Hollow Fiber-protected Liquid-phase Microextraction Research Articles

Application of hollow fiber-protected liquid-phase microextraction combined with GC-MS in determining Endrin, Chlordane, and Dieldrin in rice samples.

This paper introduces a novel and minimized sample preparation technique based on hollow fiber-protected liquid-phase microextraction that can be used in joint with gas chromatography-mass spectrometry (GC-MS) detection to extract three organochlorine pesticides-Endrin, Chlordane, and Dieldrin-from rice samples. To that end, a single-walled carbon nanotube (SWCNT) and a proper ionic liquid (IL) were ultrasonically dispersed and injected into the lumen of hollow fiber as the extraction phase for preconcentrating and extracting the target analytes from the rice samples. The effects of the type of nanoparticles, ILs, and desorption solvent on the efficiency of extracting the analytes were investigated based on the one-factor-at-a-time (OFAT) approach. In addition, other parameters influencing the extraction procedure were optimized using an experimental design that decreased the number of experiments, reagent consumption, and costs. Under optimized conditions, the limits of detection and quantification in determining mentioned pesticides varied between 0.019-0.029 and 0.064-0.098ng mL-1, respectively. The calibration graphs to measure Endrin, Chlordane, and Dieldrin were linear over the concentration range of 0.064-13.2, 0.098-16.7, and 0.092-11.4ng mL-1, respectively. The relative standard deviations for inter-day and intra-day analysis were below 7.06 and 4.75% for the triplicate determination of three organochlorine pesticides. Besides, the relative recoveries and standard deviations of Endrin, Chlordane, and Dieldrin for analyzing several Iranian rice samples were between 86.0-92.9% and 4.5-5.8%, respectively. The results were compared with other similar works in literature, proving that the proposed method is efficient and useful for routine monitoring of organochlorine compounds in food samples.

Determination of alkylpyrazines in cocoa samples applying head-space hollow fiber protected-liquid phase microextraction followed by gas chromatography-flame ionization detection

In this research, a novel efficient analytical method for determination of alkylpyrazines (APs) in some food samples was developed based on head-space hollow fiber protected liquid phase microextraction (HS-HFLPME) method. In this method n-octanol was applied as extracting media which was inserted inside lumen of hollow fiber. The developed HFLPME method was used for the preconcentration and extraction of APs including methyl pyrazine, 2,3-dimethyl pyrazine, 2,5-dimethylpyrazine, 2,3,5-trimethyl pyrazine and 2,3,5,6-tetramethyl pyrazine in cocoa and chocolate-milk samples followed by detection applying gas chromatography-flame ionization detector. Important parameters influencing the HS-HFLPME process including extraction time, extraction temperature, salt content and the desorption solvent volume were investigated and optimized applying response surface methodology based on central composite design. Considering the method validation, developed method linear dynamic ranges were 1–200 and 5–500 ng mL−1 for various analytes and the limits of detection were in the range of 0.3 to 1 ng mL−1. The method precision (RSD%) was evaluated by six replicate experiments and RSD% values were obtained in the range of 0.8 to 8.2% for the distilled water (100 ng mL−1). The developed method was used successfully for measurement of AP compounds in cocoa and chocolate-milk samples and the relative recovery percentages (RR%) in the range of 71.7 to 110.5% were obtained.

Preparation of Biological Samples Containing Metoprolol and Bisoprolol for Applying Methods for Quantitative Analysis

