Supercritical fluid extraction of polyhalogenated pollutants from aquaculture and marine environmental samples: A review

Simultaneously characterization of multiple constituents in Valeriana jatamansi Jones using an online supercritical fluid extraction-high-performance liquid chromatography/supercritical fluid chromatography-mass spectrometry system

Valeriana jatamansi Jones is a commonly used traditional Chinese medicine, boasting rich effective compositions with versatile chemical structures and wide polarity, including iridoids, chlorogenic acid, and flavonoids. Previous reports indicate that conventional high-performance liquid chromatography (HPLC) analytical methods have proven inefficient performance in comprehensively characterizing components in Valeriana jatamansi. In the present study, a hybrid online analytical platform combining supercritical fluid extraction with both conventional HPLC separation (reverse phase) and supercritical fluid chromatography (normal phase) has been established and validated. This system can provide online extraction with two different chromatographic separation modes to increase separation ability and has been connected to a mass spectrometer to acquire high-resolution mass spectrometry data. Then, the online platform was applied to screening components in Valeriana jatamansi. A total of 117 compounds were identified, including five lignans, 18 organic acids, six flavonoids, and 88 iridoids. Thirty-three compounds were reported from Valeriana jatamansi for the first time. These results enrich our understanding of the components of Valeriana jatamansi and prove that the developed online platform in this study is a robust approach for accelerating working efficiency in comprehensively analyzing complicated samples.

Quantitative and qualitative characterization of mango kernel seed oil extracted using supercritical CO2 and solvent extraction techniques

Characterization of mango kernel seed oil extracted using supercritical CO₂ (SC-CO₂) and conventional solvent (hexane, petroleum ether, ethanol and acetone) extraction techniques was carried out using differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), Gas chromatography mass spectroscopy (GC-MS) and fluorescence microscope. The extractor and separator temperatures of the SC-CO₂ were 60 and 50 °C respectively while the pressure was varied from 35 to 40 MPa. Solvent extractions were maintained at the boiling points of the various solvents. The results indicated that solvent extraction had higher yields (8.02-19.88%) while SC-CO₂ had a lower yield (2.5-3.6 %); the yield of conventional solvent extraction increased with decreasing particle sizes. Ethanol extracted oil had lowest enthalpies of endothermic reaction (1.17-2.74 J/g); while other solvents were between 42.54 and 45.64 J/g with SC-CO₂ having 37.40 J/g. The melting points for ethanol extracted oil were 7.34 and 35.20 °C; other solvents ranged between 13.39 and 15.15 °C while, SC-CO₂ was 35.05 °C. SC-CO₂ extracted oil had no crystallization parameter, while conventional solvent extracted oil with the exception of ethanol were between -33.23 and -33.97 J/g. The FTIR showed that CH₃, CH₂ and COH were the predominant functional groups in hexane, petroleum ether, acetone and SC-CO₂-extracted oil; ethanol extracted oil had -OH and CH₂. The extracted oil using solvent extraction technique was higher in unsaturated fatty acid (UFA) with the exception of acetone extracted oil. SC-CO₂ extracted oil had higher saturated fatty acid (SFA) content (47.01%). The predominant UFA and SFA were oleic acid stearic acid.

Development and validation of a subcritical 1,1,1,2-tetrafluoroethane extraction technique: Gas chromatography-mass spectrometry method for the simultaneous determination of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and polybrominated biphenyl ethers in aquatic products

A simple, rapid, and green method was developed for the simultaneous analysis of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and polybrominated biphenyl ethers in aquatic products using subcritical 1,1,1,2-tetrafluoroethane extraction coupled with gas chromatography and mass spectrometry. Effects of the extraction temperature, pressure, and cosolvent volume on the extraction efficiency were investigated by extracting spiked oyster samples. The results show that the maximum extraction efficiency was obtained at 40°C, 12 MPa, and a cosolvent (dichloromethane) volume of 5.0 mL. Under these conditions, the calibration curves had good linearity with square of the correlation larger than 0.998 in the concentration range of 5-800 ng/mL; limit of detection and limit of quantitation were 0.16-2.83 and 0.55-9.43 ng/g, respectively. At spiked levels of 10, 30, and 50 ng/g, the average recoveries were 70.4-80.4% for polycyclic aromatic hydrocarbons, 74.0-83.6% for polychlorinated biphenyls, and 66.9-78.0% for polybrominated biphenyl ethers, with average relative standard deviations of less than 16.3%. The established method has no significant differences in recovery compared to traditional methods and is suitable for the analysis of real samples.

