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.     

Development and optimization of a method for the analysis of phenols and chlorophenols from aqueous samples by gas chromatography-mass spectrometry, after solid-phase extraction and trimethylsilylation

A 3-step analytical procedure was developed and optimized for the simultaneous determination of 6 phenols (phenol, o-, m-, p-cresol, catechol and resorcinol) and 19 chlorophenols (all mono-, di-, tri-, and tetrachlorophenol isomers and pentachlorophenol) from environmental water samples. The analytical scheme consists of (1) solid-phase extraction (SPE) carried out on hypercrosslinked styrene-divinylbenzene (Isolute ENV+) cartridge; (2) derivatization with trimethylsilyl-N,N-dimethylcarbamate (TMSDMC); (3) analysis of the derivatives with capillary gas chromatography-mass spectrometry, in the selective ion monitoring mode. Ethyl acetate, ethyl acetate/acetic acid (5 v/v%) mixture, dichloromethane and acetonitrile were compared as to their ability to elute the phenols and chlorophenols from the ENV + sorbent in the smallest solvent volume possible. The optimized extraction step uses a minimal amount of organic solvent (4 mL ethyl acetate). Derivatization of the phenols and chlorophenols with TMSDMC was studied with respect to conversion, reagent excess, medium, temperature and the stability of the trimethylsilyl derivatives. If the reagent is applied in sufficient excess, the reaction takes place instantaneously at room temperature, and the derivatives remain stable for 24 h, making the procedure simple, fast and convenient. The overall method gave detection limits of 0.05-100 ng/L for all compounds except resorcinol which could not be retained on the SPE cartridge. The complete optimized analytical scheme was applied to ground water and river water samples collected in Hungary.     

Isotope dilution gas chromatography with mass spectrometry for the analysis of 4‐octyl phenol, 4‐nonylphenol,and bisphenol A in vegetable oils

By the combination of solid‐phase extraction as well as isotope dilution gas chromatography with mass spectrometry, a sensitive and reliable method for the determination of endocrine‐disrupting chemicals including bisphenol A, 4‐octylphenol, and 4‐nonylphenol in vegetable oils was established. The application of a silica/N‐(n‐propyl)ethylenediamine mixed solid‐phase extraction cartridge achieved relatively low matrix effects for bisphenol A, 4‐octylphenol, and 4‐nonylphenol in vegetable oils. Experiments were designed to evaluate the effects of derivatization, and the extraction parameters were optimized. The estimated limits of detection and quantification for bisphenol A, 4‐octylphenol, and 4‐nonylphenol were 0.83 and 2.5 μg/kg, respectively. In a spiked experiment in vegetable oils, the recovery of the added bisphenol A was 97.5–110.3%, recovery of the added 4‐octylphenol was 64.4–87.4%, and that of 4‐nonylphenol was 68.2–89.3%. This sensitive method was then applied to real vegetable oil samples from Zhejiang Province of China, and none of the target compounds were detected.     

Focused ultrasound solid-liquid extraction and selective pressurised liquid extraction to determine bisphenol A and alkylphenols in sewage sludge by gas chromatography-mass spectrometry

A new method for determining endocrine disrupter compounds (EDCs) in sewage sludge is described in this paper. EDCs studied were bisphenol A (BPA) and alkylphenols (APs). In order to obtain a fast and simple method, selective pressurised liquid extraction (SPLE) and focused ultrasound solid-liquid extraction (FUSLE) were tested. Best results for SPLE were obtained using Florisil as clean-up sorbent and dichloromethane as extraction solvent, while temperature was the only significant variable. Analyte extraction by SPLE was completed in only one extraction cycle of 1 min at 130 °C. FUSLE was carried out in one step of 20 s at 75% power (0.5 cycles) and with 8 mL of ethyl acetate. Although the optimised FUSLE process was faster, simpler and cheaper, SPLE provided higher recovery values (ranging from 81 to 105%) and therefore SPLE-based method was selected and validated. The SPLE and GC-MS method showed an LOD of 10.7 ng/g for BPA and LODs between 1.2 and 41.6 ng/g for APs. Relative standard deviation values lower than 6% were obtained for all analytes. As a result, an efficient, fast and simple method based on SPLE and GC-MS for the determination of BPA and APs in sewage sludge is proposed.     

