Headspace single drop and hollow fiber liquid phase microextractions for HPLC determination of phenols

Two methods based on headspace single drop microextraction (HS-SDME) and headspace hollow fiber liquid phase microextraction (HS-HF-LPME) were developed and critically compared with HPLC-UV determination of phenols (including phenol (Ph), 2-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP)) in this paper. The significant parameters affecting the extraction efficiency of the target analytes in both extraction modes were studied and the optimal extraction conditions were established. Under the optimal conditions, the detection limits (S/N = 3) for Ph, CP, DCP and TCP obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 2.1, 0.2, 0.8,1.1 ng/mL and 4.2, 0.4, 0.4, 0.4 ng/mL with enrichment factors of 15.8, 198.9, 159.7, 194.8 and 9.2, 149.9, 301.9, 411.1, respectively. The RSDs obtained by HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were 3.7, 4.0, 9.8, 6.7% and 6.3, 3.6, 3.1, 4.8% for Ph, CP, DCP and TCP, respectively. Both extraction modes have a comparable analytical performance, but HS-HF-LPME was more robust than HS-SDME, while HS-SDME was simpler than HS-HF-LPME. The two headspace microextraction modes were applied for HPLC-UV determination of target phenols in water, honey and toner samples, and the determined values obtained by both techniques were in good agreement with each other.     

Stir membrane liquid-liquid microextraction

In this article, a novel liquid phase microextraction technique, called stir membrane liquid-liquid microextraction (SM-LLME), is presented. The new approach combines the advantages of liquid phase microextraction and stirring in the same unit allowing the isolation and preconcentration of the analytes in a simple and efficient way. In the construction of the unit, a polymeric membrane is employed to protect the small volume of the extractant phase. The extraction technique is characterized for the resolution of a model analytical problem: the determination of five selected chlorophenols in water. A two-phase extraction mode is used for the extraction of the analytes with an organic solvent in which an in situ derivatization reaction takes place. The analytes are finally analyzed by gas chromatography/mass spectrometry. All the variables involved in the extraction process have been clearly identified and optimized. The new extraction mode allows the determination of chlorophenols with limits of detection in the range from 14.8 ng/L (for 2,4,5-trichlorophenol) to 22.9 ng/L (for 3-chlorophenol) with a relative standard deviation lower than 8.7% (for 2,6-dichlorophenol).     

Microwave assisted headspace controlled-temperature single drop microextraction for liquid chromatographic determination of chlorophenols in aqueous samples

We report on an efficient one-step sample preconcentration technique by coupling microwave heating and cloud vapor zone (CVZ)-based headspace controlled-temperature single drop microextraction (HS-CT-SDME), and its application to headspace extraction of chlorophenols in aqueous solutions. Microwave irradiation is utilized to accelerate evaporation of analytes into the headspace sampling zone for the direct extraction of aqueous chlorophenols. A microdrop of extractant is suspended at the bottom of a bell-mouthed micropipette tip connected to a microsyringe needle. An external cooling system was adopted to control the formation of the CVZ around the SDME tip in the headspace sampling area. In the CVZ procedure, the warm headspace vapor is quickly cooled near the SDME tip, thus forming a dense cloud of analyte-water vapor; thereby enhancing the partition of the analytes into the SDME solvent. The chlorophenols are then determined by LC-UV detection. Under the optimized experimental conditions, the analytical signal is linearly related to the concentration of the chlorophenols range of 2.5–250?ng?mL^?1. The detection limits vary from 0.3 to 0.7?ng?mL^?1, and the precision (expressed as the relative standard deviation) from 3.7 to 13.3?%. The method was validated with real water samples, and the spiked recovery ranged between 92 and 103.1?% for river water, and between 85.1?% and 98.6?% for lake water. Compared to other methods, microwave assisted HS-CT-SDME is simple, rapid, sensitive, inexpensive and eco-friendly, and requires less sample and organic extractant.