Abstract Arterial hypertension is a complex disease with many serious complications, representing a leading cause of mortality. Selective beta-blockers such as metoprolol and bisoprolol are frequently used in the management of hypertension. Numerous analytical methods have been developed for the determination of these substances in biological fluids, such as liquid chromatography coupled with mass spectrometry, gas chromatography coupled with mass spectrometry, high performance liquid chromatography. Due to the complex composition of biological fluids a biological sample pre-treatment before the use of the method for quantitative determination is required in order to remove proteins and potential interferences. The most commonly used methods for processing biological samples containing metoprolol and bisoprolol were identified through a thorough literature search using PubMed, ScienceDirect, and Willey Journals databases. Articles published between years 2005-2015 were reviewed. Protein precipitation, liquid-liquid extraction and solid phase extraction are the main techniques for the extraction of these drugs from plasma, serum, whole blood and urine samples. In addition, numerous other techniques have been developed for the preparation of biological samples, such as dispersive liquid-liquid microextraction, carrier-mediated liquid phase microextraction, hollow fiber-protected liquid phase microextraction, on-line molecularly imprinted solid phase extraction. The analysis of metoprolol and bisoprolol in human plasma, urine and other biological fluids provides important information in clinical and toxicological trials, thus requiring the application of appropriate extraction techniques for the detection of these antihypertensive substances at nanogram and picogram levels.

Hollow fiber-protected liquid-phase microextraction followed by high performance liquid chromatography for simultaneously screening multiple trace level β-blockers in environmental water samples

A two-phase hollow fiber liquid-phase microextraction (HF-LPME) pretreatment technique was developed for simultaneously screening multiple β-blockers.

Hollow-Fiber Liquid-Phase Microextraction Followed by Gas Chromatography Flame Ionization Detection for the Determination of Amitraz in Honey and Water Samples

This paper reports a two-phase hollow fiber-protected liquid-phase microextraction (HF-LPME) followed by gas chromatography-flame ionization detection as a simple, fast, low-cost, and sensitive method for the determination of amitraz in honey and water samples. The effect of factors effective on the extraction efficiency of amitraz was studied and optimized. The effect of type of extracting solvent was optimized by the one-variable-at-a-time method. The effect of other factors was optimized using the Taguchi method (an orthogonal array design (OAD)) with OA16 (44) matrix. The optimal conditions for HF-LPME procedure were found as 1-undecanol as the extracting solvent, sample pH of 6.0 (adjusted with 0.01 mol/L sodium acetate), stirring rate of 1,000 rpm, and extraction time of 45 min without the addition of NaCl. The figures of merit of the method were evaluated in honey and water matrices. In water matrix, the method was linear in the range of 5–2,500 μg/L with a coefficient of determination (r 2) corresponding to 0.9996 and relative standard deviation (RSD%) lower than 11 %. Also, in honey samples, a calibration curve was linear in the range of 20–1,000 μg/L with RSD% of 13.8 % and r 2 > 0.9901. The enrichment factors were 170 and 75, and the limits of detection (LODs) based on S/N = 3 were 3 and 10 μg/L in water and honey samples, respectively. Finally, applicability of the proposed method was evaluated by extraction and determination of amitraz in some honey and water samples and good recoveries (>90 %) were obtained.

Investigation of bioaccumulation profile of oestrogens in zebrafish liver by hollow fibre protected liquid phase microextraction with gas chromatography–mass spectrometric detection

The applicability of hollow fibre protected liquid phase microextraction (HF-LPME) for the determination of three oestrogens, namely estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) from individual zebrafish liver samples, in a bioaccumulation study on these organisms, is reported. The oestrogens were extracted from single, mechanically crushed and minced livers from fish that were heaved in tubes containing water spiked at low concentration of the analytes. Extraction was performed with ∼3μL of toluene contained in the hollow fibre. In order to achieve high extraction efficiency, the parameters that could affect the effectiveness of HF-LPME were optimized, i.e. the extracting organic solvent, extraction time, stirring speed and pH of the aqueous phase. For gas chromatography/mass spectrometry (GC/MS) analysis, injection port derivatization of the oestrogens with bis(trimethylsilyl)trifluoroacetamide was conducted. Under the most favourable extraction and derivatization conditions, enrichment factors of 158–279 were obtained. Linearity of the HF-LPME–GC/MS method was evaluated from 1 to 50μg/L and the coefficient of determination (r2) ranged from 0.9687 to 0.9926. The LODs were between 0.017 and 0.033μg/L (at a signal to noise ratio of 3) with relative standard deviations (RSDs, analytes spiked at 5μg/L) of between 15 and 17% (n=3).

