The Extraction of Solid Samples

Sample Microwave assisted extraction Conventional extraction  

50-100 ml), which makes their operation inexpensive [26], Guerin [27] compared the extraction recoveries of polynuclear aromatic hydrocarbons (PAHs) from aged clay soil using classical and automatic Soxhlet assemblies, and the author reported comparable results from the two technologies when the extraction was carried out for only 8 h. 

Accelerated solvent extraction (ASE) is a sample preparation technique that works at elevated temperature and pressure, using very small amounts of solvent. The restrictions and limitations of this method are more or less similar to those of Soxhlet extraction technology. The method development is simple, as it involves few operational parameters. The selection of the 

ASE method development is very easy, as it requires the selection of the temperature and solvents, which govern the efficiency of the extraction. The other parameters that control the recovery of the extraction are the static time, the flushing volume and the number of static cycles used in the extraction. It is very interesting to note that the first application of this method was reported in the extraction of environmental pollutants [30-38]. Therefore, the ASE method has become very popular in the extraction of environmental samples [39]. Moreover, its use has been expanded for the extraction of many organic and inorganic substances from foodstuffs, polymers, pharmaceuticals and other types of sample. The application of the ASE technique for environmental samples is summarized in Table 5.3. 

Supercritical fluid extraction (SEE) is a selective technique of sample preparation that enables the preparation of matrices by varying several physical parameters. Nowadays, it is considered to be the best replacement for many extraction technologies, such as accelerated solvent, Soxhlet solvent, microwave assisted extraction and so on. It was originally marketed as a universal extraction tool in 1988 by Isco Inc. (Lincoln, Nebraska, USA), Lee Scientific (Salt Lake City, Utah, USA) and Suprex Corp. (Pittsburgh, Pennsylvania, USA). The basic components of the SFE instmment are a carbon dioxide reservoir, a pump, an extraction vessel, an oven, a restrictor 

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SPE methods with different cartridge packings have been employed for the pre-concentration and clean up of sulfonated azo dyes from waters and soil extracts [110,111], The extraction of solid samples has been carried ont by sonication or Soxhlet extraction and the extracts treated like the water samples. C18 cartridges and columns [111] were used followed by the elution with aqueous organic solvents in the presence of TEA with recovery yields always greater than 65% [93,111], Higher recoveries have been obtained by using C18 columns, pre-conditioned with an ammonium acetate buffer and elnted with methanol [111], The use of styrene-divinylbenzene [93,112], as well as of cross-linked polymeric sorbents with sulfonate functions, was shown to be suitable in the SPE of the more polar componnds [111],... 

Instead of a liquid, a supercritical fluid can be for the extraction of solid samples. Carbon dioxide is an ideal solvent. The solvation strength can be controlled via the pressure and temperature. The high volatility of CO2 enables concentration of the sample and easy removal of the extraction liquid. 

SFE usually refers to the extraction of solid samples with CO2 above its critical temperature and pressure. SFE greatly reduces extraction time, is inexpensive and nontoxic, and its properties can be tuned by changing temperature and pressure or adding modifiers. USEPA Method 3561 provides a method for the extraction of PAHs from soils, sediments, fly ash, solid-phase media, and other solids. Two- and three-ring PAHs can be extracted in pure CO2 while the higher molecular mass PAHs require the addition of modifiers. Supercritical CO2 is similar in solvent properties to HEX and can be modified by the addition of water or organic solvents. 

This mode of chromatogram development is, in principle, almost identical with continuous development. The only feature that varies is the length of the developing path. In short bed-continuous development (SB/CD), this path is very short, typically equal to several centimeters [23-25]. This is the reason why this mode is preferentially applied for analytical separations. However, a similar technique is applied for zonal sample application and online extraction of solid samples, which are described in the following text. 

The procedure described earlier for sample preconcentration can be easily extended for the online extraction of solid samples, e.g., powdered plant materials. Horizontal conbguration of the chromatographic plate in the chamber facihtates this procedure, because the sample to be extracted is then placed on a carrier plate at the begiiming part of the adsorbent layer (or in the scrapped channel of the adsorbent layer), which should be directed upward [15,26]. The chamber is covered with a narrow plate, and the development is started with a snitable extracting solvent. In some cases, it is advantageous to put the narrow plate directly on the adsorbent layer to press the sample to be extracted. Extracted components are preconcentrated on the adsorbent layer at the end of the narrow plate, as shown in Fignre 6.26 [15]. 

