Determination of haloethers in water with dynamic hollow fiber liquid-phase microextraction using GC-FID and GC-ECD

Dynamic hollow fiber liquid-phase microextraction (HF-LPME) coupled with gas chromatography with flame ionization detection (GC-FID) and GC-electron capture detecion (GC-ECD) was used for quantification of toxic haloethers in lake water. The analytes were extracted from 5 ml of aqueous sample using 4 μl of organic solvent through a porous polypropylene hollow fiber. The effects on extraction performance of solvent selection, agitation rate, extraction time, extraction temperature, concentration of salt added and volumes of solvent for extraction and injection were optimized. The proposed method provided a good average enrichment factor of up to 231-fold, reasonable reproducibility ranging from 9 to 12% (n = 3), and good linearity (R² ≧ 0.9973) for spiked water samples. Method detection limits (MDLs) ranged from 0.55 to 4.30 μg/l for FID and 0.11-0.34 μg/l for ECD (n = 7).     

In-syringe demulsified dispersive liquid–liquid microextraction and high performance liquid chromatography–mass spectrometry for the determination of trace fungicides in environmental water samples

An in-syringe demulsified dispersive liquid–liquid microextraction (ISD–DLLME) technique was developed using low-density extraction solvents for the highly sensitive determination of the three trace fungicides (azoxystrobin, diethofencarb and pyrimethanil) in water samples by high performance liquid chromatography–mass spectrometry chromatography–diode array detector/electrospray ionisation mass spectrometry. In the proposed technique, a 5-mL syringe was used as an extraction, separation and preconcentration container. The emulsion was obtained after the mixture of toluene (extraction solvent) and methanol (dispersive solvent) was injected into the aqueous bulk of the syringe. The obtained emulsion cleared into two phases without centrifugation, when an aliquot of methanol was introduced as a demulsifier. The separated floating organic extraction solvent was impelled and collected into a pipette tip fitted to the tip of the syringe. Under the optimal conditions, the enrichment factors for azoxystrobin, diethofencarb and pyrimethanil were 239, 200, 195, respectively. The limits of detection, calculated as three times the signal-to-noise ratio (S N⁻¹), were 0.026 μg L⁻¹ for azoxystrobin, 0.071 μg L⁻¹ for diethofencarb and 0.040 μg L⁻¹ for pyrimethanil. The repeatability study was carried out by extracting the spiked water samples at concentration levels of 0.02 μg mL⁻¹ for all the three fungicides. The relative standard deviations varied between 4.9 and 8.2% (n = 5). The recoveries of all the three fungicides from tap, lake and rain water samples at spiking levels of 0.2, 1, 5 μg L⁻¹ were in the range of 90.0–105.0%, 86.0–114.0% and 88.6–110.0%, respectively. The proposed ISD–DLLME technique was demonstrated to be simple, practical and efficient for the determination of different kinds of fungicide residues in real water samples.     

Determination of environmental estrogens in human urine by high performance liquid chromatography after fluorescent derivatization with p-nitrobenzoyl chloride

A high performance liquid chromatographic method (HPLC) for the simultaneous determination of 4-nonylphenol, bisphenol A, 17α-ethinylestradiol and three endogenic estrogens including 17α-estradiol, 17β-estradiol, estriol in urine sample, based on precolumn derivatization with p-nitrobenzoyl chloride, is presented in this paper. The estrogens mentioned above in urine were firstly hydrolyzed with 0.6 mol/l HCl, and then enriched and cleaned-up by ENV-18 C18 solid phase extraction (SPE) column. The estrogens on column were eluted with dichloromethane, and the eluent was evaporated to dryness under gentle nitrogen flow. The residue was allowed to react with p-nitrobenzoyl chloride at 25 °C for 30 min. Separation was performed on a C18 column with gradient elution using acetonitrile and water as mobile phase. A fluorescence detection system was used to detect the fluorescent derivatization products. The detection limit of the method was 2.7 μg/l for bisphenol A and 17β-estradiol, 2.9 μg/l for 4-nonylphenol, 4.6 μg/l for 17α-estradiol and 17α-ethinylestradiol and 8.3 μg/l for estriol, respectively. The relative standard deviations (R.S.D.) ranged from 1.29 to 4.52% and the recoveries ranged from 85.5 to 99.9%. The method was applied to the determination of those six estrogens mentioned above in human urine samples collected from 20 healthy volunteers (aged 21-29). Bisphenol A (BPA) and 4-nonylphenol (NP) were detected with average contents of 1.22 ± 1.38 mg/l and 0.38 ± 0.77 mg/l in 10 male urine samples and 1.29 ± 1.22 mg/l and 0.05 ± 0.05 mg/l in 10 female urine samples, respectively. 17α-ethinylestradiol (α-EE2) was also detected with average contents of 0.13 ± 0.41 mg/l and 0.06 ± 0.15 mg/l in male and female urine samples, respectively.     