Temperature-controlled headspace liquid-phase microextraction device using volatile solvents

A novel temperature-controlled headspace liquid-phase microextraction (TC-HS-LPME) device was established in which volatile solvents could be used as extractant. In this device, a PTFE vial cap with a cylindrical cavity was used as the holder of the extraction solvent. Up to 40 μl of extraction solvent could be suspended in the cavity over the headspace of aqueous sample in the vial. A cooling system based on thermoelectric cooler (TEC) was used to lower the temperature of extractant in PTFE vial cap to reduce the loss of volatile solvent during extraction process and increase the extraction efficiency. The selection of solvents for HS-LPME was then extended to volatile solvents, such as dichloromethane, ethyl acetate and acetone. The use of volatile extraction solvents instead of semi-volatile solvent reduced the interference of the large solvent peak to the analytes peaks, and enhanced the compatibility of HS-LPME with gas chromatograph (GC). Moreover, the use of larger volume of extractant solvent increases the extraction capacity and the injection volume of GC after extraction, thus improving detection limits. Several critical parameters of this technique were investigated by using chlorobenzenes (CBs) as the model analytes. High enrichment factors (498–915), low limits of detection (0.004–0.008 μg/L) and precision (3.93–5.27%) were obtained by using TC-HS-LPME/GC-FID. Relative recoveries for real samples were more than 83%.     

Microwave-assisted headspace controlled temperature liquid-phase microextraction of chlorophenols from aqueous samples for gas chromatography-electron capture detection

A modified headspace liquid-phase microextraction (HS-LPME) method was studied for the extraction of chlorophenols (CPs) from aqueous samples with complicated matrices, before gas chromatographic (GC) analysis with electron capture detection (ECD). Microwave heating was applied to accelerate the evaporation of CPs into the headspace, and an external-cooling system was used to control the sampling temperature. Conditions influencing extraction efficiency, such as the LPME-solvent, the sampling position of LPME, the sampling temperature, microwave power, and irradiation time (the same as sampling time), sample pH, and salt addition were thoroughly optimized. Experimental results indicated that the extraction of CPs from a 10mL aquatic sample (pH 1.0) was achieved with the best efficiency through the use of 1-octanol as solvent, microwave irradiation of 167W, and sampling at 45 degrees C for 10min. The detections were linear in the concentration of 5.0-100microg/L for 2,4-dichlorophenol (2,4-DCP), and 0.5-10microg/L for 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP). Detection limits were found to be 0.7, 0.04, 0.07, and 0.08microg/L for 2,4-DCP, 2,4,6-TCP, 2,3,4,6-TeCP, and PCP, respectively. A landfill leachate sample was analyzed with recovery between 83 and 102%. The present method was proven to serve as a simple, sensitive, and rapid procedure for CP analysis in an aqueous sample.     

Ionic liquid based three-phase liquid-liquid-liquid solvent bar microextraction for the determination of phenols in seawater samples

For the first time, an ionic liquid based three-phase liquid-liquid-liquid solvent bar microextraction (IL-LLL-SBME) was developed for the analysis of phenols in seawater samples. The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]), was used as the intermediary solvent for LLL-SBME, enhancing the extraction efficiency for polar analytes. In the procedure, the analytes were extracted from the aqueous sample into the ionic liquid intermediary and finally, back-extracted into an aqueous acceptor solution in the lumen of the hollow fiber. The porous polypropylene membrane acted as a filter to prevent potential interfering materials from being extracted, and no additional cleanup was required. After extraction, the acceptor solution could be directly injected into a high-performance liquid chromatographic system for analysis. Six phenols, 2-nitrophenol, 4-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were selected here as model compounds for developing and evaluating the method. The most influential extraction parameters were evaluated, including the ionic liquid, the composition of donor solution and acceptor solution, the extraction time and the extraction temperature, the effect of ionic strength, and the agitation speed. Under the most favorable extraction parameters, the method showed good linearity (from 0.05-50 to 0.5-50 μg/L, depending on the analytes) and repeatability of extractions (RSD below 8.3%, n=5). The proposed method was compared to conventional three-phase LLL-SBME and ionic liquid supported hollow fiber protected three-phase liquid-liquid-liquid microextraction, and showed higher extraction efficiency. The proposed method was demonstrated to be a simple, fast, and efficient method for the analysis of phenols from environmental water samples.     