Simultaneous analysis of chlorophenols, alkylphenols, nitrophenols and cresols in wastewater effluents, using solid phase extraction and further determination by gas chromatography-tandem mass spectrometry

An analytical methodology has been developed for the simultaneous extraction of 13 phenolic compounds, including chlorophenols (CPs), nitrophenols (NTPs), cresols and alkylphenols (APs) in different types of wastewater (WW) effluents. A solid-phase extraction (SPE) method has been optimized prior to the determination by gas chromatography coupled to triple quadrupole tandem mass spectrometry (GC-QqQ-MS/MS). Due to the complexity of the matrix, a comparison study of matrix-matched-calibration (MMC) and standard addition calibration (SAC) was carried out for quantification purposes. The optimized procedure was validated using the SAC approach since it provided the most adequate quantification results (in terms of recovery and precision values). Recoveries were in the range 60-135% (0.5 μg L⁻¹), 70-115% (1 μg L⁻¹), and 78-120% (5 μg L⁻¹), with precision values (expressed as relative standard deviation, RSD) ≤30% (except for 2-nitrophenol) involving intra-day and inter-day precision studies. Limits of detection (LODs) and quantification (LOQs) were also evaluated, and LOQs ranged from 0.03 μg L⁻¹ to 2.5 μg L⁻¹. The proposed method was applied to the analysis of 8 real WW effluent samples, finding some phenolic compounds (e.g. 2-chlorophenol, 2,4,6-trichlorophenol and 4-tert-octylphenol) at concentrations higher than the established LOQs.     

Optimization of some experimental parameters in the electro membrane extraction of chlorophenols from seawater

An electro membrane extraction (EME) methodology was utilized to study the isolation of some environmentally important pollutants, such as chlorophenols, from aquatic media based upon the electrokinetic migration process. The analytes were transported by application of an electrical potential difference over a supported liquid membrane (SLM). A driving force of 10 V was applied to extract the analytes through 1-octanol, used as the SLM, into a strongly alkaline solution. The alkaline acceptor solution was subsequently analyzed by high performance liquid chromatography-ultraviolet (HPLC-UV) detection. The parameters influencing electromigration, including volumes and pH of the donor and acceptor phases, the organic solvent used as the SLM, and the applied voltage and its duration, were investigated to find the most suitable extraction conditions. Since the developed method showed a rather high degree of selectivity towards pentachlorophenol (PCP), validation of the method was performed using this compound. An enrichment factor of 23 along with acceptable sample clean-up was obtained for PCP. The calibration curve showed linearity in the range of 0.5–1000 ng/mL with a coefficient of estimation corresponding to 0.999. Limits of detection and quantification, based on signal-to-noise ratios of 3 and 10, were 0.1 and 0.4 ng/mL, respectively. The relative standard deviation of the analysis at a PCP concentration of 0.5 ng/mL was found to be 6.8% (n = 6). The method was also applied to the extraction of this contaminant from seawater and an acceptable relative recovery of 74% was achieved at a concentration level of 1.0 ng/mL.     

Direct thermal extraction and gas chromatographic-mass spectrometric determination of volatile compounds of extra-virgin olive oils

The instrumental performances of a Thermo Desorption-Cooled Injection System coupled with a gas chromatography-mass spectrometer (GC-MS) were improved by a Plackett-Burman experimental design for the direct thermal extraction of volatile compounds from extra-virgin olive oils. The obtained experimental conditions were applied to the analysis of samples from West Liguria (cv. Taggiasca > or = 90%) and Spain (cv. Arbequina), which shared such similar sensorial features that Taste Panel did not distinguish them. Principal component analysis (PCA) was then applied to the experimental data. Three linear combinations of the amounts of the lipoxygenase oxidation products proved to be decisive and sufficient in the differentiation of the two groups of samples.     

Magnetic sorbent modified by humate for the extraction of alkylphenols,bisphenol A and estradiol

A sorbent has been synthesized from magnetite nanoparticles and a humic acid extracted from sapropel. The sizes of the sorbent nanoparticles and their magnetic core are 218–302 and 14 nm, respectively, the saturation magnetization is 35 emu g^–1. The sorbent provides 87–95% recoveries of alkylphenols, bisphenol A and estradiol with enrichment factors of 1550–1815.     

Automated high-capacity sorption probe for extraction of organic compounds in aqueous samples followed by gas chromatographic analysis

An automated high-capacity sorption device for GC analysis of ultra trace components has been developed. The scope of the presented technique was to combine the simplicity of solid-phase microextraction (SPME) with the high extraction efficiency of the stir bar sorptive extraction technology. Sorptive extractions of water samples were performed using polydimethylsiloxane (PDMS) rubber tubing (120 microl) mounted onto a glass rod. The sampling procedure was carried out by a robotic autoinjector. Since the setup is fully automated, unattended and precise time-controlled extraction of samples is possible and makes quantitation with non-equilibrium extractions feasible. The sorption probes are easy to exchange, which facilitates off-line/in-field sampling. The system was evaluated with a test mixture of 44 environmentally hazardous compounds. Detection limits were found to be in the sub-ppt region. The performance of the system was demonstrated with the analysis of polycyclic aromatic hydrocarbons in urban snow.     