Determination of the fungicides vinclozolin and dicloran in soils using ultrasonic extraction coupled with solid-phase microextraction

Solid-phase microextraction (SPME) coupled to ultrasonic extraction was evaluated for extracting trace amounts of two agrochemical fungicides, vinclozolin and dicloran, in soil samples. Extraction was performed following two experimental approaches prior to the submission of the aqueous extracts to SPME-GC analysis. In the first approach, extraction involved sample homogenization with a water solution containing 5% (v/v) acetone and centrifugation prior to fiber extraction. In the second approach, the extraction of the fungicides from the soil samples was conducted using acetone as organic solvent which was then diluted with water to give a 5% (v/v) content. The pesticides were isolated with fused silica fiber coating with 85 μm polyacrylate. Parameters that affect both the extraction of the fungicides by the soil samples and the trapping of the analytes by the fiber were investigated and their impact on the SPME-GC-MS was studied. The procedures with respect to repeatability and limits of detection were evaluated by soil spiked with both analytes. Repeatability was between 5.6 and 14.2% and the limits of detection were 2-13 ng g⁻¹. The efficiency of acetone/SPME was generally better than that for water/SPME procedure showing good linearity (R²>0.99) with coefficient variations below 9%, recoveries higher than 91% and limits of detection between 2 and 3 ng g⁻¹. Finally, the recoveries obtained with acetone/SPME procedure were compared with the conventional liquid-liquid extraction using real soil samples. The acetone/SPME method was shown to be an inexpensive, fast and simple preparation method for the determination of target analytes at low nanogram per gram levels in soils.     

On-line preconcentration and speciation of arsenic by flow injection hydride generation atomic absorption spectrophotometry

A flow injection-column preconcentration-hydride generation atomic absorption spectrophotometric (FI-column-HGAAS) method was developed for determining μg/l levels of As(III) and As(V) in water samples, with simultaneous preconcentration and speciation. The speciation scheme involved determining As(V) at neutral pH and As(III + V) at pH 12, with As(III) obtained by difference. The enrichment factor (EF) increased with increase in sample loading volume from 2.5 to 10 ml, and for preconcentration using the chloride-form anion exchange column, EFs ranged from 5 to 48 for As(V) and 4 to 24 for As(III + V), with corresponding detection limits of 0.03-0.3 and 0.07-0.3 μg/l. Linear concentration range (LCR) also varied with sample loading volume, and for a 5-ml sample was 0.3-5 and 0.2-8 μg/l for As(V) and As(III + V), respectively. Sample throughput, which decreased with increase in sample volume, was 8-17 samples/h. For the hydroxide-form column, the EFS for 2.5-10 ml samples were 3-23 for As(V) and 2-15 for As(III + V), with corresponding detection limits of 0.07-0.4 and 0.1-0.5 μg/l. The LCR for a 5-ml sample was 0.3-10 μg/l for As(V) and 0.2-20 μg/l for As(III + V). Sample throughput was 10-20 samples/h. The developed method has been effectively applied to tap water and mineral water samples, with recoveries ranging from 90 to 102% for 5-ml samples passed through the two columns.     

