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.     

Application of microwave-assisted desorption/headspace solid-phase microextraction as pretreatment step in the gas chromatographic determination of 1-naphthylamine in silica gel adsorbent

Pretreatment of silica gel sample containing 1-naphthylamine by microwave-assisted desorption (MAD) coupled to in situ headspace solid phase microextraction (HS-SPME) has been investigated as a possible alternative to conventional methods prior to gas chromatographic (GC) analysis. The 1-naphthylamine desorbs from silica gel to headspace under microwave irradiation, and directly absorbs onto a SPME fiber located in a controlled-temperature headspace area. After being collected on the SPME fiber, and desorbed in the GC injection port, 1-naphthylamine is analyzed by GC-FID. Parameters that influence the extraction efficiency of the MAD/HS-SPME, such as the extraction media and its pH, the microwave irradiation power and irradiation time as well as desorption conditions of the GC injector, have been investigated. Experimental results indicate that the extraction of a 150 mg silica gel sample by using 0.8 ml of 1.0 M NaOH solution and a PDMS/DVB fiber under high-powered irradiation (477 W) for 5 min maximizes the extraction efficiency. Desorption of 1-naphthylamine from the SPME fiber in GC injector is optimal at 250 °C held for 3 min. The detection limit of method is 8.30 ng. The detected quantity of 1-naphthylamine obtained by the proposed method is 33.3 times of that obtained by the conventional solvent extraction method for the silica gel sample containing 100 ng of 1-naphthylamine. It provides a simple, fast, sensitive and organic-solvent-free pretreatment procedure prior to the analysis of 1-naphthylamine collected on a silica gel adsorbent.     

Determination of Aniline in Water by Microwave-Assisted Headspace Solid-Phase Microextraction and Gas Chromatography

Determination of aniline in wastewater was investigated by microwave-assisted headspace solid-phase microextraction (MA-HS-SPME), for one-step in-situ sample preparation, and gas chromatography. Aniline in the water was evaporated into the headspace under the action of microwave irradiation and adsorbed directly by the SPME fiber. After desorption in the GC injection port and gas chromatography aniline was detected by FID. Conditions affecting the extraction efficiency, for example the pH of the water, addition of salt, microwave power and irradiation time, and desorption conditions were investigated. Experimental results indicated that adjustment of the pH of the water sample to 12 and headspace SPME sampling with a PDMS-DVB fiber under medium–high power irradiation (345 W) for 3 min resulted in the best extraction efficiency. Desorption of aniline was optimum when the SPME fiber was heated at 230 °C for 3 min. The detection limit was approximately 0.01 g mL^–1. The proposed method is a simple, fast, and organic-solvent-free procedure for analysis of aniline in water. Application was illustrated by analysis of aniline in wastewater from a polymer factory.     

Determination of chlorophenols in soil samples by microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection

Microwave-assisted extraction coupled to headspace solid-phase microextraction was studied and applied for one-step in-situ sample preparation prior to analysis of chlorophenols (CPs) in soil samples. The CPs in soil sample were extracted into the aqueous solution and then directly onto the solid-phase microextraction (SPME) fiber in headspace under the aid of microwave irradiation. After being desorbed from SPME fiber in the GC injection port, CPs were analyzed with a GC-electron-capture detection system. Parameters affecting the extraction efficiency such as the extraction solutions, the pH in the slurry, the humic acid content in the soil, the power and the irradiation time of microwave as well as the desorption parameters were investigated. Experimental results indicated that the extraction of a 1.0 g soil sample with a 6-ml aqueous solution (pH 2) and a polyacrylate fiber under the medium-power irradiation (132 W) for 9 min achieved the best extraction efficiency of about 90% recovery and less than 10% RSD. Desorption was optimal at 300 degrees C for 3 min. Detection limits were obtained at around 0.1-2.0 microg/kg levels. The proposed method provided a simple, fast, and organic solvent-free procedure to analyze CPs from soil sample matrix.     

