Sample preparation of sewage sludge and soil samples for the determination of polycyclic aromatic hydrocarbons based on one-pot microwave-assisted saponification and extraction

A microwave-assisted sample preparation (MASP) procedure was developed for the analysis of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge and soil samples. The procedure involved the simultaneous microwave-assisted extraction of PAHs with n-hexane and the hydrolysis of samples with methanolic potassium hydroxide. Because of the complex nature of the samples, the extracts were submitted to further cleaning with silica and Florisil solid-phase extraction cartridges connected in series. Naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene, were considered in the study. Quantification limits obtained for all of these compounds (between 0.4 and 14.8 μg kg⁻¹ dry mass) were well below of the limits recommended in the USA and EU. Overall recovery values ranged from 60 to 100%, with most losses being due to evaporation in the solvent exchange stages of the procedure, although excellent extraction recoveries were obtained. Validation of the accuracy was carried out with BCR-088 (sewage sludge) and BCR-524 (contaminated industrial soil) reference materials.     

Comparison of accelerated solvent extraction with microwave-assisted extraction and Soxhlet for the extraction of chlorinated biphenyls in soil samples

The extraction and determination of chlorinated biphenyls (CBs) in soils and solid wastes is an ongoing subject of study. This is an overview article that compares the microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) techniques. The extraction of CBs by ASE has been optimised taking into account the variation of pressure, temperature and extraction time by means of experimental design and the Simplex approach. The recoveries obtained under the optimum conditions are compared and discussed with those obtained from MAE and Soxhlet extractions.     

Solvent-free microwave-assisted extraction of fluoroquinolones from soil and liquid chromatography-fluorescence determination

Presented hereafter is a novel method entailing solvent free microwave-assisted extraction (MAE) and HPLC equipped with Fluorimetric Detector (HPLC-FD) for the simultaneous determination at μgkg(-1) concentration of eight fluoroquinolone antibiotics (FQs) (Ciprofloxacin, Danofloxacin, Enrofloxacin, Flerofloxacin, Levofloxacin, Marbofloxacin, Norfloxacin and Orbifloxacin) in agricultural soils. The extraction was quantitatively performed, in a single step, by using an aqueous solution containing Mg(II) as complexing agent, thus avoiding consumption of organic solvents. The optimal MAE conditions have been established through a chemometric approach by considering temperature, irradiation time and matrix moisture or solvent, as the most important recognized variables affecting the extraction yield. Satisfying recoveries (69-110%, spikes 0.03-0.5mgkg(-1)) were gained with a single MAE cycle of 20min, at 80°C in 20% (w/v) Mg(NO(3))(2) solution as leaching agent. MAE-SPE recoveries at 10μgkg(-1), concentration near method quantification limits (MQLs), were in the range 60-85%. Good repeatability and within-lab reproducibility were observed (both in the range 1-16%). The applicability of the method to real samples was assessed on natural contaminated soils. Compared to ultrasonic-assisted extraction (UAE), MAE was shown to be highly competitive in terms of extraction efficacy and analysis speed.     

Optimisation of microwave-assisted extraction for the determination of nonylphenols and phthalate esters in sediment samples and comparison with pressurised solvent extraction

Microwave-assisted extraction (MAE) of nonylphenols (NP), nonylphenol mono- and diethoxylates (NP1EO and NP2EO, respectively) and phthalate esters was optimised using an experimental design approach. A D-optimal mixture design was used to optimise the pressure inside the extraction vessel (110-207 kPa), the extraction time (5-25 min) and the extraction solvent (methanol, acetone or n-hexane) or the solvent mixture for the microwave-assisted extraction. Percentage of microwave power (80%) and solvent volume (15 ml) were fixed in all the experiments. As a consequence, the optimum extraction of these compounds was carried out at an intermediate pressure (159 kPa) with pure methanol and during 15 min. Moreover, solid phase extraction was also optimised for the clean-up of the extracts and C-18, LiChrolut^® and Oasis^® cartridges were studied in order to obtain the best recoveries of the compounds of interest. The highest recoveries were obtained with LiChrolut^® cartridges after the elution with ethyl acetate. The cleaned extracts were analysed in a gas chromatograph with mass spectrometric detection and in a liquid chromatograph with diode array and fluorescence detection (HPLC-DAD-UV-FLD). The same sediment was also extracted twice in order to check that an exhaustive extraction of the analytes had occurred. Finally, the optimised extraction method was compared with pressurised solvent extraction (PSE), using an estuarine sediment sample.     