Field analysis of benzene, toluene, ethylbenzene and xylene in water by portable gas chromatography-microflame ionization detector combined with headspace solid-phase microextraction

In this work, portable gas chromatography-microflame ionization detection (portable GC-μFID) coupled to headspace solid-phase microextraction (HS-SPME) was developed for the field analysis of benzene, toluene, ethylbenzene and xylene (BTEX) in water samples. The HS-SPME parameters such as fiber coating, extraction times, stirring rate, the ratio of headspace volume to sample volume, and sodium chloride concentration were studied. A 65 μm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 900 rpm, 3.0 ml of headspace (1.0 ml water sample in 4.0 ml vial), and 35% sodium chloride concentration (w/v) were respectively chosen for the best extraction response. An extraction time of 1.0 min was enough to extract BTEX in water samples. The relative standard deviation (R.S.D.) for the procedure varied from 5.4% to 8.3%. The method detection limits (MDLs) found were lower than 1.5 μg/l, which was enough sensitive to detect the BTEX in water samples. The optimized method was applied to the field analysis of BTEX in wastewater samples. These experiment results show that portable GC-μFID combined with HS-SPME is a rapid, simple and effective tool for field analysis of BTEX in water samples.     

Multiresidue determination of pesticides in juice by solid-phase extraction and gas chromatography-mass spectrometry

A multiresidue method based on solid-phase extraction was developed for the simultaneous determination of 50 pesticides in commercial juices. The extraction procedure was carried out in C₁₈ columns preconditioned with acetonitrile and water. The subsequent elution of pesticides was performed with a mixture of hexane-ethyl acetate (1:1, v/v) prior to the determination by gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC-MS-SIM), using one target and two qualifier ions. Standards were prepared spiking blank juice samples to counteract the observed matrix effect. Average recoveries for all the pesticides studied were higher than 91% with relative standard deviations lower than 9% in the concentration range of 0.02-0.1 μg/mL and the detection limits achieved ranged from 0.1 to 4.6 μg/L. The proposed method was applied to the analysis of these compounds in commercial juices and diazinon, ethion and procymidone were the pesticides encountered, although the levels found were very low.     

Preparation and evaluation of graphene-coated solid-phase microextraction fiber

In this paper, a novel graphene (G) based solid-phase microextraction (SPME) fiber was firstly prepared by immobilizing the synthesized G on stainless steel wire as coating. The new fiber possessed a homogeneous, porous and wrinkled surface and showed excellent thermal (over 330 °C), chemical and mechanical stability, and long lifespan (over 250 extractions). The SPME performance of the G-coated fiber was evaluated in detail through extraction of six pyrethroid pesticides. Although the thickness of G-coated fiber was only 6-8 μm, its extraction efficiencies were higher than those of two commercial fibers (PDMS, 100 μm; PDMS/DVB, 65 μm). This high extraction efficiency may be mainly attributed to huge delocalized π-electron system of G, which shows strong π-stacking interaction with pyrethroid pesticide. The G-coated fiber was applied in the gas chromatographic determination of six pyrethroids, and their limits of detection were found to be ranged from 3.69 to 69.4 ng L⁻¹. The reproducibility for each single fiber was evaluated and the relative standard deviations (RSDs) were calculated to be in the range from 1.9% to 6.5%. The repeatability of fiber-to-fiber and batch-to-batch was 4.3-9.2% and 4.1-9.9%. The method developed was successfully applied to three pond water samples, and the recoveries were 83-110% at a spiking of 1 μg L⁻¹.     

Liquid chromatography with time-of-flight mass spectrometry for simultaneous determination of chemotherapeutant residues in salmon