Solvent-bar microextraction—Using a silica monolith as the extractant phase holder

In this paper, a novel liquid-phase microextraction (LPME) approach, based on solvent-bar microextraction (SBME), was developed in which a silica monolith was used as the extractant solvent holder. Owing to the porous nature of the monolith, the extractant solvent could be easily held in the material; when the monolith containing the extractant solvent was exposed to the sample solution, analytes could directly diffuse from the sample solution into the extractant solvent. Polycyclic aromatic hydrocarbons (PAHs) were used as model analytes to evaluate the procedure. Through the investigation of the effect of agitation speed, extraction time, length of the monolith (that determined the volume of organic extractant solvent) and salt concentration on extraction efficiency, the following optimal extraction conditions were obtained: stirring at 1000 rpm for 30 min without salt addition using a 4-mm silica monolith. The limits of detection ranged from 3.9 pg/mL to 28.8 pg/mL, with relative standard deviations of between 8.16% and 10.5% on the same silica monolith. The linearity was 0.05–200 ng/mL for fluoranthene and pyrene, and 0.5–200 ng/mL for chrysene and benzo[b]fluoranthene, with acceptable correlation coefficient. When this method was applied for the spiked real river sample, the relative recoveries ranged from 87.1% to 100.7% for the tested PAHs. This method was also compared to polymeric hollow fiber-based SBME and hollow fiber-protected LPME and found to provide better results. Additionally, compared with the polymeric hollow fiber, the silica monolith possesses good resistance to extreme conditions, such as high temperature and pH, and is more compatible with various organic solvents. This is the first report of an application of a monolithic material for LPME, and as a solvent holder for SBME. It extends the scope of applications of such materials, to analytical chemistry, specifically to sample preparation.     

Determination of chlorophenols in environmental water samples using directly suspended droplet liquid-liquid-liquid phase microextraction prior to high-performance liquid chromatography

A new sample preparation method named directly suspended droplet liquid-liquid-liquid phase microextraction was used in this research for determination of three chlorophenols in environmental water samples. The analytes (2-chlorophenol, 3-chlorophenol and 4-chlorophenol) were extracted from 4.5?mL acidic donor phase, (pH 2, P1) into an organic phase, 350?µL?of benzene/1-octanol (90?:?10 v/v, P2) and then were back-extracted into a 7?µL droplet of an basic (pH 13) aqueous solution (acceptor phase, P3). In this method, contrary to the ordinary single drop liquid-phase microextraction technique, an aqueous large droplet is freely suspended on the surface of the organic solvent, without using a microsyringe as supporting device. This aqueous microdroplet is delivered at the top-centre position of an immiscible organic solvent which is laid over the aqueous donor sample solution while the solution is being agitated. Then, the acceptor phase containing chlorophenols was withdrawn back into a HPLC microsyringe and neutralised by adding of 7?µL HCl 0.1?M. The total amount was eventually injected into the HPLC system with UV detection at 225?nm for further analysis. Parameters such as the organic solvent, phases volumes, extraction and back-extraction times, stirring rate and pH values were optimised. The calibration graphs are linear in the range of 10–2000?µg?L^?1 with r?≥?0.9973. The enrichment factors were ranged from 115 to 170, and the limit of detection (LOD, n?=?7) varied from 5 to 10?µg?L^?1. The relative standard deviations (RSDs, n?=?5) were found 6.8 to 7.4 at S/N?=?3. All experiments were carried out at room temperature, (22?±?0.5°C).     

Automation and optimization of liquid-phase microextraction by gas chromatography

Several fully automated liquid-phase microextraction (LPME) techniques, including static headspace LPME (HS-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and exposed to the headspace of the sample solution), exposed dynamic HS-LPME (the solvent is exposed in the headspace of sample vial for different time, and then withdrawn into the barrel of the syringe. This procedure is repeated a number of times), unexposed dynamic HS-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the gaseous sample is withdrawn into the barrel and then ejected), static direct-immersed LPME (DI-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and directly immersed into the sample solution), dynamic DI-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the sample solution is withdrawn and ejected), and two phase hollow fiber-protected LPME (HF-LPME) (a hollow fiber is used to stabilize and protect the solvent), auto-performed with a commercial CTC CombiPal autosampler, are described in this paper. Critical experimental factors, including temperature, choice of extraction solvent, solvent volume, plunger movement rate, and extraction time were investigated. Among the three HS-LPME techniques that were evaluated, the exposed dynamic HS-LPME technique provided the best performance, compared to the unexposed dynamic HS-LPME and static HS-LPME approaches. For DI-LPME, the dynamic process can enhance the extraction efficiency and the achieved method precision is comparable with the static DI-LPME technique. The precision of the fully automated HF-LPME is quite acceptable (RSD values below 6.8%), and the concentration enrichment factors are better than the DI-LPME approaches. The fully automated LPME techniques are more accurate and more convenient, and the reproducibility achieved eliminates the need for an internal standard to improve the method precision.     