Triple quadrupole tandem mass spectrometry: A real alternative to high resolution magnetic sector instrument for the analysis of polychlorinated dibenzo-p-dioxins, furans and dioxin-like polychlorinated biphenyls

This paper reports on the optimisation, characterisation, validation and applicability of gas chromatography coupled to triple quadrupole mass spectrometry in its tandem operation mode (GC-QqQ(MS/MS) for the quantification of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs, dioxins) and dioxin-like polychlorinated biphenyls (DL-PCBs) in environmental and food matrices. MS/MS parameters were selected to achieve the high sensitivity and selectivity required for the analysis of this type of compounds and samples. Good repeatability for areas (RSD = 1-10%, for PCDD/Fs and DL-PCBs) and for ion transition ratios (RSD = 0.3-10%, for PCDD/Fs, and 0.2-15%, for DL-PCBs) and low instrumental limits of detection, 0.07-0.75 pg μL(-1) (for dioxins) and 0.05-0.63 pg μL(-1) (for DL-PCBs), were obtained. A comparative study of the congener specific determination using both GC-QqQ(MS/MS) and gas chromatography-high resolution mass spectrometry (GC-HRMS) was also performed by analysing several fortified samples and certified reference materials (CRMs) with low (feed and foodstuffs), median (sewage sludge) and high (fly ash) toxic equivalency (TEQ) concentration levels, i.e. 0.60, 1.83, 72.9 and 3609 pg WHO-TEQ(PCDD/Fs) g(-1). The agreement between the results obtained for the total TEQs (dioxins) on GC-QqQ(MS/MS) and GC-HRMS in all the investigated samples were within the range of ±4%, and that of DL-PCBs at concentration levels of 0.84 pg WHO-TEQs (DL-PCBs) g(-1), in the case of feedstuffs, was 0.11%. Both instrumental methods have similar and comparable linearity, precision and accuracy. The GC-QqQ(MS/MS) sensitivity, lower than that of GC-HRMS, is good enough (iLODs in the down to low pg levels) to detect the normal concentrations of these compounds in food and environmental samples. These results make GC-QqQ(MS/MS) suitable for the quantitative analysis of dioxins and DL-PCBs and a real alternative tool to the reference sector HRMS instruments.

Fungal Community Successions in Rhizosphere Sediment of Seagrasses Enhalus acoroides under PAHs Stress

Seagrass meadows represent one of the highest productive marine ecosystems and are of great ecological and economic values. Recently, they have been confronted with worldwide decline. Fungi play important roles in sustaining the ecosystem health as degraders of polycyclic aromatic hydrocarbons (PAHs), but fewer studies have been conducted in seagrass ecosystems. Hence, we investigated the dynamic variations of the fungal community succession under PAH stress in rhizosphere sediment of seagrasses Enhalus acoroides in this study. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), quantitative PCR (qPCR) and a clone library have been employed to analyze the fungal community’s shifts. Sequencing results of DGGE and the clone library showed that the predominant species belong to phyla Ascomycota and Basidiomycota. The abundance of three groups decreased sharply over the incubation period, whereas they demonstrated different fungal diversity patterns. Both the exposure time and the PAH concentrations affected the microbial diversity as assessed by PCR-DGGE analysis. Redundancy analysis (RDA) indicated that significant factors driving community shifts were ammonium and pH (p < 0.05). Significant amounts of the variations (31.1%) were explained by pH and ammonium, illustrating that those two parameters were the most likely ones to influence or be influenced by the fungal communities’ changes. Investigation results also indicated that fungal communities in seagrass meadow were very sensitive to PAH-induced stress and may be used as potential indicators for the PAH contamination.

Polyphenols from fresh frozen tea leaves (Camellia assamica L.,) by supercritical carbon dioxide extraction with ethanol entrainer - application of response surface methodology

Fresh frozen tea leaves (Camellia assamica L.) were extracted with SC-CO2 to obtain polyphenols rich in EGCG and compared with conventional solvent extraction. Extraction parameters such as temperature, pressure and solvent to material ratio were critical factors in extraction and optimized by response surface methodology (RSM). The maximum yield of extractable solids using SC-CO2 with ethanol entrainer was carried out at pressures 150 to 350 bar, temperatures from 40 °C to 60 °C and solvent to material ratio 100 to 200. The theoretical yield was 3.91 % (w/w), while experimental yield was 4.20 ± 0.27 % (w/w) at temperature of 50 °C, pressure 250 bar and solvent to material ratio of 200. The chemical compositions of extracted solids were investigated by HPLC which showed 722.68-848.09 ± 1.12 mg of EGCG/g of extractable solids were separated in SC-CO2. Also, 54.62 ± 1.19 mg of EGCG/g of extractable solids was separated using conventional extraction which is quantitatively lesser than SC-CO2 extraction yield. Thus, SC-CO2 extraction was proved to be effective technique in obtaining extracts rich in EGCG (>95 %).

