Residue analysis supercritical fluid extraction

J.W. King and K.S. Nam, Coupling enzyme immunoassay with supercritical fluid extraction, in Immunoassays for Residue Analysis, ed. R.C. Beier and L.H. Stanker, American Chemical Society, Washington, DC, Chapter 34, pp. 422-438 (1996). 

Before the extraction procedure may commence, the sample must be prepared in such a way that it is in a condition for extraction of the analyte(s). For analyzing sulfonamide residues in liquid samples such as milk, a pretreatment dilution step with water prior to direct fluorometric detection may be required (207). Dilution of milk with aqueous buffer (208) or sodium chloride solution (209) prior to sample cleanup has also been reported. For the analysis of honey a simple dissolution of the sample in water (210, 211) or aqueous buffer (212) is generally required. Semisolid samples such as muscle, kidney, and liver, require, however, more intensive sample pretreatment. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. The most popular approach for tissue break-up is through use of a mincing and/or homogenizing apparatus. Lyophilization (freeze-drying) of swine kidney has been carried out prior to supercritical-fluid extraction of trimethoprim residues (213). 

Extraction of fat by supercritical carbon dioxide was investigated as an important option for minimizing the expanded use of frequently flammable and carcinogenic solvents in food analysis. Unfortunately, the presence of moisture in foods has an adverse effect on the quantitative extraction of fat by supercritical fluid extraction (SEE). Hence, samples have to be lyophilized first. The total fat content of freeze-dried meat and oilseed samples was found to be comparable to values derived from Soxhlet-extracted samples (26). Besides, only small amounts of residual lipids could be recovered by an additional extraction of the SFE-extracted matrix by the Bligh and Dyer solvent extraction procedure. As far as the minor constituents are concerned, it was found that the extraction recovery ranged from 99% for PC to 88% for PA. Hence, Snyder et al. concluded that SFE can be used as a rapid, automated method to obtain total fat, including total phospholipids, from foods (26). 

The adaptation of supercritical fluid extraction (SFE) in routine residue and metabolism analysis as well as other extraction/separation laboratories and applications has been slow. This is despite the demonstrated feasibility of using SFE for the removal of sulfonylureas, phenylmethylureas and their metabolites from soil and plant materials (1-2), as well as widespread demonstrated use of supercritical fluid extraction for other applications (3-6). The reason for this is simple. Although automated, SFE extraction apparatus typically only analyzes a single sample at a time. The technique could not compete effectively with the productivity of an experienced technician performing many sample extractions simultaneously. In essence, with a one vessel automated supercritical fluid extractor, operator attendance is high and throughput is about the same or even less than current conventional liquid-liquid and solid-liquid extraction techniques. 

The introduction of commercial instrumentation in this automated area has been too slow and too disappointing to meet the need for routine analysis of numerous samples. The options have been the extraction of one sample at a time or individual samples in parallel. Either of these options make the repetitive analysis of the same sample or the sequential analysis of different samples exceptionally time consuming. Parallel analysis, proposed by one manufacturer, is susceptible to cross-contamination and across the board sample loss with clogging of one extraction vessel. In order to move supercritical fluid extraction into the realm of routine operations for residue analysis, rapid analysis of multiple samples needed to be addressed. 

Ramsey, E.D., Perkins, J.R., Games, D.E., and Startin, J.R. 1989. Analysis of drug residues in tissue by combined supercritical-fluid extraction-supercritical-fluid chromatography-mass spectrometry-mass spectrometry. Journal of Chromatography, 464 353-64. 

Fig.l Schematic diagram of the main steps of the solid-liquid extraction (SLE) and supercritical fluid extraction (SEE) methodologies for pesticide residue analysis. 

Fig. 2 Gas chromatogram (BCD) resultant from the analysis of captafol residues in tomato, after supercritical fluid extraction with neat CO2 without further cleanup.

Motohashi, N., Nagashima, H., and Parkanyi, C., Supercritical fluid extraction for the analysis of pesticide residues in miscellaneous samples, J. Biochem. Biophys. Methods, 43, 313-328, 2000. 