LC-Ultrasound-Assisted Headspace Liquid Microextraction for the Analysis of Phenols in Water

An ultrasound-assisted headspace liquid microextraction method is presented. The organic solvent droplet is suspended at the bottom of a polychloroprene rubber tube. More extractant can be held and the stability of microdrop is better than by using a syringe needle so that extraction aided by ultrasonication can be carried out. Compared with traditional methods, the extraction efficiency is about ten times higher. The method has been used to determine phenols in real water samples, and good recoveries were obtained. It is a promising alternative for analyzing volatile or semivolatile pollutants in environmental samples due to its simplicity, rapidity and stability.     

Solvent-bar microextraction of herbicides combined with non-aqueous field-amplified sample injection capillary electrophoresis

Solvent-bar microextraction (SBME) based on two-phase (water-to-organic) extraction was for the first time used as the sample pretreatment method for the non-aqueous capillary electrophoresis (NACE) of herbicides of environmental concern. Due to the compatibility of the extractant organic solvent and the NACE separation system, the extract could be introduced directly to the CE system after SBME. Through investigations of the effect of sample pH, extraction time, agitation speed and salt addition on extraction efficiency, the most suitable extraction conditions were determined: sample solution at a pH of 1, without added salt, and stirring at 700 revolutions per minute for 30 min. SBME as applied here was also compared with single-drop microextraction and hollow fiber-protected liquid-phase microextraction. SBME showed the highest extraction efficiency. In addition, field-amplified sample injection with pre-introduced organic solvent plug removal using the electroosmotic flow as a pump (FAEP) was used to enhance the sensitivity further in NACE. Based on studies of the effect of different organic solvents, different lengths of the organic plugs and different volumes of sample injection on stacking efficiency under the most suitable separation conditions, methanol was found to be the most efficient solvent for on-line preconcentration. Combined with SBME, FAEP-NACE achieved limits of detection of between 0.08 ng/mL and 0.14 ng/mL for the studied analytes. This preconcentration approach for NACE was demonstrated to be amenable to aqueous environmental samples by applying it to spiked river water.     

In-line coupling headspace liquid-phase microextraction with capillary electrophoresis

An analytical technique of in-line coupling headspace liquid-phase microextraction (HS-LPME) with capillary electrophoresis (CE) was proposed to determine volatile analytes. A special cover unit of the sample vial was adopted in the coupling method. To evaluate the proposed method, phenols were used as model analytes. The parameters affecting the extraction efficiency were investigated, including the configuration of acceptor phase, kind and concentration of acceptor solution, extraction temperature and time, salt-out effect, sample volume, etc. The optimal enrichment factors of HS-LPME were obtained with the sample volume of about half of sample vials, which were confirmed by both the theoretical prediction and experimental results. The enrichment factors were obtained from 520 to 1270. The limits of detection (LODs, S/N = 3) were in the range from 0.5 to 1 ng/mL each phenol. The recoveries were from 87.2% to 92.7% and the relative standard deviations (RSDs) were lower than 5.7% (n = 6). The proposed method was successfully applied to the quantitative analysis of the phenols in tap water, and proved to be a simple, convenient and reliable sample preconcentration and determination method for volatile analytes in water samples.     

