超临界流体萃取—气相色谱法测定粮谷和茶叶中有机氯农药残留量

介绍了一种用超临界流体萑取进行样品前处理，用吸附小柱进行富集和净化，气相色谱－电子捕获检测器定粮茶叶中１７种有机氯农药残卵留量的方法。对于ＳＦＥ的温度，压力，流速以及吸附小柱的吸附剂类型和用量，洗脱条件等均作了考查。     

Supercritical Fluid Extraction of Organochlorine Pesticides from Soil

Abstract

A supercritical fluid extraction (SFE) method was developed for the extraction of 21 organochlorine (OC) pesticides from soil using dichloromethane as cosolvent and magnesium sulfate as drying agent. Average recoveries of spiked OCs from six different soils generally ranged from 70 to 95%, with an average replicate precision of ± 13%. For the extraction of two soils containing “native” OCs, the SFE method gave generally similar or higher concentrations compared to Soxhlet extraction. The precision of replicate analyses of native OCs using SFE and Soxhlet extraction was ± 0.009 and ± 0.007 ug/g, with 24 and 13 degrees of freedom respectively.     

Clean up Procedures for Determination of Amphetamine in Urine Samples.

ABSTRACT

A comparative study of the main sample preparation techniques used for spectrofluorimetric amphetamine determination in urine is presented. The advantages and disadvantages of three procedures based on liquid-liquid or solid-liquid extraction are tested, and a method for amphetamine determination in presence of methamphetamine and its metabolites is proposed. The results obtained are in agreement with the theoretical contents (spiked samples) or the results provided by a reference (GC) method (r8543161 sample).     

Automatic Headspace Sampling for Determination of Ethylene Dibromide Residues in Cereals

Abstract

The possibility was investigated to apply a commercially available automatic head-space sampler in trace analysis of ethylene dibromide (EDB, 1,2-dibromoethane), in cereals.

Samples of rice and wheat flour were thermostatted in closed vials at 70[ddot]C for 30min. The top gas was then automatically introduced into a gas chromatograph equipped with an electron capture detector. Quantitation was performed using external standards (untreated samples spiked with solutions of EDB in N,N′-dimethylacetamide).

The relative standard deviation of the method was 3.4% for rice and 4.5% for wheat flour, at a residue level of 0.008 mg/kg. The detection limit was 0.001 mg/kg (the official EC residue tolerance is 0.01 mg/kg).

Preliminary experiments with other fumigants were carried out as well.

The headspace technique in question has the following advantages over other methods for determining EDB residues in cereals: 1. No sample pre-treatment like extraction, steam distillation, purge and trap etc.; 2. Automated sample handling; 3. “Clean” chromatograms.     

The use of supercritical fluid extraction for the determination of 4-deoxynivalenol in grains: The effect of the sample clean-up and analytical methods on quantitative results

Summary Deoxynivalenol (DON) is one of the trichothecene mycotoxins produced byFusarium molds in grains. Polar cosolvents in supercritical carbon dioxide (SC-CO₂) are needed to extract and isolate the polar DON moiety. This unfortunately results in the extraction of many interfering compounds from the grains into the extracts obtained by supercritical fluid extraction (SFE). Analysis of DON by high performance liquid chromatography (HPLC) using ultraviolet detection (UV) does not provide a specific detection method, although specific detection of DON can be enhanced by using purification steps after SFE. Alternatively, combining SFE with an immunoaffinity method can improve detection specificity and sample cleanup. In this study, SFE was employed to determine DON in grains and cereal products. The effectiveness of the SFE method was compared with two different solvent extraction methods. The extracted DON was quantitatively determined by HPLC-UV using external standardization or competitive enzymelinked immunosorbent assay (ELISA). In some cases, extracts were purified prior to quantitative analysis of the DON by using solvent partitioning, and/or solid phase extraction, or immunoaffinity columns. Therefore, this paper describes the analysis of DON in cereals using different extraction, cleanup and analysis methods. Names are necessary to report factually on available data: however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the products to the exclusion of others that may also be suitable.     

Dry ice-originated supercritical and liquid carbon dioxide extraction of organic pollutants from environmental samples

Packed in a high-pressure vessel and under calculated conditions, dry ice can be used as a source of carbon dioxide for supercritical CO₂ extraction or liquid CO₂ of organic compounds from environmental samples. Coupled with a fluid modifier such as toluene, dry ice-originated supercritical CO₂ (Sc CO₂) achieves quantitative extraction of many volatile organic compounds (VOCs) and semivolatile organic compounds (SOCs) including polycyclic aromatic hydrocarbons (PAHs), n-alkanes, and polychlorinated biphenyls (PCBs) from solid matrices. Compared to contemporary manual or automated supercritical fluid extraction (SFE) technologies, this novel technique simplifies SFE to a minimum requirement by eliminating the need of a high-pressure pump and any electrical peripherals associated with it. This technique is highly suitable to analytical areas where sample preservation is essential but difficult in the sampling field, or where sample collection, sample preparation, and analysis are to be done in the field.     