The application of hollow fibre-liquid phase micro-extraction on the bioassay experiment of oestrogen chemicals

The object of this study was to improve pre-concentration techniques using hollow fibre protected-liquid phase micro-extraction (LPME) for its application on biotic samples and limited environmental samples provided in small volumes. Five parameters, including extraction time, type of solvent, extents of agitation, fibre length and salt content of HF-LPME were optimised for the yeast two-hybrid assay and gas chromatography-mass spectrometer (GC/MS) chemical analysis. The results of chemical analysis were compared to the results of a bioassay using the yeast two-hybrid system to analyse endocrine-disrupting chemicals (EDCs). For the yeast two-hybrid assay, the optimised parameters comprised of an extraction time of 40 min, toluene as the extraction solvent, a stirring rate of 500 rpm, a fibre length of 2.0 cm and a salt concentration of 20% (w/v). For GC/MS analysis, HF-LPME conditions were optimised with an extraction time of 40 min, toluene: dichloromethane at a ratio of 1 : 1 (v : v) as the extraction solvent, a stirring rate of 700 rpm, a fibre length of 2.0 cm and a salt concentration of 30% (w/v). The results indicated that fibre length, extraction time, and degree of agitation were major contributing parameters for HF-LPME in EDCs analysis. Consequently, bioassays such as yeast two-hybrid assay could be easily, rapidly, and inexpensively conducted with small volume of sample using HF-LPME for the measurement of oestrogenic activity.

Novel multifunctional acceptor phase additive of water-miscible ionic liquid in hollow-fiber protected liquid phase microextraction

In this paper, water-miscible ionic liquid (IL) such as 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) is introduced for the first time as a novel multifunctional acceptor phase additive in hollow-fiber protected liquid phase microextraction (HF-LPME). For investigating the performances of [BMIM]Cl, it was respectively mixed with NaOH, HCl and deionized water. And their extraction performance was preliminary evaluated with alkaline compounds (clenbuterol, metoprolol, carteolol and propranolol), acidic compounds (diethylstilbestrol, hexestrol, phenol and bisphenol A) and neutral compounds (acenaphthylene, fluorene and fluoranthene). Furthermore, a complete extraction and determination method using IL-three phase HF-LPME and liquid chromatography was established for polycyclic aromatic hydrocarbons (PAHs) in river water. The extraction conditions, such as concentration of IL, extraction temperature, extraction time, stirring speed, ionic strength and the addition of methanol were studied in detail. Under the optimum conditions, the linear ranges of acenaphthylene, fluorene and fluoranthene were 1–100, 1–200 and 1–200ngmL−1, respectively. Limit of detections (LODs) were lower than 0.25ngmL−1. The recoveries of PAHs in three kinds of spiked real water are between 90.97 and 109.7% and the precisions are in the range of 2.53–7.01%. Since water-miscible ionic liquids had various forms, similar extraction capabilities to organic solvents and could be conveniently adjusted by acid, alkaline and buffer, this proposed method should have great potentiality in sample preparation of HF-LPME.

Orthogonal array design for the optimization of hollow fiber protected liquid-phase microextraction of salicylates from environmental waters

In the present study, a three phase-based hollow fiber protected liquid-phase microextraction (HF-LPME) method combined with high-performance liquid chromatography (HPLC) for the determination of salicylates in environmental waters was developed. The HF-LPME procedure was optimized by an L 16(4 5) orthogonal array experimental design (OAD) with five factors at four levels. Under the optimal extraction condition (pHs of donor and receiving phases of 3.0 and 6.2, respectively, extraction time of 45 min, stirring speed of 1000 rpm, and salt addition of 20% (w/v)), salicylates could be determined in a linear range from 0.025 to 1.0 μg mL −1 with a good correlation ( r 2 > 0.9930). The limits of detection (LODs) ranged between 0.6 ng mL −1 and 1.2 ng mL −1 for the target analytes. The relative standard deviations (RSDs) of intra-day and inter-day were in the range of 0.64–14.58% and 0.16–15.45%, respectively. This procedure afforded a convenient, sensitive, accurate and cost-saving operation with high extraction efficiency for the model analytes. The method was applied satisfactorily to the determination of salicylates in two environmental waters.

