Supercritical fluid extraction laboratory analysis

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. 

A supercritical fluid is a substance that comes into existence after the so-called critical point has been exceeded, that is, when it simultaneously exhibits the properties of a gas and a liquid, but is actually neither the one nor the other. In 1962, Klesper, Corwin, and Turner were the first researchers to use supercritical fluids for analytical purposes. A supercritical fluid was used in high-pressure fluid chromatography, where it was part of the mobile phase. Extraction with a supercritical fluid was first achieved in 1978, since when the supercritical fluid extraction (SFE) technique has been undergoing active development, finding many applications in laboratory analysis and industry.212... 

Sample preparation represents a formidable challenge in the chemical analysis of the real-world samples. Not only is the majority of total analysis time spent in sample preparation, but also it is the most error-prone, least glamorous, and the most labor-intensive task in the laboratory. The components to be separated from the matrix are usually taken up with an auxiliary substance such as a carrier gas, an organic solvent, or an adsorbent. These separation processes can be regarded as extraction procedures (i.e., liquid-liquid extraction, liquid-solid extraction, Soxhlet extraction, solid-phase extraction, supercritical fluid extraction, solid-phase microextraction, etc.). 

Steam distillation is the main commercial extraction procedure for the production of essential oils from almost any type of plant material. Solvent extraction is also used commercially and yields a resinoid, concrete or absolute according to the solvents and techniques used (see Chapter 4). Both steam distillation and solvent extraction are used on a laboratory scale to produce oils and extracts for analysis. Other methods of extraction, such as supercritical fluid extraction (SFE), which uses supercritical CO2 as the extraction solvent, are now being developed and used on both commercial and laboratory scales. The extracts produced by SFE may contain different materials from the steam-distilled oil because of the solvating power of C02 and the lower extraction temperature, which reduces thermal degradation. The C02 extract may therefore have an odour closer to that of the original material and may contain different fragrant compounds. The choice of extraction procedure depends on the nature and amount of material available, and the qualities desired in the extract. Solvent extraction is better suited to small sample amounts or volatile materi-... 

Interest in supercritical fluid (SF) technology has increased because of its effectiveness in the extraction and analysis of natural products and concern related to the use and disposal of conventional organic solvents. Several laboratories have employed supercritical fluid extraction (SFE) methodologies in the extraction of garlic and onion [56-58]. 

The growing interest in secondary metabolites of plants leads to the requirement of the development on analytical method for the secondary product analysis. Chromatographic procedures for the determination of alkaloids have been well established. Based on the literatures published in past years, further improvement of the current methods for the analysis of Catharanthus alkaloids are needed [4]. Besides, the chemical complexity and unique bisindole alkaloid structure of the aforementioned molecules hindered their laboratorial synthesis. The isolation of VLB and VCR is laborious and costly, mainly due to their low contents in the plant and coexistence in a large number of other alkaloids [5]. Therefore, it is important for separation, identihcation, and quantiflcation of these Catharanthus alkaloids. The methods of extraction and purification were focused on liquid-liquid extraction, solid-phase extraction, supercritical fluid extraction (SFE), and molecularly imprinted polymers (MlPs)-based extraction. For separation, GC is not suitable for the bisindole alkaloids due to their high boiling point. The major methods for analysis of Catharanthus alkaloids are liquid chromatography (LC) and capillary electrophoresis (CE). 

Major applications of SFE-SFC are somewhat limited at the moment to the analysis of lipids and pesticides from foods and similar matrices and different types of additives used in the production of polymers [79,146,188-194]. The approaches used cover a wide range of sophistication and automation from comprehensive commercial systems to simple laboratory constructed devices based on the solventless injector [172,174,175,188]. Samples usually consist of solid matrices or liquids supported on an inert carrier matrix. Aqueous solutions are often analyzed after solid-phase extraction (SPE-SFE-SFC) to minimize problems with frozen water in the interface [178,190]. The small number of contemporary applications of SFE-SFC reflects a lack of confidence in supercritical fluid chromatography as a separation technique and competition for... 

In connection with the more recent interest in SFC, methods for the analytical application of extraction with supercritical fluids have been extensively developed. At the Arrhenius Laboratories SFE has been applied to the extraction of different types of rapeseeds and other oil seeds as a part of a breeding project. SFCs of two of these extracts are shown in Fig. 2.8. Traditionally, such seeds are examined for total fat content, either gravimet-rically after Soxhlet extraction or by means of elementary analysis. In addition, the fatty acid pattern is analysed by GC after hydrolysis and methylation. Soxhlet extraction can be replaced by SFE followed by a gravimetric analysis to quantify the extract. Alternatively, quantification can be performed on a detector (ELDS) that has been connected directly to... 

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