Determination of dichlorvos by on-line microwave-assisted extraction coupled to headspace solid-phase microextraction and gas chromatography-electron-capture detection

The pretreatment technique of microwave-assisted extraction on-line headspace solid-phase microextraction (MAE-HS-SPME) was designed and studied for one-step in-situ sample preparation prior to the chromatographic analysis of a pesticide on vegetables. The pesticide on chopped vegetables was extracted into an aqueous solution with the aid of microwave irradiation and then directly onto the SPME fiber in headspace. After being collected on to the SPME fiber and desorbed in the GC injection port, the pesticide (dichlorvos) was analyzed with a GC-electron-capture detection system. The optimum conditions for obtaining extraction efficiency, such as the pH, the polarity modifier, and the salt added in sample solution, the microwave irradiation, as well as the desorption parameters were investigated. Experimental results indicated that the proposed MAE-HS-SPME technique attained the best extraction efficiency of 106% recovery under the optimized conditions, i.e. irradiation of extraction solution (10% aqueous ethylene glycol) at pH 5.0 with medium microwave power for 10 min. Desorption at 220 degrees C for 3 min offered the best detection result. The detection was linear at 5-75 microg/l with correlation coefficient of 0.9985. Detection limit was obtained at approximately 1.0 microg/l level based on S/N=3. The proposed method provided a very simple, fast, and solvent-less procedure to collect pesticides directly from vegetables for GC determination. Its application was illustrated by the analysis of trace dichlorvos in vegetables.     

Monitoring of PAHs in air by collection on XAD-2 adsorbent then microwave-assisted thermal desorption coupled with headspace solid-phase microextraction and gas chromatography with mass spectrometric detection

Microwave-assisted thermal desorption (MAD) coupled to headspace solid-phase microextraction (HS-SPME) has been studied for in-situ, one-step, sample preparation for PAHs collected on XAD-2 adsorbent, before gas chromatography with mass spectrometric detection. The PAHs on XAD-2 were desorbed into the extraction solution, evaporated into the headspace by use of microwave irradiation, and absorbed directly on a solid-phase microextraction fiber in the headspace. After desorption from the SPME fiber in the hot GC injection port, PAHs were analyzed by GC–MS. Conditions affecting extraction efficiency, for example extraction solution, addition of salt, stirring speed, SPME fiber coating, sampling temperature, microwave power and irradiation time, and desorption conditions were investigated. Experimental results indicated that extraction of 275 mg XAD-2, containing 10–200 ng PAHs, with 10-mL ethylene glycol–1 mol L⁻¹ NaCl solution, 7:3, by irradiation with 120 W for 40 min (the same as the extraction time), and collection with a PDMS–DVB fiber at 35 °C, resulted in the best extraction efficiency. Recovery was more than 80% and RSD was less than 14%. Optimum desorption was achieved by heating at 290 °C for 5 min. Detection limits varied from 0.02 to 1.0 ng for different PAHs. A real sample was obtained by using XAD-2 to collect smoke from indoor burning of joss sticks. The amounts of PAHs measured varied from 0.795 to 2.53 ng. The method is a simple and rapid procedure for determination of PAHs on XAD-2 absorbent, and is free from toxic organic solvents.     

Analysis of aqueous pyrethroid residuals by one-step microwave-assisted headspace solid-phase microextraction and gas chromatography with electron capture detection

A one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) has been applied to be a pretreatment step in the analysis of aqueous pyrethroid residuals by gas chromatography (GC) with electron capture detection (ECD). Microwave heating was applied to accelerate the vaporization of pyrethroids (bioallenthrin, bifenthrin, fenpropathrin, cyhalothrin, permethrin, cyfluthrin, cypermethrin, fluvalinate, fenvalerate and deltamethrin) into the headspace, and then being absorbed directly on a SPME fiber under the controlled conditions. Optimal conditions for the SPME sampling, such as the selection of sampling fiber, sample pH, sampling temperature and time, microwave irradiation power, desorption temperature and time were investigated and then applied to real sample analysis. Experimental results indicated that the extraction of pyrethroids from a 20-mL aquatic sample (pH 4.0) was achieved with the best efficiency through the use of a 100-μm PDMS fiber, microwave irradiation of 157 W and sampling at 30 °C for 10 min. Under optimum conditions, the detections were linear in the range of 0.05-0.5 μg/L with the square of correlation coefficients (R²) of >0.9913 for pyrethroids except bifenthrin being 0.9812. Method detection limits (MDL) were found to be varied from 0.2 to 2.6 ng/L for different pyrethroids based on S/N (signal to noise) = 3. The coefficients of variation (CVs) for repeatability were 7-21%. A field underground water sample was analyzed with recovery between 88.5% to 115.5%. This method was proven to be a very simple, rapid, and solvent-free process to achieve the sample pretreatment before the analysis of trace pyrethroids in aqueous samples by gas chromatography.     