Characterization of Mechanisms of Pesticide Retention in Soils Using the Supercritical Fluid Extraction Technique

Abstract

This research determined the relative effectiveness of supercritical fluid extraction (SFE) in extracting atrazine and its metabolites from soils which had been treated with atrazine for varying periods of time in order to characterize binding mechanisms. Aqueous methanol extraction was more effective than SFE in removing ¹⁴C atrazine residues from “aged” soils. The more polar the solvent system, the more ¹⁴C-atrazine residues were extracted. The order of polarity and extractability was aqueous methanol > SF-CO₂/5% methanol > SF-CO². Atrazine extraction efficiency using SF-CO₂, and SF-CO₂/.5% methanol decreased as samples “aged” in the field. The less than complete recovery of atrazine residues using the SFE technique could be seen as an indication that different binding mechanisms were involved in the retention of atrazine as well as its metabolites and that the binding mechanisms changed with time.     

Efficiency of Different Methods and Solvents for the Extraction of Polycyclic Aromatic Hydrocarbons from Soils

The efficiencies of supercritical fluid extraction (SFE), accelerated solvent extraction (ASE), Soxhlet, and ultrasonic extraction in the analysis of polycyclic aromatic hydrocarbons (PAHs) in soils were evaluated. Solvents with different polarity were used to extract the PAHs from two soils, one with high and one with low contamination level. ASE showed good results with all solvents almost independent of the solvent polarity and the best results with acetone-toluene (1 : 1). Ultrasonic extraction with acetone-toluene for the uncontaminated soil and acetone-ethanolamine for the highly contaminated also showed good recoveries. The time-consuming Soxhlet extraction with pentane or dichloromethane was less effective. The PAH recovery from SFE was related to the soil matrix or the contamination level. The best extraction conditions (CO 2 /10% pentane) are successful for the soil with a low contamination level and a high humic acid content whereas the extractions of the highly contaminated soil gave poor results irrespective of the solvent used.     

Determination of Microcystins in Cyanobacteria by Supercritical Fluid Extraction and Liquid Chromatography‐Tandem Mass Spectrometry

Abstract

A method for the detection of microcystins (microcystin LR, RR, and YR) in cyanobacteria by supercritical fluid extraction (SFE) and liquid chromatography‐mass spectrometry (LC/MS) has been developed. Supercritical fluids for the analytical extraction of nonvolatile, higher molecular weight compound, and microcystins from cyanobacteria were investigated. The microcystins included in this study are sparsely soluble in neat supercritical fluid CO₂. However, the microcystins was successfully extracted with a ternary mixture (90% CO₂, 9.5% methanol, 0.5% water) at 40°C and 250 atm. The polar carbon dioxide‐aqueous methanol fluid system gave high extraction efficiency for the extraction of the polar microcystins from cyanobacteria. The microcystins were determined by liquid chromatography‐tandem mass spectrometry (LC/MS/MS).     

Supercritical fluid extraction in herbal and natural product studies - a practical review

Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compounds in many analytical and industrial processes. In the past decade, SFE has been applied successfully to the extraction of a variety of organic compounds from herbs and other plants. This review article presents the practical aspects of SFE applications in sample preparation, selection of modifiers, collection methods, on-line coupling techniques, means for avoiding mechanical problems, and approaches to optimization of SFE conditions. SFE can also be used to clean up pesticides from herb medicines. SFE processes can be modeled to acquire useful information for better understanding of the extraction, mechanisms and optimization of the extraction procedures. With increasing public interest in natural products, SFE may become a standard extraction technique for studying herbal, food and agricultural samples.     

Determination of 2,4-D and Dicamba in food crops by MEKC

Summary The determination of 2,4-D (2,4-dichlorophenoxyacetic acid) and Dicamba (2-methoxy-3,6-dichlorobenzoic acid) residues in sugar cane, rice and corn was performed by a supercritical fluid extraction (SFE) method using CO₂/acetone as extraction mix and an SFE apparatus developed in our laboratory. The extracts were cleaned up after extraction by both liquid-liquid partition and a Florisil column. Micellar electrokinetic capillary chromatography (MEKC) coupled with ultraviolet on-column detection was used for the analysis of these pesticides. The detection limits were improved by the preparation of a special detection cell with an increased pathlength that gave detection limits of ca. 0.6 pg for 2,4-D and Dicamba. Our results demonstrated that capillary electrophoresis can be a powerful new analytical tool for pesticide residue analysis.     

