微波萃取技术

介绍了在气相／液相色谱测定前的一种新的样品制备技术——微波萃取技术及其所使用的试剂、设备和条件。通过一些数据以及与Ｓｏｘｈｌｅｔ法、超声萃取法比较说明,微波萃取是一种快速、试剂用量少、回收率高、灵敏以及易于自动控制的方法。     

A gradient anion exchange chromatographic method for the speciation of arsenic in lobster tissue extracts

A gradient anion exchange chromatographic technique was developed for the separation of arsenobetaine (AsB), arsenocholine (AsC), arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) in one chromatographic run. This technique used low residue ammonium carbonate buffer and the inductively coupled plasma-mass spectrometry (ICP-MS) chromatograms showed little baseline drift. Gradient elution improved peak shape and peak separation. The separation was completed in approximately 27 min with low detection limits (0.017-0.029 mug As kg(-1)). Baseline resolution of all the arsenic species evaluated was achieved when the concentration of AsC was less than approximately 12.5 mug As kg(-1). This technique was successfully applied to different extracts of a standard reference material, TORT-2, and lobster tissue. AsB was found to be the major arsenic species present. AsC, DMAA, MMAA and As(V) were also found, although MMAA was not detected in all of the TORT-2 extracts. Two unknown peaks found may be due to the presence of arsenosugars or other arsenic species. Discrepancy between extraction recoveries previously determined using flow injection-ICP-MS and the high-performance liquid chromatography-ICP-MS was observed in some cases. The differences may be due to the extraction technique and/or conditions at which the extractions were performed.     

紫草中活性成分的非极性溶剂动态微波提取及高效液相色谱法测定

用非极性溶剂动态微波辅助提取,高效液相色谱法测定紫草中的紫草素和β,β′-二甲基丙烯酰紫草素.考察了微波吸收介质类型、提取溶剂种类、提取溶剂流速、微波功率和样品粒度对提取产率的影响,优化提取参数.在优化条件下,将所建立的方法与超声提取和索氏提取相比,所得紫草素和β,β′-二甲基丙烯酰紫草素的产率相差不大,但本文所建立的方法所需提取时间短(5min)、溶剂消耗少(10mL).与极性溶剂动态微波辅助提取相比,提取产率大幅度提高.结果说明,所建立的方法是一种有效的提取中草药中一些活性成分的方法,特别是对于一些在非极性溶剂中有更高溶解度的化合物,此方法更具优势.     

A Unified Sample Preparation System for Extraction of Various Analyte/Matrix Combinations

A supercritical fluid extraction/enhanced solvent extraction system (SFE/ESE) was used to remove polar and non-polar analytes from various matrices. Extraction of environmental pollutants from soil, additives from low density polyethylene, sulfa drugs from animal tissue, and drug from tablet was performed using both SFE and ESE. Results showed that a single instrumental system can be used to perform both ESE with organic solvents and SFE with carbon dioxide-based fluids. Each method has its own unique advantages and applications. The ability to carry out both solvent extraction and supercritical fluid extraction with one system has obvious economical advantages.     

Use of open-tubular trapping columns for on-line extraction–capillary gas chromatography of aqueous samples

The applicability of open-tubular trapping columns for on-line extraction–capillary GC analysis is evaluated. The extraction step involves sorption of the analytes from water into the stationary phase of an open-tubular column, removal of the water by purging the trap with nitrogen, and desorption of the analytes with an organic solvent. The effect of swelling of the stationary phase with organic solvents on the retention power of the trap is studied. When using pentane or hexane as swelling agent breakthrough volumes of at least 10 ml can easily be obtained for non-polar compounds. For a number of medium polarity compounds breakthrough volumes of 5 ml can be achieved when chloroform is used as the swelling agent. The required drying time is less than 1 minute. Quantitative desorption requires only 75 μl of organic solvent. Solvent elimination prior to transfer to the GC column is carried out using a PTV injector and a multidimensional GC system. The system is applied for the analyses of river water, urine, and serum samples.     