Silicone glue coated stainless steel wire for solid phase microextraction

A new solid phase microextraction (SPME) fiber based on high-temperature silicone glue coated on a stainless steel wire is presented. The fiber coating can be prepared easily in a few minutes, it is mechanically stable and exhibits relatively high thermal stability (up to 260 °C). The extraction properties of the fiber to benzene, toluene, ethylbenzene, and xylenes (BTEX) were examined using both direct and headspace SPME modes coupled to gas chromatography-flame ionization detection. The effects of the extraction and desorption parameters including extraction and desorption time, sampling and desorption temperature, and ionic strength on the extraction/desorption efficiency have been studied. For both headspace and direct SPME the calibration graphs were linear in the concentration range from 0.5 μg L⁻¹ to 10 mg L⁻¹ (R² > 0.996) and detection limits ranged from 0.07 to 0.24 μg L⁻¹. Single fiber repeatability and fiber-to-fiber reproducibility were less than 6.8 and 21.5%, respectively. Finally, headspace SPME was applied to determine BTEX in petrol station waste waters with spiked recoveries in the range of 89.7-105.2%.     

Determination of organophosphorus pesticides in ecological textiles by solid-phase microextraction with a siloxane-modified polyurethane acrylic resin fiber

A novel solid-phase microextraction (SPME) fiber coating was prepared with siloxane-modified polyurethane acrylic resin by photo-cured technology. The ratio of two monomers was investigated to obtain good microphase separation structure and better extraction performance. The self-made fiber was then applied to organophosphorus pesticides (OPPs) analysis and several factors, such as extraction/desorption time, extraction temperature, salinity, and pH, were studied. The optimized conditions were: 15 min extraction at 25 °C, 5% Na₂SO₄ content, pH 7.0 and 4 min desorption in GC inlet. The self-made fiber coating exhibited better extraction efficiency for OPPs, compared with three commercial fiber coatings. Under the optimized conditions, the detection limits of 11 OPPs were from 0.03 μg L⁻¹ to 0.5 μg L⁻¹. Good recoveries and repeatabilities were obtained when the method was used to determine OPPs in ecological textile.     

Determination of chlorophenols in landfill leachate using headspace sampling with ionic liquid-coated solid-phase microextraction fibers combined with gas chromatography–mass spectrometry

A new microextraction technique based on ionic liquid solid-phase microextraction (IL-SPME) was developed for determination of trace chlorophenols (CPs) in landfill leachate. The synthesized ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), was coated onto the spent fiber of SPME for extraction of trace CPs. After extraction, the absorbed analytes were desorbed and quantified using gas chromatography–mass spectrometry (GC/MS). The term of the proposed method is as ionic liquid-coated of solid-phase microextraction combined with gas chromatography–mass spectrometry (IL-SPME-GC/MS). No carryover effect was found, and every laboratory-made ionic liquids-coated-fiber could be used for extraction at least eighty times without degradation of efficiency. The chlorophenols studied were 2,4-dichlorophenol (2,4-DP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and pentachlorophenol (PCP). The best results of chlorophenols analysis were obtained with landfill leachate at pH 2, headspace extraction for 4 min, and thermal desorption with the gas chromatograph injector at 240 °C for 4 min. Linearity was observed from 0.1 to 1000 μg L⁻¹ with relative standard deviations (RSD) less than 7% and recoveries were over 87%. The limit of detection (LOD) for pentachlorophenol was 0.008 μg L⁻¹. The proposed method was tested by analyzing landfill leachate from a sewage farm. The concentrations of chlorophenols were detected to range from 1.1 to 1.4 μg L⁻¹. The results demonstrate that the IL-SPME-GC/MS method is highly effective in analyzing trace chlorophenols in landfill leachate.     

A new interface for coupling solid phase microextraction with liquid chromatography

A modified Rheodyne 7520 microsample injector was used as a new solid phase microextraction (SPME)–liquid chromatography (LC) interface. The modification was focused on the construction of a new sample rotor, which was built by gluing two sample rotors together. The new sample rotor was further reinforced with 3 pieces of stainless steel tubing. The enlarged central flow passage in the new sample rotor was used as a desorption chamber. SPME fiber desorption occurred in static mode. But all desorption solvent in the desorption chamber was injected into LC system with the interface. The analytical performance of the interface was evaluated by SPME–LC analysis of PAHs in water. At least 90% polycyclic aromatic hydrocarbons (PAHs) were desorbed from a polyacrylonitrile (PAN)/C18 bonded fuse silica fiber in 30 s. And injection was completed in 20 s. About 10–20% total carryovers were found on the fiber and in the interface. The carryover in the interface was eliminated by flushing the desorption chamber with acetonitrile at 1 mL min⁻¹ for 2 min. The repeatability of the method was from 2% to 8%. The limit of detection (LOD) was in the mid pg mL⁻¹ range. The linear ranges were from 0.1 to 100 ng mL⁻¹. The new SPME–LC interface was reliable for coupling SPME with LC for both qualitative and quantitative analysis.     