Liquid chromatography with time-of-flight mass spectrometry (LC-TOF-MS) method has been developed for simultaneous confirmation by accurate mass measurement and quantitative determination of antibiotics (enrofloxacin, oxolinic acid, flumequine, erythromycin), fungicides (malachite green MG, leucomalachite green LMG) and parasiticide (emamectin benzoate) residues in edible portion of salmon. Confirmation of chemotherapeutant residues has been based on the system of identification points (IPs) established in the Commission Decision 2002/657/EC concerning the use of mass spectrometry (MS) techniques. A validation study on matrix is presented evaluating accuracy in terms of precision (λ_ppm 0.83-1.15) and trueness (0.22-0.70 Da). Limits of detection (LODs) and limits of quantification (LOQs) were in ranges of 1-3 and 3-9 μg/kg, below the maximum residue limits (MRLs) established in current EU legislation (100-200 μg/kg) for these chemotherapeutants. Considering the EU guidelines, decision limits (CCα) and detection capabilities (CCβ) were determined (ranges of 103-218 and 107-234 μg/kg, respectively) for authorised substances. For no authorised compounds (MG and LMG), LODs were 2 and 1 μg/kg, respectively, but exceed the MRPL (minimum required performance limit) established in the legislation which corresponds to the sum of MG and LMG (2 μg/kg). Acceptable intra-day and inter-day variability, in terms of relative standard deviation (R.S.D.) of the analytical method, were obtained (2-15%). Linearity was demonstrated from the LOQs of the analytes to 600 μg/kg (r > 0.9991). The method has involved an extraction procedure based on solid-liquid extraction (SLE) with recoveries higher than 80% for most target chemotherapeutants, with exception of enrofloxacin (40%).     

Dynamic supported liquid membrane tip extraction of glyphosate and aminomethylphosphonic acid followed by capillary electrophoresis with contactless conductivity detection

A dynamic supported liquid membrane tip extraction (SLMTE) procedure for the effective extraction and preconcentration of glyphosate (GLYP) and its metabolite aminomethylphosphonic acid (AMPA) in water has been investigated. The SLMTE procedure was performed in a semi-automated dynamic mode and demonstrated a greater performance against a static extraction. Several important extraction parameters such as donor phase pH, cationic carrier concentration, type of membrane solvent, type of acceptor stripping phase, agitation and extraction time were comprehensively optimized. A solution of Aliquat-336, a cationic carrier, in dihexyl ether was selected as the supported liquid incorporated into the membrane phase. Quantification of GLYP and AMPA was carried out using capillary electrophoresis with contactless conductivity detection. An electrolyte solution consisting of 12 mM histidine (His), 8 mM 2-(N-morpholino)ethanesulfonic acid (MES), 75 μM cetyltrimethylammonium bromide (CTAB), 3% methanol, pH 6.3, was used as running buffer. Under the optimum extraction conditions, the method showed good linearity in the range of 0.01–200 μg/L (GLYP) and 0.1–400 μg/L (AMPA), acceptable reproducibility (RSD 5–7%, n = 5), low limits of detection of 0.005 μg/L for GLYP and 0.06 μg/L for AMPA, and satisfactory relative recoveries (90–94%). Due to the low cost, the SLMTE device was disposed after each run which additionally eliminated the possibility of carry-over between runs. The validated method was tested for the analysis of both analytes in spiked tap water and river water with good success.     

Differential pulse cathodic stripping voltammetric speciation of trace level inorganic arsenic compounds in natural water samples

A simple, fast and sensitive speciation method is described for inorganic arsenic in water at the μg/l level, applicable in the laboratory and in the field, based on differential pulse cathodic stripping voltammetry (DPCSV). Only As(III) is deposited on a Hg electrode in the presence of Cu and Se in HCl medium. Determination of total As is performed by reducing As(V) to As(III) using sodium meta-bisulfite/sodium thiosulfate reagent stabilized with ascorbic acid. As(V) is quantified by difference. The detection limit (S/N>3) was 0.5 μg/l with a linear range from 4.5 to 180 μg/l. The relative standard deviation (n=6) was 2.4, 2.5, 4.2% for As(III) and 8.0, 6.8, 9.0% for As(V) at levels of 45, 10, and 5 μg/l, respectively. Analysis of the NIST 1640 natural water standard yielded total arsenic concentration 26.5±3.4 μg/l (n=3) compared to the certified value of 26.7 μg/l. Results obtained on several natural water samples analyzed both in the laboratory and on-site compared well with those obtained by HR ICP-MS, GFAAS and IC-AFS. Ions (phosphate, iron, manganese) commonly found in groundwater containing arsenic were found to have negligible interference.     

