Glossary of HPLC/LC Separation Terms - - Chromatography Online
Glossary of HPLC/LC Separation Terms


LCGC North America


log k w : The extrapolated intercept of a plot of log k versus volume fraction of organic modifier in reversed-phase LC. See also S.

Longitudinal diffusion: Same as molecular diffusion term. B term in van Deemter equation. See also van Deemter equation.

Low pressure mixing: See high pressure mixing

M

μ: See electrophoretic mobility.

Macroporous resin (macroreticular): Cross-linked ion-exchange resins that have molecular-scale micropores and also macropores of several hundred angstroms. These highly porous resins have large internal surface areas that are accessible to large molecules.

Mass transfer (interphase): The process of solute movement between the moving and stationary zones. The C term of the van Deemter equation is called the interphase mass transfer term. The faster the mass transfer process, the better the column efficiency. In HPLC, slow mass transfer is the most important factor affecting column efficiency. Its rate can be increased by using small-particle packings, thin stationary-phase layers, low-viscosity mobile phases, and high temperatures.

Mean pore diameter: The average diameter of the pore of a porous packing. It most commonly is determined by the BET method and is reported as fourfold the specific pore volume divided by the specific surface area (4V/A) based on the assumption of uniform cylindrical pores. The pore diameter is important in that it must allow free diffusion of solute molecules into and out of the pore so that the solute can interact with the stationary phase. Additionally, the pores must be well-connected, with a minimum of dead ends, so many paths can allow a molecule to access any part of the pore space. In SEC, the packings have different pore diameters; therefore, molecules of different sizes can be separated. For a typical substrate such as silica gel, 60- and 100- pore diameters are most popular. Pore diameters greater than 300 are used for the separation of biomolecules. Pores usually are classified as micro (<20 ), meso (20–500 ), and macro (>500 ).

MECC: See micellar electrokinetic capillary chromatography.

Megapores: See perfusion chromatography.

MEKC: See micellar electrokinetic capillary chromatography.

Metal-affinity chromatography: A special form of ligand-exchange chromatography used to separate biopolymers with a particular affinity for a specific metal cation, typically copper(II), zinc(II), and iron(II).

Metalophile: A compound that has high affinity for active acidic silanol groups on silicas surface. Usually a strongly basic amine or multifunctional carboxylate or phenol.

Method development: A process for optimizing the separation, including the sample pretreatment, to obtain a reproducible and robust separation. Usually, it emphasizes the search for the stationary phase, eluent, and column temperature combination that provides an adequate, if not optimum, separation.

Method validation: A process of testing a method to show that it performs to the desired limits of precision and accuracy in retention, resolution, and quantitation of the sample components of interest.

Micellar chromatography: Adding micelles to the mobile phase to cause separation. The micelles may act as displacing or partitioning agents and provide another parameter to change selectivity. Surfactants at concentrations greater than their critical micelle concentration are used in micellar chromatography and in MEKC.


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