Column temperature influence

Using other methods for the calculation of plate count can result in different numbers, depending on peak shape. It should also be kept in mind that many other operational parameters, such as eluent viscosity, column temperature, flow rate, and injection volume, will influence the results of the plate count determination. 

Temperature has an influence on the retention and consequently on the capacity factors of carotenoids in HPLC columns. Usually, as the column temperature increases, the retention decreases however, in a polymeric C30 column, after an initial decrease of the t values of cis isomers of carotenoids, the retention of cis isomers actually increases at temperatures above 35°C. This different behavior can be explained by the increased order and rigidity of the C30 stationary phase at lower temperatures that in turn induce preferential retention of long, narrow solutes as the trans isomer and partial exclusion of bent and bulky cis isomers. The greater chain mobihty and less rigid conformation of the C30 at higher temperatures may increase the contact area available for interaction with the cis isomers and also may lower... 

Rush, R. S., Cohen, A. S., and Karger, B. L., Influence of column temperature on the electrophoretic behavior of myoglobin and a-lactalbumin in high-performance capillary electrophoresis, Anal. Chem., 63, 1346, 1991. 

In summary, it can be stated that the stationary phase and the mobile phase (buffer) pH are the most important factors determining the generic selectivity of a CS. The organic modifier composition and the column temperature can influence the selectivity locally, i.e., when separating a specific mixture of rather similar compounds, e.g., a drug impurity profile. 

An increase in temperature decreases the viscosity and hence increases the EOF. Thus, for a given voltage, more rapid analysis is possible. Temperature also affects the solute partitioning between the mobile and stationary phases and therefore the chromatographic retention. The distribution of the solute between the mobile and stationary phases is a function of its solubility in the liquid phase and adsorption on the solid stationary phase. This is characterized by the distribution ratio K defined as the ratio of the concentration of the solute in the stationary phase to its concentration in the mobile phase. Retention factors are influenced by increasing column temperature because of the increased partition into the mobile phase according to the Van t Hoff equation ... 

Temperature changes will result in a shift of the pH of the buffer, and the AAA readily makes use of this property for improving separations. This is applicable mainly to the later part of the analysis. An increase of the column temperature may also influence the binding characteristics of the amino acids with the resin. 

Carotenoid retention and separation are influenced by column temperature at temperatures above 20° to 25°C, lutein and zeaxanthin may not be well separated. 

Also, Jensen (86) studied the influence of column temperature upon the retention of TGs retention was found to increase as column temperature decreased, and linear plots between log k and 1 IT were obtained. 

Robustness Systematically change chromatographic conditions (examples column temperature, flow rate, gradient composition, pH of mobile phase, detector wavelength). Check influence of parameters on separation and/or peak areas. 

Separation of TPE and REE by Extraction Chromatography - Extraction chromatography was used for the separation of trivalent TPE and REE. HDEHP was used as the stationary phase on red-kieselguhr as the inert support. Trivalent TPE and REE were loaded on the column filled with this stationary phase from dilute nitric acid. Then, the column was eluted with a solution of 0.05M DTPA-1M lactic acid at pH=3.0. Trivalent TPE were eluted from the column. The influence of aluminum ion was studied, and the pH and flow rate of elution solution and column temperature were also studied as a function of separation. 

The small heat capacity of silica CEC columns means that column temperature is easily changed. Temperature influences EOF velocity through its effect on zeta potential and mobile-phase viscosity [Eq. (4)]. Increased temperature reduces r via an exponential relation ... 

We reinforce the concept that this approach is not acceptable because it does not account for the charge density of the stationary phase verified by extensive experimental evidence. The disregarded electrostatic potential that develops depends on column temperature, as explained above. Hence a sound theoretical description of the influence of temperature on retention enthalpy is still needed. The concept of the weighted... 

L. C. Sander and S. A. Wise, The influence of column temperature on selectivity in reversed-phase hquid chromatography for shape-constrained solutes,/. Sep. Sci. 24 (2001), 910-920. 

The nature of a cation influences the sequence of elution of different pairs of hydrocarbons for example, ethylene on NaX is eluted after propane at the column temperature of 80°-100°C. When temperature rises to 120°-140°C, there is no appreciable separation of these components. At 160 °C and higher, separation of the mixture propane-... 

G. Tsitsishvili Interaction of LP with molecules of unsaturated hydrocarbons and CO is very sensitive to the presence of water molecules in a zeolite and to column temperature increase. On a zeolite containing hydrophilic lithium cations, with most of the substitutions corresponding to Li" in open positions Sn and Sm, the adsorption heat of the studied compounds is lower than with the sodium form. In lithium forms with a high percentage of lithium ions, the Li" in nonhydrated positions influence adsorbate molecules, causing an increase of adsorption heat in comparison with NaX zeolite. Migration of Li" ions from Si to other positions is also possible. 

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