The most widely employed techniques for the extraction of water samples for triazine compounds include liquid-liquid extraction (LLE), solid-phase extraction (SPE), and liquid-solid extraction (LSE). Although most reports involving SPE are off-line procedures, there is increasing interest and subsequently increasing numbers of reports regarding on-line SPE, the goal of which is to improve overall productivity and safety. To a lesser extent, solid-phase microextraction (SPME), supercritical fluid extraction (SEE), semi-permeable membrane device (SPMD), and molecularly imprinted polymer (MIP) techniques have been reported. 

There are a number of procedures described in the literature dealing with the extraction of emerging contaminants from solid matrices. For extractions of solid samples, Soxhlet is widely accepted as a robust liquid-solid extraction technique. 

This relatively new method is quite different from other mass spectrometric techniques usually used for this topic. ToF-SIMS presents two main advantages. First, it permits the analysis of solid samples with minimal sample preparation. This avoids the necessity of extractions, and therefore, it can be very useful for small and precious samples. 

Solvent extraction reduction is most frequently performed mainly in connection with the extraction of solid and biological samples by liquid partition. Extractions are typically accomplished using a Soxhlet apparatus that provides the benefits of multiple extractions. By repeated distillation and condensation of the solvent, the apparatus allows multiple extractions using the same (small) volume of solvent. Soxhlet extraction has been a standard method for many decades, and it is often the method against which other extraction methods are measured and verified [14]. 

Matrix solid-phase dispersion (MSPD) is the extraction method of choice for the analysis of solid samples, such as plant material, foodstuffs or tissue samples [26]. This method has been developed especially for solid or viscous matrices. MSPD is preferable to other extraction techniques, because the solid or viscous sample can be directly mixed with the sorbent material of the stationary phase [27]. As the carotenoid stereoisomers stay bound in their biological matrix until the elution step, they are protected against isomerisation and oxidation [28]. The extraction scheme of MSPD is shown in Figure 5.2.1. 

Although analytical chemists have shown little interest in the use of ultrasound, its potential usually surpasses that of other, conventional auxiliary energies. Thus, ultrasound is of great help in the pretreatment of solid samples as it facilitates and accelerates operations such as the extraction of organic and inorganic compounds [2,3], slurry dispersion [4], homogenization [5] and various others [6-8]. 

This chapter describes the principal applications of microwaves to the pretreatment of solid samples, with special emphasis on digestion and extraction, which are their two main uses in analytical chemistry. The description is preceded by a discussion of the fundamentals of microwave energy and its interaction with matter, and also of the equipment used by analytical laboratories, which can be of the open or closed type depending on whether they operate at atmospheric pressure or a higher level and whether they use multi-mode or focused microwaves. Selected designs developed for specific purposes are also commented on. 

After the initial euphoria of the late 1980s and 1990s, SFE has consolidated as a powerful tool for the analysis of environmental, pharmaceutical, polymer and, especially, food samples (particularly fat analyses, which have boosted SF extractor sales recently) [17]. Notwithstanding its major restrictions (especially in relation to the extraction of polar analytes and the treatment of natural samples), SFE can undoubtedly expedite the pretreatment of solid samples with the aid of special approaches to the extraction of medium-polar and polar analytes. Foreseeing the direction in which SFE applications will move in the future entails considering the nature of its latest uses. 

The method of standard additions has been used to suppress the influence of the bulk composition of solid samples. It requires that the analyte contained in the solid sample and the added analyte be identically affected by the matrix. This method can be used in three different ways in connection with solid samples. One involves adding increasing amounts of analyte to fixed amounts of sample. In the second, a single amount of sample is subjected to a single addition of analyte from a standard solution, which can lead to inaccuracy in the final result. In the third approach, both the amount of solid sample used and that of standard added are varied the instrumental signal is a function of two independent variables and can be extracted by multiple linear regression. 

A number of alternatives to Soxhlet extraction have been described. By pressurized liquid or accelerated solvent extraction, the extraction efficiency can be enhanced. Superheated water extraction, taking advantages of the decreased polarity of water at higher temperature and pressure, has been used for liquid extraction of solid samples as well. 

Supercritical fluid chromatography (SEC) was developed at an earlier stage (hrst demonstrated in 1962) than SF extraction (SFE), which emerged in the mid-1980s as a promising tool to overcome the difficulties of solid sample extractions. ... 

The advantage of SPE over LEE is that large concentration factors can be obtained with little or no solvent concentration, and thus there is no concentration of phthalate traces from the organic solvent. The major limitation of SPE is in the extraction of water samples containing solids or heavily contaminated samples. In the hrst case, samples have to be hltered and the phthalates measured separately in the aqueous and the solid phases. In the second case, low recoveries could be achieved as a result of the incomplete enrichment of the sorbent material. ... 