Extraction of polycyclic aromatic hydrocarbons and organochlorine pesticides from soils: a comparison between Soxhlet extraction, microwave-assisted extraction and accelerated solvent extraction techniques

The methods of simultaneous extraction of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) from soils using Soxhlet extraction, microwave-assisted extraction (MAE) and accelerated solvent extraction (ASE) were established, and the extraction efficiencies using the three methods were systemically compared from procedural blank, limits of detection and quantification, method recovery and reproducibility, method chromatogram and other factors. In addition, soils with different total organic carbon contents were used to test the extraction efficiencies of the three methods. The results showed that the values obtained in this study were comparable with the values reported by other studies. In some respects such as method recovery and reproducibility, there were no significant differences among the three methods for the extraction of PAHs and OCPs. In some respects such as procedural blank and limits of detection and quantification, there were significant differences among the three methods. Overall, ASE had the best extraction efficiency compared to MAE and Soxhlet extraction, and the extraction efficiencies of MAE and Soxhlet extraction were comparable to each other depending on the property such as TOC content of the studied soil. Considering other factors such as solvent consumption and extraction time, ASE and MAE are preferable to Soxhlet extraction.     

Monodisperse silica nanoparticles coated with gold nanoparticles as a sorbent for the extraction of phenol and dihydroxybenzenes from water samples based on dispersive micro‐solid‐phase extraction: Response surface methodology

A selective and sensitive method was developed based on dispersive micro‐solid‐phase extraction for the extraction of hydroquinone, resorcinol, pyrocatechol and phenol from water samples prior to high‐performance liquid chromatography with UV detection. SiO₂, SiO₂@MPTES, and SiO₂@MPTES@Au nanoparticles (MPTES = 3‐mercaptopropyltriethoxysilane) were synthesized and characterized by scanning electronic microscopy, thermogravimetric analysis, differential thermogravimetric analysis, and infrared spectroscopy. Variables such as the amount of sorbent (mg), pH and ionic strength of sample the solution, the volume of eluent solvent (μL), vortex and ultrasonic times (min) were investigated by Plackett–Burman design. The significant variables optimized by a Box–Behnken design were combined by a desirability function. Under optimized conditions, the calibration graphs of phenol and dihydroxybenzenes were linear in a concentration range of 1–500 μg/L, and with correlation coefficients more than 0.995. The limits of detection for hydroquinone, resorcinol, pyrocatechol, and phenol were 0.54, 0.58, 0.46, and 1.24 μg/L, and the limits of quantification were 1.81, 1.93, 1.54, and 4.23 μg/L, respectively. This procedure was successfully employed to determine target analytes in spiked water samples; the relative mean recoveries ranged from 93.5 to 98.9%.     

An absorbing microwave micro-solid-phase extraction device used in non-polar solvent microwave-assisted extraction for the determination of organophosphorus pesticides

A single-step extraction-cleanup method, including microwave-assisted extraction (MAE) and micro-solid-phase extraction (μ-SPE), was developed for the extraction of ten organophosphorus pesticides in vegetable and fruit samples. Without adding any polar solvent, only one kind of non-polar solvent (hexane) was used as extraction solvent in the whole extraction step. Absorbing microwave μ-SPE device, was prepared by packing activated carbon with microporous polypropylene membrane envelope, and used as not only the sorbent in μ-SPE, but also the microwave absorption medium. Some experimental parameters effecting on extraction efficiency was investigated and optimized. 1.0 g of sample, 8 mL of hexane and three absorbing microwave μ-SPE devices were added in the microwave extraction vessel, the extraction was carried out under 400 W irradiation power at 60 °C for 10 min. The extracts obtained by MAE-μ-SPE were directly analyzed by GC–MS without any clean-up process. The recoveries were in the range of 93.5–104.6%, and the relative standard deviations were lower than 8.7%.     

Response surface methodology toward the optimization of high-energy carotenoid extraction from Aristeus antennatus shrimp

High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.     

