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PubMed2004

Liquid-phase microextraction of tributyltin and triphenyltin coupled with gas chromatography-tandem mass spectrometry. Comparison between 4-fluorophenyl and ethyl derivatizations.

This paper describes the liquid-phase microextraction (LPME) of tributyltin (TBT) and triphenyltin coupled with gas chromatography-tandem mass spectrometry. The 4-fluorophenylation and ethylation reactions were used for the derivatization of the organotins. For the two derivatizations, the LPME parameters such as organic solvent, stirring rate, temperature, extraction time and the other additional conditions were examined. Using pure water, the calibration curves, method detection limits (MDLs) and reproducibilities (RSDs) of the two derivatizations were compared under the respective optimized procedures. The 4-fluorophenyl derivatization, which showed a lower MDL (0.36 ng/l) and better reproducibility (RSD = 11% at 10 ng/l) for TBT, was applied to the analysis of seawater. The TBT was detected in the range from 1.1 to 2.0 ng/l in the seawater samples collected in Osaka Bay.

Buffers↗
PubMed2006

Experiences with carrier-mediated transport in liquid-phase microextraction.

Different organic borates, phosphates, sulphates, and carboxylic acids are evaluated as extraction carriers in three-phase liquid-phase microextraction (LPME). Hydrophilic basic drugs form ion-pairs with the carriers and are extracted as ion-pair complexes into an organic liquid membrane of n-octanol or peppermint oil immobilized in the pores of a polypropylene hollow fiber. From this point, the basic drugs are released into a 20-microL solution of 50mM HCl placed inside the lumen of the hollow fiber (acceptor solution). Simultaneously, the carrier is neutralized by protons from the acceptor solution (protonated to maintain the charge balance). Both water-soluble and water-insoluble carriers are tested. One promising candidate among the water-soluble carriers is 1-heptanesulfonic acid. This is added to the sample solution to a final concentration of 25mM and served to ion-pair the analytes within the sample solution. Among the less water-soluble candidates, a mixture of di(2-ethylhexyl) phosphate (DEHP) and tris(2-ethylhexyl) phosphate (TEHP) serve as efficient carriers. Ten percent (w/w) of each of DEHP and TEHP are added to the organic liquid membrane, and these carriers principally worked through ion-pairing with the analytes at the interface between the sample solution and the organic liquid membrane. Several carriers are found to be compatible with human plasma samples, and bromthymol blue is particularly efficient in combination with these protein-containing matrices. Following optimization of the conditions for bromthymol blue, including saturation of the plasma samples with sodium sulphate, extraction recoveries between 45% and 75% are obtained for eight model drugs after 60 min of extraction. With bromthymol blue as the carrier, highly acceptable validation data are obtained for phenylpropanolamine and practolol extracted from human plasma.

Anions↗
PubMed2003

Liquid-phase microextraction of hydrophilic drugs by carrier-mediated transport.

Basic studies on carrier-mediated transport as a mechanism to extract polar drugs by hollow fibre-based liquid-phase microextraction are presented for the first time. Hydrophilic alkaline drugs with log P (octanol/water partition coefficient) values less than 1 were selected as model substances. Sodium octanoate served as carrier and was added to the sample solution at pH 7 to form hydrophobic ion-pair complexes with the analytes. The ion-pair complexes were extracted into octanol as liquid membrane immobilised in the pores of the hollow fibre. Further extraction into an aqueous acceptor phase inside the lumen of the hollow fibre was facilitated by counter transport of protons from the acceptor solution to the sample solution. Protons from the acceptor solution released the analytes at the liquid membrane-acceptor interface and neutralized the carrier. The acceptor phase was analysed by capillary electrophoresis. The studies show that high extraction recoveries of ionic hydrophilic drugs can be obtained at a sample-acceptor volume ratio of 10. Linear calibration graphs and clean electropherograms indicate that carrier-mediated transport is a promising technique in microextraction of polar drugs from biological matrices.

Calibration↗
PubMed2005

Analysis of persistent organic pollutants in marine sediments using a novel microwave assisted solvent extraction and liquid-phase microextraction technique.

