Ultrasonic supercritical fluid extraction

Off-line supercritical fluid extraction, ultrasonic supercritical fluid extraction, and on-line supercritical fluid extraction-gas chromatography methodologies that have been developed specifically for analytical sample preparation and analysis are described. These methods offer the potential for extraction rate increases of over an order of magnitude, and are compatible with online analysis which provides the basis for automated sample preparation and analysis. These methods are particularly useful for small sample sizes or trace levels of analytes, and have been demonstrated to operate quantitatively. Combined ultrasonic supercritical fluid extraction can further enhance extraction rates from macro-porous materials by inducing convection through internal pores. The apparatus and instrumentation are described in detail and several examples are presented illustrating the applicability of these methodologies. 

Figure 4. Schematic diagram of the ultrasonic supercritical fluid extraction apparatus.

Off-line supercritical fluid extraction, simultaneous ultrasonic supercritical fluid extraction, and on-line supercritical fluid extraction-gas chromatography have been described. These analytical supercritical fluid extraction methods provide the potential for very rapid extraction rates and compatibility with on-line analytical methods. Extraction rate increases of over an order of magnitude compared to Soxhlet methods have been demonstrated and even greater increases seem feasible. Optimization of fluid solvating conditions also provides the potential for selective fractionation of specific analytes. The application of ultrasound during supercritical fluid extraction provides an efficient... 

Soxhlet extraction Ultrasonic disruption Supercritical fluid extraction Accelerated solvent extraction... 

S, Soxhlet S , Soxtec R, reflux SF, shake-flask US, ultrasonics SFE, supercritical fluid extraction MAE, microwave-assisted extraction PFE, pressurised fluid extraction (ASE , ESE ) D/P, dissolution/precipitation. 

Ideally, the pollutants to be determined should be removed from the matrix as completely as possible with a minimum amount of the other non-target components. This type of selectivity was certainly anticipated from supercritical fluid extraction. However, trace organic pollutants cover a wide range of polarity, volatility, and molecular size, making selective extraction very difficult to achieve. Currently the most popular extraction methods are Soxhlet [191,400, 402-404], blending [189, 408, 409, 411-455], liquid column extraction and ultrasonic extraction [456], and more recently supercritical fluid extraction [386,456-463]. 

The main comparisons between extraction methods have been made between the Soxhlet, ultrasonication, and supercritical fluid extraction [377, 398,456,461,462]. This has primarily been prompted by the need to evaluate critically the relative merits of SFE as an alternative to the more established methods. Richards and Campbell [456] made a comparison between SFE, Soxhlet, and sonication methods for the determination of some priority pollutants in soil. The SFE apparatus was the same, relatively standard system as described by Campbell et al. [457] with the addition of a C02 cryogenic trap to... 

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

Microwave-assisted extraction [115] has been compared with ultrasonic extraction [116] in the context of soil extraction. Microwave-assisted extraction [117,195-198] and supercritical fluid extraction coupled with on-line infrared spectroscopy detection [ 118,119] have been compared as methods for the extraction of hydrocarbons from soil. 

Ultrasonic extraction, methanol extraction [147] and supercritical fluid extraction have all been applied to the extraction of or the determination of volatile organic compounds [121,122] in soils. However, methods based on headspace analysis or on mass spectrometry are now the methods of choice. 

This chapter covers techniques for the extraction of semivolatile organics from solid matrices. The focus is on commonly used and commercially available techniques, which include Soxhlet extraction, automated Soxhlet extraction, ultrasonic extraction, supercritical fluid extraction (SFE), accelerated solvent extraction (ASE), and microwave-assisted extraction (MAE). The underlying principles, instrumentation, operational procedures, and selected applications of these techniques are described. In a given application, probably all the methods mentioned above will work, so it often boils down to identifying the most suitable one. Consequently, an effort is made to compare these methodologies. 

Novel sample preparation techniques include ultrasonic extractions that use high frequency acoustic waves to heat and break up samples (9), as well as microwave-assisted extractions (MAE) that use long wavelength radiation for faster and less energy intensive extractions of thermally sensitive analytes (JO-13). Other innovations treat samples with high pressure and high temperature solvents in the liquid or in the supercritical state. These adaptations reduce the overall solvent use and speed the extractions. These methods include accelerated solvent extraction (ASE) (14) and supercritical fluid extraction (SEE) (8). 

Drugs [130] and vitamins [131] in medical foods compounds such as felodipine [132] and diltiazem [133] in tablets and corticosteroid residues in bovine liver [134] have also been extracted by ASE, with results comparable to those of conventional techniques such as Soxhlet, ultrasonic or supercritical fluid extraction. 

Traditional methods of extraction, such as Soxhlet, have been replaced by modern techniques as supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), ultrasonic extraction, and accelerated solvent extraction (ASE) during recent years. The application of specific methods to these kinds of samples has permitted the development of a great number of other extraction methods. In the following list, a brief description is given ... 

The focus in Chapters 7 and 8 is on the specific sample preparation approaches available for the extraction of organic compounds from environmental matrices, principally soil and water. Chapter 7 is concerned with the role of Soxhlet, ultrasonic and shake-flask extraction on the removal of organic compounds from solid (soil) matrices. These techniques are contrasted with newer developments in sample preparation for organic compound extraction, namely supercritical fluid extraction, microwave-assisted extraction and pressurized fluid extraction. Chapter 8 is arranged in a similar manner. Initially, details are provided on the use of solvent extraction for organic compounds removal from aqueous samples. This is followed by descriptions of the newer approaches, namely solid-phase extraction and solid-phase microextraction. 