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.

Application of Double-Phase Liquid Phase Microextraction in the Determination of Partition Coefficients and Analysis of Pesticides in Water Samples

A simple and solvent-minimized sample preparation technique based on two-phase hollow fiber-protected liquid-phase microextraction has been developed and used for the determination of partition coefficient and analysis of selected pesticides in environmental water samples. The analysis was performed by gas chromatography–electron capture detector. Three pesticides namely hexaconazole, quinalphos, and methidathion were considered as target analytes. Extraction conditions such as solvent identity, salt concentration, stirring speed, extraction time, length of the hollow fiber, and volume of donor phase were optimized. The analytes were extracted from a donor phase (water sample) through 3 μL of an organic solvent immobilized in the pores of a porous polypropylene hollow fiber and then into the acceptor phase present inside the hollow fiber. Excellent extractions of the analytes were achieved under the optimized conditions, with relative standard deviations of 4.6–7.9%, correlation coefficients (r 2) of 0.9954–0.9986 and limits of detection of 3–7 ng L−1. The proposed method provided good average enrichment factors of up to 250-fold. The partition coefficients of the analytes determined were found to be directly correlated with the enrichment factor. The present methodology also confirms the robustness of microextraction for monitoring trace levels of pesticides in 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.

Analysis of β-agonists and β-blockers in urine using hollow fibre-protected liquid-phase microextraction with in situ derivatization followed by gas chromatography/mass spectrometry

A method using hollow fibre-protected liquid-phase microextraction (HF-LPME) with in situ derivatization followed by gas chromatography/mass spectrometry (GC/MS) was established for the analysis of β-agonists and β-blockers in urine. Because it can simultaneously extract and derivatize compounds of interest by methylbenzol and N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA) in HF-LPME, the approach overcomes the drawbacks of considerable time-consuming and tedious operation, meanwhile improves enrichment multiple. The optimized conditions were extraction for 20 min at 35 °C with 5.0 μL of mixed extraction solvent (methylbenzol/MSTFA = 1:1, v/v) with stirring speed of 925 rpm in 5.0 mL sample under pH 12.0 and 14% (w/v) NaCl. The method provided very wide linear ranges (0.25–400 ng mL −1) and low detection limits in the range of 0.08–0.10 ng mL −1 for clenbuterol, metoprolol and propranolol while enrichment factors reached up to 256. The analytes could be determined in spiked urine by the method with high extraction efficacy (93.79–109.04% recoveries) and precision (<9.70% RSD). It has a satisfactory result for metoprolol in practical human urine samples for a single-dose administration of 50 mg after 36 h. The proposed method only needs few microliters of organic solvent and derivatizing agent; the operation is simple, convenient and rapid for the trace analysis of β-agonists and β-blockers in biological fluids; it can be readily generalized for high sample throughput. So, it is hopeful that the study will facilitate the monitoring of β-agonists and β-blockers in the competition sports.

Development of negligible depletion hollow fiber–protected liquid‐phase microextraction for sensing freely dissolved triazines