Microwave-assisted extraction for qualitative and quantitative determination of brominated flame retardants in styrenic plastic fractions from waste electrical and electronic equipment (WEEE)

A fast method for the determination of brominated flame retardants (BFRs) in styrenic polymers using microwave-assisted extraction (MAE) and liquid chromatography with UV detection (HPLC-UV) was developed. Different extraction parameters (extraction temperature and time, type of solvent, particle size) were first optimised for standard high-impact polystyrene (HIPS) samples containing known amounts of tetrabromobisphenol A (TBBPA) and decabromodiphenyl ether (Deca-BDE). Complete extraction of TBBPA was achieved using a combination of polar/non-polar solvent system (isopropanol/n-hexane) and high extraction temperatures (130 °C). Lower extraction yields were, however, obtained for Deca-BDE, due to its high molecular weight and its non-polar nature. The developed method was successfully applied to the screening of BFRs in standard plastic samples from waste electrical and electronic equipment (WEEE); TBBPA could be fully recovered, and Deca-BDE could be identified, together with minor order polybrominated diphenyl ether (PBDE) congeners.     

Comparison of extraction techniques for isolation of steroid oestrogens in environmentally relevant concentrations from sediment

The comparison of four extraction techniques for isolation of five native and one labelled steroid oestrogens from sediment was described. The three conventional extraction techniques Soxhlet warm extraction (SWE), accelerated solvent extraction (ASE), microwave-assisted extraction (MAE) and a promising technique QuEChERS were tested for isolation of low environmentally relevant oestrogen concentrations using different extraction conditions. The least expensive and time-consuming method QuEChERS provided the best extraction recoveries (53–84%) from all techniques. MAE achieved the highest recovery from conventional techniques for less polar oestrogens using dichloromethane: acetone 3:1 mixture as an extraction solvent (50–71%), but for extraction of the whole group of oestrogens including more polar estriol acetone or methanol must be used. ASE provided higher extraction recoveries using dichloromethane at 60°C (53–74%) for less polar oestrogens. However, the repeatability of results was unsatisfactory and recoveries using other extraction conditions were lower than for MAE. The most time-consuming SWE achieved the worst extraction recoveries and for isolation of low oestrogen concentrations from sediments, it is completely unsuitable.     

Subcritical water extraction of organic matter from sedimentary rocks

Subcritical water extraction of organic matter containing sedimentary rocks at 300 °C and 1500 psi produces extracts comparable to conventional solvent extraction. Subcritical water extraction of previously solvent extracted samples confirms that high molecular weight organic matter (kerogen) degradation is not occurring and that only low molecular weight organic matter (free compounds) are being accessed in analogy to solvent extraction procedures. The sedimentary rocks chosen for extraction span the classic geochemical organic matter types. A type I organic matter-containing sedimentary rock produces n-alkanes and isoprenoidal hydrocarbons at 300 °C and 1500 psi that indicate an algal source for the organic matter. Extraction of a rock containing type II organic matter at the same temperature and pressure produces aliphatic hydrocarbons but also aromatic compounds reflecting the increased contributions from terrestrial organic matter in this sample. A type III organic matter-containing sample produces a range of non-polar and polar compounds including polycyclic aromatic hydrocarbons and oxygenated aromatic compounds at 300 °C and 1500 psi reflecting a dominantly terrestrial origin for the organic materials. Although extraction at 300 °C and 1500 psi produces extracts that are comparable to solvent extraction, lower temperature steps display differences related to organic solubility. The type I organic matter produces no products below 300 °C and 1500 psi, reflecting its dominantly aliphatic character, while type II and type III organic matter contribute some polar components to the lower temperature steps, reflecting the chemical heterogeneity of their organic inventory. The separation of polar and non-polar organic compounds by using different temperatures provides the potential for selective extraction that may obviate the need for subsequent preparative chromatography steps. Our results indicate that subcritical water extraction can act as a suitable replacement for conventional solvent extraction of sedimentary rocks, but can also be used for any organic matter containing mineral matrix, including soils and recent sediments, and has the added benefit of tailored extraction for analytes of specific polarities.     

Separation and Detection of Arsenic and Selenium Species in Environmental Samples by HPLC-ICP-MS

