Number of Fractions

To find a suitable process concept, the final differentiation is given by the number of fractions to be collected. Notably, one fraction can contain either one single component (e.g., one target product) or a group of many similar components (e.g., several impurities). Some process concepts, such as SMB and SSR chromatography, can only separate a feed mixture into two fractions. In contrast, batch elution chromatography, annular chromatography, ISEP, and so on separate feed streams into three or more fractions. 

Multistage processes should be considered for production-scale processes with three or more fractions. An intermediate step by SMB or batch separation reduces the separation problem, finally, to a two-fraction problem that can be performed by applying one of the above-mentioned concepts. 

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Packed columns are gaining ground on trayed columns. Lieberman states that based on his design and operating experience, a properly designed packed tower can have 20-40% more capacity than a trayed tower with an equal number of fractionation stages. 

From the foregoing discussion, it is apparent that heparin may be subdivided into an unlimited number of fractions when different separation approaches are applied to each fraction obtained by another procedure. More than a hundred fractions have been obtained by sequential use of affinity chromatography on antithrombin, precipitation with barium, and isoelectrofocusing.214 Although these fractions can scarcely be referred to as species, such an extensive fractionation stresses the concept of the heterogeneity of heparin, and the influence of minor differences in chemical constituents, or chain length, or both, on the physicochemical (and, conceivably, biological) properties of this polysaccharide. 

Number of fractions sampled into second dimension Technique example References... 

As discussed above, in a typical proteomic experiment with a limited number of fractions collected, the practical peak capacity of 2DLC is well below 1000. This resolution is dramatically lower than the values considered in literature. 

The proposed estimate has several limitations. When taking into account the limited orthogonality of investigated 2DLC modes, the practical peak capacity is reduced approximately to half. It needs to be also emphasized that a full separation power of the first LC dimension is realized only when the number of collected fractions exceeds its peak capacity (Murphy et al., 1998). If the number of fractions analyzed is low, the achievable chromatographic peak capacity suffers. 

It has been argued that in a typical 2DLC proteomic experiment, with only a limited number of fractions submitted for analysis in the second LC dimension, chromatographic peak capacity is less than 1000. This value is considerably lower than the expected sample complexity. Additional resolution is offered by MS, which represents another separation dimension. With the peak capacity defined as the number of MS/MS scans (peptide identifications) accomplished within the LC analysis time, the MS-derived peak capacity was estimated to be in an order of tens of thousands. While the MS peak capacity is virtually independent of LC separation performance, the complexity of the sample entering the MS instrument still defines the quality of MS/MS data acquisition. The primary goal of 2DLC separation is to reduce the complexity of the sample (and concentrate it, if possible) to a level acceptable for MS/MS analysis. What is the acceptable level of complexity to maintain the reliability and the repeatability of DDA experiments remains to be seen. 

After centrifugation, collect multiple fractions from the gradient. The number of fractions to collect depends on the desired resolution a reasonable number of fractions to start with is 18 (fraction vol. 0.6 ml). 

Number of fractions into which the gradient is separated 179... 

Fractions from a sucrose gradient can be separated either according to the complexes that they contain or to a fixed volume. When the gradient is separated to a small number of fractions (e.g., free mRNA, monosomes, and... 

The amount of mix to add depends on the experimental setting and the number of fractions collected. We typically add 70 pi of spike-in mix into an entire sucrose gradient, where each fraction receives the relative share from that amount. For example, 35 pi of the spike-in mix will be added to each fraction of a gradient that was divided into two, and 7 pi of this mix will be added to each fraction of a gradient that was divided into 10fractions. The added amounts should consider losses during purification steps and that a minimum of 0.2 ng of each spike is needed to yield sufficient signal in the microarray hybridization. 

As shown, the system incorporates an integrated plate changer that accommodates plates for analysis as well as plates for collecting fractions of interest. Plates can be of different formats for sampling and collection, for example, a 384-well plate could be used for samples and a 96-well plate for collection (of course, the same plate type may be used for both sampling and collection). The system also incorporates a dedicated rinse station at the fraction collection end. The number of fractions and the time intervals for collection are defined by the user and automatically controlled by the software. In this way, analytes can be isolated and collected using /.tPLC. Collected fractions can, for example, be injected onto MS instrumentation with minimal cycle time by employing a flow injection analysis approach. 

It is fundamentally important that the different COD fractions in wastewater be quantified and determined by direct measurement methods. The number of fractions must be minimized, determined by the details desirable and required, for example, for modeling purposes. 

The number of fractions of hydrolyzable substrate is determined by the quality of the wastewater, i.e., when fractions can be identified in terms of their... 

A number of fractional crystallisation schemes have been devised by Mullin(3) and Gordon etalSn5 and the use of such schemes has been discussed by Joy and Payne(116) and Salutsky and Sm s(l l7). 

Most of the frequently used comprehensive HPLC are operated in a continuous mode, which means that the time of the second-dimension analysis corresponds to the transfer time of a fraction from the first into the second dimension. The total analysis time will be the product of the second-dimension analysis time and the total number of fractions injected onto the secondary column. 

Coal liquids, petroleum crudes, and their distillation cuts have been separated into four or five fractions by SEC (5 15). The SEC fractions were analyzed by use of GC. The procedure was performed manually. It was inefficient, and susceptible to human error. The automated fraction collection followed by injection of the fraction into the GC reduces analysis time, and offers an option for collection of the desired number of fractions at predetermined time intervals. The manual collection of up to 10 one-ml fractions is also used in order to study the effectiveness of the automated method. 

The principal innovations that have been made in the discussion of the theory of the chemical bond in this edition are the wide application of the electroneutrality principle and the use of an empirical equation (Sec. 7-10) for the evaluation of the bond numbers of fractional bonds from the observed bond lengths. A new theory of the structure of electron-deficient substances, the resonating-valence-bond theory, is described and used in the discussion of the boranes, ferrocene, and other substances. A detailed discussion of the valence-bond theory of the electronic structure of metals and intermetallic compounds is also presented. 

The main difficulty with the classical fractionation process is that, as the fractionation progresses, the number of fractions increases, and their size becomes smaller. With fractional precipitation processes, the number of operations practicable is much smaller than the fractional crystallization, because of the trouble in redisolving the precipitates and following another reprecipitation. In fractional crystallization schemes sometimes the liquor and crystal fractions can be combined with the help of modem analytical techniques by determining their compositions, thus achieving multiplication of stages. 

An alternative method of handling crude oil is the energy refinery in which crude is split into a number of fractions which can be treated by proven processes to yield two products, SNG and low sulfur fuel oil One such scheme is shown m Fig, 3. The advantages of using the CRG process as the final stage m the production of SNG are high efficiency and low capital cost, the predictable quality of the product gas, and the absence of by-products,... 

Large numbers of fractions having preselected volumes of between less than 1 ml and 50 or 100 ml are most easily collected with the aid of one of the many designs of automatic collectors. 

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