Development and characterization of an immunoaffinity monolith for selective on-line extraction of bisphenol A from environmental water samples

Matrix interference and contamination from analytical procedures are two major issues in the detection of trace level of bisphenol A (BPA) in environmental water. In this paper, we report a highly selective and efficient method for on-line extraction of BPA from water samples followed by quantification with liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI/MS/MS). Poly(ethylene dimethacrylate-glycidyl methacrylate) monolith was synthesized in 50 mm × 4.6 mm i.d. stainless steel cartridges and the epoxy-groups on the surface of the monolith were hydrolyzed and oxidized to aldehyde functions. Antibodies against BPA were covalently immobilized onto the monolithic column via Schiff base reaction. The optimum application buffer and elution buffer were found to be pH 5.5 phosphate buffered saline (PBS) and methanol–water (70:30, v/v), respectively. The obtained immunoaffinity monolithic columns were on-line coupled to LC–MS/MS using column-switching valves and the system was applied to analyze BPA in real environmental water samples. The method achieved a detection limit of 0.3 ng L⁻¹ using a sample volume of 100 mL. The linear calibration range was 1.0–160 ng L⁻¹. Samples including tap water, lake water and effluent from municipal sewage treatment plant were all measured with satisfactory results.     

Application of SPME to the determination of alkylphenols and bisphenol A in cyanobacteria culture media

In order to survey the influence of estrogenic compounds on cyanobacteria, solid-phase microextraction (SPME) with a carbowax-divinylbenzene fibre was used for the determination of tert-octylphenol (tert-OP), n-nonylphenol (n-NP), technical nonylphenol (tech-NP) and bisphenol A (BPA) in cyanobacteria culture media by gas chromatography with flame ionization detection. Determinations were carried out without derivatization in deionized water and filtered culture media. A comparison between f2 and Fraquil culture media was performed, which showed that only f2 allowed quantitative recoveries. Headspace SPME with salting out, requiring only 10 mL of sample, was suitable for tert-OP, n-NP, and tech-NP determination with limits of detection (LOD) of <0.05 μg L⁻¹. For BPA, direct immersion SPME could provide a LOD of 1 μg L⁻¹. Automated sampling allowed reproducible extraction. No exudate substances overlapped with the studied compounds during the chromatographic separation and no matrix effects were observed. Ecotoxicity tests can be performed by single spiking of tert-OP and tech-NP and multiple spiking of n-NP due to its lower stability.     

Simultaneous determination of bisphenol A, triclosan, and tetrabromobisphenol A in human serum using solid-phase extraction and gas chromatography-electron capture negative-ionization mass spectrometry

This study aimed at optimizing and validating a sensitive method for simultaneous determination of bisphenol A (BPA), triclosan (TCS), and tetrabromobisphenol A (TBBPA) in human serum using solid-phase extraction (SPE) and gas chromatography coupled to electron-capture negative-ionization mass spectrometry (GC-ECNI/MS). Sample preparation involved denaturation of serum proteins with formic acid followed by SPE on an Oasis HLB cartridge. Fractionation was performed on Florisil from which the phenolic compounds were eluted with methanol-dichloromethane (DCM) (5:1, v/v). The phenolic fraction was further derivatized with pentafluoropropionic acid anhydride (30 min at 70 degrees C). Further liquid-liquid partitioning using hexane-DCM (4:1, v/v) and K(2)CO(3) 3% aqueous solution was used to eliminate excess reagent and acidic by-products formed during derivatization. The cleaned extract was injected into a GC-ECNI/MS system operated in selected ion monitoring mode. For thorough method validation, each step of the procedure was rigorously optimized. The method limits of quantitation for BPA, TCS, and TBBPA were 0.28 ng mL(-1), 0.09 ng mL(-1) and 0.05 ng mL(-1), respectively. Furthermore, the method was applied to 21 Belgian human serum samples. The median concentrations obtained for BPA (0.71 ng mL(-1)) and TCS (0.52 ng mL(-1)) in Belgian human serum samples were similar to previously reported data for human fluids. Slightly higher levels of TBBPA (0.08 ng mL(-1)) were found in Belgium samples compared to Norwegian serum.     