A method is presented for arsenic speciation analysis of an oyster sample using ion chromatography coupled with an inductively coupled plasma mass spectrometry (ICP-MS) instrument. A strong anion exchange resin was employed with a step gradient elution of 0.1 mM/0.1 M K 2 SO 4 at pH 10.2. Arsenobetaine and dimethylarsinic acid were determined following extraction based on trypsin enzymolysis with 95-100% extraction efficiency. Limits of detection in the range 0.1-0.3 mg kg m 1 of arsenic were obtained for organic arsenic species. No inorganic arsenic was detected. Validation was performed using TORT-2 as a certified reference material. Although high performance liquid chromatography (HPLC) coupled to ICP-MS is an effective method for speciation analysis it is not always necessary to obtain such a detailed picture. A simple liquid chromatographic separation technique based upon mini-column technology is presented. It was developed to obtain a fast, efficient and reliable separation of inorganic from organic, i.e. assumed toxic from non-toxic, arsenic and selenium species suitable for use as an initial screening method for environmental analysis. Two types of strong anion exchange resin were tested. Excellent separation was obtained for both min-column resins and analysis times were within 7 min. Limits of detection obtained for inorganic arsenic, organic arsenic, selenomethionine, Se IV and Se VI were 1.6, 1.8, 66, 32 and 22 µg kg m 1 , respectively.     

Sol-gel-coated oligomers as novel stationary phases for solid-phase microextraction

Amphiphilic and hydrophilic oligomers were synthesized and coated on fused silica capillaries using a sol-gel technique. Sol-gel-coated capillaries were evaluated for the solid-phase microextraction and preconcentration of a wide variety of non-polar and polar analytes. Both types of coatings were stable under high temperature (up to 280 degrees C). The extraction efficiency of the sol-gel coatings was evaluated for the extraction of both non-polar and polar analytes, including organochlorine pesticides, triazine herbicides, estrogens and alkylphenols (APs) and bisphenol-A (BPA). Compared with commercially available solid-phase microextraction (SPME) adsorbents such as poly(dimethylsiloxane)divenylbenzene and polyacrylate, the new materials showed comparable selectivity and sensitivity towards both non-polar and polar analytes. The new coatings gave good linearity and detection limits. For example with triazines, a detection limit of <0.005 microl l(-1), precision from 5.0 to 11.0% (n = 6) and linearity of the calibration plots (0.5 to 50 microl l(-1)) were obtained. The sol-gel coated SPME capillaries were used for the determination of triazine herbicides in reservoir water samples collected in Singapore.     

On-line coupling of subcritical water extraction with high-performance liquid chromatography via solid-phase trapping

Although ambient water is very polar and cannot dissolve many organic species, water at elevated temperatures behaves like a polar organic solvent. Thus, subcritical water has been proven to be an effective extraction fluid for several classes of organic compounds. While solvent trapping was used to collect the extracted analytes in most of previous subcritical water extractions, sorbent trapping has also been developed for subcritical water extraction. In this study, an on-line system for subcritical water extraction and high-performance liquid chromatography (HPLC) was built and tested. A sorbent trap was used as the interface between subcritical water extraction and HPLC. Several shut-off valves have been utilized to switch the system from one mode to another (e.g., from the extraction mode to HPLC mode). The coupling technique of subcritical water extraction and HPLC eliminates the liquid-liquid extraction used in solvent trapping subcritical water extraction and provides higher sensitivity. Compared to the off-line system reported in an earlier work, the operation of this on-line system is even easier. Some peak broadening occurred after the coupling the water extraction with HPLC for the analytes studied. The performance of this on-line system was evaluated by the extraction and determination of caffeine, nitrotoluenes, polychlorinated biphenyls, chlorophenols and anilines.     

Development and application of an analytical protocol for evaluation of treatment processes for landfill leachates. I. Development of an analytical protocol for handling organic compounds in complex leachate samples

A strategy is presented for evaluation of treatment procedures for landfill leachate with emphasis on organic pollutants. An analytical scheme, the LAQUA protocol, was developed as a guide for the analytical work. The protocol includes organic as well as metals, inorganic ions, water-quality parameters, and toxicity. The proposed strategy considers the behaviour of both polar and non-polar organic substances at trace levels. For polar substances, phenols were chosen as markers and determined with an automated supported liquid membrane extraction device, coupled on-line to HPLC with a diode-array detector. For non-polar substances, PCBs and 10 unidentified compounds were chosen as markers and analysed by solid-phase extraction combined with supercritical fluid extraction with GC analysis. The chosen measurement strategy, based on the use of marker substances, difference measurements, and versatile data-handling procedures, provided essential information about complex systems at relatively low cost.     

Gel chromatography: Interactions between gel matrix, solvent and solute

The partitioning behaviour of homologous series of low-molecular-weight polar and non-polar compounds has been studied on gels of cellulose and various derivative forms in dimethylformamide. The nature of the functional groups present in the gel matrix, solute and solvent markedly affects the solute partitioning. The observed partitioning is discussed in terms of the structures of the components.     