Evaluation of Soxhlet extraction, accelerated solvent extraction and microwave-assisted extraction for the determination of polychlorinated biphenyls and polybrominated diphenyl ethers in soil and fish samples

Three commonly applied extraction techniques for persistent organic chemicals, Soxhlet extraction (SE), accelerated solvent extraction (ASE) and microwave-assisted extraction (MAE), were applied on soil and fish samples in order to evaluate their performances. For both PCBs and PBDEs, the two more recent developed techniques (ASE and MAE) were in general capable of producing comparable extraction results as the classical SE, and even higher extraction recoveries were obtained for some PCB congeners with large octanol-water partitioning coefficients (K_ow). This relatively uniform extraction results from ASE and MAE indicated that elevated temperature and pressure are favorable to the efficient extraction of PCBs from the solid matrices. For PBDEs, difference between the results from MAE and ASE (or SE) suggests that the MAE extraction condition needs to be carefully optimized according to the characteristics of the matrix and analyte to avoid degradation of higher brominated BDE congeners and improve the extraction yields.     

A new molecularly imprinted polymer for selective extraction of cotinine from urine samples by solid-phase extraction

Cotinine, the main metabolite of nicotine in human body, is widely used as a biomarker for assessment of direct or passive exposure to tobacco smoke. A method for molecularly imprinted solid-phase extraction (MISPE) of cotinine from human urine has been investigated. The molecularly imprinted polymer (MIP) with good selectivity and affinity for cotinine was synthesized using cotinine as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the cross-linker. The imprinted polymer was evaluated for use as a SPE sorbent, in tests with aqueous standards, by comparing recovery data obtained using the imprinted form of the polymer and a non-imprinted form (NIP). Extraction from the aqueous solutions resulted in more than 80% recovery. A range of linearity for cotinine between 0.05 and 5 μg mL⁻¹ was obtained by loading 1 mL blank urine samples spiked with cotinine at different concentrations in acetate buffer of pH 9.0, and by using double basic washing and acidic elution. The intra-day coefficient of variation (CV) was below 7% and inter-day CV was below 10%. This investigation has provided a reliable MISPE–HPLC method for determination of cotinine in human urine from both active smokers and passive smokers. Figure     

Extraction of phenolic compounds from water samples by dispersive micro‐solid‐phase extraction

In this article, the use of magnetically separable sorbent polyaniline/silica‐coated nickel nanoparticles is evaluated under a dispersive micro‐solid‐phase extraction approach for the extraction of phenolic compounds from water samples. The sorbent was prepared by in situ chemical polymerization of aniline on the surface of silica‐modified nickel nanoparticles and was characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X‐ray powder diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectrometry, and vibrating sample magnetometry. Effective variables such as amount of sorbent (milligrams), pH and ionic strength of sample solution, volume of eluent solvent (microliters), vortex, and ultrasonic times (minutes) were investigated by fractional factorial design. The significant variables optimized by a Box–Behnken design were combined by a desirability function. Under the optimized conditions, the calibration graphs of analytes were linear in a concentration range of 0.02–100 μg/mL, and with correlation coefficients more than 0.999. The limits of detection and quantification were in the ranges of 10–23 and 33–77 μg/L, respectively. This procedure was successfully employed in the determination of target analytes in spiked water samples; the relative mean recoveries ranged from 96 to 105%.     

Application of multivariate optimization in the development of an ultrasound-assisted extraction procedure for multielemental determination in bean seeds samples using ICP OES

In this paper, multivariate optimization was applied for the development of an ultrasound-assisted multielemental extraction procedure for analysis of bean samples by inductively coupled plasma optical emission spectrometry. For this procedure, powdered samples were treated with an acid mixture and submitted to ultrasound energy for extracting the target elements (Ba, Ca, Cu, Fe, K, Mg, Mn, Sr and Zn). Centroid simplex mixture design was used for optimize the acid proportions (nitric, acetic and chloride acid) and Box Behnken design was applied for optimize the process variables (particle size, final concentration of extracting solution and sonication time) after mixture optimization. Iron had not presented quantitative extractions and it was excluded from final samples analysis. The developed method presents the follow limits of quantification in μg g^{− 1}: Ba (0.90); Ca (5.2); Cu (4.0); K (0.90); Mg (1.4); Mn (0.22); Sr (0.25) and Zn (4.0). Accuracy was accessed by comparison of determined concentration with the values obtained by the microwave digestion procedure. The proposed method was applied toward the determination of elemental composition in bean samples collected in the country zone from Jequié city located on the Bahia State, Brazil. The trace elements content ranged from 0.21 to 3.04, 3.84 to 10.8, 0.60 to 5.23, 31.0 to 46.5 and 10.8 to 19.6 μg g^{− 1} Ba, Cu, Sr, Zn, Mn, respectively. The major elements content ranged from 0.0418 to 0.0877, 0.109 to 0.153 and 1.30 to 1.56% (w/w) Ca, Mg and K, respectively.     

