Mobile phase solvent strength

A method that can decrease the viscosity of the mobile phase without impacting the mobile phase solvent strength (i.e., maintaining k) would therefore decrease the analysis time linearly. The next section illustrates the diffusion coefficients and viscosities, the unique relationship between them for EEL mixtures, their solvent-strength and other important properties. 

Use of Solvatochromic Dyes To Correlate Mobile Phase Solvent Strength to Chromatographic Retention in Supercritical Fluid Chromatography... 

The most widely used supercritical fluids are not very polar and cannot elute polar compounds in reasonable times. The addition of a more polar modifier to such fluids increases the mobile phase solvent strength allowing the elution of more polar solutes. Methanol appears to be the most polar modifier that is completely miscible with carbon dioxide. On an absolute scale, however, methanol is not very polar (1) and most polar solutes cannot be eluted from standard stationary phases with methanol-carbon dioxide mixtures. 

In this work correlations between mobile phase solvent strength and chromatographic retention of a number of different solute families will be presented. The first solvent strength measurements on ternary mobile phases will also be presented. Finally, a retention mechanism for packed column SFC is proposed. 

Tertiary systems. With methanol/carbon dioxide mixtures the addition of even the most polar additives has only a small impact on the mobile phase solvent strength as measured with Nile Red. With TFA concentrations below 1 to 2 % in methanol, ternary mixtures of TFA/methanol/carbon dioxide produce the same apparent solvent strength as binary methanol/carbon dioxide mixtures. As much as 5 or 10 % TFA in methanol is required to noticeably increase the solvent strength of TFA/methanol/carbon dioxide mixtures above those for binary methanol/carbon dioxide mixtures, as shown in Figure 4. 

Therefore, in liquid-solid chromatographic systems selectivity in a separation is determined by the mobile phase solvent strength and interaction with the adsorbent. The general selectivity triangle... 

Figure 2.10. Six RPLC chromatograms illustrating the effect of mobile phase solvent strength on solute retention and resolution. LC conditions were column Waters Symmetry C18, 3pm, 75x4.6 mm, 1 mL/min, 40°C, Detection at258nm. Mobile phase is mixture of acetonitrile (ACN) and water. Solutes were nitrobenzene (NB) and propylparaben (PP).

First, find the mobile phase solvent strength which optimizes the separation of the four phthalate esters. Second, retrieve the UV absorption spectrum for each of the four and build a library. Third, inject the unknown sample and retrieve its UV spectrum. Fourth, make arrangements with the staff to get your unknown sample analyzed using GC-MS which is available at the Research Complex-Engineering. 

Solvent strength refers to the ability of a particular mobile phase (solvent) to elute mixture components. For example, if use of a particular solvent results in short retention times for mixture components, the solvent is strong. If use of a solvent increases retention times, it is a weak solvent. 

In many forms of secondary equilibria separations, the concentration of the equilibrant, or the mobile phase component which participates in the secondary equilibria, controls, at least partially, the strength and selectivity of the mobile phase. In micellar chromatography the concentration of micelles plays this role, which means that for all separations carried out with micellar mobile phases, the strength of the mobile phase can be changed while maintaining an unchanging bulk solvent composition. This unique aspect of micellar mobile phases does indeed allow the solution to "problems that cannot be solved by other means . 

As the title implies, the main purpose of this work was to study mobile phase solvent power. This results from the fact that, even though a supercritical fluid has a variable solvent power, there is a maximum value of the solvent power—essentially that of the substance as a liquid. If that maximum solvent power is not high enough, a higher value can be achieved by using a mixture of the chosen supercritical fluid with a second, higher-solvent-strength component. The second component is often referred to as a "modifier."... 

Tabie13.1 Eluant Strengths, s°, and Polarity Indices, P, of Selected Mobile Phase Solvents... 

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