A simple and novel analytical method for quantifying persistent organic pollutants (POPs) in marine sediments has been developed using microwave assisted solvent extraction (MASE) and liquid-phase microextraction (LPME) using hollow fibre membrane (HFM). POPs studied included twelve organochlorine pesticides (OCP) and eight polychlorinated biphenyl (PCB) congeners. MASE was used for the extraction of POPs from 1 g of sediment using 10 ml of ultrapure water at 600 W for 20 min at 80 degrees C. The extract was subsequently subjected to a single step LPME-HFM cleanup and enrichment procedure. Recovery varied between 73 and 111% for OCPs; and 86-110% for PCBs, and exceeded levels achieved for conventional multi-step Soxhlet extraction coupled with solid-phase extraction. The method detection limit for each POP analyte ranged from 0.07 to 0.70 ng g(-1), and peak areas were proportional to analyte concentrations in the range of 5-500 ng g(-1). Relative standard deviations of less than 20% was obtained, based on triplicate sample analysis. The optimized technique was successfully applied to POP analysis of marine sediments collected from the northeastern and southwestern areas of Singapore's coastal environment.

Environmental Monitoring↗
PubMed2004

A liquid-phase microextraction method, combining a dual gauge microsyringe with a hollow fiber membrane, for the determination of organochlorine pesticides in aqueous solution by gas chromatography/ion trap mass spectrometry.

A liquid-phase microextraction (LPME) method has been demonstrated for the extraction and determination of organochlorine pesticides (OCPs) in aqueous solution. The method combines a dual gauge microsyringe with a hollow fiber membrane (LPME/DGM-HF) followed by detection by gas chromatography/ion trap mass spectrometry (GC/ITMS). The advantages include speed, low solvent and sample consumption, simplicity and ease of use. The extraction time, solvent selection, salt concentration and sample stirring rate have been investigated in order to optimize extraction efficiency. The viability is evaluated by measuring the linearity and detection limit of the five OCPs in aqueous solution. Detection linearity for the OCPs has been achieved over a range of concentrations between 1 and 500 microg/L (r2 > 0.930), with a detection limit of 0.1 microg/L for each OCP.

Gas Chromatography-Mass Spectrometry↗
PubMed2006

Dynamic hollow fiber protected liquid phase microextraction and quantification using gas chromatography combined with electron capture detection of organochlorine pesticides in green tea leaves and ready-to-drink tea.

The dynamic hollow fiber protected liquid phase microextraction (DHFP-LPME) technique was evaluated for the extraction of organochlorine pesticides (OCPs) in green tea leaves and ready-to-drink tea prior to gas chromatography combined-electron capture detection (GC-ECD) analysis. A conventional microsyringe with a 1.5 cm length of hollow fiber attached to its needle was connected to a syringe pump to perform the extraction. The microsyringe was used as both the microextraction device and the sample introduction device for GC-ECD analysis. In this work, the organochlorine pesticides were extracted and condensed to a volume of 3 microl of organic extracting solvent (1-octanol) confined within a 1.5 cm length of hollow fiber. The effects of extraction solvent, extraction time, sample agitation, plunger speed, and extraction temperature and salt concentration content on the extraction performance were also investigated. Good enrichments were achieved (34-297-fold) with this method, and good repeatabilities of extraction were obtained, with full name (RSDs) below 12.57%. Detection limits were much below 1 microg l(-1) for ready-to-drink tea and much below 1 microg g(-1) for green tea leaves.

1-Octanol↗
PubMed2006

Determination of valproic acid in human serum and pharmaceutical preparations by headspace liquid-phase microextraction gas chromatography-flame ionization detection without prior derivatization.

An efficient and fast extraction technique for the enrichment of valproic acid from human blood serum samples using the headspace liquid phase microextraction (HS-LPME) combined with gas chromatography (GC) analysis has been developed. The extraction was conducted by suspending a 2 microL drop of organic solvent in a 1 mL serum sample; following 20 min of extraction, withdrawing organic solvent into a syringe and injection into a GC with a flame ionization detector (FID), without any further pre-treatment. Four organic solvents, 1-decanole, benzyl alcohol, 1-octanol and n-dodecane, were studied as extractants, and n-dodecane was found to be the most sensitive solvent for valproic acid. The results revealed that HS-LPME is suitable for the successful extraction of valproic acid from human blood serum samples. Parameters like extraction time, ionic strength, pH, organic solvent volume, and temperature of the sample were studied and optimized to obtain the best extraction results. An enrichment factor of 27-fold was achieved in 20 min. The procedure resulted in a relative standard deviation of <13.2% (n=7) and a linear calibration range from 2 to 20 microg mL(-1) (r>0.98), and the limit of detection was 0.8 microg mL(-1) in serum blank samples. Overall, LPME proved to be a fast, sensitive and simple tool for the preconcentration of valproic acid from real samples. The proposed method was also applied to the analysis of valproate in pharmaceutical preparations.

