Stationary phase volume determination

For the assessment of the extent of change of the phase ratio of a HPLC column system with temperature or another experimental condition, several different experimental approaches can be employed. Classical volumetric or gravimetric methods have proved to be unsuitable for the measurement of the values of the stationary phase volume Vs or mobile phase volume Vm, and thus the phase ratio ( = Vs/Vm). The tracer pulse method266,267 with isotopically labeled solutes as probes represents a convenient experimental procedure to determine Vs and V0, where V0 is the thermodynamic dead volume of the column packed with a defined chromatographic sorbent. The value of Vm can be the calculated in the usual manner from the expression Vm = Eo — Vs. In addition, the true value of Vm can be independently measured using an analyte that is not adsorbed to the sorbent and resides exclusively in the mobile phase. As a further independent measure, the extent of change of 4> with T can be assessed with weakly interacting neutral or... 

Figure 2-12 represents the temperature dependencies of a homologous series of alkylbenzenes retention at 60% MeCN/40% water on a Phe-noemenex Luna-C18 column. The intercepts for each analyte is different from others, which essentially means that each analyte requires the determination of its own stationary phase volume. 

Second, one of the phases (stationary one) must be retained in the rotating column to a required extent. The most important factor, which determines the separation efficiency and peak resolution for both organic and inorganic compounds, is the ratio of the stationary-phase volume retained in a column to the total col-... 

A gel-filtration column prepared using Bio-Gel P-100 had a void volume of 5.0 mL and a stationary-phase volume of 50.0 mL. The column was calibrated using six proteins of known molecular weight, by measuring the elution volume of each peak (Table. 14.7). An unknown protein was then applied to the column, and its elution volume was measured. Given the data in the table below, determine the molecular weight of the unknown protein. 

The volume of a chromatographic column consists of the stationary-phase volume and the void volume, the volume occupied by the mobile phase. The latter can be determined from and the flow rate. One void volume of the mobile phase is required to flush the column once. 

Adding a mass-transfer term to Eq. (9.9) it is valid in this model for the mobile phase. Therefore the surface area of the adsorbent interfaced between the mobile and the stationary phase is determined for each differential volume element. 

To use Equation 4.13, we will need to relate the retention factor A to the distribution coefficient. Chromatographers can measure retention factors directly from the chromatogram if the unretained peak time is known. The distribution coefficient K in Equation 4.13, however, is not directly evident, but it can be computed from the measured retention factor, if the column film thickness d and inner diameter are known. These two column measurements determine the phase ratio P, which is the ratio of the gas to stationary-phase volumes in the column ... 

This remarkably simple relationship is depicted in Figure 14. It was apparent from his results that the volume fraction of the solvent determined the probability of interaction with the solute in much the same way that the partial pressure of a gas determines the probability of collision. It also indicated that the influence of each stationary phase component was independent and unaffected by presence of the other. 

The theoretical treatment given above assumes that the presence of a relatively low concentration of solute in the mobile phase does not influence the retentive characteristics of the stationary phase. That is, the presence of a small concentration of solute does not influence either the nature or the magnitude of the solute/phase interactions that determine the extent of retention. The concentration of solute in the eluted peak does not fall to zero until the sample volume is in excess of 100 plate volumes and, at this sample volume, the peak width has become about five times the standard deviation of the normally loaded peak. 

ISEC is a size-exclusion chromatography technique, in which the stationary phase is the CFP to be to characterized [16-18] and the eluates are geometrically well-defined steric probes. From the determined retention volumes in a given solvent and on the basis of suitable morphological models, ISEC analysis provides the... 

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