The influence of experimental parameters such as stirring velocity, temperature, pH-value, salt concentration, and the presence of surfactants as well as humic substances was studied. Under all conditions chosen the combined drugs permeate simultaneously through the natural membranes as the permeation kinetics of the individual compounds are very similar, while humic compounds were retained. Additional treatment of the permeate with liquid or solid phase extraction techniques increases crucially the depletion of the drugs from the feed. The mass transfer of the pharmaceuticals through the liquid membranes was carried out in three-compartment transport cells and supported liquid membrane-chambers. The three-phase liquid bulk membrane systems consisted of an aqueous feed solution, an organic solvent (dihexyl ether, decane, undecane, or decanol) with and without a dissolved sulfonic acid, tertiary amine or Cu(II)-chelate compound as a liquid bulk membrane and an aqueous stripping solutions containing dilute solutiuons of Na2CO3, NaOH, HCl, or HClO4. The transport of the drugs shows some differences, which can be attributed to their acid/base-behavior and partition coefficients log Kow. High extraction yields were obtained for sulfamethoxazol and carbamazepine by using polar organic solvents. Maximum transport efficiencies were obtained for the acidic compounds ibuprofen and diclofenac. They were completely extracted by using dihexyl ether loaded with octane sulfonic acid. A pH-gradient between feed and strip increases the efficiency of the transport. Certain three-phase compositions were successfully utilized in supported liquid membrane systems (SLM) so that high enrichment factors (approximately 75) were achieved for traces of diclofenac and ibuprofen. The solid and liquid membrane systems employed aim for technical as well as analytical purposes, such as sample pretreatment prior to HPLC-UV or LC-MS analysis of drug traces.

Three-layer flow membrane system on a microchip for investigation of molecular transport

A stable three-layer flow system, water/organic solvent/water, has been successfully applied for the first time in a microchannel to get rapid transport through an organic liquid membrane. In the continuous laminar flow region, the analyte (methyl red) was rapidly extracted across the microchannel from the donor to the acceptor phase through the organic solvent phase (cyclohexane). Thermal lens microscopy was used to monitor the process. The thickness of the organic phase, sandwiched by the two aqueous phases, was approximately 64 microm, and it was considered as a thin liquid organic membrane. Permeability studies showed the effects of molecular diffusion, layer thickness, and organic solvent-water partition coefficient on the molecular transport. In the microchip, complete equilibration was achieved in several seconds, in contrast to a conventionally used apparatus, where it takes tens of minutes. The thickness of the organic and aqueous boundary layers was defined as equal to the microchannel dimensions, and the organic solvent-water partition coefficient was determined on a microchip using the liquid/liquid extraction system. Experimental data on molecular transport across the organic membrane were in agreement with the calculated permeability based on the three-compartment water/organic solvent/water model. This kind of experiment can be performed only in a microspace, and the system can be considered as a potential biological membrane for future in vitro study of drug transport.

Membrane-based techniques for sample enrichment

Sample preparation techniques based on non-porous membrane extraction generally offer a high degree of selectivity and enrichment power, together with convenient possibilities for direct and automated connections to chromatographic and other analytical instruments. In this review principles and applications for techniques as supported liquid membrane extraction, microporous membrane liquid-liquid extraction, polymeric membrane extraction and membrane extraction with a sorbent interface are described and compared.