Corticosteroid Analysis by HPLC-UV Facilitated byv Use of an Injector-Mounted Extraction Column

Abstract

A method for integrating solid phase extraction of corticosteroids from biological samples with normal operation of reversed-phase HPLC is described. This method uses an extraction column mounted in place of the sample loop of a conventional injection valve to separate corticosteroids from some interfering compounds, and to effectively concentrate steroids from dilute samples. Both manual and fully automated chromatographs using this principle are described. A specific application to measurement of corticosterone in a rabbit serum preparation allows routine measurement of as little as 300 pg corticosterone per sample.     

Supercritical fluid extraction

Supercritical fluid extraction (SFE) provides for the first time a viable option to conventional and widely used Soxhlet extraction. The ability to change the solvating power of a single supercritical fluid by changing its density is an exceedingly attractive feature. An environmentally safe alternative such as supercritical carbon dioxide to organochlorine solvents which are widely used today in many government and industrial analytical laboratories for sample preparation is desirable. SFE may also constitute a viable alternative to other popular sample preparation techniques such as liquid-liquid extraction, solid phase extraction and purge/trap. Much research, however, must be done in order to understand, optimize and apply this technology. For example, (a) automation of extraction, (b) matrix effects, (c) new fluids/modifiers/additives, (d) trapping efficiency, (e) recovery of extracted analytes, and (f) extraction kinetics are some areas which need a greater understanding. This review is concerned with many of these topics as they relate to trace organic analysis wherein SFE is the primary sample preparation technique.     

Determination of Pesticide Residues in Cereals by Liquid Chromatography and UV Detection

Abstract

A chromatographic method to determine pesticide residues in cereals by high-performance liquid chromatography (HPLC) and ultraviolet (UV) detection has been described. The study focused on the preliminary purification procedure because of the analytical problems associated with the presence in these food matrices of high-molecular-weight compounds, such as lipids, triglycerides, celluloses, and starch, which can interfere and reduce the chromatographic separation efficiency of the analytes. The method proposed is based on the extraction of pesticide residues from 5 g of sample extracted with the use of petroleum ether and on cleanup with a C18 cartridge. The pesticides were eluted with acetonitrile. The column packed with solid support was eluted with a suitable solvent, and only a portion of flow outlet side of the UV detector was collected. Using the information of standard UV trace, it was possible to establish an appropriate portion and to ensure the collection of all pesticides analyzed. The simple and rapid proposal method has shown good recovery (70–110%) for different spiked levels of samples (0.025–0.1 mg/Kg) and could be applied to other food matrices that containing high-molecular-weight compounds.     

Ultrasonic-Assisted Nebulization Extraction Coupled with SPE and HPLC for the Determination of Triterpenoids in Root of Euphorbia pekinensis Rupr.

In this work, a novel method based on ultrasonic-assisted nebulization extraction coupled with solid phase extraction (UANE-SPE) and determined by high performance liquid chromatography was developed for the determination of triterpenoids in root of Euphorbia pekinensis Rupr. The experimental conditions for the UANE-SPE, such as type of extraction solvent, sample amount, type and amount of sorbent, extraction time and volume of the elution solvent, were examined and optimized. The method was successfully applied to determine euphol and tirucallol in the dried root of E. pekinensis Rupr. The recoveries of the analytes were in the range of 89.1–102.0 %. The limits of detection were 12 μg g⁻¹ for tirucallol and 10 μg g⁻¹ for euphol. The extraction yields obtained by the proposed method are higher than those obtained by the conventional extraction methods, such as reflux and ultrasonic-assisted extraction. Compared with the traditional methods, the proposed method can reduce the consumption of the labor, shorten the sample preparation time and increase the efficiencies in the extraction of active constituents from plant materials.

     

Multiresidue Analysis of Organic Pollutants in Water by SPE with a C8 and SDVB Combined Cartridge

Abstract

A multi-component target method for screening purposes to determine organic pollutants of different polarities in water is reported. The following classes of chemicals were tested: base-neutral and acidic herbicides, phenolic compounds, polycyclic aromatic hydrocarbons and phthalic acid esters.