Anticonvulsants↗
PubMed2003

Headspace liquid-phase microextraction of chlorobenzenes in soil with gas chromatography-electron capture detection.

The organic solvent film formed in a microsyringe barrel was used as an extraction interface in headspace liquid-phase microextraction (HS-LPME) of chlorobenzenes. Some common organic solvents with different vapor pressures (9.33-12 918.9 Pa) were studied as extractants. The results indicated that even the solvent with the highest vapor pressure (cyclohexane) can be used to carry out the extraction successfully. In general, the reasons for successful extraction are the very small space (5 mm3) within the microsyringe barrel and the fast equilibrium between gaseous analytes and organic solvent film. Both of these factors significantly reduced the risk of solvent loss during extraction. Thus, the choice of extraction solvent for the present method was very flexible. From the viewpoint of extraction efficiency, toluene (which has relatively low vapor pressure) was found to provide the best extraction efficiency. The effects of sampling volume, organic solvent volume, syringe withdrawal rate, and number of extraction cycles were also investigated. The procedure with respect to repeatability and limits of detection was evaluated by soil spiked with chlorobenzenes. Repeatabilitywas between 5.7 and 17.7%, and the limits of detection were 6-14 ng/g. HS-LPME was shown to be an inexpensive, fast, and simple sample preparation method for volatile compounds.

Chlorobenzenes↗
PubMed2006

Direct combination of immersed single-drop microextraction with atmospheric pressure matrix-assisted laser desorption/ionization tandem mass spectrometry for rapid analysis of a hydrophilic drug via hydrogen-bonding interaction and comparison with liquid-liquid extraction and liquid-phase microextraction using a dual gauge microsyringe with a hollow fiber.

This study presents the feasibility of direct coupling of the immersed single-drop microextraction (SDME) technique with atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI-MS) for the rapid analysis of a hydrophilic drug (dopamine) from aqueous solution and human urine in an ion trap tandem mass spectrometer through hydrogen-bonding interaction of dopamine with the extraction solvent (octanol). The optimum conditions for the SDME experiments coupled to AP-MALDI/MS were: stirring rate, 240 rpm; extraction time, 5 min; sample pH value, 8; and matrix concentration, 2000 ppm, using alpha-cyano-4-hydroxycinnamic acid (alpha-CHCA) as matrix. The limits of detection (LODs) for the SDME/AP-MALDI-MS experiments were 25 and 40 ppm in water and human urine, respectively. In a comparison of this method with the traditional liquid-liquid extraction (LLE), the SDME method shows better LODs than the LLE (40 ppm) and the same LODs (25 ppm) as the liquid-phase microextraction using a dual gauge microsyringe with a hollow fiber (LPME/DGM-HF). However, the SDME method is more convenient than the LPME/DGM-HF method.

Atmospheric Pressure↗
PubMed2002

Combination of liquid-phase microextraction and on-column stacking for trace analysis of amino alcohols by capillary electrophoresis.

We described a new method for the enrichment of basic drugs present in water samples via liquid-phase microextraction (LPME) combined with on-column stacking in capillary electrophoresis. Two steps were employed to enhance the detection sensitivity of four amino alcohols. The analytes were first extracted from aqueous sample (donor solution) that were adjusted to basic through a thin layer of 1-octanol entrapped within the pores of a polypropylene hollow fiber, and then into a 5-microl acidic acceptor solution inside the hollow fiber. The extract was then further enriched through on-column stacking in capillary electrophoresis. With this two-step enrichment procedure, the method provided 72-110-fold preconcentration of the target amino alcohols. The limits of detection were 0.08-0.5 microg/ml. Relative standard deviation (n=6) ranged between 4.3 and 6.9% for the studied drugs utilizing 2-amino-1-phenylethanol as internal standard. The extraction of amino alcohols in spiked urine samples was evaluated using the developed procedure.

Amino Alcohols↗
PubMed2006

Application of liquid-phase microextraction and on-column derivatization combined with gas chromatography-mass spectrometry to the determination of carbamate pesticides.

