the essence of chromatography

[...]... average mobile phase velocity The distribution constant for a substance in the chromatographic system is equal to the product of the retention factor and the phase ratio (K = k~) The phase ratio, ~, is defined as the ratio of the volume of mobile phase and stationary phases in the column for a partition system, or the ratio of the volume of the mobile phase to the surface area of the stationary phase for... trapped in the pores of the column packing and is stagnant The volume of stagnant mobile phase is considered part of the stationary phase and thus the column hold-up volume is less than the volume of liquid or fluid filling the column For a gas the column hold-up volume and the unoccupied volume of the column are identical The time the solute spends in the stationary phase is called the adjusted retention... separations and in the formulation of theoretical models the retention factor (sometimes referred to as the capacity factor), k, is more important than retention time The retention factor is the ratio of the time a substance spends in the stationary phase to the time it spends in the mobile phase (Eq 1.2) (1.2) If the distribution constant is independent of the sample amount then the retention factor... be obtained directly from the gas-liquid distribution constant using ~Go = -RTcln KL From the slope of a plot of log Vg against the reciprocal of the column temperature over a narrow temperature range, 10-30 K, the enthalpy of solution is obtained The entropy for the same process is obtained from a single value of the specific retention volume and the value of the enthalpy of solution calculated as... dispersion of solute zones around an average value, such that they occupy a finite distance along the stationary phase in the direction of migration The extent of dispersion restricts the capacity of the chromatographic system to separate, and independently of favorable thermodynamic contributions to the separation, there are a finite number of dispersed zones that can be accommodated in the separation... compressibility of the carrier gas is the corrected hold-up volume VMo The latter is equivalent to the gas phase volume of the column at the average column pressure and temperature VM = tM Fe = (0.23) (28.18) = 6.48 ml and VMo = j VM = (0.9596) (6.48) = 6.22 m1 • The retention volume (VR) is the volume of mobile phase entering the column between sample injection and the emergence of the peak maximum for the substance... from the number of observed peaks; qualitative identification of sample components from the accurate determination of peak position; quantitative assessment of the relative concentration or amount of each component from their peak areas; and characteristic physical properties of either the solute or the chromatographic system from peak positions and profiles The fundamental information of the chromatographic... Compared to gas chromatography liquid chromatography is used far less for physicochemical measurements [37,38] Inadequate knowledge of the true composition of the stationary phase and the absence of quantitative models for the accurate description of retention are the principal reasons for this A few exceptions are the determination of equilibrium constants that affect the form of a solute in the mobile... position in the column will depend on the flow resistance of the column and the ratio of the column inlet to outlet pressure An average linear velocity, u, is always available as the ratio of the column length to the retention time of an unretained solute (L / tM) For open tubular columns this definition is unambiguous For packed columns the measured value will depend on the ability of the unretained... ions in the mobile phase and those on the stationary phase then the technique is referred to as ion-exchange chromatography (lEC) or ion chromatography (IC) If the stationary phase is a solid with immobilized molecular recognition sites in which the dominant separation mechanism is the three-dimensional specificity of the interaction between the molecular recognition site and the sample then the technique . defined as the ratio of the volume of mobile phase and stationary phases in the column for a partition system, or the ratio of the volume of the mobile phase to the surface area of the stationary. not provide the desired result of a contemporary picture of the practice of chromatography at the turn of the century. The only workable solution was to start afresh, maintaining the same general. supercritical fluid chromatography a fraction of the mobile phase can be trapped in the pores of the column packing and is stagnant. The volume of stagnant mobile phase is considered part of the stationary