Parameter void volume

The important parameters to consider are the selectivity (dKJdlogR), the ratio of pore volume, Vp, over void volume, Vq, the plate height, H, and the column length, L. The distribution coefficient, Kq, has a slight effect on resolution (with an optimum at Kp 0.3-0.5). In addition to this, extra column effects, such as sample volume, may also contribute to the resolution. 

Illustration 6.2 indicates how void volume and surface area measurements can be combined in order to evaluate the parameters involved in the simplest model of catalyst pore structure. 

To develop analytical models for processes employing porous catalysts it is necessary to make certain assumptions about the geometry of the catalyst pores. A variety of assumptions are possible, and Thomas and Thomas (15) have discussed some of these. The simplest model assumes that the pores are cylindrical and are not interconnected. Develop expressions for the average pore radius (r), the average pore length (L), and the number of pores per particle (np) in terms of parameters that can be measured in the laboratory [i.e., the apparent particle dimensions, the void volume per gram (Vg), and the surface area per gram (Sg). ... 

The functional dependence of jD on Reynolds number has been the subject of study by many investigators [e.g., Thodos and his co-workers (77, 78), and Wilson and Geankoplis (79)]. A variety of equations have been proposed as convenient representations of the experimental data. Many of these correlations also employ the bed porosity (eB) as an additional correlating parameter. This porosity is the ratio of the void volume between pellets to the total bed volume. 

A number of other parameters can be calculated from true, bulk, and tap density measurements. These include void volume, porosity, bulkiness, and compressibility. 

Figure 1 shows a typical chromatogram, which includes a time axis, an injection point, and an analyte peak. The time between the sample injection point and the analyte reaching a detector is called the retention time (t ). The retention time of an unretained component (often marked by the first baseline disturbance cansed by the elution of the sample solvent) is termed void time (tg)- Void time is related to the column void volume (Vq), which is an important parameter that will be elaborated later. 

This chapter provides an overview of essential concepts in HPLC including retention, selectivity, efficiency, and resolution as well as their relationships with key column and mobile phase parameters such as particle size, column length and diameter, mobile phase strength, pH, and flow rate. The significance of several concepts important in pharmaceutical analysis such as peak capacity, gradient time, void volume, and limit of quantitation are discussed. 

In order to understand monolithic supports and the effects of polymerization parameters, a brief description of the general construction of a monolith in terms of microstructure, backbone and relevant abbreviations is given in Fig. 8.1 [63, 64]. As can be deduced therefrom, monoliths consist of interconnected microstrac-ture-forming microglobules, which are characterized by a certain diameter dp) and microporosity (gp). In addition, the monolith is characterized by an inter-microglobule void volume sfj, which is mainly responsible for the backpressure at a certain flow rate. The sum of gp and g directly translates into the total porosity gf. 

The second stage is data acquisition. This stage is entered when the operator starts the instrument. The instrument makes the first injection and signals the microcomputer via Intelink. After a delay proportional to the void volume of the column set, data are collected on a time basis (constant flow rate assumed) at the predetermined rate from each of the detectors selected, up to a maximum of three simultaneous detectors. VHien the sample run is complete, the instrument again signals the microcomputer which places the instrument in a hold state while it reads the operational parameters from the instrument for that sample and... 

An important theme of this book is impressing upon the reader the possibilities that are opened by adding aspects of chemical reactivity to the structure shown in Figure 1.1. In addition to describing how reticulated foams are produced and their physical parameters are varied, we will describe the ways we and others have used such structures. As noted area, the high surface area and low void volume make the reticulated foam a unique structure in material science. 

Some important aspects of foam are not included in this list. We mentioned void volume earlier. This parameter is related to density by a comparison of bulk density to absolute density. We will discuss each of these measures of foam quality and relate their applicability to the theme of this book. Later in the chapter we will show how formulation and processing techniques are used to adjust and control the most important parameters. 

The most advanced technology is the extracorporeal hollow fiber reactor. It is currently in Phase III trial and achieved a good Phase II record to support it. Other techniques including a polyurethane system devised in Japan and encapsulated hepatocytes from UCLA are or were in large animal trials. Whether a device is extracorporeal or is intended for implantation, clinical significance requires a suitable scaffold to support a sufficiently large colony of hepatic cells. For both extracorporeal and implant use, the physical structure of the scaffold must meet certain requirements of strength, void volume, biocompatibility, and other parameters. 

The void volumes in a coupled system are relatively high. The NMR probe, or the storage loop which is located further downstream, is reached ca. 1CM0 s after the peak first appears in the LC detector. The software must calculate such delays depending on the system parameters and the actual flow rate of the separation. When the peak has reached the desired position, the necessary actions for storage or measurement must be started. 

Calculation of the timings for the movements of the peak between the different positions in the hyphenated system. The time taken for the peak to reach the NMR unit or the storage loop depends on the void volume between the LC detector and the NMR spectrometer loop. This is also a function of the flow rate. For precise and reproducible positioning of the peaks, the software must allow interactive selection of the peaks from the chromatogram and the automatic calculation of these time delays based on the actual parameters. 

The two parameters are determined experimentally by measuring the bed void volume at different linear velocities and a double-log plot of evsU.n and Ut are found as slope and intercept of a linear regression of experimental data in this plot. Additionally the parameters may be evaluated from literature correlations, which give a good estimate of the range of flow rates applicable for the fluidization of a certain matrix. Martin et al. [19] used two dimensionless... 

The characteristics of pore structure in polymers is a key parameter in the study of diffusion in polymers. Pore sizes ranging from 0.1 to 1.0 pm (macroporous) are much larger than the pore sizes of diffusing solute molecules, and thus the diffusant molecules do not face a significant hurdle to diffuse through polymers comprising the solvent-filled pores. Thus, a minor modification of the values determined by the hydrodynamic theory or its empirical equations can be made to take into account the fraction of void volume in polymers (i.e., porosity, e), the crookedness of pores (i.e., tortuosity, x), and the affinity of solutes to polymers (i.e., partition coefficient, K). The effective diffusion coefficient, De, in the solvent-filled polymer pores is expressed by ... 

The aim of the present paper is double. Firstly, we wish to question more precisely the role of TEA+ ions in competition with the Na+ cations and possibly in close relation with other synthesis parameters such as the silica source, or the alumina content, by comparing a series of other physicochemical characterizations(chemical composition, nature of the occluded organics, void volume...) of zeolites ZSM-20 and Beta. In a second step, we conduct a more in depth investigation of the whole synthesis conditions and their modification in order to propose selective preparation routes for both zeolites and to possibly define further favorable conditions for the formation of other potential open phases. 

Let s consider the case of a wood with an air-dried density 7 = 0.45, corresponding to a cell wall density of 1.45, to a void volume fraction of 0.69. In Table 1, the physical quantities used for estimating the values of the parameters used in the model are shown. The volumes indicated are normalized for untreated wood, so that -I- =. Ef = 134... 

The parameter P can be found from the value of the Peclet number for high values of hd /hSL, where hai. and hiL are the dynamic and static holdups (fractions of void volume). At other values of hn./hsL, P is assumed to remain constant. If... 

The void volume or void time is a very important parameter, and its correct determination could be critical for the interpretation of the experimental results. 

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