Statistical evaluation of an analytical GC/MS method for the determination of long chain fatty acids

In-depth evaluation of an analytical method to detect and quantify long chain fatty acids (C₈-C₁₆) at trace level concentrations (25-1000 μg/l) is presented. The method requires derivatization of the acids with methanolic boron trifluoride, separation, and detection by gas chromatography-mass spectrometry. The calibration experiments passed all the tested performance criteria such as linearity, homoscedasticity, and ruggedness. The detection limits and related quantities were computed by applying the method detection limit, and the calibration line approximation. The values obtained by applying the latter approach were more reliable and consistent with the actual statistical theory of detection decisions and yielded the following concentrations: C₈, 87.6 μg/l; C₁₀, 45.2 μg/l; C₁₁, 39.9 μg/l; C₁₂, 37.7 μg/l; C₁₄, 41.4 μg/l and C₁₆, 40.6 μg/l. Two different gas-liquid chromatographic columns were tested and similar results achieved, which shows the ruggedness of the method.     

Determination of polycyclic aromatic hydrocarbons in aqueous samples by microwave assisted headspace solid-phase microextraction and gas chromatography/flame ionization detection

The novel pretreatment technique, microwave-assisted heating coupled to headspace solid-phase microextraction (MA-HS-SPME) has been studied for one-step in situ sample preparation for polycyclic aromatic hydrocarbons (PAHs) in aqueous samples before gas chromatography/flame ionization detection (GC/FID). The PAHs evaporated into headspace with the water by microwave irradiation, and absorbed directly on a SPME fiber in the headspace. After being desorbed from the SPME fiber in the GC injection port, PAHs were analyzed by GC/FID. Parameters affecting extraction efficiency, such as SPME fiber coating, adsorption temperature, microwave power and irradiation time, and desorption conditions were investigated.Experimental results indicated that extraction of 20 mL aqueous sample containing PAHs at optional pH, by microwave irradiation with effective power 145 W for 30 min (the same as the extraction time), and collection with a 65 μm PDMS/DVB fiber at 20 °C circular cooling water to control sampling temperature, resulted in the best extraction efficiency. Optimum desorption of PAHs from the SPME fiber in the GC hot injection port was achieved at 290 °C for 5 min. The method was developed using spiked water sample such as field water with a range of 0.1-200 μg/L PAHs. Detection limits varied from 0.03 to 1.0 μg/L for different PAHs based on S/N = 3 and the relative standard deviations for repeatability were <13%. A real sample was collected from the scrubber water of an incineration system. PAHs of two to three rings were measured with concentrations varied from 0.35 to 7.53 μg/L. Recovery was more than 88% and R.S.D. was less than 17%. The proposed method is a simple, rapid, and organic solvent-free procedure for determination of PAHs in wastewater.     

Sensitive capillary electrophoresis microchip determination of trinitroaromatic explosives in nonaqueous electrolyte following solid phase extraction

A capillary electrophoresis (CE) microchip is utilized for the sensitive separation and detection of three trinitroaromatic explosives: 1,3,5-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrophenyl-N-methylnitramine (tetryl), in the presence of 10 other explosives and explosive derivatives in nonaqueous electrolyte (acetonitrile/methanol 87.5/12.5 (v/v), 2.5 mM NaOH, 1 mM sodium dodecyl sulfate (SDS)). The chemical reaction of bases, e.g. hydroxide or methoxide ions, with trinitroaromatic compounds forms red colored derivatives that can be easily detected using a green light emitting diode (LED) on the microchip. Two surfactants bearing opposite charge, cetyltrimethylammonium bromide (CTAB) and SDS are compared with respect to their effect on separation times, detection limits and resolving powers for separating these explosives. All microchip separations were achieved in <20 s. In the absence of solid phase extraction (SPE), the detection limits obtained for the trinitroaromatic explosives were as follows: TNB, 60 μg/l; TNT, 160 μg/l and tetryl, 200 μg/l. By coupling the microchip separation with ex situ SPE, the detection limits for detecting these three explosives in seawater were lowered by 240 to more than 1000 times: TNB, 0.25 μg/l; TNT, 0.34 μg/l and tetryl, 0.19 μg/l.     