Data was initially obtained from the extraction of one liter of water sample, using separate octyl bonded porous silica (C8) and highly crosslinked polystyrene based polymer columns (SDVB) cartridges. A second set of data was obtained using for the extraction a combined cartridge containing both phases. The analysis was carried out directly by GC-MS in SIM mode, without any derivatisation, with the exception of acidic herbicides, derivatised with pentafluorobenzylbromide. The obtained results showed recoveries between 75% and 98% at two different spiking levels, with relative standard deviations below 15%.     

Supercritical fluid extraction in plant essential and volatile oil analysis

The use of supercritical fluids, especially carbon dioxide, in the extraction of plant volatile components has increased during two last decades due to the expected advantages of the supercritical extraction process. Supercritical fluid extraction (SFE) is a rapid, selective and convenient method for sample preparation prior to the analysis of compounds in the volatile product of plant matrices. Also, SFE is a simple, inexpensive, fast, effective and virtually solvent-free sample pretreatment technique. This review provides a detailed and updated discussion of the developments, modes and applications of SFE in the isolation of essential oils from plant matrices. SFE is usually performed with pure or modified carbon dioxide, which facilitates off-line collection of extracts and on-line coupling with other analytical methods such as gas, liquid and supercritical fluid chromatography. In this review, we showed that a number of factors influence extraction yields, these being solubility of the solute in the fluid, diffusion through the matrix and collection process. Finally, SFE has been compared with conventional extraction methods in terms of selectivity, rapidity, cleanliness and possibility of manipulating the composition of the extract.     

Overview of Analytical Methodologies for Dioxin Analysis

Abstract

Poly(chlorinated) dibenzo‐p‐dioxins and dibenzofurans (PCDDs/PCDFs) are persistent organic pollutants which are globally distributed in practically all environmental compartments and which exert a broad spectrum of toxic and biochemical effects. Humans are exposed to these compounds mainly through the diet with food of animal origin usually being the predominant source.

Multiple step isolation and clean up procedures are necessary to determine trace levels of these analytes in complex environmental and biological samples. This article reviews some of the recent developments in the extraction procedures, such as SFE, PLE, HS‐SPME, MAE, SCWE, ASE; clean‐up areas and instrumental analysis of dioxins in biological/environmental samples. Due to its specificity and sensitivity gas chromatography coupled with high resolution mass spectrometry (GC–HRMS), high‐resolution gas chromatography high‐resolution mass spectrometry (HRGC‐HRMS), or GC‐MS/GC techniques have been extensively applied to environmental, medicinal, and biological studies.     

Dispersive solid-phase extraction based on mesoporous melamine-formaldehyde polymer for sensitive determination of five chlorinated herbicides residues in water by high-performance liquid chromatography

ABSTRACT

In this work, a low-cost melamine-formaldehyde polymer with large-surface-area mesoporous structure was prepared and applied as an efficient solid sorbent for pre-concentration of five kinds of chlorinated herbicides including fomesafen, atrazine, pyrithiobac-sodium, benazolin and acifluorfene from water samples. Extraction parameters such as pH of the sample solution, amount of mesoporous melamine-formaldehyde polymer (mMFP), extraction time, type of desorption solv-ent and volume of the sample were systematically investigated. Combining dispersive solid-phase extraction with high-performance liquid chromatography (HPLC), the detection limits (S/N = 3) of the five herbicides were ranged from 0.04 to 0.18 μg L^?1 with good linearity (R² ≥ 0.9908). Then the tap water and river water samples were analysed by the developed method, and the obtained results indicated that this method provides acceptable recoveries and precisions. mMFP can be prepared through one-pot catalyst-free polymerisation from low-cost starting materials, so that they could be easily scaled up for the sample pre-treatment and have the powerful potentiality in purification of contaminated water.     

Sub-critical fluid extraction of morphinic alkaloids in urine and other liquid matrices after adsorption on solid supports

Summary Supercritical fluid extraction (SFE) of liquid matrices is difficult and requires special instrumentation. An alternative is to load the liquid on a solid support prior to extraction. This procedure yields higher selectivity and can be used as a clean-up step when very complex liquid matrices, such as urine, are to be analyzed. This paper demonstrates the use of various solid supports in order to extract morphinic alkaloids with subcritical fluids (CO₂ + polar modifier). Optimization of the procedure with regard to loading conditions, SFE parameters such as pressure, extraction time, flow rate and eluent composition, was carried out with morphinic alkaloids in aqueous solution. As a real-life application, SFE of opiates in urine were tested with two silica bonded phase supports (C18 (polygosil 60-4063, from Macherey-Nagel) and Bond Elut Certify from Analytichem International). Recovery, variation coefficients and linearity are described for each procedure. Bond Elut Certify silica was chosen as the best solid support and SFE is compared with conventional solid phase extraction.