Molecularly imprinted layer-coated silica nanoparticles for selective solid-phase extraction of bisphenol A from chemical cleansing and cosmetics samples

Highly selective molecularly imprinted layer-coated silica nanoparticles for bisphenol A (BPA) were synthesized by molecular imprinting technique with a sol-gel process on the supporter of silica nanoparticles. The BPA-imprinted silica nanoparticles were characterized by fourier transform infrared spectrometer, transmission electron microscope, dynamic adsorption and static adsorption tests. The equilibrium association constant, K_a, and the apparent maximum number of binding sites, Q_max, were estimated to be 1.25 × 10⁵ mL μmol⁻¹ and 16.4 μmol g⁻¹, respectively. The BPA-imprinted silica nanoparticles solid-phase extraction (SPE) column had higher selectivity for BPA than the commercial C18-SPE column. The results of the study indicated that the prepared BPA-imprinted silica nanoparticles exhibited high adsorption capacity and selectivity, and offered a fast kinetics for the rebinding of BPA. The BPA-imprinted silica nanoparticles were successfully used in SPE to selectively enrich and determine BPA from shampoo, bath lotion and cosmetic cream samples.     

Application of multivariate analysis to the screening of molecularly imprinted polymers for bisphenol A

A key issue in the synthesis of molecularly imprinted polymers (MIPs) is the identification and optimisation of the main factors that affect the material structure and its molecular recognition properties. This paper describes the application of an experimental design and multivariate analysis method for the synthesis of bisphenol A (BPA)-selective MIPs. Six factors with a large impact on the MIP synthesis and its analytical performance have been optimised: the amount of template, the type and the percentage of functional and cross-linking monomers, the polymerisation method (i.e. thermal or UV initiation) and the porogenic solvent. The polymers have been prepared in small-scale (mini-MIPs) and, after careful removal of the template, their BPA rebinding capacity has been evaluated and related to the MIP composition. Among the two functional monomers tested, namely 4-vinylpyridine (4-vpy) and methacrylic acid (MAA), the former rendered the best selectivity for BPA analysis. The partial least squares (PLS) models revealed that the photoinitiated polymers with a 1:1 ratio of 4-vinylpyridine to cross-linker (EDMA or TRIM) yield the highest specific binding. Such procedure is time and cost effective and can be used as a general tool in the preparation of MIPs for different analytes.     

Development of a molecularly imprinted polymer for selective extraction of bisphenol A in water samples

A cross‐linked methacrylate molecularly imprinted polymer (poly‐4‐vinylpyridine‐co‐trimethylolpropane‐trimethacrylate) selective for bisphenol A (BPA) was synthesized, using a fluorinated BPA derivative (4,4′‐(hexafluoroisopropylidene)‐diphenol) as a mimic template, and applied to the analysis of real‐world samples of process and potable waters. The molecularly imprinted polymer also showed a high affinity and selectivity for 17‐β‐estradiol and ethynylestradiol. A method to analyze BPA, 17‐β‐estradiol, and ethynylestradiol at ultratrace levels was thus developed from a screening procedure to monitor endocrine‐disrupting chemicals in water samples. The method consists of the BPA‐selective cleanup by molecularly imprinted SPE using cartridges packed with the polymer developed, its recovery by stir bar sorptive extraction after ad hoc derivatization to obtain the corresponding BPA‐acetate, and its analysis by GC‐time window‐SIM‐MS after online thermal desorption. The method showed good linearity in the working range (R²=0.9969), high repeatability (RSD% <10.1), recoveries always above 90%, and very low LOD (10 pg/L) and LOQ (1 ng/L) and can easily be extended to the determination of 17‐β‐estradiol and ethynylestradiol ultratraces. The method's effectiveness was evaluated by analyzing the real‐world water samples; it enabled preconcentration and detection of BPA at ultratrace levels.     

Continuous solid-phase extraction and preconcentration of bisphenol A in aqueous samples using molecularly imprinted columns

A bisphenol A (BPA) molecularly imprinted polymer, the composition of which was optimised using a chemometric approach, has been applied to the selective preconcentration of the template from aqueous samples. The selectivity of the polymer toward BPA and related compounds was evaluated chromatographically. The BPA-imprinted polymer was packed in a column and used for continuous on-column solid-phase extraction (MISPE) of aqueous samples followed by subsequent analysis by HPLC with fluorescence detection of the eluted fractions. The composition of the washing solvent applied in the MISPE procedure was optimised to favour the specific interactions of the MIP with BPA and to remove the non-selectively bound matrix components. The MISPE method has proven to be effective for selective preconcentration of BPA in aqueous samples (recoveries >84% obtained in the eluate for 10–100 mL sample volumes) enabling detection and quantification limits of 1.0 and 3.3 ng mL^–1, respectively (based on 25 mL sample size). Analytical recoveries were between 92 and 101% for river water samples spiked with known amounts of BPA (30, 60, and 80 ng mL^–1); relative standard deviations (RSD) were lower than 5.0%.     