Monitoring of selenium in water samples using dispersive liquid-liquid microextraction followed by iridium-modified tube graphite furnace atomic absorption spectrometry

A simple and powerful microextraction technique was used for determination of selenium in water samples using dispersive liquid-liquid microextraction (DLLME) followed by graphite furnace atomic absorption spectrometry (GF AAS). DLLME and simultaneous complex formation was performed with rapid injection of a mixture containing ethanol (disperser solvent), carbon tetrachloride (extraction solvent) and ammonium pyrrolidine dithiocarbamate (APDC, chelating agent) into water sample spiked with selenium. After centrifuging, fine droplets of carbon tetrachloride, which were dispersed among the solution and extracted Se-APDC complex, sediment at the bottom of the conical test tube. The concentration of enriched analyte in the sedimented phase was determined by iridium-modified pyrolitic tube graphite furnace atomic absorption spectrometry. The concentration of selenate was obtained as the difference between the concentration of selenite after and before pre-reduction of selenate to selenite. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of chelating agent were optimized. Under the optimum conditions, the enrichment factor of 70 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the range of 0.1-3 μg L^− 1 with detection limit of 0.05 μg L^− 1. The relative standard deviation (RSDs) for ten replicate measurements of 2.00 μg L^− 1 of selenium was 4.5%. The relative recoveries of selenium in tap, river and sea water samples at spiking level of 2.00 μg L^− 1 were 106, 96 and 98%, respectively.     

Determination of fluoroquinolones in environmental waters by in-tube solid-phase microextraction coupled with liquid chromatography-tandem mass spectrometry

We developed a sensitive and useful method for the determination of five fluoroquinolones (FQs), enoxacin, ofloxacin, ciprofloxacin, norfloxacin, and lomefloxacin in environmental waters, using a fully automated method consisting of in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC/MS/MS). These compounds were analysed within 7 min by high-performance liquid chromatography (HPLC) using a CAPCELL PAK C8 column and aqueous ammonium formate (pH 3.0, 5 mM)/acetonitrile (85/15, v/v) at a flow rate of 0.2 mL/min. Electrospray ionization conditions in the positive ion mode were optimized for MS/MS detection. In order to optimize the extraction of FQs, several in-tube SPME parameters were examined. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40 μL of sample at a flow-rate of 150 μL/min, using a Carboxen 1010 PLOT capillary column as an extraction device. The extracted compounds were easily desorbed from the capillary by passage of the mobile phase. Using the in-tube SPME LC/MS/MS method, good linearity of the calibration curve (r ≥ 0.997) was obtained in the concentration range from 0.1 to 10 ng/mL for all compounds examined. The limits of detection (S/N = 3) of the five FQs ranged from 7 to 29 pg/mL. The in-tube SPME method showed 60-94-fold higher sensitivity than the direct injection method (5 μL injection). This method was applied successfully to the analysis of environmental water samples without any other pretreatment and interference peaks. Several surface waters and wastewaters were collected from the area around Asahi River, and ofloxacin was detected in wastewater samples of a sewage treatment plant and other two hospitals at 17.5-186.2 pg/mL. The recoveries of FQs spiked into river water were above 81% for a 0.1 or 0.2 ng/mL spiking concentration, and the relative standard deviations were below 1.9-8.6%.     

Automatic screening method for the preconcentration and determination of N-nitrosamines in water

A screening method was developed to discriminate among water samples contaminated or uncontaminated with N-nitrosamines in order to reduce the use of expensive instruments such as chromatographs. The system is based on the preconcentration of the analytes onto a sorbent column, elution and derivatization to form nitrite, then formation of a coloured product (Griess reaction) and photometric detection. The limit of detection achieved for 100 ml of sample volume was 0.2 μg/l and the sample frequency 3 h⁻¹. The reliability of the proposed method of the N-nitrosamines was established at five concentrations (between 0.5 and 3 times the limit of detection). For a level concentration of 0.6 μg/l (three times the limit of detection), the percentage of false negatives is 0%. The method was applied to the screening of several water samples (river, pond, well, tap and waste) with a positive response only for waste water samples.     

