Single-component mobile phase

Equation (2-46) is only applicable for binary systems (analyte—single component mobile phase). Similar expression could be derived if we assume that the adsorption of the analyte does not disturb the equilibrium of the binary eluent system. 

Mixing Mobile Phase Components Single-Component Mobile Phase... 

Standard Development. The standard method of development has already been described in the preceding paragraphs. If the TLC characteristics of the analyte are unknown, a simple single-component mobile phase is preferable for preliminary experiments aimed at establishing separation behavior. If no single-component mobile phase provides the separation desired, however, multicomponent systems should be examined. 

If no in-line degasser is available, mobile phases may be degassed by ultrasonication under aspirator vacuum (caution non-spherical glass flasks may implode). Single-component mobile phases should not be used, as it has been found that even after the most careful degassing bubbles are formed upon mixing of methanol and aqueous buffers. 

The following solvents are used as single component mobile phase distilled or tap water, acetone, acetonitrile, benzene, carbon tetrachloride, chloroform, dioxane, ethanol, ethylacetate, methanol, o-xylene, petroleum ether, toluene, n-octanol, n-nonane and cyclohexane (73,80,82,95,103,138,139, 166,171,172,176,182,189,195). 

A single solvent only rarely provides suitable separation selectivity and retention in normal-phase systems, which should be adjusted by selecting an appropriate composition of a two- or a multi-component mobile phase. The dependence of retention on the composition of the mobile phase can be described using theoretical models of adsorption. With some simplification, both the Snyder and the Soczewinski models lead to identical equation describing the retention (retention factor. A) as a function of the concentration of the stronger (more polar) solvent, (p. in binary mobile phases comprised of two solvents of different polarities [,121 ... 

In addition to the stationary and mobile phases, separations obtained in TLC are affected by the vapor phase, which depends on the type, size, and saturation condition of the chamber during development. The interactions of these three phases as well as other factors, such as temperature and relative humidity, must be controlled to obtain reproducible TLC separations. The development process with a single (isocratic) mobile phase is complicated because of progressive equilibration between the layer and mobile phase and separation of the solvent components of the mobile phase as a result of differential interactions with the layer, which leads to the formation of an undefined but reproducible mobile phase gradient. 

If the metal atoms are not mobile (as is the case in low—temperature reactions) only hydride phases can result in which the metal lattice is structurally very similar to the starting intermetallic compound because the metal atoms are essentially frozen in place. In effect the system may be considered to be pseudo-binary as the metal atoms behave as a single component. 

Mobile phase Gas, SCF, liquid, ionic solution Pressure, density Single vs. multiple component Polar vs. nonpolar... 

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