Optimisation of supercritical fluid extraction of polycyclic aromatic hydrocarbons and their nitrated derivatives adsorbed on highly sorptive diesel particulate matter

Supercritical fluid extraction (SFE) was performed to extract complex mixtures of polycyclic aromatic hydrocarbons (PAHs), nitrated derivatives (nitroPAHs) and heavy n-alkanes from spiked soot particulates that resulted from the incomplete combustion of diesel oils. This polluted material, resulting from combustion in a light diesel engine and collected at high temperature inside the particulate filter placed just after the engine, was particularly resistant to conventional extraction techniques, such as soxhlet extraction, and had an extraction behaviour that differed markedly from certified reference materials (SRM 1650). A factorial experimental design was performed, simultaneously modelling the influence of four SFE experimental factors on the recovery yields, i.e.: the temperature and the pressure of the supercritical fluid, the nature and the percentage of the organic modifier added to CO₂ (chloroform, tetrahydrofuran, methylene chloride), as a means to reach the optimal extraction yields for all the studied target pollutants. The results of modelling showed that the supercritical fluid pressure had to be kept at its maximum level (30 MPa) and the temperature had to be kept relatively low (75 °C). Under these operating conditions, adding 15% of methylene chloride to the CO₂ permitted quantitative extraction of not only light PAHs and their nitrated derivatives, but also heavy n-alkanes from the spiked soots. However, heavy polyaromatics were not quantitatively extracted from the refractory carbonaceous solid surface. As such, original organic modifiers were tested, including pyridine, which, as a strong electron donor cosolvent (15% into CO₂), was the most successful. The addition of diethylamine to pyridine, which enhanced the electron donor character of the cosolvent, even increased the extraction yields of the heaviest PAHs, leading to a quantitative extraction of all PAHs (more than 79%) from the diesel particulate matter, with detection limits ranging from 0.5 to 7.8 ng for 100 mg of spiked material. Concerning the nitrated PAHs, a small addition of acetic acid into pyridine, as cosolvents, gave the best results, leading to fair extraction yields (approximately 60%), with detection limits ranging from 18 to 420 ng.     

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.     

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.     

A new analytical methodology for a fast evaluation of semi-volatile polycyclic aromatic hydrocarbons in the vapor phase downstream of a diesel engine particulate filter

A new sampling method was developed to collect vapor-phase polycyclic aromatic compounds (PAHs) downstream of a diesel engine equipped with a diesel particulate filter (DPF). This configuration allowed us to collect separately the particulate phase, which was trapped inside the DPF, and the vapor phase, which was sampled downstream of the DPF. PAHs, which were not predominantly absorbed into the poor organic fraction of the diesel soot, but were rather physically sorbed on high energetic adsorption sites, should be extracted using very drastic extraction conditions Microwave-assisted extraction using solvent mixtures composed of pyridine and diethylamine were used to desorb particulate PAHs, and the total PAH amounts corresponded to a very low value, i.e., 8 μg g⁻¹ or 0.24 μg km⁻¹, with a predominance of low weight PAHs. For collection of the vapor phase, gas bubbling in an aqueous medium was preferred to conventional methods, e.g., trapping on solid sorbents, for several reasons: aqueous trapping allowed us to use a solid phase enrichment process (SPE) that permitted PAH sampling at the sub-picogram levels. Consequently, low volume sampling was possible even if the sampling duration was very short (20 min). Additionally, the amount of time saved for the analysis was considerable when coupling SPE to the analytical system (liquid chromatography with fluorimetric detection). Solvent consumption for the overall sampling and analytical processes was also drastically reduced. Experiments on a diesel engine showed that vapor phase samples collected downstream of the DPF contained all of the 15 target priority PAHs, even the heaviest ones. The total vapor-phase PAH amount was 6.88 μg N m⁻³ or 10.02 μg km⁻¹, which showed that the gaseous fraction contains more PAHs than the particulate fraction. Partitioning coefficients (K_p) were estimated showing the predominance in the vapor phase of all the PAHs. However, the DPF technology effects a considerable decrease in the total PAH emission when compared to non-equipped diesel vehicles.     

