Chromatographic equation, main

In its simplest form the competition model assumes the entire adsorbent surface is covered by a monolayer of solute and mobile phase molecules. Under normal chromatographic conditions, the concentration of sample molecules will be small and the adsorbed monolayer will consist mainly of mobile phase molecules. Retention of a solute molecule occurs by displacing a roughly equivalent volume of mobile phase molecules from the monolayer to make the surface accessible to the adsorbed solute aiolecule. For elution of the solute to occur -the above process must be reversible, and can be represented by the equilibrium depicted by equation (4.6)... 

For this type of equation an almost complete mathematical theory exists which is based on the method of characteristics [33, 34, 38]. This theory has been applied to distillation processes [17, 20, 29] and to chromatographic processes [33, 34] among others. An alternative approach based on physical insight has also been proposed [16]. The main results will be summarized in the next section. 

Assumption of the presence of single partitioning mechanism of analyte chromatographic retention has been the basis for the development of various methods for the evaluation of specific analyte interaction energies from retention data [44-46]. All these methods are only applicable in ideal chromatographic systems with proven absence of secondary equilibria effects, and all require specific assumptions regarding the volume of the stationary phase. Equation (2-43) is the main basis for these theories. 

The amount of each of the components subtracted in the above equation is expressed on a weight percent basis. In early phases of drug development, it is typically assumed that all related impurities have similar chromatographic response factors in comparison to the main component. In later phases of drug development, the amount of impurities is usually determined on a weight percent basis, using working standards. 

This equation assumes that the contribution of the probe vapour to the gas flow rate across the column is negligible and can be considered as ideal, and that the contribution of the injection band and diffusion processes along the column play a minor role. One of the main advantages of the chromatographic method, especially when applying the Rudzinski-Jagiello s method, is the fact that this method provides directly the first derivative of the isotherm and therefore, in a very direct way the DFCA. 

The amount of discodermolide produced would equate to around 3000 kg of sponge, a quantity that probably does not exist The total number of steps is 36 with an overall yield of 0.2% (main chain). This is on the low side, but it should be remembered that the yields for each step have not been optimized. The description of the various optimization processes in this article have only related to the various scale-up and reproducibility issues, not to obtaining the maximum possible yield, so there is plenty of scope for increasing the yield. There were, in this second campaign, some 18 chromatographic purifications. This has now been somewhat reduced to 14. The number of crystalline intermediates stands currently at 7. 

The main purpose of a chromatographic study is the separation of compounds with closely similar properties. The factor separation Rjj of the chromatographic zones of two compounds / and i is described by the equation... 

The main aim of a chromatographic investigation is usually the separation of compounds with similar properties. The separation coefficient, R, of two compounds j and i between chromatographic zones is described (e.g., refs. 1 and 143) by the equation... 

By input compounds names or chemical formulas to RPS, suitable descriptors for the compounds group desired are calculated with the same procedures as in the main function of RPS by the computer and then capacity factor s for the solutes at v u ious mobile phase compositions are predicted by step-by-step with the interval of X=0.01 for both aqueous acetonitrile and methanol mobile phases. The range available in this procedure is from 0.3 to 0.7 of X-values for acetonitrile system and from 0.4 to 0.8 for methanol system, respectively. After calculations of capacity factors for the desired solutes, Rgand Tp, for each step are estimated according to the equation-9 and 10, at five different flow rates of the mobile phase such as 1, 2, 4, 8 and 16 uL/min (because we use microcolumns) and then quality of the separation is Judged using a simple numerical chromatographic response function (CRF) defined as follows ... 

The appearance of Keuleman s book made the van Deemter equation (published by a physicist in a chemical engineering journal ) much better known to chemists. As a result this paper has been cited many times (more than 370 between 1961 and 1980 alone) the author himself attributed this to the fact that the equation describes in a simple and intuitive way (that nonetheless can be expressed mathematically to permit quantitative evaluation) the role of the main design parameters of the chromatographic column. In 1978 van Deemter was one of the scientists honored by the Academy of Sciences of the USSR by presentation of a memorial medal celebrating the 75th anniversary of the discovery of chromatography by M.S. TswetL... 

Moreover, the chromatographic retention and selectivity is always affected to a certain extent by the interplay of the molecular configuration of analyte and stationary phase. This so-called molecular or steric recognition is one of the main reasons for the excellent selectivities that can be achieved in liquid chromatography. These parameters form the basis of the following equation (Eq. 6) to describe the retention relative to that of a reference solute. Therefore, Eq. (6) does not include an intercept value, which usually reflects, among other things, the phase ratio of the column. 

It is a consequence of Equation (2.10) that the Mw/Mn values for an AB-block copolymer should be smaller than the values normally observed for A and B homopolymers with molar mass comparable to the blocks provided the block copolymerisation reaction proceeds in a similar manner to the homopolymerisation. The vast majority of the Mw/M data presented in the literature is based on SEC measurements. In fact SEC is problematic for the characterization of very narrow MMDs. For homopolymers the axial dispersion phenomenon is the main problem, whereas for block copolymers it is also questionable to what extent true noninteracting conditions are accessible. A development has started towards the use of alternative techniques to SEC for the characterization of diblock copolymers. Apart from the popular MALDI-TOF mass spectroscopy various newer chromatographic techniques have been used. A series of PS samples prepared under as identical conditions as possible (/CHX/sBuLi/45 C/ZCHsOH/) were analysed by SEC and TGIC and the measured Mw/M values compared with the Poisson distribution predictions. 

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