Microwave-assisted extraction of trichloroethylene from clay samples

A new method for volatile organic compounds (VOCs) extraction from low-permeability media, such as clay, has been developed and tested using trichloroethylene (TCE) as a model compound. The method is based on microwave-assisted extraction (MAE), which uses microwave energy to heat the extracting solvent and the sample. MAE allows the extraction process to be carried out at elevated temperatures and pressures, which dramatically reduces the time required to complete the process. A custom-made PTFE vessel was used for extraction investigations. TCE analysis was performed using gas chromatography with electron capture detection (GC-ECD). Three different solvents were tested: methanol, 1?:?1 hexane?:?acetone mixture, and 10?:?1 hexane?:?acetone mixture. A comparison of TCE recoveries from clay samples using the new method and the standard methanol extraction method was carried out. The newly developed method and the method currently in use were found to recover similar amounts of TCE. The major advantage of the MAE technique is the very short time needed to obtain complete analyte recovery (6–10?min), which makes it possible to analyse a large number of samples without the need for sample preservation or prolonged storage. Thus, the new method is much more efficient than the existing methods. The technique has a good potential for field application.     

Response surface methodology and support vector machine for the optimization of separation in linear gradient elution

Experimental design methodology was used to optimize the linear gradient elution chromatography. The effect of initial mobile phase composition (φ_in), initial isocratic time (t_in), and gradient time (t_G) on the retention times of phenyl thiohydantoin aminoacids (PTH‐amino acids) was investigated. The experiments were performed according to Box–Behnken experimental design to map the chromatographic response surface. Then multiple linear regression and support vector machine (SVM) methods were used to fit the retention times of solutes. Results shows the SVM models have better ability to predict retention time and used for grid search in factor space. The SVM models were verified, as good agreement was observed between the predicted and experimental values of retention time in the optimal condition.     

Determination of the oil content of seeds by focused microwave-assisted soxhlet extraction

Sumamry Soybean, rape and sunflower lipids have been extracted with a focused microwave-assisted Saxhlet extractor. The main factors affecting extraction efficiency, namely microwave irradiation power, number of cycles and microwave irradiation time were optimised by means of a power, number of cycles and microwave irradiation time were optimised by means of a central composite design based on a two-level-three-factor factorial design. A study of the influence of particle size on the extraction procedure was also performed. The results obtained were compared with those obtained by use of an ISO method using a conventional Soxhlet extractor. Quantitative results for lipid content based on gravimetric determinations and qualitative results based on analysis of fatty acid methyl esters and polymeric compounds were similar to those obtained by Soxhlet extraction with hexane. Substantial reduction of sample manipulation. analysis time and solvent wastage is achieved by use of the proposed method.     

Optimization of supercritical fluid extraction of geniposidic acid from plantain seeds using response surface methodology

The process parameters of supercritical CO₂ (SCCO₂) plus modifer for the extraction of geniposidic acid from plantain seeds were studied using a Box–Behnken design. The effects of independent variables, that is, ethanol concentration (0–70%, ethanol:water, v/v), extraction pressure (10–30 MPa), and temperature (50–80°C) on the yield of geniposidic acid were evaluated. Results indicated that the data could be well fitted to a second-order polynomial model. The effects of ethanol concentration and temperature, as well as the interaction between ethanol concentration and temperature were significant (p < 0.05). The yield (8.9 mg/g) of modified SCCO₂ extraction at optimal conditions was compared with that obtained by Soxhlet extraction or ultrasound assisted extraction.     

Microwave extraction of phthalate esters from marine sediment and soil

Summary As part of an on-going ASEAN⁺⁾-Canada Cooperative Programme on Marine Science, microwave-assisted solvent extraction has been employed for the extraction of six phthalate esters from marine sediment and soil samples. Five of the six esters studied are among the United States Environmental Protection Agency's list of top priority pollutants. The effects of extraction solvent, extraction temperature, duration of extraction and extraction volume on the mean recoveries of the six phthalate esters were quantitatively evaluated by means of an analysis of variance, followed by testing the differences among the level means for each condition with least significant difference method. Microwave-assisted solvent extraction allowed comparable or higher recoveries of the six phthalate esters (70.1–91.0%) in comparison with conventional soxhlet (65.5–89.5%) and sonication (64.6–88.6%). The precision of results by microwave-assisted solvent extraction was improved significantly compared to the conventional techniques. The microwave extraction system has many advantages over the soxhlet and sonication extraction, e.g., no laborious clean-up procedure, lower usage of hazardous organic solvent, and larger sample throughput. The technique has been employed for the analysis of native marine sediment and soil samples in Singapore.     