Detailed analytical methods were as previously described [18]. Gel permeation chromatography (GPC) and capillary columns were employed for the precise analysis of the products. After each reaction, residual products remaining within the catalyst and the reactor were extracted by supercritical n-hexane at 250 °C (10 °C higher than the reaction temperature) and 35 bar, with additional N2 pressure of 10 bar. The supercritical fluid extraction after the reaction was conducted for 1 h, after which the products were also determined by chromatography [19]. 

Analysis of plants normally involves a sample preparation stage such as extraction or distillation followed by analysis with gas chromatography or liquid chromatography. The common methods used currently for the isolation of essential oils from natural products are steam distillation and solvent extraction (Ozel Kaymaz, 2004). Losses of some volatile compounds, low extraction efficiency, degradation of xmsaturated compounds through thermal or hydrolytic effects, and toxic solvent residue in the extract may be encountered with these extraction methods. Recently, more efficient extraction methods, such as supercritical fluid extraction (SFE) (Simandi et al., 1998) and accelerated solvent extraction (ASE) (Schafer, 1998) have been used for the isolation of organic compounds from various plants. Subcritical or superheated water extraction (SWE) is non-toxic, readily available, cheap, safe, non-flammable and is a recyclable option. 

Examples of basic studies of offline extraction and preconcentration of pesticide residues using other techniques, such as online dialysis, steam distillation, supercritical fluid extraction, pressurized liquid extraction, cloud point extraction, or liquid-liquid membranes, have been reported. The large amounts of matrix coextractives and the need for clean extracts in CE/ultraviolet (UV) analysis are the main reasons for their scarce application. 

See also Dioxins. Extraction Solvent Extraction Principles Supercritical Fluid Extraction. Food and Nutritional Analysis Antioxidants and Preservatives Pesticide Residues Mycotoxins Packaging Materials. Gas Chromatography Overview. Hormones Steroids. 

Choi, J.H. Abd El-Aty, A.M. Shen, J.Y. Kim, M.R. Shim, J.H. Analysis of fluoroquinolone residues in edible chicken tissues using supercritical fluid extraction. Berl Munch Tierarztl Wochenschr 2006,119, 456-460. 

Solid-phase extraction (SPE) using small, disposable cartridges, columns, or disks is employed for isolation and cleanup of pesticides from water and other samples prior to TLC analysis, especially using reversed-phase (RP) octa-decyl (C-18) bonded silica gel phases. Microwave-assisted extraction (MAE) is a time- and solvent-saving method for removing residues from samples such as soils. Supercritical fluid extraction (SEE) has been used for sample preparation in the screening of pesticide-contaminated soil by conventional TLC and automated multiple development (AMD). Ultrasonic solvent extraction (USE) and videodensitometry have been combined for quantification of pesticides in sod. Matrix solid-phase dispersion (MSPD) with TLC and GC has been used to determine diazinon and ethion in nuts. 

In this context, studies about the development of relevant analytical methods allowing the detection of pesticide residues in VOO are usually focused on an optimization of the various steps of the analysis process, namely extraction, clean-up, identification, and quantitation of pesticide content. The common extraction methods are Soxhlet extraction, microwave-assisted extraction (MAE), supercritical fluid extraction (SEE), and accelerated solvent extraction (ASE). Cleanup methods include SPE, matrix solid-phase dispersion (MSPD), and gel permeation chromatography (GPC). 

The first article in IMS involving soils was the determination of 2,4-D residues in soils. In this method, samples were extracted, esterifled with methanol in the presence of a boron trifluoride catalyst, and then analyzed by capillary GC with an IMS as detector. The procedure depended on the use of an IMS analyzer, for which mobility selection of an ion was made using a dual-shutter design. Selective monitoring of the product ion formed with the methyl ester of 2,4-D permitted direct analysis of the derivatized extract without further preparation. Recovery was 93% of 2,4-D for 50 ppb in spiked soils. Later, supercritical fluid chromatography was substituted for the GC, ° allowing measurements without derivatization of the soil extract. The detection limit for 2,4-D was estimated as 500 ppb. 

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