Solvents in Liquid Chromatography

The second major component in modern high-performance liquid chromatography (HPLC) is the mobile phase. Since the stationary phase is a nonpolar entity, the mobile phase must be more polar to allow retention of the analytes. The most polar solvent for RP-HPLC is water, but the overall polarity of the mobile phase can be adjusted by introducing variable amounts of any of a number of organic solvents. In liquid chromatography, retention of solutes is a result of its relative affinity for the stationary and mobile phases. This can be described mathematically by the equation... 

Stated that depending on the thermodynamic quality of solvent, the same macromolecule can assnme various conformations and consequently also different sizes in solution Similar thoughts are to be applied also considering role of solvents in liquid chromatography systems, in which macromolecules necessarily interact with eluent molecules. However, the third component has to be taken into account in polymer HPLC, namely the column packing and its interactions not only with the macromolecules of sample but also with the eluent moleeules. 

The solvents used for liquid chromatography are the commoner ones such as water, acetonitrile, and methanol. For the reasons just stated, it is not possible to put them straight into the ion source without problems arising. On the other hand, the very viscous solvents that qualify as matrix material are of no use in liquid chromatography. Before the low-boiling-point eluant from the LC column is introduced into the ion source, it must be admixed with a high-boiling-point matrix... 

Today, lipophilicity can be determined in many systems that are classified by the characteristics of the nonaqueous phase. When the second phase is an organic solvent (e.g. n-octanol), the system is isotropic, when the second phase is a suspension (e.g. liposomes), it is anisotropic, and when the second phase is a stationary phase in liquid chromatography, it is an anisotropic chromatographic system [6]. Here, we discuss the main aspects of isotropic and anisotropic lipophilicity and their biological relevance the chromatographic approaches are investigated in the following chapter by Martel et al. 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

Some fairly broad generalizations can be made about the selection of certain preferred solvents for liquid chromatography from the relatively large number of liquids that might be employed as solvents. A suitable solvent will preferably have a low vi jslty, be compatible with the detection system, be readily available in a pure form, and if possible, have a low flammability and toxicity. Since detection in HFLC occurs on-line,... 

SOLVENT STRENGTH AND SOLVENT SELECTIVITY PARAMETERS FOR SOME COMMON SOLVENTS USED IN LIQUID CHROMATOGRAPHY. 

However, not withstanding the above objections, further discussion of the Snyder solvent triangle classification method is justified by its common use in many solvent optimization schemes in liquid chromatography. The polarity index, P, is given by the sum of the logarithms of the polar distribution constants for ethanol, dioxane and nltromethane and the selectivity parameters, X, as the ratio of the polar distribution constant for solute i to... 

Figure 1 Ultraviolet spectra for benzaldehyde and benzoic acid solvent, methanol reference, methanol cell, 1.0 cm. (From Pfeiffer, C. D., Larson, J. R., and Ryder, J. F., Linearity testing of ultraviolet detectors in liquid chromatography, Anal. Chem., 54, 1622, 1983. Copyright American Chemical Society Publishers. With permission.)...

High-performance liquid chromatography (HPLC) grade Solvents of suitable purity for use in liquid chromatography procedures. 

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