Screening, optimization and validation of microwave-assisted extraction for the determination of persistent organochlorine pesticides

In the present study, a microwave-assisted extraction method has been investigated for the extraction of persistent organochlorine pesticides from sediment in comparison to the classical Soxhlet extraction. The extraction procedure has been screened by a complete factorial design for statistically significant parameters. Thereafter, the identified parameters, composition of extraction solvent (mixtures of n-hexane-acetone), extraction temperature and time were optimized by a Box-Behnken design. Finally, the optimized microwave-assisted procedure has been validated by extraction of two different matrix reference materials, a sediment and a mallow powder. The data obtained for both materials were in good agreement with those obtained by Soxhlet extraction and published values. Special emphasis has been given to an accurate determination of p,p′-DDT, since DDT is known as instable during GC-injection. In order to evaluate the DDT-degradation, ¹³C₁₂-p,p′-DDT-solutions were analyzed and the degradation rates during GC-injection were calculated. Furthermore, ¹³C₁₂-p,p′-DDT was added to the sediment samples prior to extraction and the degradation rates during the optimization experiment have been investigated.     

Optimisation of the extraction of polycyclic aromatic hydrocarbons and their nitrated derivatives from diesel particulate matter using microwave-assisted extraction

Pressurised microwave-assisted extraction was used to extract a complex mixture containing polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs and heavy n-alkanes from a particularly refractory carbonaceous material resulting from the combustion in a diesel engine. A second-order central composite design was used to determine the optimal conditions of extraction in terms of time, temperature, volume and nature of extracting solvent from spiked diesel soots. To begin, methylene chloride, tetrahydrofuran and chloroform were tested for extracting the spiked diesel particulates; however, the nature of these solvents was not really an influential factor. Volume was the most influential factor and was kept at a medium level to enhance the extraction of heavy PAHs without introducing an important dilution factor. Temperature and time were not influential as main factors but interacted with the other factors. Finally, high temperature and duration associated with a medium volume of methylene chloride were better for the extractions. After this optimisation, five-ring and six-ring PAHs were nevertheless not satisfactorily desorbed. Other solvents were therefore tested. Only aromatic ones, and particularly heterocyclic aromatic solvents, managed to desorb the heaviest PAHs. Pyridine, with its both aromatic and its basic character, was the most successful solvent. Desorption was even complete with an addition of 17% of diethylamine into pyridine. So, using MAE, we succeeded in extracting quantitatively, from the spiked refractory diesel soot surface, two-ring to six-ring PAHs, heavy n-alkanes and short nitrated PAHs. However, heavy nitrated PAHs were better extracted with a small addition of acetic acid (1%) into pyridine instead of a basic cosolvent.     

Ultrasonic solvent extraction of organochlorine pesticides from soil

Ultrasonic solvent extraction of the organochlorine pesticides (OCP) including α-, β-, γ- and Δ-hexachlorocyclohexane (HCH), heptachlor, aldrin, o,p′-DDE, dieldrin, p,p′-DDE, p,p′-DDT, methoxychlor, mirex from soil is reported. The extraction procedure was optimized with regard to the solvent type, amount of solvent, duration of sonication and number of extraction steps. Determination of pesticides was carried out by gas chromatography (GC) equipped with electron capture detection (ECD). Twice ultrasonic extraction using 25 mL of a mixture of petroleum ether and acetone (1/1 v/v) for 20 min of sonication showed satisfactory extraction efficiency. Recoveries of pesticides from fortified soil samples are over 88% for three different fortification levels between 15 and 200 μg kg⁻¹, and relative standard deviations of the recoveries are generally below 6%. Real soil samples were analyzed for OCP residues by optimized ultrasonic solvent extraction and shake-flask as well as soxhlet extraction technique. Investigated all extraction methods showed comparable extraction efficiencies. Optimized ultrasonic solvent extraction is the most rapid procedure because the use of time in ultrasonic extraction was considerably reduced compared to shake-flask and soxhlet extraction.