A method has been established for the determination of five carbamate pesticides in water samples using liquid-phase microextraction (LPME) followed by on-column derivatization and gas chromatography-mass spectrometric (GC-MS) determination. Trimethylphenylammonium hydroxide (TMPAH) and trimethylsulfonium hydroxide (TMSH) were used as derivatization reagent for extracts prior to GC-MS analysis as carbamate pesticides are thermally labile compounds. Parameters that affect the extraction efficiency (selection of organic solvent and extraction time) and derivatization efficiency (choice of derivatization reagent and concentration of derivatization reagent) were investigated. The proposed method provided good enrichment factors up to 224, with reproducibility ranging from 4.86 to 7.81%, and good linearity from 1 to 400 microg/L. The limits of detection (LODs) ranged between 0.2 and 0.8 microg/L (S/N = 3) using GC-MS with selective ion monitoring. This method was applied to the determination of carbamate pesticides in tap water and waste water.

Carbamates↗
PubMed2005

Analysis of polycyclic aromatic hydrocarbons in wastewater treatment plant effluents using hollow fibre liquid-phase microextraction.

A simple and efficient method for the enrichment of low molecular weight polycyclic aromatic hydrocarbons (PAHs) in effluents originating from wastewater treatment plants is presented here. The proposed protocol couples the recently introduced hollow fibre liquid-phase microextraction (LPME) method with gas chromatography-mass spectrometry. Method parameters were controlled and the optimised experimental conditions were: 5 ml aqueous samples, containing 2.5% NaCl w/v, stirred at 1000 rpm, extracted with toluene for 15 min. The developed protocol yielded a linear calibration curve in the concentration range from 0.5 to 50 microg l(-1) for all target analytes (namely acenaphthene, phenanthrene, fluoranthene and pyrene) and limits of detection in the low microg l(-1) level (0.005-0.011 microg l(-1)). The repeatability and inter-day precision of the method varied between 2.7% and 11.3% and 7.9% and 14.4% respectively. The relative recoveries from different types of natural water samples revealed that matrix had a small effect on the hollow fibre LPME process. The developed method was then applied for the determination of PAHs contamination in effluent samples taken from two major municipal wastewater treatment plants. The results were compared with those obtained with solid-phase microextraction. The ability of both microextraction methods to concentrate organic analytes was demonstrated as both methods confirmed the presence of PAHs as well as of phthalates in the examined effluent samples.

Chemistry Techniques, Analytical↗
PubMed2006

Application of liquid-phase microextraction and gas chromatography-mass spectrometry for the determination of chloroform in drinking water.

In this paper, a novel method for the determination of chloroform in drinking water has been described. It is based on liquid-phase microextraction (LPME) and gas chromatography-mass spectrometry (GC-MS). Extraction conditions such as solvent selection, organic solvent dropsize, stirring rate, content of NaCl and extraction time were found to have significant influence on extraction efficiency. The optimized conditions were 1.5 microl xylene, 20 min extraction time at 400 rpm stirring rate without NaCl addition. The linear range was 1.0 - 100 microg l(-1) for chloroform. The limit of detection (LOD) was 1.0 microg l(-1); and relative standard deviation (RSD) at the 30 microg l(-1) level was 2.9%. Tap water samples from a laboratory were successfully analyzed using the proposed method. The relative recovery of spiked water samples was 104%.

Algorithms↗
PubMed2004

Optimization of nonequilibrium liquid-phase microextraction for the determination of nitrobenzenes in aqueous samples by gas chromatography-electron capture detection.

In the present work, a novel method for the determination of nitrobenzenes in water has been described. It is based on nonequilibrium liquid-phase microextraction and gas chromatography-electron capture detection (GC-ECD). Extraction conditions such as solvent selection, organic solvent dropsize, stirring rate, content of NaCl and extraction time were found to have significant influence on extraction efficiency. The optimized conditions were 1.5 microl toluene and 20 min extraction time at 400 rpm stirring rate without NaCl addition. The linear range was 0.1 - 50 microg l(-1) for most nitrobenzenes. The limits of detection (LODs) ranged from 0.02 microg l(-1) (for 2.6-DNT) to 0.4 microg l(-1) (for NB); and relative standard deviations (RSD) for most of the nitrobenzenes at the 10 microg l(-1) level, except for 2,6-DNT in 3 microg l(-1), were below 10%. Natural samples collected from Miyun Reservoir and tap water samples from a laboratory were successfully analyzed using the proposed method, but none of the analytes were detected. The relative recoveries of spiked water samples (at the 10 microg l(-1) level except for 2,6-DNT in 3 microg l(-1)) were from 82.6 to 118.7%.