Clean-up is the most important step for biological samples because they are rich in fat and lipids, etc. Liquid-solid chromatography and gel permeation chromatography (GPC) are widely used for the clean-up of extracts. GPC is very useful in removing fats from the extracts of biological samples. The most widely used gel column is SX-3 BioBeads (200-400 mesh) in a range of column sizes and solvents. The eluents used in GPC are mostly mixtures such as cyclohexane-ethyl acetate, cyclohexane-dichloromethane, toluene-ethyl acetate and... 

More than one hundred papers reporting diverse applications to analyse wines were published until know. The majority of the referred methodologies use the headspace mode (HS-SPME) instead of the direct immersion mode (DI-SPME). In terms of performance, SPME showed comparable results to LLE or SPE. However, SPME is simpler and solvent-free, and uses smaller volumes of sample nevertheless, on the other hand, LLE had the possibility of carrying out simultaneously the extraction of several samples (Bohlscheid et al., 2006 Castro et al, 2008). When the interest is to obtain the maximum information about the volatile fraction of a wine, the coating DVB/CAR/PDMS seem to be the most suitable (Tat et al., 2005). On the other hand, for specific applications, the choice of a suitable solid-phase, depends on the class of compounds be analyzed, e.g. CAR/PDMS for volatile sulphides and disulphides (Mestres et al., 1999), on-fibre derivatization (PA) for the determination of haloanisoles and halophenols (Pizarro et al, 2007). 

As stated before, MAE has been used mainly for extraction of solid samples. The use of MAE is a continuously expanding area of research at present. As a... 

Extraction of pesticide residues from liquid samples can be performed using a solid sorbent material. Currently available sorbent extraction techniques include (1) solid-phase extraction (SPE), (2) solid-phase microextraction (SPME), and (3) stir-bar sorptive extraction (SBSE). In the case of solid samples, a liquid extraction of pesticide residues (transfer into a solution) usually precedes the sorption step thus, it should be considered rather as a clean-up than an extraction. Matrix solid-phase dispersion (MSPD) represents a unique SPE approach that combines extraction and clean-up of solid or semisolid food samples in one step. In MSPD, the sample is mixed with a sorbent (Florisil, Cig, Cg) that serves as a solid support in sample disruption and dispersion. The resulting mix is packed into a column from which the analytes are eluted while separated matrix components are retained by the sorbent. The main drawbacks of this approach comprise rather small sample sizes ( 0.5g) and a relatively high consumption of expensive sorbents. 

Schaefer et al. (19) studied the interphase microstructure of ternary polymer composites consisting of polypropylene, ethylene-propylene-diene-terpolymer (EPDM), and different types of inorganic fillers (e.g., kaolin clay and barium sulfate). They used extraction and dynamic mechanical methods to relate the thickness of absorbed polymer coatings on filler particles to mechanical properties. The extraction of composite samples with xylene solvent for prolonged periods of time indicated that the bound polymer around filler particles increased from 3 to 12 nm thick between kaolin to barium sulfate filler types. Solid-state Nuclear Magnetic Resonance (NMR) analyses of the bound polymer layers indicated that EPDM was the main constituent adsorbed to the filler particles. Without doubt, the existence of an interphase microstructure was shown to exist and have a rather sizable thickness. They proceeded to use this interphase model to fit a modified van der Poel equation to compute the storage modulus G (T) and loss modulus G"(T) properties. 

In addition to the mass spectrometer itself, there are a number of instrument components that are required to enable mass spectrometric analysis on/at another solar system body. In the case of solid samples (rock, soil, or ice), sampling systems (e.g., pyrolysis, laser abla-tion/desorption, or liquid extraction) are required to extract chemical compounds of interest [14]. After sampling is accomplished, compounds of interest can be preseparated using techniques such as gas chromatography (GC), which serve to improve selectivity and hence better identification of compounds in the analysis. Such gas chromatography-mass spectrometry (GC-MS) systems have been successfully deployed in the past on a variety of solar system exploration missions. 

In the case of water or liquid biological samples, extraction is the next step after filtration, while in case of solid samples it comes after homogenization. Many different devices have been used for extraction procedures. The most important techniques in this field are the classical methods of extraction, liquid-liquid extraction, solid phase extraction and liquid chromatographic techniques. The extraction of solid and liquid samples of environmental and biological origin is described separately. 

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