Alternative extraction methods

The overall method includes sample collection and storage, extraction, and analysis steps. Sampling strategy is an important step in the overall process. Care must be taken to assure that the samples collected are representative of the environmental medium and that they are collected without contamination. There is an extensive list of test methods for water analysis (Tables 8.2, 8.3, and 8.4), which includes numerous modifications of the original methods, but most involve alternative extraction methods developed to improve overall method performance for the analysis. Solvent extraction methods with hexane are also in use. 

Producing data that cannot be compared directly with other total petroleum hydrocarbons data or guidelines because one data set is the result of a Soxhlet extraction method and the other reflects a sonication or other alternative extraction method. 

Much of the current interest in using analytical-scale SFE systems comes from the need to replace conventional liquid solvent extraction methods with sample preparation methods that are faster, more efficient, have better potential for automation, and also reduce the need for large volumes of potentially hazardous liquid solvents. The need for alternative extraction methods is emphasized by current efforts to reduce the use of methylene chloride as an extraction fluid for environmental sample preparation [158]. The potential for applying SFE to a wide variety of environmental and biological samples for both qualitative and quantitative analyses is widely described in reviews [159-161] and the references therein. Analytical-scale SFE is most often applied to relatively small samples (e.g., several grams or less). 

Alternative extraction methods [20, 35], oximation [9, 35], and derivatization agents [26] are available, but will not be discussed further in this chapter. 

Ultrasonic extraction is an alternative extraction method for abiota and biota samples. Blubber samples of seal have been extracted with an acetone hexane mixture (1 1) in a water bath by ultrasonication [33,113]. The mixture of blubber and sodium sulfate was extracted twice with the solvent mixture. 

Although the traditional Soxhlet and solvent extraction techniques are widely accepted, they have inherent limitations and problems. Thus, Soxhlet extraction requires 12-24 h in most cases and uses high volumes of organic solvents (hundreds of millilitres). In contrast to conventional methods, microwave-assisted extraction can reduce the extraction time to less than 30 min and solvent consumption to under 50 ml [12]. Moreover, the recoveries obtained with microwave-assisted extraction are comparable with those provided by alternative extraction methods [7]. 

The objective of this research was to determine the quantity and chemical composition of supercritical CO2 extractables from cranberry seeds. SFE parameters such as CO2 pressure, extraction temperature/time, and CO2 flow rate were optimized to obtain the best possible extraction conditions. The amount and type of SF extractables have been compared with Soxhlet extractables to evaluate the feasibility of SFE as an alternative extraction method. The SF and Soxhlet extracts were compared by gravimetric determination followed by derivatization of the fatty acids into their methyl esters with subsequent determination of their compositions by GC-MS. 

SPE began to be extensively used in sample preparation processes in the 1970s but the great breakthrough in SPE occurred over the past seven or eight years with many improvements in formats, automation and introduction of new phases. In fact, SPE is currently accepted as an alternative extraction method to LLE for 22 of the official methods for the U.S. EPA. 

Solid samples, such as soils and solid wastes which are quite insoluble in solvents, have to be submitted to an analyte extraction process. In some cases, such as in elemental analysis, it is adequate to digest the sample in a strong acid. However, in other cases, the analyte may be destroyed under strongly acidic conditions and alternative extraction methods have to be used. The most important and internationally used techniques are discussed in the following sections. 

A long-standing interest is shown in alternative extraction methods that use solvents other than hexane to extract soybeans due to safety and emission issues over hexane use as well as periodic hexane shortages when petroleum supplies are tight (Johnson Lusas, 1983 Hron, 1982 Wan Wakelyn, 1997). Hexane is highly flammable, and periodic accidents result in explosion and fire with loss of life or injury. Hexane is... 

An alternative extraction method is supercritical fluid extraction with CO2, which has been widely used in different fields of environmental analysis. The development of a suitable extraction method for organoarsenic compounds requires a systematic optimization of the parameters chamber temperature, pressure, extraction time, number of extraction steps, modifier and rinse solvent, which could influence the extraction result crucially (Tena et al., 1993). 

These conventional methods used to isolate valuable compounds from aromatic plants have important drawbacks, such as low yields, formation of by-products due to the degradation of thermally unstable and unsaturated compounds by temperature or hydrolytic effects, as well as large extraction times. Therefore, some alternative extraction methods were proposed to overcome these drawbacks. 

In the ion chromatographic analysis of meat products, a number of constituents elute close to the void volume of the anion exchanger used, so Interferences cannot be excluded. Because chloride concentrations in meat products can easily exceed nitrite and nitrate concentrations by a factor of 5000, UV detection at low wavelengths (207-225 nm) is usually applied. At those wavelengths, chloride absorption is usually very low. Siu and Henshall [372] described an alternative extraction method, which requires neither protein precipitation nor extraction with SPE cartridges. According to this method, 10 g of sample is mixed with... 

Hexane extraction of stabilized rice bran has been the most commonly used method for obtaining rice bran oil. Hexane has the advantage of high oil recovery, but safety concerns regarding hexane have led to a search for alternative extraction methods. Less hazardous approaches such as the use of isopropyl alcohol, supercritical fluid extraction, or enzyme-assisted extraction are potential alternative processing methods. 

Supercritical fluid extraction (SFE), a newly developed technique, is used for laboratorial and industrial purposes because it presents a series of advantages compared to the conventional extraction processes, especially for the extraction of thermolabile components [21,22]. It was first presented as a patent for decaffeination of coffee [23]. Since then, SFE has been used for many years as an alternative extraction method, which causes less pollution to the environment. The concept of the critical point was defined in 1822 as the highest pressure and temperature at which a pure substance could exist in vapor-liquid equilibrium. Above this point, supercritical fluid (SCF) is formed. These qualities make SCFs have higher diffiisivities and less degradation of solutes than ordinary solvents to extract active components. 

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