Extraction from solid matrices

Classical solvent extraction is a phase transfer of solute from the solid phase to solution. All analytical extractions from solid matrices undergo three processes ... 

In this Chapter, fundamentals of design criteria in relation to processes and equipment are reviewed for dense-gas-extraction from solid matrices. Although, as mentioned in previous chapters, numerous dense gases can be used as solvents. In the following discussion we concentrate on the most extensively used gas-carbon dioxide. The reason for this is its nontoxic, non-flammable and inert nature, the possibility of gentle treatment of thermally sensitive materials, and the fact that it is inexpensive and an environmentally acceptable material. 

J. Kronholm, P. Revilla-Ruiz, S.P. Porras, K. Hartonen, R. Carabfas-Martfnez and M.-L. Riekkola, Comparison of gas chromatography-mass spectrometry and capillary electrophoresis in analysis of phenolic compounds extracted from solid matrices with pressurized hot water, J. Chromatogr. A. 1022, 9, 2004. 

Traditionally, the extraction of PAHs from solid samples has been conducted using a Soxhlet method, which, while being efficient, usually takes more than 6 h and uses large volumes of solvent. Several reports have indicated that PAHs can be extracted from solid matrices such as soil and plant and animal tissues... 

Other analytical procedures, such as supercritical fluid extraction (SFE) and microwave-assisted extraction (MAE), are gaining significant attention. SFE is commonly applied to many analyses that require extraction from solid matrices and has found important applications in the... 

This method is similar to ASE. except that healing power is supplied by microwaves. MASE has been used for the extraction of pesticides from soil supercritical fluid extraction of CM pesticides from soil. Lopez-Avila ei al. (1998) studied the stability of OCs and OPs when extracted from. solid matrixes with microwave energy. 

Lopez-Avila, V., Benedicto, I., and Bauer, K. M. (1998). Stability of organochlorine and organophosphorous pesticides when extracted from solid matrixes with microwave energy. J. AOAC Int. 81, 1224-1232. 

Regarding the combination of different levels of salt and sunflower oil, a 3% of fat in the matrix caused a lower extraction of most PAHs as salt concentration increased (Table 2). The opposite trend was observed for most PAHs when there was a 6% of fat in the matrix and increasing salt concentrations were considered, showing a recovery of the extraction of PAHs. It seems that salt and fat shghtly tend to enhance the PAHs extraction from solid matrixes of gelatine only when both ingredients were present at high levels. The combined effect of salt and fat on the release of PAHs from solid matrixes is not simple and most likely depends upon the physicochemical nature of the matrix. 

Extraction Eiltering limits particulate gravimetry to solid particulate analytes that are easily separated from their matrix. Particulate gravimetry can be extended to the analysis of gas-phase analytes, solutes, and poorly filterable solids if the analyte can be extracted from its matrix with a suitable solvent. After extraction, the solvent can be evaporated and the mass of the extracted analyte determined. Alternatively, the analyte can be determined indirectly by measuring the change in a sample s mass after extracting the analyte. Solid-phase extractions, such as those described in Ghapter 7, also may be used. 

To satisfy the Resource Conservation and Recovery Act (1977) and its amendment for hazardous and solid waste (1984), the 80(K) Series Methods have been designed to analyze solid waste, soUs, and groundwater. In particular, methods 8240/8260 require the use of a purge-and-trap device in conjunction with packed or capillary GC/MS, respectively, for the analysis of purgeable organic compounds. Methods 8250/8270 concern analyses for the less-volatile bases, neutrals, and acids by GC/MS after extraction from the matrix by an organic solvent. 

Solid-phase microextraction (SPME) is also a useful alternative to conventional sample cleanup with LLE or SPE. SPME is based on the enrichment of analytes by a partitioning process between a polymeric phase coated on a fused-silica fiber and its surrounding aqueous solution. SPME combines sample preparation in terms of extraction from a matrix of interfering compounds with an enrichment process in a single step. A method for the determination of metazachlor in wastewater samples is described in the literature [34]. In this study, SPME was shown to be a suitable and simple sample preparation method for the determination of metazachlor in wastewater by GC-AED. 

When solid samples are analyzed, OAs are extracted from a matrix by the following procedures (1,2) ... 

Another use of trace enrichment for environmental samples, such as soil and sediment, is the concentration of analytes from organic solvents that have been used to extract the solid matrix, such as methanol, acetone, or acetonitrile (water-miscible solvents). Commonly, water-miscible organic solvents may be used to recover analytes from soils and sediments. These polar organic... 

This method, developed at the end of the 19th century, is still the most widely used when organic compounds have to be extracted from solid materials, like dusts, sand, soil, and marine sediments. It is particularly suitable when the organic material is strongly adsorbed on a porous solid matrix. Such a simple method presents several advantages the sample is repeatedly brought into contact with fresh portions of the solvent and no filtration is required after the leaching step, simultaneous extraction in parallel can be performed since the basic equipment is inexpensive, and finally it has the possibility to extract more sample mass than most of the latest methods [microwave extraction,... 

