Mobile phase dependence

Another important issue that must be considered in the development of CSPs for preparative separations is the solubility of enantiomers in the mobile phase. For example, the mixtures of hexane and polar solvents such as tetrahydrofuran, ethyl acetate, and 2-propanol typically used for normal-phase HPLC may not dissolve enough compound to overload the column. Since the selectivity of chiral recognition is strongly mobile phase-dependent, the development and optimization of the selector must be carried out in such a solvent that is well suited for the analytes. In contrast to analytical separations, separations on process scale do not require selectivity for a broad variety of racemates, since the unit often separates only a unique mixture of enantiomers. Therefore, a very high key-and-lock type selectivity, well known in the recognition of biosystems, would be most advantageous for the separation of a specific pair of enantiomers in large-scale production. 

In TLC the choice of mobile phase depends primarily on the additive in question. Gedeon el al. [394] have listed mobile phases for the separation of AOs and plasticisers. Bataillard et al. [351] have reported R values for various solvents and visualisation modes for a great variety of primary and secondary AOs, UVAs, HALS and metal deactivators. 

The potential of this reference electrode versus the mobile phase depends on the chosen mobile phase composition and [Cl ]... 

Chromatography is a differential migration process where sample components are distributed between a stationary and a mobile phase. Depending on the affinity of a component for either or both of these phases, the rate of migration varies from zero to the velocity of the mobile phase. The distribution coefficient (D) for an analyte between the two phases is... 

Thin-layer chromatography is a separation technique in which the components of a lipid mixture are differently distributed between a solid stationary phase, spread as a thin layer on a plate made of inert material, and a solvent mobile phase. Depending on their type, the components are retained with different strengths on the layer to give distinctive spots or bands. The migration of a band is presented quantitatively by the corresponding Rf value. The stronger the retention, the lower is the Rf value. 

The most important criterion for solvent selection is throughput, which mainly depends on a sufficient solubility of the solutes and the corresponding selectivity of the separation. Because solubility and selectivity depend on the interaction between the three elements of the chromatographic system, the selection of the mobile phase dependent on these parameters is further discussed in Section 4.3. 

GC coupled to TEA detection is the most suitable analytical method to determine volatile nitrosamines. However, a large number of A/-nitrosamines are not generally adequate for direct analysis by GC, either because of low volatility or thermal instability. In these cases, HPLC seems to be the method of choice for the analysis of volatile and nonvolatile nitrosamines. The correct choice of stationary phase and type of composition of the mobile phase depends on the detection method used. 

Among the parameters related to the retention time, the distribution constant K — defined for a compound as the ratio between its concentrations in the stationary phase and in the mobile phase — depends only on analyte, stationary phase, and temperature, and can be used to compare retention data. K can be calculated from chromatographic measures from its definition. 

The addition of salt or buffer to the mobile phase can also be used to manipulate retention. Retention decreases with the addition of salt. The influence of the pH of the mobile phase depends on the nature of the analyte charged forms are more polar and generally more strongly retained than uncharged forms of the analyte. 

General term defining a diverse group of techniques used to separate a sample mixture. The separation is based on differences in the relative affinities of the sample components for two different media, the mobile phase (a moving fluid) and the stationary phase (a porous solid or gel or a liquid coated on a solid support). The velocity at which each component is carried along with the mobile phase depends on its solubility and on its affinity for the stationary phase. 

Retention in RPLC with aqueous-organic mobile phases depends mainly on hydrophobic interactions. In general, some correlation between RPLC retention data and log is observed for a given series of solutes. The observed relationships support the assumption that in RPLC, partitionii rather than adsorption processes are decisive for retention. 

The ratio of the distribution factors obtained with the two mobile phases depends on their difference in... 

When aluminum plates precoated with the mixture of silica gel 60 and Kieselguhr F254 ( 1.05567) were used, the selection of mobile phases depended on the kind of bile acids which are being separated. The mobile phase 25 20 8 (v/v/v) allows separation of all pairs of bile acids, with the exception of the pair of LC and DC. Using mobile phases in other volume compositions can separate the pair of LC and DC. In this case— the separation on the silica gel 60 and Kieselguhr F254 mixture—the biggest problem was to... 

An investigation on the approach of inverse compensation gradients in liquid chromatography with mobile phase dependent detectors. Presentation at HPLC 2010, Boston, MA, USA. 

---