Specific retention

Hydiocaibon mistuies containing cyclohexane can be analyzed using gas chiomatogiaphy. Specific retention volumes for several stationary phases have... 

In fact, this procedure can be used for any aliphatic series such as alcohols, amines, etc. Consequently, before dealing with a specific homologous series, the validity of using the methylene group as the reference group needs to be established. The source of retention data that will be used to demonstrate this procedure is that published by Martire and his group [5-10] at Georgetown University and are included in the thesis of many of his students. The stationary phases used were all n-alkanes and there was extensive data available from the stationary phase n-octadecane. The specific data included the specific retention volumes of the different solutes at 0°C (V r(To)) thus, (V r(T)) was calculated for any temperature (Ti) as follows. 

The separation of mixtures involving N-methyl-JLtetrahydropyridines into their pure components by means of gas-liquid chromatography was discussed in a report by Holik et al. (87). They found that, using tris(/3-cyanoethoxymethyl)-y-picoline as the stationary phase, the primary factors involved in the specific retention volumes of these enamines is the electronic effect of a methyl substituent and the nitrogen atom on the carbon-carbon double bond. It was observed that 1,3-dimethyl-Zl -tetrahydropyridine (141) has a smaller specific retention volume and, hence, is eluted before... 

Once the proteins have passed the quality control system of the early secretory pathway, they are transported in vesicles via the individual compartments of the Golgi apparatus to the plasma membrane. Soluble proteins are transported in the vesicle lumen, membrane proteins are integrated in the vesicle membrane. The transport to the cell surface is the default pathway for secretory and membrane proteins. Proteins may also become part of one of the intracellular compartments along the secretory pathway, but only if they contain specific retention signals. 

Documentation - procedures, specifications, retention of records, electronic data... 

The specific retention of sample molecules to be separated in a straight phase or adsorption chromatographic system is mainly determined by two factors their interactions with polar surface centers of the solid stationary phase, and by the different sample solubility in the rather nonpolar mobile phase. The most important interactions... 

The net retention volume and the specific retention volume, defined in Table 1.1, are important parameters for determining physicochemical constants from gas chromatographic data [9,10,32]. The free energy, enthalpy, and. entropy of nixing or solution, and the infinite dilution solute activity coefficients can be determined from retention measurements. Measurements are usually made at infinite dilution (Henry s law region) in which the value of the activity coefficient (also the gas-liquid partition coefficient) can be assumed to have a constant value. At infinite dilution the solute molecules are not sufficiently close to exert any mutual attractions, and the environment of each may be considered to consist entirely of solvent molecules. The activity... 

Specific Retention Volume V, Net retention volUM at 0 C for unit weight of stationary phase V, 273 W, T. 

The gas-liquid partition coefficient is evaluated froa the specific retention volune using equation (1.6)... 

Figure 2.12 Plot of the logaritlm of the specific retention volune and colunn efficiency (plates per aeter) as a function of column tM erature for benzaldehyde (BZA) and n-tridecane (C ) on the stationary phase tetra-n-butylanmonium picrate. (Reproduced with permission from ref. 58. Copyright Blsevier Scientific Publishing Co.)...

In an unconfined aquifer the permeability relates to the specific yield. This term express the ability for the aquifer to be drained and is clearly related to the grain size. The specific retention reflects the capillary forces that tend to retain water close to the grains. How these parameters relate to each other is shown in Figure 38. 

Figure 38. The relation of porosity, specific yield, specific retention and grain size in an unconfined aquifer...

LC ESI MS allows also the identification of other anthraquinones in madder preparations. Based on structural information obtained by NI mass spectra and specific retention times (signals corresponding to quasi-molecular ions [M—H] and fragment ions [M—C02—H] ), pseudopurpurin (peaks at m/z 299.1 and 255.3) and munjistin (at m/z 283.1 and 239.3) are found in the natural material. Alizarin glycoside is identified by deprotonated quasi-molecular ions at m/z 401.1 and ions formed by the loss of glucose at m/z 239.1. Similar ions are found to be characteristic of lucidin... 

The first interaction has favorable orbital phase overlap for a concerted (2ns + vizs) reaction. The interaction integral y, Eqs. 3—6, for a concerted process would have a maximum value if the two molecules approached each other so that the reacting orbitals could overlap in the most efficient manner. The best geometry would involve a face-to-face reaction of the two reactant species. The stereochemical consequence of such a reaction would be specific retention of substituent relative geometries. 

The quantity of water that can be retrieved from a medium is related to size and shape of the connected pore spaces within that medium. The quantity of water that can be freely drained from a unit volume of porous medium is referred to as the specific yield. The volume of water retained in the medium by capillary and surface active forces is called the specific retention. The sum of specific retention and specific yield is equal to the effective porosity (see Table 3.4). Neither term has a time value attached. Drainage can occur over long periods (i.e., weeks or months). 

Similar studies done by Hall et al. (1984) on hydrocarbon of lower API gravities (i.e., gravities between 34 and 40°) show that specific retention for more viscous hydrocarbons can range between 35 to 50% of the pore volume for fine sands with porosities of approximately 30%. The loss due to retention in the aquifer as the hydrocarbon migrates to the recovery well can be significant. Wilson and Comad (1984) claim that residual losses are much higher in the saturated zone (i.e., capillary zone) than in the unsaturated zone. 

Thus, Xi exemplifies both extremes of the histone code, namely the general deacetylation of all four core histones and the specific retention of H3 dimethylated at lysine 9/27. It also illustrates the great stability of epigenetic signals carried by the histone tails. The general underacetylation of Xi, the undermethylation of H3 lysine 4 and the selective retention of H3 dimethylated at lysine 9/27, are all maintained in human x hamster somatic cell hybrids in which Xi is the only human chromosome and therefore exists in an almost completely foreign (i.e., hamster) cellular environment [73]. 

The system provides a very sensitive means of detection levels of 10 picograms absolute are measurable with the continuous (permanent) trapping system. A further advantage is that the software calculates the analytical results directly in concentration in the unit volume of sample introduced. However, it should he stressed that the level of mercury measured is an absolute quantity and while the detection Hmit is of the order of 10 picograms, this quantity can be contained in any volume of gas. In addition, the fact that the mercury both absorbs and fluoresces to provide a measurement which can be measured with a specific retention time provides more positive evidence of the presence of mercury. 

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