Mobile phase column chromatography

Recently, Janjic et al. published some papers [33-36] on the influence of the stationary and mobile phase composition on the solvent strength parameter e° and SP, the system parameter (SP = log xjx, where and denote the mole fractions of the modiher in the stationary and the mobile phase, respectively) in normal phase and reversed-phase column chromatography. They established a linear dependence between SP and the Snyder s solvent strength parameters e° by performing experiments with binary solvent mixtures on silica and alumina layers. 

Stationary phases for modern, reversed-phase liquid chromatography typically consist of an organic phase chemically bound to silica or other materials. Particles are usually 3, 5, or 10 p,m in diameter, but sizes may range up to 50 p,m for preparative columns. Small particles thinly coated with organic phase allow fast mass transfer and, hence, rapid transfer of compounds between the stationary and mobile phases. Column polarity depends on the polarity of the bound functional groups, which range from relatively nonpolar octadecyl silane to very polar nitrile groups. 

Figure 14-6B shows how the compounds distribute themselves down the column. Figure 14-6C shows the concentration profile for this type of separation. Notice that the compounds can be separated completely, but that each is mixed with the mobile phase. Partitioning chromatography is used when a quantitative separation is required. 

RP systems dominate analytical applications because of their robustness and reduced equilibration time. This fast column equilibration makes RP phases applicable for gradient operation. For preparative chromatography, normal phase systems are preferred because of some disadvantages of the RP systems. Although water is a very cheap eluent it is not an ideal mobile phase for chromatography because it evaporates at higher temperatures, the enthalpy for evaporation is quite... 

The first step in the selection of the size-exclusion separation system is the choice of the mobile phase. We need to select a mobile phase in which the analytes, usually polymers, are soluble. This, in turn, determines the selection of the stationary phase, spedfically, whether we select a padring designed for organic or aqueous size-exclusion chromatography (the term aqueous may include polar solvents). If the goal of the separation is a molecular-weight determination, the requirements for the mobile phase-column combination are quite stringent ... 

Simulated Moving-Bed Chromatography (SMBC) As the name suggests, this technique is based on the principle of liquid mobile phase and chromatography phase moving in opposite directions. Establishment of equilibrium helps in the improved efficacy of separation of the component of a mixture—often, a mixture of two enantiomers—which are fed into the middle of the column. The advantages are the continuous feeding of the sample... 

Analytical method Expert system to model rules of configuration of method Optimization of method variables Suggested conditions for given problem, e.g., mobile phase, column, and detector for ion chromatography... 

In the present chapter we describe the relation between three classes of mobile phases in chromatography gas, supercritical fluid and liquid. Further, the relation between packed and open tubular columns is discussed. Mobile and stationary phases relevant to lipid separations are reviewed as well as instrumental aspects such as injection and detection. SFE of lipids for analytical and semi-preparative purposes is discussed. 

As noted in the discussion of TLC, the strength of the adsorption of an organic compound to the solid support depends on the polarity and nature of the adsorbent as well as on the nature of the functional groups present in the molecule. When normal-phase column chromatography is performed, a polar stationary phase such as alumina or silica gel is used in combination with organic solvents as the mobile phase or eluant. Under these conditions, the elutropic series described for TLC in Section 6.2 applies. 

In reverse-phase column chromatography, which phase is the more polar the stationary phase or the mobile phase ... 

A typical eluting solvent for reverse-phase column chromatography is acetonitrile (CH3CN), water, and a buffer. In what way is this mobile phase different from the one you used to separate fluorene (5) from 9-fluorenone (6)7... 

Haney et al [1,2], Waters Associates [3], and Knox et al. [4,5] - to name just a few - found that by adding lipophilic ions such as alkanesulfonic acid or quaternary ammoniiun compoimds to the mobile phase, solute ions of opposite chaise can be separated on a chemically bonded reversed-phase column. The term reversed-phase ion-pair chromatography (RPIPC) has generally been adopted for this technique. The term mobile-phase ion chromatography (MPIC) describes a method that combines the major elements of RPIPC with suppressed conductivity detection. Besides the above-mentioned chemically bonded reversed phases, neutral divinylbenzene resins featuring a high surface area and a weakly polar character are also used as stationary phases. 

Chromatography and DD. These methods have common features of mass transfer from chromatographic column to detector and from stoichiographic reactor to analyzer detector. Therewith, selectivity and efficiency of separation of the tested components depend on the same factors (thermodynamic parameters and diffusion effects), for example, on the flow rate of a mobile phase feas chromatography) and on the rate of changes in the concentration of solvent active component (DD). 

Anionic surfactants may be determined by conventional ion chromatography, especially if only one anionic or a simple mixture is present. However, most separations require paired ion chromatography, as described above. One vendor uses the term mobile-phase ion chromatography to describe paired-ion HPLC with a conductivity detector and a system to chemically suppress the baseline conductivity of the mobile phase. A number of variations on this theme have been demonstrated, using either polymer backbone or sihca backbone reversed-phase columns, varying levels of organic solvent in the mobile phase, and either isocratic or gradient elution conditions (3,13-15). 

Mobile-phase ion chromatography, a technique which uses traditional ion chromatography equipment, a nonpolar poly(styrene/divinylbenzene) separation column, a suppressor column, and conductivity detection, is suitable for analysis of cationic surfactants. Dilute perchloric acid in 70 volume percent acetonitrile is used as eluent (13). The separation mechanism is the same as in the reversed-phase HPLC methods discussed above. 

Ci4 alkyltrimethylammonium chloride, Ci4-Cifi alkyldimethylbenzyl-ammonium chlorides, benzethonium chloride assay MPIC-NSl mobile phase ion chromatography column, 4 x 200 mm 70 30 or 75 25 CH3CN/O.OO5 M HCIO4 Conductivity 13 ... 

---