Trace analysis of trichlorobenzenes in fish by microwave-assisted extraction and gas chromatography-electron-capture detection

An analytical method consisting of extraction, clean-up, and analysis by gas chromatography-electron-capture detection (GC-ECD) was developed for the determination of trichlorobenzenes (TCBs) in fish samples. Two extraction methods, saponification and liquid-liquid extraction (S-LLE), and microwave-assisted extraction (MAE), were evaluated. In both cases, n-pentane was used as the extraction solvent. For S-LLE, the recoveries ranged from 66.6+/-9.1% for 1-bromo-4-chlorobenzene (4-BCB) to 93.5+/-4.9% for 1,2,4-trichlorobenzene (1,2,4-TCB). The recoveries were significantly lower, between 31.0+/-3.9% for 1,2,3-trichlorobenzene (1,2,3-TCB) and 52.3+/-3.0% for 1,3,5-trichlorobenzene (1,3,5-TCB), in the absence of fish. Proteins and glycerides of the fish tissue seemed to compete with TCBs for the base, and hence decreased their decomposition rate. In the case of MAE, the recoveries were highly dependent on the pressure applied during extraction. At 5 bar, much higher recoveries were obtained, from 66.7+/-15.6% for 4-BCB to 79.9+/-13.6% for 1,2,4-TCB, than at 1 bar. Sulfur formation was, however, observed at 5 bar, and interfered with the GC-ECD analysis of TCBs. Sulfur was adequately removed by copper powder treatment, which was shown not to affect the recovery of analytes. The recoveries of target analytes by S-LLE and MAE did not differ statistically (t-test, alpha = 0.01). Both methods were appropriate for the detection of TCBs at concentration levels typically observed in marine biota, i.e. approximately 1 ng/g. S-LLE was, however, more time consuming, and required larger volumes of high-purity organic solvents than MAE.     

Studies on the uptake of different arsenic forms and the influence of sample pretreatment on arsenic speciation in White mustard (Sinapis alba)

The concentration and speciation of arsenic incorporated by plants grown in the presence of different arsenic compounds was compared, and the influence of plant sample pretreatment and extraction procedures on the recovery and reliability of speciation analyses was studied. It was concluded that sample pretreatment greatly affected the extraction efficiency, but did not change arsenic speciation. The most suitable extraction procedure involved dried plant material without the use of liquid nitrogen. To assess the ability of White mustard to uptake arsenic in different forms, samples were cultivated in nutrient solutions containing either As(III), As(V), monomethylarsonic acid (MMA) or dimethylarsinic acid (DMA). The translocation factor was the highest (0.70) when DMA was added to the nutrient solution, however the overall As concentration in plant tissues was the lowest in this case. Only inorganic As was found in plant tissues when either As(III) or As(V) was added to the nutrient solution. When organic arsenic was present in the nutrient medium, however, it was partially transformed by the plants into inorganic forms.     

Radiochemical studies on the extraction of arsenic(III) by trilaurylamine oxide and benzene from aqueous iodide solutions and its determination in water samples by spectrophotometry

An extraction system consisting of trilaurylamine N-oxide and benzene has been identified as a possible extractant for tracer arsenic (<10^–3 M) from hydrochloric or sulfuric acid solutions with or without iodide. Benzene alone is less efficient as an extractant for arsenic when compared with trilaurylamine oxide dissolved in benzene. The mechanism of extraction is attributed to the formation of hydrated AsCl₃, while the iodide complex is most probably AsI ₄ ^– . The role of the solvent and the other parameters affecting the extraction have been investigated. The results have been employed to determine arsenic in water samples by spectrophotometry using the molybdenum blue method. The extraction procedure was used for the analysis of 10 ml water samples containing 0.2–0.5 g of arsenic.     

Rapid method for the determination of organochlorine pesticides and PCBs in fish muscle samples by microwave-assisted extraction and analysis of extracts by GC-ECD

