Temperature and retention volume

If the relationship between retention volume and temperature is known, as well as its dependence on solvent composition, then the combined effect of both solvent... 

The relationship between retention volume and temperature is, in fact, logarithmic, but over the small range of temperatures concerned, it is approximately linear, so a linear function is force-fitted to the results for the three solvents. A summary of the results obtained from the regression analysis of the data used in Figure 2 is shown in Table 2. It is seen that, to attain a precision of 0.1%, the temperature of the solvent and column must be maintained to within 0.04°C. It is not difficult to maintain this level of temperature control on the thermostat bath, but it can be extremely difficult to return to a given temperature to... 

There are two major factors that influehce retention volume measurement and they are temperature and solvent composition. In order to measure retention volume with adequate precision it is necessary to know the relationship between retention time and temperature so that the control limits of the column temperature can be specified. 

Habgood and Harris (5) derived the following equation showing the relationship between isothermal retention volumes and retention volumes obtained under linear temperature-programming ... 

Figure 3.1 provides an illustration of the relationship between the specific retention volume and the temperature. 

Tyagi, O. S. Deshpande, D. D., "Inverse Gas Chromatography of Poly(n-butyl methacrylate) Effect of Flow Rate on Specific Retention Volume and Detection of Glass Transition Temperature," 34, 2377 (1987). 

The desorption of the bubbler was quantified as a function of sample volume and temperature as shown in Figure 13. Retention of the contaminant in the bubbler after 8 hours of aeration is sufficient for analytical evaluation. 

Band broadening and temperature The five terms of Equation (24-14) can be examined in the context of the influence of temperature on flow rates, retention volumes, and diffusion coefficients to obtain an estimate of the overall influence of temperature on band broadening. Through thermal expansion, temperature also influences such factors as thickness of a liquid film and particle and column diameters, and it may also influence slightly the empirical constants in (24-14). With a liquid mobile phase, flow velocity (with the same inlet and outlet pressures) is strongly dependent on temperature. But with flow velocity u maintained constant the first term of (24-14) becomes smaller as diffusion coefficients increase in the mobile phase. For flow rates near the optimum the first term is approximately inversely proportional to The second and third terms increase in direct proportion to the diffusion coefficients in the mobile and stationary phases D and D, whereas the fourth and fifth... 

To speak of the retention volume is usually inappropriate in temperature programming instead, the characteristic quantity is retention temperature Tr, the temperature reached by the column at the solute peak maximum. Retention temperature is related to heating rate, mobile-phase flow rate, and isothermal retention volumes. In temperature programming, as indicated above, the rate of band movement increases sharply with time. Nevertheless, even with isothermal elution, solute bands do not move at a uniform rate, but more rapidly as the carrier gas expands from the inlet to the outlet of the column. For a band at a distance z from the column inlet, the rate of movement is given by... 

At point B, corresponding to the glass transition, penetration of the solute into the bulk of the polymer begins, causing an inaease of retention volume with temperature. Due to an initially slow rate of diffusion of the solute into and out of the stationary phase, nonequilibrium conditions prevail. As the temperature is increased in region BC the diffusion coefficient rises sharply, leading to equilibrium conditions at point C. 

At temperatures above Fg, or for a semicrystalline polymer, the magnitude of the retention volume is a direct measure of the solubility of the probe in the polymer. At infinite dilution of the solute the relation between the bulk retention volume and the activity coefficient is (5,37,38)... 

Thus liquid chromatography makes it possible to determine the equilibrium constant at small coverage (the retention volume or Henry constant) and to characterize the compounds adsorption from multicomponent solutions. From the dependence of retention volumes on temperature the changes of enthalpy and entropy of adsorption can be calculated. 

The most convenient method of study of adsorption at small coverage is gas chromatography. By this method it is possible to determine the constant of adsorption equilibrium (retention volume) and from the retention volumes at different temperatures to calculate the heat of adsorption and changing of differential standard entropy of adsorption. If the support for fullerene crystals is the adsorbent with inert and small specific surface area so the retention of compounds will be determined by intermolecular interaction of compounds with fullerene crystal surface. The deposition of fullerene crystals on support surface is quite difficult owing to small solubility of fullerene in organic solvents [21, 22] as well as small vapour pressure of fullerene [23]. 

Analysis of Products. The three fractions collected from each sample were analyzed by gas chromatography. The noncondensable fraction, containing hydrogen and methane, was analyzed on silica gel at room temperature. The fraction containing C2-C4 hydrocarbons was analyzed at 75 °C. on silica gel treated with didecyl phthalate. Aliquots of the liquid fraction were analyzed on three columns of different selectivity Bentone-34-didecyl phthalate silicone SE-30 and m-polyphenyl ether (five-ring). Products were identified, and their yields were determined by comparison of retention volumes and peak areas with values for known amounts of authentic samples. 

Malto-oligosaccharides can be studied by gel chromatography on Bio-Gel P-2 and a multi-column system Bio-Gel P-2 and P-6 at increased temperature [138]. Under these conditions oligosaccharides have different retention volumes and the method is suitable also for preparative separation of hnear and branched oligosaccharides. 

In GC the retention volume must be corrected for the compressibility of the gaseous mobile phase due to the pressure differential along the column. A compression correction factor (y) is therefore used giving the net retention volume, and net retention time. In, for a given temperature and initial pressure ... 

It follows that the net retention volume and therefore the adjusted retention volume (Fr) and retention volume (Fr) vary as the logarithm of l/T. Similarly, adjusted retention time (/r) and retention time (Jr) will decrease logarithmically as temperature increases. 

Variability in retention volumes and peak widths in gradient elution chromatography is due primarily to the limits of precision and reproducibility of the mobile phase composition, the flow rate, and the column temperature. Random or systematic deviations from the preset mobile phase composition and flow rate are caused by... 

Standard partial molar free enthalpies, enthalpies, and entropies of vaporization from infinitely dilute solutions in Apiezon M were calculated from retention volumes determined over a range of temperatures data are listed for many organic and a few MR4 compounds (M = Si, Ge, and Sn), including Ge(C2H5)4 [29]. Apiezon L and two polar stationary phases were used in similar studies on a variety of MRr,R4 n compounds, yielding relative molar enthalpies and entropies of solution at 100°C referred to Si(CH3)4 as the standard [43]. Retention volumes and heats of solutions on two stationary phases have also been compared for M(C2H5)4 and M(C2H5)3H compounds with M = Si, Ge, and Sn [38]. 

The range of molecular masses (MM) which may be eluted in SEC is virtually unequalled, but the efficiency of separation is inevitably low because of the proportionality between retention volume and the logarithm of MM. The separating power of gas chromatography (GC) with capillary columns is unparalleled, but the limited volatility and thermal stability of polymers severely limits its application. SFC allows the high-resolution separation of high-MM solutes at temperatures well below those of thermal decomposition. 

The peak retention volume and fector are due to chemical equilibria which are temperature dependent. The classical Gibbs free energy equation can be applied ... 

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