Extraction typical separations

Separation processes are based on some difference in the properties of the substances to be separated and may operate kinetically, as in settling and centrifugation, or by establishing an equilibrium, as in absorption and extraction. Typical separation processes are shown in Table 6.1. Better separations follow from higher selectivity or higher rates of transport or transformation. The economics of separation hinges on the required purity of the separated substance or on the extent to which an unwanted impurity must be removed (Figure 6.13). 

Figure 2.4 Comparison of a typical separation on a packed and a open tubular column. The seunple (solvent extract of river water) is the same in both cases. (Reproduced with permission from ref. 135. Copyright Ann Arbor Science Publishers).

Property measurements of fullerenes are made either on powder samples, films or single crystals. Microcrystalline C6o powder containing small amounts of residual solvent is obtained by vacuum evaporation of the solvent from the solution used in the extraction and separation steps. Pristine Cgo films used for property measurements are typically deposited onto a variety of substrates (< . , a clean silicon (100) surface to achieve lattice matching between the crystalline C60 and the substrate) by sublimation of the Cr,o powder in an inert atmosphere (e.g., Ar) or in vacuum. Single crystals can be grown either from solution using solvents such as CS and toluene, or by vacuum sublimation [16, 17, 18], The sublimation method yields solvent-free crystals, and is the method of choice. 

An example of a schematic for sample treatment, extraction, and separation procedures is given in Simoneit, and it follows the method first used by Simoneit and Mazurek with minor modifications for data comparison purposes. The samples are powdered and dried, then typically extracted using ultrasonic agitation multiple times with a mixture of dichloromethane (CH2CI2) and methanol (3 1 v/v). The solvent extracts are filtered through an annealed glass fiber filter for the removal of insoluble particles, concentrated by rotary evaporation and then by a stream of filtered nitrogen gas. 

Np through Lr are all prepared artificially by bombardment with neutrons and/or light element ions (He-4, B-10, B-11, C-12,0-16,0-18, Ca-48, Fe-56). Some routes are presented in Table 18.1. The elements have been separated from the targets and other product species by redox reactions, ion exchange, and solvent extraction. In a typical separation, a sulfonic acid ion exchange resin is placed in a column, the tripositive ions of Am through Lr are poured into the column where they are taken up, then the column is eluted with a solution of ammonium a-hydroxybutyrate. As elution proceeds, the An+ ions come off in this order Lr-Md-Fm-Es-Cf-Bk-Cm-Am. They are detected by the distinctive energies of their radioactive emissions. 

The anthocyanins exist in solution as various structural forms in equilibrium, depending on the pH and temperature. In order to obtain reproducible results in HPLC, it is essential to control the pH of the mobile phase and to work with thermostatically controlled columns. For the best resolution, anthocyanin equilibria have to be displaced toward their flavylium forms — peak tailing is thus minimized and peak sharpness improved. Flavylium cations are colored and can be selectively detected in the visible region at about 520 nm, avoiding the interference of other phenolics and flavonoids that may be present in the same extracts. Typically, the pH of elution should be lower than 2. A comparison of reversed-phase columns (Ci8, Ci2, and phenyl-bonded) for the separation of 20 wine anthocyanins, including mono-glucosides, diglucosides, and acylated derivatives was made by Berente et al. It was found that the best results were obtained with a C12 4 p,m column, with acetonitrile-phosphate buffer as mobile phase, at pH 1.6 and 50°C. 

Fig. 3. Typical separation of four arsenosugars and DMA by HPLC/ICP-MS using an ODS reversed-phase column at pH 3.2 under conditions described in Ref. 60. The sensitivity and specificity of the detector allows the determination of arsenosugars and other arsenic compounds to be conducted on dilute aqueous extracts of the marine samples.

A renewed interest in studying the chemical properties of the transactinide elements in more detail both experimentally and theoretically arose in the late 1980s, see [18-26] for recent reviews. A series of manually performed separations of 261Rf in aqueous solutions was performed by the Berkeley group at the Berkeley 88-Inch Cyclotron [2-6,27], Their experiments involving liquid-liquid extractions typically comprised the following steps ... 

In the mid-1960s liquid—liquid extraction processes were introduced and today all large-scale commercial production is done in this way. An aqueous solution of the Ln3+ ions is extracted in a continuous countercurrent process into a nonpolar organic liquid containing tri-n-butylphosphine oxide or bis(2-ethylhexyl)phosphinic acid (DEHPA). Typical separation factors for adjacent rare earths using DEHPA are 2.5 per extraction step so that under automatic multistep or countercurrent conditions purities of 99 to 99.9% are routinely achieved. 

Because of comparatively poor oil yields, sole use of mechanical extraction to separate the oil and meal fraction is not as commonly used as solvent extraction. The mechanical extraction process can reduce the oil in meal to 5% to 10% by weight, whereas the solvent extraction process reduces the oil in meal to less than 1 % by weight. As the value of the oil fraction is typically two to three times the value of the meal fraction by weight, the loss of yield is very costly. The mechanical extraction process also has comparatively higher energy and maintenance costs per ton of oleaginous materials processed. 

The determination of Type-A and Type-B trichothecenes in wheat and stmcture elucidation by means of multi-stage positive-ion LC-APCl-MS" on an ion-trap instrument was reported [100]. The analytes were liquid extracted from wheat. After SPE clean-up, the extract was separated on a 125x2-mm-ID C,8 column with a hnear gradient of 25-98% methanol in water at a flow-rate of 250 pl/min. Confirmation of identity was done by retention time and fragmentation pattern in MS", while quantitation was based on peak areas in the mass chromatograms of [M+H]" or of abundant fragments. Typical LOQ range from 10 to 100 pg/kg in wheat. 

Sample preparation is important here because matrices of biological fluids are so comphcated that interfering signals are likely to appear in typical separation-based determinations. Among various sample preparation techniques, there are two major approaches combined with CE liquid-hquid extraction (LEE) and solid-phase extraction (SPE) [or solid-phase microextraction (SPME)]. 

Fig. 2 shows a typical separation of 3 g of three alkaloids from a crude extract of Crinum moorei using a binary... 

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