Extraction of herbicides from solid matrixes has frequently been done by Soxhlet extraction, which required large volumes of solvent and was a time consuming process. Therefore, new extraction techniques have been developed and applied for the past ten years. Herbicides and their main metabolites can be extracted from sohd samples by these new methods such as, SFE, subcritical water extraction (SWE), microwave-assisted extraction (MAE), or pressurized fluid extraction (PFE). From a general point of view. Camel evaluated potentials and pitfalls of SEE, MAE, and PFE. ... 

The limited availability of certified reference materials for herbicides in soils is detrimental to the development of robust extraction methods. In many works, soils are then spiked with known quantities of herbicides and recoveries are calculated to check the applicability of the extraction method. However, although recoveries are often quantitative, they must be interpreted with caution because herbicides have no time to interact properly with the soil matrix constituents. Bearing in mind these hmitations, several techniques to extract herbicides from solid matrixes will be described in this chapter. 

Papilloud, S. and Haerdi, W., Supercritical fluid extraction of triazine herbicides from solid matrixes, Chromatographia, 38, 514-519, 1994. 

Sorptive extraction techniques are based on the distribution equilibria between the sample matrix and a non-miscible liquid phase. Matrices are mostly aqueous and the non-miscible phase is often coated onto a solid support. Analytes are extracted from the matrix into the non-miscible extracting phase. Unlike adsorption techniques, where the analytes are bound to active sites on the surface, the total volume of extraction phase is important. Extraction of analytes depends on the partitioning coefficient of solutes between the phases (Ridgway et al., 2007). Two extraction techniques are commonly employed solid phase microextraction (SPME) and stir-bar sorptive extraction (SBSE). 

A relatively new automated extraction method is PLE, also called accelerated solvent extraction (ASE), which is based on an extraction under elevated temperature (50-200°C) and pressure (3-205 bar) during a short period of time (5-15 min). This technique has been used for the extraction of phenolic compounds from foods such as vegetables and fruits. In PLE, a solid sample is packed into the extraction cell and analytes are extracted from the matrix with conventional low-boiling solvents or solvent mixtures at elevated temperatures up to 200°C and pressure (30-200 bar) to maintain the solvent in the liquid state [61]. 

The recovery of phenolic compounds from solid matrix is a more complex process where different methods can be applied, and it must be mentioned that in this case, the extraction of polyphenols requires special care, because they are easily oxidized and rapidly degraded by light and high temperatures. Antioxidants such as butylated hydroxytoluene (BHT) and ascorbic acid are often added to samples to avoid oxidation of the polyphenols when high temperatures are required [2, 8, 35]. 

Stahl interfaced supercritical fluid extraction (SFE) with TLC more than 15 years ago (84), and the great interest today in SFE, e.g., for extraction of pesticide residues from foods and environmental samples, should lead to development of many applications of this sample preparation method prior to TLC. As an example, hydroperoxides in combustion aerosols were separated from solid matrixes using SFE with on-line sample transfer to TLC plates (84a). 

PAHs from Solid Matrixes Extracted by SPME-DED... 

In summary, SPME-DED satisfactorily extracts low MW PAHs from smoked foodstuffs but it seems that the application of SPME-DED on solid matrixes and foodstuffs is limited by the volatility of the targeted compounds. However, this circumstance does not invalidate the potential application of SPME-DED on PAHs analysis from solid matrixes, since SPME-DED would be a useful screening method for those studies in which the aim is the evaluation... 

Effect of Fat and Salt on the Extraction of PAHs from Solid Matrixes by SPME-DED... 

As suggested above, the presence of salt and fat on the solid matrixes may influence the extraction of PAHs from solid matrixes. We applied the SPME-DED method for analysing the effect of the presence of salt and fat in the solid matrix on the analysis of PAHs. It is known that the presence of lipids in the matrixes hinders the release of some compounds during the extraction by SPME (Keszler and Heberger, 1999) or by other traditional methods such as saponification or liquid-liquid partition (Phillips, 1999 Moret and Conte, 2000) since lipophilic compounds, as PAHs, interact with the non-polar groups of lipids. 

In a solid-phase extraction the analytes are first extracted from their solution matrix into a solid adsorbent. After washing to remove impurities, the analytes are removed from the adsorbent with a suitable solvent. Alternatively, the extraction can be carried out using a Soxhlet extractor. 

Removing the analyte from its matrix by filtration or extraction must be complete. When true, the analyte s mass can always be found from the analytical signal thus, for the determination of suspended solids we know that... 

Two approaches have been used to separate the analyte from its matrix in particulate gravimetry. The most common approach is filtration, in which solid particulates are separated from their gas, liquid, or solid matrix. A second approach uses a liquid-phase or solid-phase extraction. 

Volatile analytes can be separated from a nonvolatile matrix using any of the extraction techniques described in Ghapter 7. Fiquid-liquid extractions, in which analytes are extracted from an aqueous matrix into methylene chloride or other organic solvent, are commonly used. Solid-phase extractions also are used to remove unwanted matrix constituents. 

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