Sample preparation is often more difficult and time-consuming than the actual analysis procedure. Furthermore, extraction of analytes from the matrix is generally the most time-consuming step of sample preparation and it can lead to relatively inefficient analyte recoveries. Off-line supercritical fluid extraction provides an alternative to traditional Soxhlet or ultrasonic liquid extraction methods. Several recent studies have shown analytical SFE provides comparable or better extraction efficiencies than Soxhlet... 

Extraction, isolation and quantitation steps for POPs are summarized in Figure 1. Soxhlet extraction remains the method used by most analysts for recovery of chorinated pesticides and PCBs from sediments, and the one which other techniques such as shaking with solvent, ultrasonication, microwave assisted extraction, pressurized fluid extraction (PFE) and supercritical fluid extraction, are compared. 

A, acaricide AV, avicide I, insecticide F, fungicide H, herbicide GR, growth regulator N, nematocide R, rodenticide US, ultrasonication LLE, liquid-liquid extraction CU, cleanup ImCU, immuno cleanup SPE, solid-phase extraction MSPD, matrix solid-phase dispersion SBSE, stir bar sorptive extraction SD, steam distillation FMSE, focused microwave Soxhiet extraction PFE, pressurized fluid extraction ASE, assisted solvent extraction ScFE, subcritical fluid extraction SFE, supercritical fluid extraction SEC, size-exclusion chromatography LC, liquid chromatography (fraction collection) LTLP, low temperature lipid precipitation. 

Efficient extraction of PAHs from the sample matrix is a crucial step in the preparation of a sample for PAH determination. Knowledge of extraction recoveries allows corrections to be made for PAH quantities not extracted and losses in analytical measurements. Solvent extraction methods, employing Soxhlet, ultrasonic, and supercritical fluid extraction (SEE) procedures are widely used. 

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. 

Phenols are an important group of phytochemicals with significant health beneficial effects. Extraction of phenols firom the biological sources is a growing field of interest and is an integrated part of analytical methods. Some of the common methods of extraction of phenolic compounds are solvent extraction, accelerated solvent extraction, supercritical fluid extraction, ultrasonic extraction, and microwave extractimi. Separation is the next important step of analytical methods, which is done to separate the required phenolic components from the unwanted part of the extract. In case of phenols, methods such as... 

Supercritical fluid extraction (SFE) has been used increasingly since the mid-1980s for extracting components of interest from solid samples prior to chromatographic analyses. Liquids can be placed in an extraction thimble and extracted successfully, but procedures are more difficult (Majors, 1997). Extractions with a supercritical fluid are generally faster compared to conventional extraction with liquid solvents (e.g., Soxhlet or ultrasonic) other advantages include reductions... 

Saponins from plant materials can be extracted using different techniques and solvents. The conventional techniques for saponin extraction used soxhlet, liquid-liquid or solid-liquid extraction (Berhow et al. 2002 Hassan et al. 2010a, b). These methods consume a lot of solvent, time and may lead to potentially deleterious degradation of labile compounds (Kerem et al. 2005). Therefore, in recent years, new extraction techniques include accelerated solvent extraction, supercritical fluid extraction, solid-phase microextraction, sonication, extraction with supercritical or subcritical water, and microwave-assisted extraction have been developed and are considered to be more efficient than the conventional methods (Wu et al. 2001 Kerem et al. 2005 Ligor et al. 2005 Gii lii-Ustundag and Mazza 2007). Ultrasonication-assisted extraction of ginseng saponins was about three times faster than the liquid-liquid extraction and can be carried out at lower temperature (Wu et al. 2001). Kerem et al. (2005) reported that methanol- microwave assisted method to extract saponin of chiclqtea proved to be faster and more efficient than soxhlet extraction. 

Bruni, R., Guerrini, A., Scalia, S., Romagnoli, C. and Sacchetti, G. 2002. Rapid techniques for the extraction of vitamin E isomers from Amaranthus caudatus seeds Ultrasonic and supercritical fluid extraction, Phytochem. Anal. 13 257-261. 

Sensitive, rapid, simple, and accurate analytical methods have been developed to determine PAHs and their derivatives in the atmospheric particles. Extensively used are GC and coupled methods like GC-FTD, GC-MS, and HPLC-EL as highly efficient separation tools have been used for analyzing aU kinds of samples. The direct determination of traces of PAHs and their derivatives by modem chromatographic techniques is still difficult. There are some limitations associated with the insufficient sensitivity of these techniques and also problems related to matrix interference. For instance in the case of samples of atmospheric particulates, extraction methods of PAHs and their derivatives include traditional Soxhlet extraction, ultrasonic extraction, supercritical fluid extraction, microwave-assisted extraction, and accelerated solvent extraction. ... 

For the analysis of organic additives in polymeric materials, in most cases, prior extraction will be necessary. Depending on the nature of the additive, many different approaches are employed. These include soxhlet extraction with organic solvent or aqueous media, total sample dissolution followed by selective precipitation of the polymer leaving the additive in solution, assisted extraction using pressurised systems, ultrasonic agitation and the use of supercritical fluids. In trace analysis, solid phase extraction (SPME) from solution or solvent partition may be required to increase the analyte concentration. 

MTs = metallothioneins NMR = nuclear magnetic resonance pKa = negative logarithm of acid dissociation constant PMT = photomultiplier tube QITMS = quadrupole ion trap mass spectrometry SBSE = stir bar sorptive extraction SDS-PAGE = sodium dodecylsulfate polyacrylamide gel electrophoresis Se-Cis = selenocystine Se-Cys = selenocysteine Se-Et = selenoethionine Se-Hcy = seleno-homocysteine Se-Met = selenomethionine SEC = supercritical fluid chromatography TBT = tributyltin TETRA = tetramethylarsonium ion Tf = transferrin TMAsO = trimethylarsineoxide TMSe = trimethylselonium ion TOFMS = time of flight mass spectrometry USN = ultrasonic nebulizer. 

---