Direct determination of chlorophenols in environmental water samples by hollow fiber supported ionic liquid membrane extraction coupled with high-performance liquid chromatography

The 1-octyl-3-methylimidazolium hexafluorophosphate ([C8MIM][PF6]) ionic liquid was immobilized in the pores of a polypropylene hollow fiber for hollow fiber-protected liquid-phase microextraction. Analytes including 4-chlorophenol (4-CP), 3-chorophenol (3-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) were extracted into this ionic liquid membrane, and back extracted into 10microL sodium hydroxide acceptor solution in the lumen of the hollow fiber. Then, the acceptor solution was withdrawn into the high-performance liquid chromatography (HPLC) microsyringe connected to the hollow fiber, and directly injected into the HPLC system for analysis. Some parameters that might affect the extraction efficiency were optimized, and low detection limits (0.5microgL(-1) for 4-CP, 3-CP, DCP and 1.0microgL(-1) for TCP) were obtained. Good repeatability was achieved because of the stability of the hollow fiber-supported ionic liquid membrane. The proposed procedure was applied for direct determination of the four chlorophenols in some real water samples including groundwater, river water, wastewater and tap water. All of the four chlorophenols in these water samples were under the limits of determination, and the recoveries were in the range of 70.0-95.7% at 5microgL(-1) spiked level.     

Extraction of the Volatile and Semivolatile Compounds in Seeds of Cuminum cyminum L. Using Hydrodistillation Followed by Headspace-Ionic Liquid-Based Single-Drop Microextraction

Hydrodistillation (HD) coupled with headspace single-drop microextraction by using ionic liquid (IL) as the extraction solvent, followed by gas chromatography analysis technique, was successfully developed to determine the volatile and semivolatile compounds in seeds of Cuminum cyminum L. In the proposed method, a 1.5-??L microdrop of 1-octyl-3-methylimidazolium hexafluorophosphate, working as the extraction solvent was suspended in the headspace of a 50-mL round-bottom sample flask. After extracting for 30?min, both IL and target analytes were injected into the gas chromatographic system by thermal desorption for 5?s under 240?°C. Then, the IL was retracted back to the microsyringe. Thus, the capillary column should not be contaminated and a clean chromatogram was obtained. The parameters affecting extraction performance were investigated and optimized. The extraction efficiency of the proposed method was compared with that of HD, which is a standard extraction method. The contents of constituents in the extract obtained by the proposed method were close to those obtained by HD. It seems to be an environmentally friendly, time-saving, high efficiency and low solvent consumption technique and would be useful, especially for aromatic plants analysis.     

Simultaneous derivatization and extraction of amphetamine and methylenedioxyamphetamine in urine with headspace liquid-phase microextraction followed by gas chromatography-mass spectrometry

A new method is reported for the simultaneous extraction and derivatization of amphetamine (AM) and methylenedioxyamphetamine (MDA) using headspace hollow fiber protected liquid-phase microextraction (HS-HF-LPME); quantitation is by gas chromatograph-mass spectrometry in the selected ion monitoring (SIM) mode. The derivatizing reagent, pentafluorobenzaldehyde (PFBAY), was added to the extraction solvent. The analytes, volatile and basic, were released from the sample matrix into the headspace first, then extracted and derivatized in the solvent. After that, 2 microl of extract was directly injected into the GC-MS system. Parameters affecting extraction efficiency were investigated and optimized. This method showed good linearity in the concentration range investigated (50-350 ng ml(-1) for AM and 50-700 ng ml(-1) for MDA). Excellent repeatability of the extraction (RSD< or = 4%, n=5), and low limits of quantitation (0.25 ng ml(-1) for AM and 1.00 ng ml(-1) for MDA) were achieved. The feasibility of the method was demonstrated by analyzing human urine samples.     

Orthogonal array design for the optimization of ionic liquid-based dispersive liquid-liquid microextraction of benzophenone-type UV filters

In the present study, dispersive liquid-liquid microextraction (DLLME) using an ionic liquid (IL) as the extractant was successfully developed to extract four benzophenone-type UV filters from the different water matrices. Orthogonal array experimental design (OAD), based on five factors and four levels (L(16)(4(5))), was employed to optimize IL-dispersive liquid-liquid microextraction procedure. The five factors included pH of sample solution, the volume of IL and methanol addition, extraction time and the amount of salt added. The optimal extraction condition was as follows. Sample solution was at a pH of 2.63 in the presence of 60 mg/mL sodium chloride; 30 μL IL and 15 μL methanol were used as extractant and disperser solvent, respectively; extraction was achieved by vortexing for 4 min. Using high-performance liquid chromatography-UV analysis, the limits of detection of the target analytes ranged between 1.9 and 6.4 ng/mL. The linear ranges were between 10 or 20 ng/mL and 1000 ng/mL. This procedure afforded a convenient, fast and cost-saving operation with high extraction efficiency for the model analytes. Spiked waters from two rivers and one lake were examined by the developed method. For the swimming pool water, the standard addition method was employed to determine the actual concentrations of the UV filters.     

