Retention calculation

After an induction period of ca. 9 hours, the maximum productivity was reached. This was followed by a decrease in activity, which cannot solely be explained by the lack of retention. Calculations showed that at least 20% of the catalyst should still remain in the reactor after 80 h. Additional to this wash-out effect, a deactivation process took place, visible by precipitation of palladium black on the surface of the membrane. Although the catalytic system suffered from deactivation, its selectivity towards 3-phenylbut-l-ene was excellent, being 98% and 85% for the G0- and Gr catalysts respectively. 

A1. 0.5 g sample (on dry basis) was swollen in 100 ml distilled water for 10 minutes. The fiber suspension was poured into a sintered glass filter (porosity 1) and sucked at 700 mm Hg pressure. The volume of filtrate was measured and the water retention calculated as g of water per g of dry material. The measurement was repeated after drying the hydrolyzed sample in an oven at 60°C. 

Spicer, V. et al. Sequence-specific retention calculator a family of peptide retention time prediction algorithms in reversed-phase HPLC applicability to various chromatographic conditions and columns. Anal. Chem. 2007, 79, 8762-8768. 

Pore size was also found to be the main factor affecting separation selectivity of C18 columns from different manufacturers, compared to evaluate the applicability of sequence-specific retention calculator peptide retention prediction algorithms. Differences in end capping chemistry did not play a major role while the introduction of embedded polar groups to the C18 functionality enhanced the retention of peptides containing hydrophobic amino acid residues with polar groups [6]. 

Relative retentions calculated on the assumption of free rotation on the surface. 

The programming procedure usually involves three stages. An initial isocratic period is introduced to efficiently separate the early eluting peaks with adequate resolution. The isocratic period is followed by a linear increase in column temperature with time, which accelerates the well-retained peaks so that they also elute in a reasonable time and are adequately resolved. The effect of linear programming can be calculated employing appropriate equations and the retention times of each solute predicted for different flow rates (see the entry Programmed Temperature Gas Chromatography). To do this, some basic retention data must be measured at two temperatures and the results are then employed in the retention calculations. The tempera-... 

The polymer from which a UF membrane is made does not generally affect the retention characteristics of the membrane. However, the nature of the polymer can affect adsorption of species onto the membrane surface. For example, when processing small volumes of dilute solutions, strong adsorption of the solute can diminish its concentration in both the retentate and in the filtrate, and this can affect the apparent retention calculated from Equation 2. 

Equation 3 is used to calculate retention solely on the basis of changes in the retentate volume and concentration. Obviously, if adsorption losses are appreciable, the retention calculated from Equation 3 will be too low since CfWill be lower than it would be without adsorption. For this reason, the retention should also be calculated with reference to the solute concentration in the ultrafiltrate (permeate). 

Again, if there are significant adsorption losses, the retention calculated from Equation 4 will be too high since CUf will be lower than it would be without adsorption. 

If the initial and final retentate concentration (C0 and Cf) are measured along with the final ultrafiltrate concentration (CUf), the retentivities calculated from Equations 3 and 4 may be compared. 

In the first paper [47] in 1972, the principle of EFFF was described qualitatively and the method was applied to the analysis of some proteins — albumin, lysozyme, haemoglobin and y-globulin — with the use of 0.02 M sodium acetate solution and acetic acid at pH 4.5, and 0.02 M Tris(hydroxymethyl)aminomethane solution with acetic acid at pH 8.0 as buffering solutions. The time required for the separation was approximately 120 min. Certain deviations in the retentions calculated theoretically and the retentions measured experimentally were observed. In a subsequent paper... 

The appropriate sample size depends on whether the investigations are carried out in the range of infinite dilution or of finite-concentration . At infinite dilution, the concentrations of the components in the carrier gas may be neglected and thus the gaseous phase may be considered ideal. At finite concentration, a correction for retention calculations should be introduced, which makes them more complicated. Certain limitations of GC methods for physicochemical determinations should also be mentioned. These are mainly restricted to the study of interactions that occur on solids, in liquids, in the mobile gas phase, and at their interfaces. While measurements can be made simultaneously, it is possible that interference from other physicochemical properties of the materials may introduce inaccuracy. Another important limitation is the volatility of the stationary phase in gas-liquid chromatography. 

A gas chromatogram obtained by Krishen [78] with a mixture of ester plasticisers is shown in Figure 4.9. Many commonly used plasticisers are well separated and can be identified by their retention times. The retentions calculated relative to di(2-ethylhexyl)phthalate (DOP), are shown in Table 4.7... 

In the fifth step, the logarithmic deviation of the relative retention from an ideally hydrophobic relative retention, calculated according to Eq. (10) using an averaged solute hydrophobicity parameter ri"(avg), is determined and specified as Aj p (Eq. 11). 

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