A new sampling method, termed negligible depletion hollow fiber-protected liquid-phase microextraction, was developed for sensing the freely dissolved concentration (C(free)) and evaluating the availability of atrazine (ATR), desethyl atrazine (DEA), and simazine (SIM) in water. The sampling device was prepared by impregnating 1-octanol to both the pores and the lumen of a piece of polypropylene microporous hollow fiber membrane. After equilibrium and negligible depletion extraction, the 1-octanol in the lumen of the hollow fiber (10 microl) was collected for determination of triazines. Determination of C(free) and the distribution coefficient to 1-octanol (D(ow)) can be performed with this technique. A wide linear working range (1-200 microg/L) and low detection limits (0.1-1 microg/L) were obtained for triazines. Measured log D(ow) values of DEA (1.44 +/- 0.04), SIM (2.06 +/- 0.06), and ATR (2.33 +/- 0.05) agreed well with those reported in the literature. The measured D(ow) values were independent of the chemical concentration and sample pH (pH 3-10) and negligibly affected by the sample salinity (0-500 mM), suggesting that environmentally relevant pH and salinity have no significant effects on the availability of triazines. Although a slight (< or = 31%) increase of C(free) was observed, one-way analysis of variance indicated the C(free) of triazines were not significantly affected by the presence of Aldrich humic acid, Acros humic acid, and bovine albumin V (dissolved organic carbon [DOC], 0-100 mg/L). From 3 to 36% of the spiked triazines, however, were found to associate with the dissolved organic matter (DOM) in surface-water samples (DOC, 32.0-61.9 mg/L), suggesting the origin of the DOM is a key parameter in determining its association with and, thus, the availability of triazines.

Development of negligible depletion hollow fiber membrane-protected liquid-phase microextraction for simultaneous determination of partitioning coefficients and acid dissociation constants

A new method based on negligible depletion hollow fiber-protected liquid-phase microextraction coupled with high-performance liquid chromatography (HPLC) was developed for the simultaneous determination of partitioning coefficients ( K OW) and acid dissociation constants (p K a), by using phenol, 4-chlorophenol and 2,4-dichlorophenol as model compounds. A 37-mm length polypropylene hollow fiber membranes (600 μm inner diameter, 200 μm wall-thickness, 0.2 μm pore size, ∼70% porosity) with two-end sealed were filled with 1-octanol by ultrasonic agitation to prepare the extraction device. The extraction device was deployed in sample solutions, prepared by spiking target analytes in 1-octanol saturated aqueous solutions (500 mL), for negligible depletion extraction. After equilibrium was reached (∼5 h), the 1-octanol in the lumen of the hollow fiber membrane was collected for HPLC determination of the target analytes. As the depletion of the analytes in aqueous samples was negligible, the distribution coefficient ( D OW) could be calculated based on the measured equilibrium concentration in 1-octanol ( C O) and the initial concentration ( C W) in the aqueous sample of the target analyte ( D OW = C O/ C W). The D OW values measured at various pH values were nonlinearly regressed with pH to obtain the K OW and p K a values of a compound. Results showed that the measured values of the K OW and p K a of these model compounds agreed well with literature data.

Determination of basic degradation products of chemical warfare agents in water using hollow fibre-protected liquid-phase microextraction with in-situ derivatisation followed by gas chromatography–mass spectrometry

Hollow fibre-protected liquid-phase microextraction (HF-LPME) together with gas chromatography–mass spectrometry was, for the first time, investigated for the in-situ derivatisation and analysis of basic degradation products of chemical warfare agents in water samples. The degradation products studied were those of nerve and blister agents, and a psychotomimetic agent. Extractions with in-situ derivatisation were successfully performed using a mixture of solvent and derivatising agent. The protection of the moisture-sensitive derivatising agent was afforded by the hydrophobic hollow fibre. Parameters such as type of derivatising agent, extraction solvent, pH, salt concentration, stirring speed and extraction time were optimised using spiked deionised water samples. The linear range established was between 0.05 and 25 μg ml −1 depending on analyte, with squared regression coefficients ranging from 0.9959 to 0.9996. Relative standard deviations (RSDs) ranged from 6% to 10%. As comparison, solid-phase microextraction (SPME) was also evaluated and extraction conditions such as pH, salt concentration, stirring speed and extraction time were optimised. This work also represented the first report of such an in-situ derivatisation approach for SPME of basic analytes. The linear range established was between 0.5 and 25 μg ml −1 depending on analyte, with squared regression coefficients ranging from 0.9946 to 0.9998. RSDs ranged from 5% to 22%. The limits of detection of HF-LPME (0.04–0.36 μg l −1) showed improvement over those of SPME (0.06–0.77 μg l −1).