Journal Article↗
PubMed2004

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.

Androgen Antagonists↗
PubMed2005

Dynamic hollow fiber-supported headspace liquid-phase microextraction.

With the increasing concern over deteriorating environmental quality, the analysis of organic pollutants in air, water, and soil has become critically important. The development of simple, efficient, and inexpensive analytical sample pretreatment is crucial for monitoring and evaluating the environment. In this work, a dynamic hollow-fiber supported headspace liquid-phase microextraction (DHF-HS-LPME) approach was developed. In dynamic LPME, the extracting solvent is held within a hollow fiber, affixed to a syringe needle and immersed in the sample solution, and is moved to-and-fro by using a programmable syringe pump. The movement facilitates mass transfer from the sample to the solvent. Here, a similar approach was adopted, except that extraction was from the headspace rather than by direct immersion. Analysis of the extract was carried out by gas chromatography-mass spectrometry. The effect of sampling temperature, water, salt, dwelling time were investigated. Results indicated that this novel headspace microextraction method gave good analyte-enrichment factors, linear range, limits of detection and repeatability, all of which were evaluated by extracting PAHs from soil samples. This technique represents an inexpensive, convenient, fast and simple sample preparation of this class of semi-volatile organic compounds.

Chromatography, Liquid↗
PubMed2005

Rapid determination of acetone in human blood by derivatization with pentafluorobenzyl hydroxylamine followed by headspace liquid-phase microextraction and gas chromatography/mass spectrometry.

In the current work, a simple, rapid, accurate and inexpensive method was developed for the determination of acetone in human blood. The proposed method is based on derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA), followed by headspace liquid-phase microextraction (HS-LPME) and gas chromatography/mass spectrometry (GC/MS). In the present method, acetone in blood samples was derivatized with PFBHA and acetone oxime formed in several seconds. The formed oxime was enriched by HS-LPME using the organic solvent film (OSF) formed in a microsyringe barrel as extraction interface. Finally, the enriched oxime was analyzed by GC/MS in electron ionization (EI) mode. HS-LPME parameters including solvent, syringe plunger withdrawal rate, sampling volume, and extraction cycle were optimized and the method reproducibility, linearity, recovery and detection limit were studied. The proposed method was applied to determination of acetone in diabetes blood and normal blood. It has been shown that derivatization with HS-LPME and GC/MS is an alternative method for determination of the diabetes biomarker, acetone, in blood samples.

Acetone↗
PubMed2003

Stereospecific determination of citalopram and desmethylcitalopram by capillary electrophoresis and liquid-phase microextraction.

A chiral capillary electrophoresis (CE) system allowing simultaneous enantiomer determination of citalopram (CIT) and its pharmacologically active metabolite desmethylcitalopram (DCIT) was developed. Excellent chiral separation was obtained using 1% sulfated-beta-cyclodextrin (S-beta-CD) as chiral selector in combination with 12% ACN in 25 mM phosphate pH 2.5. Samples were prepared by liquid-phase microextraction (LPME) based on a rodlike porous polypropylene hollow fibre. CIT and DCIT were extracted from 1 ml plasma made alkaline with NaOH, into dodecyl acetate impregnated in the pores of a hollow fibre, and into 20 mM phosphate pH 2.75, inside the hollow fibre. The acceptor solution was directly compatible with the CE system. Efficient sample clean-up was seen, and the recoveries were 46 and 29% for the enantiomers of CIT and DCIT, respectively, corresponding to 31 and 19 times enrichment. The limit of quantification (S/N=10) was <11.2 ng/ml, intra-day precision was <12.8% RSD, and inter-day precision was <14.5% RSD, for all enantiomers. The validated method was successfully applied to simultaneous determination of enantiomer concentrations of CIT and DCIT in plasma samples from nine patients treated with racemic citalopram. The results confirm LPME-CE as a suitable and promising tool for enantiomeric determination of chiral drugs and metabolites in biological matrices.

Adolescent↗