Extraction mode, choosing

The variables involved in choosing extraction conditions include the fiber coating and coating thickness, whether derivatizing is necessary, selection of an extraction mode and agitation method, automation options, and injection (desorption)... 

The main issues in choosing an extraction mode and an agitation method involve the nature of the sample and matrix volatility and affinity to the matrix. From the point of view of fiber lifetime, headspace extraction is preferred, but samples must be at least somewhat volatile and not very strongly bound to the matrix. For samples with lower volatility, direct immersion is preferred, although fiber lifetime is a consideration if the matrix is especially dirty. The second consideration in choosing the extraction mode is equilibrium versus exhaustive extraction. In SPME, equilibrium extraction is much simpler to perform, so it is generally... 

The key features of a managed sensor system are that it senses the environment and chooses an appropriate waveform, beam-pattern, pulse repetition interval (PRI), etc (collectively called the sensor mode) to best extract the required information. Any such system must have, at least, the following components in addition to the basic sensor and ancillary components ... 

Another decision for the design engineer is the selection of the operation mode, whereby he can choose between the single- and cascade-mode of operation. In principle this is valid for multipurpose plants of medium scale, such as plants to extract spices and/or herbs. Fig. 8.1-6 gives data on the different production costs for a plant with a total extraction volume of 600 1, operated in different modes, but with the same capacity. The investigation is based on equal batch times (in our case 4 hours), equal mass-flow per kg of raw material and, of course, equal extraction- and separation conditions. 

The preparation of a lipid sample includes extraction of the lipid material from the examined object (seeds, tissues, food, etc.), choosing among the several widely accepted procedures. The extraction with chloroform-methanol (2 1) (the Folch extraction) is the most popular. A solution of known concentration in hexane or di-chloroethane is prepared and a suitable aliquot is applied on the plate as a small spot or, better, as a narrow band. Two, three, or more solvents, mixed in different proportions, give the mobile phase. Development is performed in common tanks (Desaga type, for example), in the ascending mode. For fine separations, cylindrical or sandwich-type tanks provide better results. 

The number of variations in the design of FI manifolds for liquid-liquid extraction has surpassed that of any other individual FI separation techniques. This may be due both to the broad interest in FI liquid-liquid separation and to the larger number of individual components in the manifold. While this may be beneficial for the user in choosing the best manifold design for a particular application, it poses difficulties for a comprehensive description of the different variations. In this section an attempt is made to characterize the different modes for each of the five basic parts of a H liquid-liquid extraction manifold (excluding the propulsion and detection systems which are described in Chapter 2). Then the user can select the proper mode of each part for a specific application, and integrate the parts to form an appropriate manifold design. 

Figure 3.11 summarizes such key experimental points. As a first point, we have to choose the appropriate ionization method for the detection of small metabolites, we have alternative choices other than MALDI, such as secondary ion mass spectrometry (SIMS) [15], nanostructure-initiator mass spectrometry (NIMS) [20,21], desorption/ionization on silicon (DIOS) [22], nanoparticle-assisted laser desorptiopn/ ionization (nano-PALDI) [23], and even laser desorption/ionization (LDI) [24,25]. We consider that MALDI is stiU the most versatile method, particularly due to the soft ionization capability of intact analyte. However, other methods each have unique advantages for example, SIMS and nano-PALDI have achieved higher spatial resolution than conventional MALDI-IMS, and above aU, these mentioned alternative methods are all matrix-free methods, and thus can exclude the interruption of the matrix cluster ion. Next, if MALDI is chosen, experimenters should choose a suitable matrix compound, solvent composition, and further matrix application method for their target analyte. All these factors are critical to obtain sufficient sensitivity because they affect efficiency of analyte extraction, condition of cocrystallization, and, above all, analyte-ionization efficiency. In addition, based on the charge state of the analyte molecule, suitable MS polarity (i.e., positive/ negative ion detection mode) should be used in MS measurement. Below, we shall describe the key experimental points for MALDI-IMS applications of representative metabolites. 

To choose the entrainer among a number of alternative entrainers, it is necessary to carry out comparative estimation of expenditures on separation. For preliminary estimation at extractive distillation, the value of minimum flow rate of entrainer can be used and, at the sequence in Fig. 8.22b, the length of possible product composition segment at the side of the concentration triangle can be used. For more precise estimation, it is necessary to calculate the summary vapor flow in the columns in the mode of minimum reflux at several values of excess factor at the flow rate of entrainer. 

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