Column phase ratio

Using the retention data and the chromatogram shown in Fig. 14.8, tabulate the following for each peak retention time ( r), adjusted retention time (t K), retention factor (k), partition coefficient (Kc) and number of theoretical plates (N). The column phase ratio was 250 and the gas hold up time ( m) was 0.995 min. 

AG°s is the standard free energy of adsorption of the solute to the stationary phase surface ([) is the column phase ratio... 

The subscripts ieS and ieM refer to the ion-exchange equilibria at the solution-stationary phase and the solution-micelle interface, respectively. The [C] concentrations are the counter anion concentration in the aqueous phase, aq, including added salts, and the one on the stationary phase, s. is the micellar counterion dissociation constant, (j) is the column phase ratio, [M] is the micellar concentration and k is the anion retention fector. Equation 13.6 obtained from ion-exchange equilibria resembles the classical Armstrong-Nome equation. The Pwm Partition coefficient of eq. 13.6 can be related to the KjeM constant by [30] ... 

In chromatography, the retention factor, or, equivalently, the capacity factor, is used to characterize the chromatographic equilibrium properties of an analyte. The retention factor of an analyte, k, is usually derived to be the product of the column phase ratio, Vr/Ve, and the distribution coefficient of the analyte between the stationary phase and eluent phase, Ca,r/ca,e, eqn [24] ... 

Fig. 2 Schematic of two chromatographic columns coupled in series. - mobile-phase flow, mobile-phase hold-up time, % retention time, k - retention factor, T- temperature, L - column length, r - column inner diameter, u - mobile-phase-flow rate, P - column phase ratio, R - column pneumatic resistance, R - pneumatic resistance, D - detector.

The retention factor and the distribution coefficient are related by the column phase ratio, as shown in this equation ... 

So, if we know the column phase ratio and the peaks retention factors at various temperatures, we can compute the distribution coefficients, and from there find the thermodynamic parameters that characterize the peaks on a specific stationary phase. Optimization programs utilize at least two, and often three, sets of known retention data at different temperatures in order to assess the thermodynamic variables. Alternatively, by making some assumptions about the value of AH, one set of calibration data can be used, but the results will be approximate. 

This deceptively simple expression incorporates all the variables mentioned previously, plus temperature and pressure programs as discrete time-based functions. Combining Equations 4.18, 4.17, and 4.13 allows us to express the pro-grammed-temperature elution process in terms of the thermodynamic coefficients, the average carrier-gas linear velocity as a function of the program time, and the column phase ratio ... 

In Eq. (1), is a perfect gas constant, T is the absolute temperature (°C + 273 in Kelvin) and 4> is the column phase ratio (ratio of the stationary phase volume over the mobile phase volume). 

An eluted solute was originally identified from its corrected retention volume which was calculated from its corrected retention time. It follows that the accuracy of the measurement depended on the measurement and constancy of the mobile phase flow rate. To eliminate the errors involved in flow rate measurement, particularly for mobile phases that were compressible, the capacity ratio of a solute (k ) was introduced. The capacity ratio of a solute is defined as the ratio of its distribution coefficient to the phase ratio (a) of the column, where... 

It is clear that the separation ratio is simply the ratio of the distribution coefficients of the two solutes, which only depend on the operating temperature and the nature of the two phases. More importantly, they are independent of the mobile phase flow rate and the phase ratio of the column. This means, for example, that the same separation ratios will be obtained for two solutes chromatographed on either a packed column or a capillary column, providing the temperature is the same and the same phase system is employed. This does, however, assume that there are no exclusion effects from the support or stationary phase. If the support or stationary phase is porous, as, for example, silica gel or silica gel based materials, and a pair of solutes differ in size, then the stationary phase available to one solute may not be available to the other. In which case, unless both stationary phases have exactly the same pore distribution, if separated on another column, the separation ratios may not be the same, even if the same phase system and temperature are employed. This will become more evident when the measurement of dead volume is discussed and the importance of pore distribution is considered. 

Phase ratio focusing is based on the higher migration speed of components through the retention gap compared to that through the analytical column. Reconcentration depends on the ratio between the retention power in the pre- and in... 

It is seen that the separation ratio is independent of the phase ratios of the two columns and the flow rates employed. It follows that the separation ratio of a solute can be used more reliably as a means of solute identification. Again, if the data is being processed by a computer, the corrected retention times will be used to calculate the separation ratios. In practice, a standard substance is often added to a mixture and the separation ratio of the substance of interest to the standard is used for identification. 

The HPLC elution pattern is affected to some extent by the pH of the mobile phase. Moderate pH adjustment to optimize the resolution between EMA and MEMA may be performed. Retention time can be affected greatly by the history of the HPLC column and also the buffer/methanol ratio. The mobile phase ratio should be adjusted to provide adequate separation and retention. Control and fortified samples should be run in the same analytical set with treated samples. 

COMPARISON OF WCOT AND MICROPACKED COLUMNS HAVING SIMILAR PHASE RATIOS... 

Column Type Length m Internal Diameter mm Film Thickness /tm Phase Ratio Capacity Factor lU mm opi cm/s Column Plate Count Plates Per Meter... 

In gas chromatography the value of the partition coefficient d ends only on the type of stationary phase and the column temperature. It is independent of column type and instrumental parameters. The proportionality factor in equation (l.ll) is called the phase ratio and is equal to the ratio of the volume of the gas (Vg) and liquid (V ) phases in the column. For gas-solid (adsorption) chromatography the phase ratio is given by the volume of the gas phase divided by the surface area of the stationary phase. 

Mazsaroff, I., Regnier, F.E. (1988). Phase ratio determination in an ion-exchange column having pores partially accessible to proteins. J. Chromatogr. 442, 15-28. 

A mixture of acetyl acetone, 1-nitronaphthalene, and naphthalene has been proposed for evaluating reversed-phase packing material [102]. This reveals the usual optimum kinetic chromatographic parameters (the naphthalene peak), the degree of activity or end-capping status of the column (the ratio of the 1-nitronaphthalene and naphthalene retention times) and trace metal activity (the shape and intensity of the acetylacetone peak). 

In contrast, chemical etching of the inner wall of the fused-silica capillaries was used to increase the surface area. This enables achievement of a higher phase ratio since more alkyl functionalities can be attached to the surface, thus improving both the separation process and loadability of the column. The surface morphology of the etched capillary depends on the time the methanol solution of ammonium hydrogen difluoride is left in contact with the capillary and temperature at which the reaction is carried out (Fig. 10) [77]. The surface features have been described by Pesek to range from spikes of silica material extending... 

The retention factor is related to the thermodynamic equilibrium constant K for solute binding by k = (IK, where f is the phase ratio of the column. The free-energy change for the chromatographic process is expressed by... 

The porosity of an SEC column can be characterized by its phase ratio (VJV0). Soft-gel SEC packings have high porosities with phase ratios of 1.5 to... 

An open-tubular column is a capillary bonded with a wall-supported stationary phase that can be a coated polymer, bonded molecular monolayer, or a synthesized porous layer network. The inner diameters of open-tubular CEC columns should be less than 25 pm that is less than the inner diameters of packed columns. The surface area of fused silica tubing is much less than that of porous packing materials. As a result, the phase ratio and, hence, the sample capacity for open-tubular columns are much less than those for packed columns. The small sample capacity makes it difficult to detect trace analytes. 

One way to increase the phase ratio of open-tubular columns is to use a polymeric stationary phase instead of a bonded molecular monolayer (Figure 6). 

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