Rapid determination of trace polycyclic aromatic hydrocarbons in particulate matter using accelerated solvent extraction followed by ultra high performance liquid chromatography with fluorescence detection

A method has been developed for the trace analysis of polycyclic aromatic hydrocarbons, which are known as persistent organic pollutants and ubiquitous constituents of fine particulate matter that causes growing airborne pollution. The method, which was especially for samples of airborne particulate matter less than 2.5 μm in diameter, utilized accelerated solvent extraction and ultra high performance liquid chromatography with fluorescence detector. Four principal parameters of accelerated solvent extraction were optimized to obtain maximum extraction efficiency. Using the established synergetic programs of gradient elution and fluorescence wavelength switching, a rapid separation was achieved in 6.56 min with good linearity for 15 polycyclic aromatic hydrocarbons (coefficient of determination above 0.999). The limits of detection ranged from 0.833 to 10.0 pg/m³. The precision of the method expressed as inter‐day relative standard deviation ranged from 0.2 to 1%, which was calculated from nine repetitive measurements of 8.00 μg/L analytes. Average spiked recoveries ranged from 71.6 to 97.7%, with the exception of naphthalene. The rapid, sensitive, and accurate method can meet the pressing needs of health risk assessment and increasingly heavy daily tasks of air quality monitoring.     

HPLC analysis of the large polycyclic aromatic hydrocarbons in a diesel particulate

Summary High performace liquid chromatography (HPLC) was used to separate the large polycyclic aromatic hydrocarbons in a diesel particulate extract. Identification of individual peaks was made using a photodiode array UV/visible detector to collect their absorbance spectra. Comparisons between standard compounds and the peaks were made using both retention times and spectra. Compounds of up to 10 rings were identified.     

Trace determination of nitrated polycyclic aromatic hydrocarbons using liquid chromatography with on-line electrochemical reduction and fluorescence detection

An efficient clean-up procedure coupled with a high performance liquid chromatography (HPLC) with on-line electrochemical (EC) reduction and fluorescence detection (FLD) was developed to quantify nitrated polycyclic aromatic hydrocarbons (NPAHs) in the airborne particulate. In this process, NPAHs were extracted ultrasonically followed by analysis by using a reversed phase column with an aqueous eluent containing 70% aqueous acetonitrile and sodium monocholoroacetate as a buffer solution. The extraction efficiencies were above 83% for 1-nitropyrene and 1,3-dinitropyrene (1,3-DNP) 1,6-DNP, and 1,8-DNP, and calibration graphs were linear with very good correlation coefficients (r>0.999) and the detection limits were in the range of 1.0-2.2 pg for dinitropyrenes and nitropyrene. The proposed method provides a relatively simple and convenient procedure for determining the NPAHs samples in airborne particulate.     

Ultrasound-assisted solvent extraction of total polycyclic aromatic hydrocarbons from mussels followed by spectrofluorimetric determination

An ultrasound-assisted solvent extraction procedure has been optimised to speed up total polycyclic aromatic hydrocarbons (T-PAHs) extraction from mussel soft tissue. The T-PAHs releases have been evaluated by spectrofluorimetry (excitation and fluorescence emission wavelengths of 300 and 382 nm, respectively, and using chrysene as calibrant). Variables such as sonication time, ultrasound frequency, n-hexane volume, dichloromethane volume, number of repeated extractions with n-hexane and number of repeated extraction with dichloromethane were simultaneously studied by applying a Plackett-Burman design (PBD) approach. Results showed that ultrasound frequency and n-hexane and dichloromethane volumes were statistically significant variables (confidence interval of 95%). These last two variables were finally optimised by using central composite designs (CCD), yielding optimum n-hexane and dichloromethane volumes of 2.5 and 6.5 ml, respectively. The lowest T-PAHs releasing at high ultrasound frequency (35 kHz) led to choice the lowest ultrasound frequency (17 kHz) to perform the extraction. Variables such as sonication time and number of repeated extraction with n-hexane or dichloromethane were statistically non-significant and they were fixed at 10 min and the extraction with n-hexane and dichloromethane were performed once. The limit of detection was 0.021 μg g⁻¹ (referred to dried mass), the repeatability of the overall method was 4.7% (n = 9) and the analytical recoveries were between 98 and 105%. The proposed method was finally applied to 16 mussel samples (Mytilus galloprovincialis) from Ría de Arousa estuary (Galicia, northwest Spain).     

Headspace solvent microextraction and gas chromatographic determination of some polycyclic aromatic hydrocarbons in water samples

Headspace solvent microextraction (HSME) was shown to be an efficient preconcentration method for extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions. A microdrop of 1-butanol (as extracting solvent) containing biphenyl (as internal standard) was used in this investigation. Extraction occurred by suspending a 3 μl drop of 1-butanol from the tip of a microsyringe fixed above the surface of solution in a sealed vial. After extraction for a preset time, the microdrop was retracted back into the syringe and injected directly into a GC injection port. The effects of nature of extracting solvent, microdrop and sample temperatures, stirring rate, microdrop and sample volumes, ionic strength and extraction time on HSME efficiency were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by water samples spiked with PAHs. The optimized procedure was successfully applied to the extraction and determination of PAHs in different water samples.     