Solid-phase microextraction coupled with capillary electrophoresis to determine ephedrine derivatives in water and urine using a sol-gel derived butyl methacrylate/silicone fiber

A sensitive method for determination of ephedrine derivatives using headspace solid-phase microextraction (SPME) with a novel fiber followed by capillary electrophoresis has been developed. The co-poly(butyl methacrylate/hydroxy-terminated silicone oil) (BMA/OH-TSO) was used as stationary phases with the aid of γ-methacryloxypropyltrimethoxysilane (KH-570) as bridge in SPME using sol-gel-coating method and cross-linking technology. It has high extraction efficiency for ephedrine derivatives in comparison with commercial poly(dimethylsiloxane) and poly(acrylate)-coated fiber. The coating exhibits good thermal and solvent stability as well as long lifetime. A simple and flexible device for desorption of analytes after headspace SPME was constructed. The effect of various experimental parameters for SPME (temperature, time, pH, ionic strength, desorption solvent, etc.) were discussed. Field amplified sample injection (FASI) was applied for on-line sample concentration and a sensitivity enhancement of two orders of magnitude was achieved. Linear ranges were found to be 20-5000 ng/ml. The detection limits for (1R,2S)-ephedrine, (1R,2R)-pseudoephedrine and (1S,2S)-pseudoephedrine were 3, 5 and 5 ng/ml, respectively. Relative standard deviation (n = 6) was found to be 4.96-7.57%. The method was successfully applied to the analysis of ephedrine derivatives in human urine.     

Evaluation of a new method for chemical coating of aluminum wire with molecularly imprinted polymer layer. Application for the fabrication of triazines selective solid-phase microextraction fiber

A new solid-phase microextraction (SPME) fiber is fabricated through ultra violet irradiation polymerization of ametryn-molecularly imprinted polymer on the surface of anodized-silylated aluminum wire. The prepared fiber is durable with very good chemical and thermal stability which can be coupled to GC and GC/MS. The effective parameters on the fabrication and application procedures such as spraying mode, ultra violet irradiation (polymerization) time, number of sprayings and polymerizations, pH and ionic strength of sample and extraction time were optimized. This fiber shows high selectivity with great extraction capacity toward triazines. SPME and GC analysis of ametryn, prometryn, terbutryn, atrazine, simazine, propazine and cyanazine using the fabricated fiber result in the detection limits of 9, 32, 27, 43, 51, 74 and 85 ng mL⁻¹, respectively. The reliability of the prepared fiber in real samples has been investigated and proved by using spiked tap water, rice, maize and onion samples.     

Selective determination of alkylmercury compounds in solid matrices after subcritical water extraction,followed by solid‐phase microextraction and GC–MS

A method for the extraction and determination of methylmercury (MeHg) in solid matrices is presented. Combining the advantages of two extraction techniques—subcritical water extraction (subWE) and solid‐phase microextraction (SPME)—selective separation of MeHg from soils is possible. The procedure is based on extraction with subcritical water without using organic solvents, followed by in situ aqueous‐phase derivatization with sodium tetraethylborate and headspace SPME with a silica fiber coated with poly(dimethylsiloxane). The optimization of the extraction parameters is described. The identification and quantification of the extracted alkylmercury compounds from spiked soil samples is performed by GC–MS after thermal desorption. Copyright © 2000 John Wiley & Sons, Ltd.     