Validation of method for determination of different classes of pesticides in aqueous samples by dispersive liquid-liquid microextraction with liquid chromatography-tandem mass spectrometric detection

In this study, a simple, rapid and efficient method has been developed for the extraction and preconcentration of different classes of pesticides, carbofuran (insecticide), clomazone (herbicide) and tebuconazole (fungicide) in aqueous samples by dispersive liquid-liquid microextraction (DLLME) coupled with liquid chromatography-tandem mass spectrometric detection. Some experimental parameters that influence the extraction efficiency, such as the type and volume of the disperser solvents and extraction solvents, extraction time, speed of centrifugation, pH and addition of salt were examined and optimized. Under the optimum conditions, the recoveries of pesticides in water at spiking levels between 0.02 and 2.0 μg L⁻¹ ranged from 62.7% to 120.0%. The relative standard deviations varied between 1.9% and 9.1% (n = 3). The limits of quantification of the method considering a 50-fold preconcentration step were 0.02 μg L⁻¹. The linearity of the method ranged from 1.0 to 1000 μg L⁻¹ for all compounds, with correlation coefficients varying from 0.9982 to 0.9992. Results show that the method we propose can meet the requirements for the determination of pesticides in water samples. The comparison of this method with solid-phase extraction indicates that DLLME is a simple, fast, and low-cost method for the determination of pesticides in natural waters.     

Simultaneous quantification of amphetamines, caffeine and ketamine in urine by hollow fiber liquid phase microextraction combined with gas chromatography-flame ionization detector

A method of hollow fiber (HF) liquid phase microextraction (LPME) combined with gas chromatography (GC)-flame ionization detection (FID) was developed for the simultaneous quantification of trace amphetamine (AP), methamphetamine (MA), methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA), caffeine and ketamine (KT) in drug abuser urine samples. The factors affecting on the extraction of six target analytes by HF-LPME were investigated and optimized, and the subsequent analytical performance evaluation and real sample analysis were performed by the extraction of six target analytes in sample solution containing 30% NaCl (pH 12.5) for 20 min with extraction temperature of 30 °C and stirring rate of 1000 rpm. Under such optimal conditions, the limits of detection (LODs, S/N = 3) for the six target analytes were ranged from 8 μg/L (AP, KT) to 82 μg/L (MDA), with the enrichment factors (EFs) of 5-227 folds, and the relative standard deviations (RSDs, n = 7) were in the range of 6.9-14.1%. The correlation coefficients of the calibration for the six target analytes over the dynamic linear range were higher than 0.9958. The application feasibility of HF-LPME-GC-FID in illegal drug monitoring was demonstrated by analyzing drug abuser urine samples, and the recoveries of target drugs for the spiked sample ranging from 75.2% to 119.3% indicated an excellent anti-interference capability of the developed method. The proposed method is simple, effective, sensitive and low-cost, and provides a much more accurate and sensitive detection platform over the conventional analytical techniques (such as immunological assay) for drug abuse analysis.     

A novel miniaturized homogenous liquid–liquid solvent extraction-high performance liquid chromatographic-fluorescence method for determination of ultra traces of polycyclic aromatic hydrocarbons in sediment samples

A novel technique called miniaturized homogeneous liquid–liquid extraction (MHLLE) followed by high performance liquid chromatographic-fluorescence detection (HPLC-FL) was developed for the extraction and determination of some polycyclic aromatic hydrocarbons (PAHs) as model for analytical problem in sediment samples. The method is based on the rapid extraction of PAHs from a methanolic sample solution into 0.5 mL n-hexane, as a solvent of lower density than water. After addition of water, the extracting solvent immediately forms a distinct water-immiscible phase at the top of the vial, which can be easily separated, evaporated and re-dissolved in 25 μL of methanol and injected to the HPLC instrument. The parameters affecting the extraction process such as type and volume of organic extraction solvent, extraction time, and salt addition were investigated and the partition coefficient between methanol/water–n-hexane phases was evaluated and used to predict the extraction efficiency. Under optimal conditions, the limits of detection were estimated for the individual PAHs as 3S_b (three times of the standard deviation of baseline) of the measured chromatogram, are in the range of 0.003–0.04 ng g⁻¹ for sediment samples. The relative recoveries of PAHs at spiking levels of 1.0 ng g⁻¹ for sediment samples were in the range of 81–92%. The method was also applied to a corresponding standard references materials (IAEA-408) successfully. The proposed method is very fast, simple, and sensitive without any need for stirring and centrifugation.