Development and optimisation of a novel three‐way extraction technique based on a combination of Soxhlet extraction,membrane assisted solvent extraction and a molecularly imprinted polymer using sludge polycyclic aromatic hydrocarbons as model compounds

A novel technique that integrates extraction and clean‐up into a single step format is reported as part of the search for new sample preparation techniques in the analysis of persistent organic pollutants from complex samples. This was achieved by combining the extraction efficiency of the Soxhlet extractor, the selectivity of a size exclusion membrane and the specificity of a molecularly imprinted polymer for the extraction of polycyclic aromatic hydrocarbons from wastewater sludge followed by quantitation using gas chromatography with time‐of‐flight mass spectrometry. The approach is described as the Soxhlet extraction membrane‐assisted solvent extraction molecularly imprinted polymer technique. This technique was optimised for various parameters such as extraction solvent, reflux time and membrane acceptor phase. The applicability of the developed technique was optimised using a wastewater sludge certified reference material and then tested on real wastewater sludge samples. The method detection limits ranged from 0.14 to 12.86 ng/g with relative standard deviation values for the extraction of the 16 US‐EPA priority polycyclic aromatic hydrocarbons from wastewater sludge samples ranging from 0.78 to 18%. The extraction process was therefore reproducible and showed remarkable selectivity. The developed technique is a promising prospect that can be applied in the analysis of organic pollutants from complex solid samples.     

Optimization and determination of polycyclic aromatic hydrocarbons in biochar‐based fertilizers

The agronomic benefit of biochar has attracted widespread attention to biochar‐based fertilizers. However, the inevitable presence of polycyclic aromatic hydrocarbons in biochar is a matter of concern because of the health and ecological risks of these compounds. The strong adsorption of polycyclic aromatic hydrocarbons to biochar complicates their analysis and extraction from biochar‐based fertilizers. In this study, we optimized and validated a method for determining the 16 priority polycyclic aromatic hydrocarbons in biochar‐based fertilizers. Results showed that accelerated solvent extraction exhibited high extraction efficiency. Based on a Box–Behnken design with a triplicate central point, accelerated solvent extraction was used under the following optimal operational conditions: extraction temperature of 78°C, extraction time of 17 min, and two static cycles. The optimized method was validated by assessing the linearity of analysis, limit of detection, limit of quantification, recovery, and application to real samples. The results showed that the 16 polycyclic aromatic hydrocarbons exhibited good linearity, with a correlation coefficient of 0.996. The limits of detection varied between 0.001 (phenanthrene) and 0.021 mg/g (benzo[ghi]perylene), and the limits of quantification varied between 0.004 (phenanthrene) and 0.069 mg/g (benzo[ghi]perylene). The relative recoveries of the 16 polycyclic aromatic hydrocarbons were 70.26–102.99%.     

Application of in-vial membrane assisted solvent extraction to the determination of polycyclic aromatic hydrocarbons in seawater by gas chromatography-mass spectrometry

A device for membrane assisted solvent extraction from an aqueous sample to an organic solvent within a micro-vial compatible with a chromatography auto-sampler was used to extract trace amounts of seven polycyclic aromatic hydrocarbons from seawater. The device consisted in an assembly of a volumetric flask containing the sample and a micro-vial containing the organic solvent by means of a screw stopper in which the septum was replaced by a sized piece of a membrane. Extraction conditions (nature of the organic solvent, extraction time, presence of ethanol in the donor phase, ionic content of the donor phase, characteristics of the membrane and volumes of donor and acceptor phases) were studied in order to find the conditions for maximum extraction. Analytical performance characteristics have also been established. The extraction efficiency was between 12.5 and 23%, which implies an enrichment factor value above 40. The repeatability and reproducibility were in the range of 8.6–10.0% and 13–19%, respectively. Detection limits were in the range of 24–39 ng L⁻¹. Nine seawater samples have been studied. Most of the concentrations were under the limits of detection. Naphthalene and phenanthrene contents have been determined in a sample using the method of standard additions, and concentrations 100 and 91 ng L⁻¹, respectively.     