Analysis of hexachlorocyclohexanes in aquatic samples by one-step microwave-assisted headspace controlled-temperature liquid-phase microextraction and gas chromatography with electron capture detection

A microwave-assisted headspace controlled-temperature liquid-phase microextraction (HS-CT-LPME) technique was applied for the one-step sample extraction of hexachlorocyclohexanes (HCHs) from aqueous samples with complicate matrices, followed by gas chromatographic (GC) analysis with electron capture detector (ECD). Microwave heating was applied to accelerate the evaporation of HCHs into the headspace and an external-cooling system was used to control the temperature in the sampling zone for HS-LPME. Parameters affecting extraction efficiency, such as LPME solvent, sampling position and temperature, microwave power and irradiation time (the same as sampling time), sample pH, and salt addition were thoroughly investigated. From experimental results, the following conditions were selected for the extraction of HCHs from 10-mL water sample (pH 2.0) by using 1-octanol as the LPME solvent, with sampling done at 38 °C for 6 min under 167 W of microwave irradiation. The detections were linear in the concentration of 0.1–10 μg/L for α-HCH and γ-HCH, and 1–100 μg/L for β-HCH and δ-HCH. Detection limits were 0.05, 0.4, 0.03 and 0.1 μg/L for α-, β-, γ- and δ-HCH, respectively. Environmental water samples were analyzed with recovery between 86.4% and 102.4% for farm-field water, and between 92.2% and 98.6% for river water. The proposed method proved to serve as a simple, rapid, sensitive, inexpensive, and eco-friendly procedure for the determination of HCHs in aqueous samples.     

Novel fiber coated with β-cyclodextrin derivatives used for headspace solid-phase microextraction of ephedrine and methamphetamine in human urine

Heptakis (2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) blending with hydroxy-terminated silicone oil (OH-TSO) coated solid-phase microextraction (SPME) fiber (DM-β-CD/OH-TSO) was first prepared with sol-gel technology and applied to headspace SPME for analysis of ephedrine (EP) and methamphetamine (MA) in human urine by gas chromatography (GC). By exploiting the advantages of the unique cavity-shaped cyclic molecular structure of CD and the superiorities of sol-gel coating technique, the novel fiber showed desirable extraction ability and operational stability. Influence of relevant experimental parameters (extraction time, extraction temperature, basicity, ionic strength, etc.) was systematically investigated. In the optimal conditions the proposed headspace SPME-GC method provided good linearity over four orders of magnitude with limit of detection (LOD) of ng/ml (0.33 ng/ml for EP, 0.60 ng/ml for MA). The recoveries of EP and MA in urine were 98.0% and 98.2%. And the relative standard deviations (R.S.D., n = 6) for EP and MA were 3.9% and 5.0%, respectively.     

Preparation of ionic liquid based solid-phase microextraction fiber and its application to forensic determination of methamphetamine and amphetamine in human urine

A new solid-phase microextraction (SPME) procedure using an ionic liquid (IL) has been developed. Reusable IL-based SPME fiber was prepared for the first time by fixing IL through cross-linkage of IL impregnated silicone elastomer on the surface of a fused silica fiber. 1-Ethoxyethyl-3-methylimidazloium bis(trifluoromethane) sulfonylimide ([EeMim][NTf₂]) ionic liquid was employed as a demonstration and the prepared fiber was applied to the forensic headspace determination of methamphetamine (MAP) and amphetamine (AP) in human urine samples. Important extraction parameters including the concentration of salt and base in sample matrix, extraction temperature and extraction time were investigated and optimized. Combined with gas chromatography/mass spectrometry (GC/MS) working in selected ion monitoring (SIM) mode, the new method showed good linearity in the range of 20–1500 μg L⁻¹, good repeatability (RSD < 7.5% for MAP, and <11.5% for AP, n = 6), and low detection limits (0.1 μg L⁻¹ for MAP and 0.5 μg L⁻¹ for AP). Feasibility of the method was evaluated by analyzing human urine samples. Although IL-based SPME is still at the beginning of its development stage, the results obtained by this work showed that it is a promising simple, fast and sensitive sample preparation method.     

Solid phase microextraction using new sol–gel hybrid polydimethylsiloxane-2-hydroxymethyl-18-crown-6-coated fiber for determination of organophosphorous pesticides

A new sol–gel hybrid coating, polydimethylsiloxane–2-hydroxymethyl-18-crown-6 (PDMS–2OHMe18C6) was prepared in-house for use in solid phase microextraction (SPME). The three compositions produced were assessed for its extraction efficiency towards three selected organophosphorus pesticides (OPPs) based on peak area extracted obtained from gas chromatography with electron capture detection. All three compositions showed superior extraction efficiencies compared to commercial 100 μm PDMS fiber. The composition showing best extraction performance was used to obtain optimized SPME conditions: 75 °C extraction temperature, 10 min extraction time, 120 rpm stirring rate, desorption time 5 min, desorption temperature 250 °C and 1.5% (w/v) of NaCl salt addition. The method detection limits (S/N = 3) of the OPPs with the new sol–gel hybrid material ranged from 4.5 to 4.8 ng g⁻¹, which is well below the maximum residue limit set by Codex Alimentarius Commission and European Commission. Percentage recovery of OPPs from strawberry, green apple and grape samples with the new hybrid sol–gel SPME material ranged from 65 to 125% with good precision of the method (%RSD) ranging from 0.3 to 7.4%.     