Dynamic headspace time-extended helix liquid-phase microextraction

Liquid-phase microextraction (LPME) has been proved to be a fast, inexpensive and effective sample pre-treatment technique for the analyses of pesticides and many other compounds. In this investigation, a new headspace microextraction technique, dynamic headspace time-extended helix liquid-phase microextraction (DHS-TEH-LPME), is presented. In this work, use of a solvent cooling system, permits the temperature of the extraction solvent to be lowered. Lowering the temperature of the extraction solvent not only reduces solvent loss but also extends the feasible extraction time, thereby improving extraction efficiency. Use of a larger volume of the solvent not only extends the feasible extraction time but also, after extraction, leaves a larger volume to be directly injected into the gas chromatography (GC) to increase extraction efficiency and instrument signal. The DHS-TEH-LPME technique was used to extract six organochlorine pesticides (OCPs) from 110 ml water samples that had been spiked with the analytes at ng/l levels, and stirred for 60 min. The proposed method attained enrichments up to 2121 fold. The effects of extraction solvent identity, sample agitation, extraction time, extraction temperature, and salt concentration on extraction performance were also investigated. The method detection limits (MDLs) varied from 0.2 to 25 ng/l. The calibration curves were linear for at least 2 orders of magnitude with R² ≧ 0.996. Relative recoveries in river water were more than 86%.     

液下单液滴微萃取-高效液相色谱法测定二氯酚

采用液下单液滴微萃取样品处理方法富集水中的2,4-二氯酚和2,6-二氯酚,高效液相色谱法测定.考察了不同萃取剂、萃取条件及测定条件对检测结果的影响.2,4-二氯酚和2,6-二氯酚的线性范围分别在0.001～20 mg/L和0.003～20 mg/L之间,检出限分别为0.001和0.003 mg/L.     

Application of instantaneous nebulization dispersive liquid-phase microextraction combined with HPLC for the determination of chalcone and isoflavone in traditional Chinese medicines

A simple and rapid instantaneous nebulization dispersive liquid-phase microextraction method was developed, and combined with high-performance liquid chromatography for determination of the contents of seven analytes in traditional Chinese medicines. In this study, using the sprinkler device to achieve instantaneous synchronous dispersion and extraction, only one spray can rapidly achieve the concentration and enrichment of seven kinds of chalcone and isoflavones. The key factors affecting the extraction efficiency were optimized including the type and volume of extractant, the pH and salt concentration of the sample phase, and the number of dispersion. Under the optimal conditions, the enrichment factor of the target analytes ranged from 103.1 to 180.9, with good linearity and correlation coefficients above 0.9970. The limits of detection ranged from 0.02 to 0.15 ng/mL, with good accuracy (recoveries 91.1 to 108.9%) and precision (relative standard deviations 1.5–7.1%). This method has short extraction time (2 s), low organic solvent consumption and high enrichment effect, so it has a wide application prospects.     

Ionic liquid-based dynamic liquid-phase microextraction: application to the determination of anti-inflammatory drugs in urine samples

Dynamic liquid-phase microextraction (dLPME) using an ionic liquid as acceptor phase is proposed for the determination of six non-steroidal anti-inflammatory drugs (NSAIDs) in human urine samples for the first time. The extraction is carried out in a simple and automatic flow configuration. The chemical affinity between the extractant (1-butyl-3-methylimidazolium hexafluorophosphate) and the analytes permits a selective isolation of the drugs from the sample matrix allowing also their preconcentration. The whole analytical method has been optimized taking into account all the chemical, physical and hydrodynamic variables. The proposed method is a valuable alternative for the analysis of these drugs in urine within the concentration range 0.1-10 microg mL(-1), allowing their determination at therapeutic and toxic levels. Limits of detection were in the range from 38 ng mL(-1) (indomethacin) to 70 ng mL(-1) (naproxen). The repeatability of the proposed method expressed as RSD (n=5) varied between 2.1% (flurbiprofen) and 3.8% (tolmetin).