Solvent mobile phase influence

Does solubility in the mobile phase influence net retention Polyethylene glycols are more soluble in cold solvents than warm. What is the noted effect if the temperature of the liquid chromatography separation of poly ethers is raised ... 

Compounds most efficiently separated by LSC are non-ionic and relatively soluble in organic solvents (4). Because the solvent (mobile phase) interacts with the surface of the stationary phase, the separation process is Influenced by... 

Preparative layer (planar) chromatography (PLC) is a liquid chromatographic technique in which the solvent (mobile phase) migrates through a porous support (stationary phase) either by capillary action or under the influence of forced flow with the aim of separating compounds in amounts of 10-1(X)0 mg (1). The compounds can be isolated for structure elucidation (MS, NMR, IR, UV, etc.), for various analytical purposes (e.g., further chromatography), or for determination of biological activity (2). 

To eluate an antibiotic from chromatographic columns as a mobile phase such solvents as methanol, ethanol, propanol, acetone, acetonitrile are usually used. Influence of these solvents on ions Eu(III) in a complex with OxTC and Cit has been investigated. It is established, that the used solvents do not reduce I Eu(III) ions, and sometimes they increase I by 16-45 %. 

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. 

It is important to know the influence of the physicochemical parameters of the mobile phase (dipole moment, dielectric constant, and refractive index) on solvent strength and selectivity. The main interactions in planar chromatography between the molecules of the mobile phases and those of solutes are caused by dispersion forces related to the refractive index, dipole-dipole forces related to the dipole moment, induction forces related to a permanent dipole and an induced one, hydrogen bonding, and dielectric interactions related to the dielectric constant. Solvent strength depends mainly on the dipole moment of the mobile phase, whereas the solvent selectivity depends on the dielectric constant of the mobile phase. 

The selection of proper mobile phase in TLC exerts a decisive influence on the separation of inorganic ions. With a particular stationary phase, the possibility of separation of a complex mixture is greatly improved by the selection of an appropriate mobile phase system. In general, the mixed aqueous-organic solvent systems containing an acid, a base, or a buffer have been the most favored mobile phases for the separation of ionic species. The mobile phases used as developers in inorganic PLC include ... 

The pKa of basic compounds as well as the buffered mobile phase were influenced by the organic solvent and depended on its proportion in the soluhon. The results indicated that the stationary phases and mobile phases studied were not suitably optimized for the estimation of lipophilicity of basic compounds. 

Buffer Salt Solvent Strength and Selectivity Solvent strength and selectivity are influenced by the nature of the counterion i.e., its value. A change in buffer salt may also change the mobile phase pH. 

Experimental variables such as temperature, flow rate, sample concentration and mobile phase composition can cause changes in the elution volume of a polymer [439,457,460-464]. Chromatographic measurements made with modem equipment are limited more by the errors in the absolute methods used to characterize the molecular weight of the calibration standards than any errors Inherent in the measurements themselves, since the determination of molecular weights by SEC is not an absolute method and is dependent on calibration [462]. The Influence of temperature on retention in SEC is not very great, since no strong sorptive interactions are involved in the retention mechanism. Temperature differences between the column and solvent delivery... 

Reciprocating-piston pumps deliver a constant flow at si fixed backpressure. At high pressures some minor flow variability ziay arise due to the compressibility of the mobile phase. Soms instruments incorporate a flow controller which provides a fixadi backpressure for the pump to work against, independent of the column backpressure. The influence of pressure fluctuations, solvent compressibility, and solvent viscosity on the volumetrie output of the pump are thereby eliminated. Reciprocating-piston pumps can provide continuous solvent delivery, fast solvent change--... 

The above discussion is applicable to layers unpeirturbed by the presence of a vapor phase, such as in a sandwich layer tank. In practice, most separations are performed in large volume chanbers in the presence of a vapor phase. It is almost impossible to fully saturate such chanbers so that a temporal and spatial vapor equilibrium is unlikely to. exist. Two opposing phenomena can be expected to influence the rate of solvent migration. Vaporization of solvent from the wetted layer might reasonably be expected to depend on the wetted surface area of the plate and the vapor pressure of the solvent in the tank. The loss of solvent from the layer will result in a reduction of the mobile phase... 

The choice of solvent directly influences the retention of the analyte on the sorbent and its subsequent elution, whereas the solvent polarity determines the solvent strength (or ability to elute the analyte from the sorbent in a smaller volume than a weaker solvent). Dean [272] gave solvent strengths for normal- and reversed-phase sorbents. The elution solvent should be one in which the analytes are soluble and should ideally be compatible with the final analysis technique. For example, for HPLC analysis, a solvent similar to the mobile phase is a good choice of elution solvent. For the elution step it is also important to consider the volume of the solvent. A minimum volume of elution solvent (typically 250 xL per 100 mg of sorbent) allows maximum concentration of the analytes. 

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