Preparation,characterization, and applications of a novel solid-phase microextraction fiber by sol-gel technology on the surface of stainless steel wire for determination of poly cyclic aromatic hydrocarbons in aquatic environmental samples

A novel solid-phase microextraction(SPME) fiber was prepared using sol–gel technology with ethoxylated nonylphenol as a fiber coating material. The fiber was employed to develop a headspace SPME–GC–MS method suitable for quantification of 13 polycyclic aromatic hydrocarbons (PAHs) in water samples. Surface characteristics of the fibers were inspected by energy dispersive X-ray (EDX) spectroscopy as well as by scanning electron microscopy (SEM). The SEM measurements showed the presence of highly porous nano-sized particles in the coating. Important parameters affecting the extraction efficiency such as extraction temperature and time, desorption conditions as well as ionic strength have been evaluated and optimized. In the next step, the validation of the new method have been performed, finding it to be specific in the trace analysis of PAHs, with the limit of detection (LOD) ranging from 0.01 to 0.5 μg L⁻¹ and the linear range from the respective LOD to 200 μg L⁻¹with RSD amounting to less than 8%. The thermal stability of the fibers was investigated as well and they were found to be durable at 280 °C for 345 min. Furthermore, the proposed method was successfully applied for quantification of PAHs in real water samples.     

Study of kinetic desorption rate constant in fish muscle and agarose gel model using solid phase microextraction coupled with liquid chromatography with tandem mass spectrometry

This study aims to use solid phase microextraction (SPME), a simple tool to investigate diffusion rate (time) constant of selected pharmaceuticals in gel and fish muscle by comparing desorption rate of diffusion of the drugs in both agarose gel prepared with phosphate-buffered saline (PBS; pH 7.4) and fish muscle. The gel concentration (agarose gel model) that could be used to simulate tissue matrix (fish muscle) for free diffusion of drugs under in vitro and in vivo conditions was determined to model mass transfer phenomena between fibre polymer coating and environmental matrix such that partition coefficients and desorption time constant (diffusion coefficient) can be determined. SPME procedure involves preloading the extraction phase (fibre) with the standards from spiked PBS for 1 h via direct extraction. Subsequently, the preloaded fibre is introduced to the sample such fish or agarose gel for specified time ranging from 0.5 to 60 h. Then, fibre is removed at specified time and desorbed in 100 μL of desorption solution (acetonitrile: water 1:1) for 90 min under agitation speed of 1000 rpm. The samples extract were immediately injected to the instrument and analysed using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS). The limit of detection of the method in gel and fish muscle was 0.01–0.07 ng mL⁻¹ and 0.07–0.34 ng g⁻¹, respectively, while the limit quantification was 0.10–0.20 ng mL⁻¹ in gel samples and 0.40–0.97 ng g⁻¹ in fish sample. The reproducibility of the method was good (5–15% RSD). The results suggest that kinetics of desorption of the compounds in fish tissue and different viscosity of gel can be determined using desorption time constant. In this study, desorption time constant which is directly related to desorption rate (diffusion kinetics) of selected drugs from the fibre to the gel matrix is faster as the viscosity of the gel matrix reduces from 2% (w/v) to 0.8% (w/v). As the concentration of gel reduces, viscosity of the gel will be reduced therefore allowing faster diffusion which invariably affect desorption time constant. Also, desorption time constant of model drugs in the fish muscle and 0.8–0.9% (w/v) gel model are similar based on free diffusion of studied compounds. In addition, in vitro and in vivo desorption time constant comparison shows that desorption time constant in an in vivo system (live fish muscle) is generally higher than an in vitro system (dead fish muscle) except for sertraline and nordiazepam. This study demonstrates SPME as a simple investigative tool to understand kinetics of desorption in an in vivo system with a goal to measure desorption rate of pharmaceuticals in fish.