Optimization and validation of a low temperature microwave-assisted extraction method for analysis of polycyclic aromatic hydrocarbons in airborne particulate matter

A low temperature microwave-assisted extraction method (MAE) is reported for the analysis of polycyclic aromatic hydrocarbons (PAHs) in airborne particulate matter (PM). The main parameters affecting the extraction efficiency (choice of extractants, microwave power, and extraction time) were investigated and optimized. The optimized procedure requires a 20 ml mixture of acetone:n-hexane (1:1) for extraction of PAHs in PM at 150 W of microwave energy (20 min extraction time). Clean-up of MAE extracts was not found to be necessary. The optimized method was validated using two different SRM (1648-urban particulate matter and 1649a, urban dust). The results obtained are in good agreement with certified values. PAHs recoveries for both reference materials were between 79 and 122% with relative standard deviation ranging from 3 to 21%. Detection limits were determined based on blank determination using two kinds of quartz filter substrates (n = 10), which ranged from 0.001 (0.03) ng m⁻³ (pg/μg) for B(k)Ft to 1.119 (37.3) for Naph in ng m⁻³ (pg/μg), respectively. The repeatability and day-to-day reproducibility obtained in this study were in the range of 4-16 and 3-25% for spiked standards and SRM 1649, respectively. The optimized and validated MAE technique was applied to the extraction of PAHs from a set of real world PM samples collected in Singapore. The sum of particulate-bound PAHs in outdoor PM ranged from 1.05 to 3.45 ng m⁻³ while that in indoor PM (cooking emissions) ranged from 27.6 to 75.7 ng m⁻³, respectively.     

Supercritical fluid extraction followed by supramolecular solvent microextraction as a fast and efficient preconcentration method for determination of polycyclic aromatic hydrocarbons in apple peels

In this work, reverse micelle‐based supramolecular solvent microextraction method coupled with supercritical fluid extraction and used for determining trace amounts of polycyclic aromatic hydrocarbons in apple peels. The extract was analyzed by high‐performance liquid chromatography equipped with a fluorescence detector. Coupling supramolecular solvent microextraction with supercritical fluid extraction method, resolve low preconcentration factor of supercritical fluid extraction method, improved limit of detection of polycyclic aromatic hydrocarbons and allow the use of supramolecular solvent microextraction in solid matrices. The effective parameters on the supramolecular solvent microextraction and supercritical fluid extraction efficiency were optimized using one variable at a time and face centered design methods, respectively. Under the optimum condition, the limits of detection and limits of quantifications were in the range of 0.34–1.27 and 1.03–3.82 µg/kg, respectively. Analysis of polycyclic aromatic hydrocarbons in apple peels showed that the supercritical fluid extraction/ supramolecular solvent microextraction method provide great potential for trace analysis of polycyclic aromatic hydrocarbons in fruit samples (RSDs < 7.7%).     

Flocculation-ultrasonic assisted extraction and solid phase clean-up for determination of polycyclic aromatic hydrocarbons in water rich in colloidal particulate with high performance liquid chromatography and ultraviolet-fluorescence detection

In the present work, a simple method of sample preparation for the determination of polycyclic aromatic hydrocarbons (PAHs) in water rich in colloidal particulate was developed. The technique was mainly based on the effect of the flocculation of aluminum sulfate and the adsorption of the flocculation aid florisil. The method contained three steps: flocculation, ultrasonic extraction, and solid-phase extraction cleanup. Major parameters of the procedure were optimized with high performance liquid chromatography (HPLC) separation and ultraviolet-fluorescence detection. When 250 mL model sample containing 16 EPA PAHs was processed, the developed method provided detection limits in the range of 0.02–5 ng/L. Both spiked and non-spiked polluted river water samples rich in suspended particles and organic matters were analyzed. Recoveries and relative standard deviations for the 16 PAHs were in ranges of 86–94% and 3–13% (n = 5), respectively.     

Appraisal of “classic” and “novel” extraction procedure efficiencies for the isolation of polycyclic aromatic hydrocarbons and their derivatives from biotic matrices

In this study the extraction efficiency of pressurized liquid extraction (PLE), employing different extraction solvent mixtures under different extraction conditions, was compared with extraction efficiencies of commonly used procedures, Soxhlet extraction and extraction enhanced by sonication. Spruce needles and fish tissue were selected as test samples. Purification of obtained extracts was carried out by gel permeation chromatography (GPC) employing gel Bio-Beads S-X3. Identification and quantitation of target PAHs was performed by high-performance liquid chromatography with fluorescence detection (HPLC–FLD).

Within optimisation of PLE conditions, temperature of extraction, type of solvent, duration and number of static cycles as well as the influence of sample pre-treatment (drying, homogenisation, etc.) were tested. Comparison of the extraction efficiency of PLE with the efficiencies of the other techniques was done under the optimised conditions, i.e. sample slurry obtained by desiccation with anhydrous sodium sulphate, extracted at 100 °C in 1 cycle lasting 5 min. Hexane:acetone (1:1, v/v) was chosen as the most suitable extraction solvent for isolation of analytes from test samples.

Comparison of mentioned isolation techniques with respect to the amount of co-extracts, procedure blank levels and time and solvent volume demands was also done.