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The distribution constant (or partition ratio) (K D) is the equilibrium constant for the distribution of an analyte in two immiscible solvents. [1] [2] [3]In chromatography, for a particular solvent, it is equal to the ratio of its molar concentration in the stationary phase to its molar concentration in the mobile phase, also approximating the ratio of the solubility of the solvent in each phase.
For example, the blood/gas partition coefficient of a general anesthetic measures how easily the anesthetic passes from gas to blood. [5] Partition coefficients can also be defined when one of the phases is solid , for instance, when one phase is a molten metal and the second is a solid metal, [ 6 ] or when both phases are solids. [ 7 ]
In chromatography substances are separated by partition between a stationary phase and a mobile phase. The analyte is dissolved in the mobile phase, and passes over the stationary phase. Separation occurs because of differing affinities of the analytes for the stationary phase. A distribution constant, K d can be defined as
However, it is also possible to get equilibria between substances in different phases, such a liquid and gas that do not mix (are immiscible). One example is gas-liquid partition equilibrium chromatography, where an analyte equilibrates between a gas and liquid phase. [2] Partition equilibria are described by Nernst's distribution law. [3]
As with the ¯ and s and individuals control charts, the ¯ chart is only valid if the within-sample variability is constant. [4] Thus, the R chart is examined before the ¯ chart; if the R chart indicates the sample variability is in statistical control, then the ¯ chart is examined to determine if the sample mean is also in statistical control.
which can be used to relate the molecular weight of any two polymers using their Mark-Houwink constants (i.e. "universally" applicable for calibration). For example, if narrow molar mass distribution standards are available for polystyrene, these can be used to construct a calibration curve (typically l o g M {\displaystyle logM} vs. retention ...
In liquid chromatography, the mobile phase velocity is taken as the exit velocity, that is, the ratio of the flow rate in ml/second to the cross-sectional area of the ‘column-exit flow path.’ For a packed column, the cross-sectional area of the column exit flow path is usually taken as 0.6 times the cross-sectional area of the column.
In gas chromatography, the Kovats retention index (shorter Kovats index, retention index; plural retention indices) is used to convert retention times into system-independent constants. The index is named after the Hungarian-born Swiss chemist Ervin Kováts , who outlined the concept in the 1950s while performing research into the composition ...