A procedure for the multiresidue determination of organochlorine pesticides and polychlorinated biphenyls in fish muscle samples has been developed. The method is based on the microwave-assisted extraction (MAE) of food samples from an acetonitrile-water (95 + 5, v/v) mixture followed by SPE cleanup of the extracts and analysis by GC with an electron capture detector. MAE operational parameters, such as the extraction solvent, temperature, and time, were optimized with respect to the extraction efficiency of the target compounds from food samples with 10-13% fat content. The chosen extraction technique allows reduction of the solvent consumption and extraction time when compared with methods already used. Acetonitrile is a good extraction solvent for low-fat matrixes (2-20% fat content), such as fish samples, because it does not significantly dissolve the highly polar proteins, salts, and sugars commonly found in food and gives high recoveries of a wide polarity range of analytes. For purification, SPE using LC-Florisil was shown to be sufficient for the removal of coextracted substances. Recoveries > 78% with RSD values < 15% were obtained for all compounds under the selected conditions. Method quantification limits were in the 5-10 microg/kg range. The method was applied to the analysis of samples of herring (Clupea harengus) purchased at the local fish market. The method is rapid and reliable for the determination of organochlorine analytes in fish muscle.     

Microfluidic Chip-Based Induced Phase Separation Extraction as a Fast and Efficient Miniaturized Sample Preparation Method

Induced phase separation extraction (IPSE) is an efficient sample clean-up technique that can replace liquid-liquid extraction (LLE). The purpose of this study was to miniaturize IPSE by carrying it out in a microfluidic chip. An IPSE chip was designed and evaluated for its ability to separate and purify samples on a microscale. The 5 × 2 cm chip was fed with a solution of polar to non-polar model compounds in acetonitrile-water (1:1). In the 100 µm wide and 40 µm deep microchannels, the sample solution was efficiently separated into two immiscible phases by adding a hydrophobic solvent as inducer. Analytes present in the sample solution each migrated to their own favorable phase upon phase separation. After optimization, extraction and fractionation were easily and efficiently achieved. The behavior of analytes with a pH-dependent partitioning could be influenced by adjusting the pH of the sample solution. Scutellaria baicalensis extract, used in Traditional Chinese Medicine (TCM), was successfully separated in aglycones and glycosides. In this microscale system, the sample and solvent consumption is reduced to microliters, while the time needed for the sample pretreatment is less than one minute. Additionally, the extraction efficiency can reach up to 98.8%, and emulsion formation is avoided.     

Determination of labile inorganic and organic species of Al and Cu in river waters using the diffusive gradients in thin films technique

The diffusive gradients in thin films (DGT) technique, using a diffusive gel or a restrictive gel, was evaluated for the determination of labile inorganic and organic species of Al and Cu in model synthetic solutions and river water samples. Experiments were performed both in situ and in the laboratory. In the solutions containing Al ions, the major labile fraction consisted of inorganic species. The organic complex fractions were mainly kinetically inert. For the model Cu solutions, the most labile fraction consisted of inorganic species; however, significant amounts of labile organic complexes of Cu were also present. A comparison was made between the results obtained using restrictive gel DGT and tangential flow ultrafiltration (TF-UF). The Cu fraction determined by restrictive gel DGT (corresponding to the "free" ions plus the labile fraction of small molecular size complexes) was larger than that determined by TF-UF (corresponding to all small molecular size ions), suggesting that the techniques exhibited different porosities for discrimination of inorganic species. For the river water samples analyzed in the laboratory, less than 45% of the analytes were present in labile forms, with most being organic species. For the in situ measurements, the labile inorganic and organic fractions were larger than those obtained in the laboratory analyses. These differences could have been due to errors incurred during sample collection and storage. All results were consistent with those found using two different methods, namely, solid-phase extraction and the DGT technique employing the apparent diffusion coefficient.     

Microwave-assisted extraction of OCPs, PCBs and PAHs concentrated by semi-permeable membrane devices (SPMDs)

Microwave-assisted extraction (MAE) has been evaluated as an alternative to dialysis for extraction of some water-borne hydrophobic contaminants sampled by semi-permeable membrane devices (SPMDs). Seven organochlorine pesticides (OCPs), 11 polychlorinated biphenyls (PCBs) and 13 polycyclic aromatic hydrocarbons (PAHs) were accumulated in SPMDs at nanogram levels and extracted with three 3-min irradiation cycles with 33 mL of a solvent mixture hexane–water (10:1,v/v) in each cycle. The developed MAE method gave for all analytes investigated statistically comparable extraction yields with those found by dialysis carried out with a total volume of 250 mL hexane for 48 h at room temperature. The recoveries of all the targeted contaminants were in the range of 65–105% with variation coefficients not exceeding 19%. The applicability of the MAE extraction was tested in field SPMDs samples deployed for 15 days in a sewage-treatment process. Our results show that MAE provides a remarkable reduction of time and solvent volume when used as an extraction method in the analysis of SPMDs.