Determination of triazine herbicides in aqueous samples by dispersive liquid–liquid microextraction with gas chromatography–ion trap mass spectrometry

A simple and rapid new dispersive liquid–liquid microextraction technique (DLLME) coupled with gas chromatography–ion trap mass spectrometric detection (GC–MS) was developed for the extraction and analysis of triazine herbicides from water samples. In this method, a mixture of 12.0 μL chlorobenzene (extraction solvent) and 1.00 mL acetone (disperser solvent) is rapidly injected by syringe into the 5.00 mL water sample containing 4% (w/v) sodium chloride. In this process, triazines in the water sample are extracted into the fine droplets of chlorobenzene. After centrifuging for 5 min at 6000 rpm, the fine droplets of chlorobenzene are sedimented in the bottom of the conical test tube (8.0 ± 0.3 μL). The settled phase (2.0 μL) is collected and injected into the GC–MS for separation and determination of triazines. Some important parameters, viz, type of extraction solvent, identity and volume of disperser solvent, extraction time, and salt effect, which affect on DLLME were studied. Under optimum conditions the enrichment factors and extraction recoveries were high and ranged between 151–722 and 24.2–115.6%, respectively. The linear range was wide (0.2–200 μg L −1) and the limits of detection were between 0.021 and 0.12 μg L −1 for most of the analytes. The relative standard deviations (RSDs) for 5.00 μg L −1 of triazines in water were in the range of 1.36–8.67%. The performance of the method was checked by analysis of river and tap water samples, and the relative recoveries of triazines from river and tap water at a spiking level of 5.0 μg L −1 were 85.2–114.5% and 87.8–119.4%, respectively. This method was also compared with solid-phase microextraction (SPME) and hollow fiber protected liquid-phase microextraction (HFP-LPME) methods. DLLME is a very simple and rapid method, requiring less than 3 min. It also has high enrichment factors and recoveries for the extraction of triazines from water.

Determination of degradation products of chemical warfare agents in water using hollow fibre-protected liquid-phase microextraction with in-situ derivatisation followed by gas chromatography–mass spectrometry

Hollow fibre-protected liquid-phase microextraction (HF-LPME) together with gas chromatography/mass spectrometry was investigated for the analysis of degradation products of chemical warfare agents in water samples. The degradation products studied were those of nerve and blister agents, and a psychotomimetic agent. Extractions were successfully performed coupled with in-situ derivatisation using a mixture of solvent and derivatising agent. The protection of the moisture-sensitive derivatising agent was afforded by the hollow fibre. Parameters such as extraction solvent, pH, salt concentration, stirring speed and extraction time were optimised using spiked deionised water samples. The linear range established was between 0.005 and 5 μg ml −1 depending on analyte, with squared regression coefficients ranging from 0.9929 to 1.0000. Relative standard deviations ranged from 9% to 22%. As compared to those of solid-phase microextraction, the limits of detection (0.01–0.54 μg l −1) of the newly-developed approach were significantly improved.

Determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples using hollow fiber-protected liquid-phase microextraction and high performance liquid chromatography

A new method based on hollow fiber-protected liquid-phase microextraction (LPME) was developed for the simultaneous determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples. In LPME, analytes were extracted into 1-octanol immobilized in the micropores of a poly(vinylidene fluoride) porous hollow fiber membrane, and back extracted into the acceptor (4 M HCl) filled in the lumen of the hollow fiber. After LPME, the analytes trapped in the acceptor were analyzed with high-performance liquid chromatography after neutralization. The effect of extraction factors such as sample pH, acceptor pH, salinity, extraction time, stirring rate, and humic acid were studied. Under the optimized conditions, the limits of detection and relative standard deviations were respectively in the range of 0.5–1.0 µg L−1 and 3.9–4.7% (n = 5). The proposed method was applied to determine atrazine, desethyl atrazine and desisopropyl atrazine in wastewater and groundwater samples. The three analytes were below the limits of detection, but good relative spiked recoveries over 90.1 ± 5.9% at 5 µg L−1 spiked level were obtained.

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.