Supercritical Algal Extracts: A Source of Biologically Active Compounds from Nature

The paper discusses the potential applicability of the process of supercritical fluid extraction (SFE) in the production of algal extracts with the consideration of the process conditions and yields. State of the art in the research on solvent-free isolation of biologically active compounds from the biomass of algae was presented. Various aspects related with the properties of useful compounds found in cells of microalgae and macroalgae were discussed, including their potential applications as the natural components of plant protection products (biostimulants and bioregulators), dietary feed and food supplements, and pharmaceuticals. Analytical methods of determination of the natural compounds derived from algae were discussed. Algal extracts produced by SFE process enable obtaining a solvent-free concentrate of biologically active compounds; however, detailed economic analysis, as well as elaboration of products standardization procedures, is required in order to implement the products in the market.

Systematic investigation of factors controlling supercritical fluid extraction (SFE) of spiked and aged PCBs from edible tissues of the blue crab (Callinectes sapidus)

Systematic investigation of factors controlling supercritical fluid extraction (SFE) of spiked and naturally incurred (aged) PCBs from edible tissues of the Blue Crab (Callinectes sapidus) was undertaken. Effects of extraction pressure, temperature and time, CO2 flow rate and total volume, and collection temperature were assessed. Temperature dramatically impacted extraction efficiency, especially at lower pressures. Surprisingly, extraction of both spiked and aged PCBs was flow rate dependent, counter to prevailing views regarding the relative ease of SFE of spiked versus aged contaminants from environmental matrices. PCBs were optimally trapped on a 1:1 mixture of C18-modified and porous silica at 0°C and eluted with <2 mL isooctane at 90°C. A combined 10 min static/30 min dynamic extraction at 35.5 MPa and 150°C with a CO2 flow rate of 3 mL min(-1) yielded maximum (quantitative) recoveries of spiked and aged PCBs. Resulting solvent extracts required no cleanup and could be analyzed directly by halogen-selective GC with MS confirmation.

Theoretical models for supercritical fluid extraction

For the proper design of supercritical fluid extraction processes, it is essential to have a sound knowledge of the mass transfer mechanism of the extraction process and the appropriate mathematical representation. In this paper, the advances and applications of kinetic models for describing supercritical fluid extraction from various solid matrices have been presented. The theoretical models overviewed here include the hot ball diffusion, broken and intact cell, shrinking core and some relatively simple models. Mathematical representations of these models have been in detail interpreted as well as their assumptions, parameter identifications and application examples. Extraction process of the analyte solute from the solid matrix by means of supercritical fluid includes the dissolution of the analyte from the solid, the analyte diffusion in the matrix and its transport to the bulk supercritical fluid. Mechanisms involved in a mass transfer model are discussed in terms of external mass transfer resistance, internal mass transfer resistance, solute-solid interactions and axial dispersion. The correlations of the external mass transfer coefficient and axial dispersion coefficient with certain dimensionless numbers are also discussed. Among these models, the broken and intact cell model seems to be the most relevant mathematical model as it is able to provide realistic description of the plant material structure for better understanding the mass-transfer kinetics and thus it has been widely employed for modeling supercritical fluid extraction of natural matters.

To remove or not to remove? The challenge of extracting the template to make the cavities available in Molecularly Imprinted Polymers (MIPs)

Template removal is a critical step in the preparation of most molecularly imprinted polymers (MIPs). The polymer network itself and the affinity of the imprinted cavities for the template make its removal hard. If there are remaining template molecules in the MIPs, less cavities will be available for rebinding, which decreases efficiency. Furthermore, if template bleeding occurs during analytical applications, errors will arise. Despite the relevance to the MIPs performance, template removal has received scarce attention and is currently the least cost-effective step of the MIP development. Attempts to reach complete template removal may involve the use of too drastic conditions in conventional extraction techniques, resulting in the damage or the collapse of the imprinted cavities. Advances in the extraction techniques in the last decade may provide optimized tools. The aim of this review is to analyze the available data on the efficiency of diverse extraction techniques for template removal, paying attention not only to the removal yield but also to MIPs performance. Such an analysis is expected to be useful for opening a way to rational approaches for template removal (minimizing the costs of solvents and time) instead of the current trial-and-error methods.

The analysis of dioxins and related compounds

The analysis of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated biphenyls, and other related compounds requires complex sample preparation and analytical procedures using highly sensitive and selective state-of-the-art instrumentation to meet very stringent data quality objectives. The analytical procedures (extraction, sample preparation), instrumentation (chromatographic separation and detection by mass spectrometry) and screening techniques for the determination of dioxins, furans, dioxin-like polychlorinated biphenyls and related compounds with a focus on new approaches and alternate techniques to standard regulatory methods are reviewed.