Gas purge microsyringe extraction for quantitative direct gas chromatographic-mass spectrometric analysis of volatile and semivolatile chemicals

Sample pretreatment before chromatographic analysis is the most time consuming and error prone part of analytical procedures, yet it is a key factor in the final success of the analysis. A quantitative and fast liquid phase microextraction technique termed as gas purge microsyringe extraction (GP-MSE) has been developed for simultaneous direct gas chromatography-mass spectrometry (GC-MS) analysis of volatile and semivolatile chemicals without cleanup process. Use of a gas flowing system, temperature control and a conventional microsyringe greatly increased the surface area of the liquid phase micro solvent, and led to quantitative recoveries of both volatile and semivolatile chemicals within short extraction time of only 2 min. Recoveries of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and alkylphenols (APs) determined were 85-107%, and reproducibility was between 2.8% and 8.5%. In particular, the technique shows high sensitivity for semivolatile chemicals which is difficult to achieve in other sample pretreatment techniques such as headspace-liquid phase microextraction. The variables affecting extraction efficiency such as gas flow rate, extraction time, extracting solvent type, temperature of sample and extracting solvent were investigated. Finally, the technique was evaluated to determine PAHs, APs and OCPs from plant and soil samples. The experimental results demonstrated that the technique is economic, sensitive to both volatile and semivolatile chemicals, is fast, simple to operate, and allows quantitative extraction. On-site monitoring of volatile and semivolatile chemicals is now possible using this technique due to the simplification and speed of sample treatment.     

Ultrasound-assisted extraction of nitropolycyclic aromatic hydrocarbons from soil prior to gas chromatography-mass detection

Continuous ultrasound-assisted extraction of nitropolycyclic aromatic hydrocarbons from soil prior to their individual separation and determination by gas chromatography (GC) with MS-MS detection is presented here. A multivariate optimisation of the variables affecting the continuous extraction step (namely, probe position, ultrasound radiation amplitude, percentage of duty cycle of ultrasonic exposure, sonication time, total extractant volume, extractant flow rate and temperature of the water-bath in which the extraction cell was placed) was performed. The method was compared with the reference EPA method 3540 using natural contaminated soils. Similar efficiencies were obtained but with a drastic reduction of both the extraction time (10 min versus 24 h) and the extractant volume (less than 10 ml versus 100 ml) by the proposed method. Detection limits of low picogram were obtained, with repeatability and reproducibility between 4.21-5.70 and 5.20-7.23%, respectively.     

Optimisation of stir bar sorptive extraction for the analysis of volatile phenols in wines

An easy, fast and reliable analytical method is proposed for the determination of the concentration of volatile phenols (ethyl- and vinylphenols) in wines. The novel stir bar sorptive extraction (SBSE) technique is employed, following a simple and fast procedure that allows 15 samples to be extracted simultaneously using very small sample volume. Extracts are desorbed in a thermodesorption system (TDS) coupled on-line to a gas chromatograph-mass spectrometry system. The SBSE offers better recovery and linear regression coefficient (r2) for the four volatile phenols than solid-phase extraction (SPE). The mass spectrometric detection in selected ion monitoring mode contributes to the lower detection limit and good sensibility obtained with this method.     

Simplified procedures for the analysis of polycyclic aromatic hydrocarbons in water, sediments and mussels

We describe in this paper simple and robust analytical protocols to determine the 16 polycyclic aromatic hydrocarbons (PAHs) of the US Environmental Protection Agency priority list in water, sediment and mussels. For water samples, eight different solid-phase extraction (SPE) sorbents have been compared and among them, C18 provided highest recoveries and limits of detection of 0.3-15 ng/L. For lyophilized sediments, Soxhlet and ultrasonic extraction were compared, and the last one permitted to recover all analytes with highest repetitivity and was validated by analysing a certified reference material. Finally, the analysis of mussels was undertaken using Soxhlet, ultrasonic and pressurized liquid extraction (PLE) and the performance of several clean-up steps are compared. Whereas for the former two, incomplete recovery or losses of some analytes were evidenced, PLE permitted a more efficient extraction and although alkaline digestion was necessary to remove coextracted compounds, the method gave acceptable recoveries and limits of detection of 0.5-7.7 microg/kg dry mass, as for sediments. In all cases, analysis was performed by gas chromatography coupled to mass spectrometry and internal standard quantification was performed using five deuterated PAHs. Each method performance is discussed for the three matrices analysed and the paper reports advantages and disadvantages of each for their routine application in monitoring programs.