Glossary Of HPLC-LC Separation Terms – L

The listing should be helpful to those just starting in HPLC but it also can serve as a refresher for long-time users in the field.

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L

L: See column length.

Laminar flow: The smooth time-invariant flow that develops when a liquid is moving under conditions in which viscous forces dominate inertial forces. Laminar flow is characterized by a low Reynolds number (see Reynolds number ). In a cylindrical tube, fluid streams in the center flow faster than those at the tube wall, which results in a radially parabolic distribution in axial fluid velocity. This nonuniformity of axial velocities in the interstices in a packed bed also causes substantial peak broadening in packed columns.

Langmuir isotherm: A specific form of an isotherm; CS = N0CM/(Kd + CM), where CS and CM are the equilibrium stationary and mobile-phase concentrations of the solute, N0 the total number of surface sites available for sorption, and Kd the sorption binding constant.

LC: See liquid chromatography.

Ligand: In ligand-exchange chromatography, it refers to the analyte that undergoes ligand exchange with the stationary phase. In affinity chromatography, it refers to the biospecific material — enzyme, antigen, or hormone — coupled with the support (carrier) to form the affinity column. In bonded-phase chromatography, it refers to the moiety covalently bound to the surface.

Ligand-exchange chromatography: A technique in which chelating ligands are added to the mobile phase and undergo sorption onto a packing. These sorbed molecules can act as chelating agents with certain solutes. For example, copper salt can be added to the mobile phase for the chelation and separation of amino acids. Chelating resins function in a similar manner: chelating groups are chemically bonded to the polystyrene backbone.

Linear elution adsorption chromatography: Refers to adsorption chromatography performed in the linear portion of an adsorption isotherm. A term coined by Lloyd Snyder.

Linear velocity (u): The velocity of the mobile phase moving through the column. Expressed in centimeters per second. Related to flow rate by the cross-sectional area of the column. Determined by dividing the column length (L) by the retention time of an unretained compound. See also void time.

Liquid chromatography (LC): A separation technique in which the mobile phase is a liquid. Most often performed in a column.

Liquid–liquid chromatography: One of the earliest separation modes of HPLC; it gave way to chemically bonded phases in the early 1970s. Same as partition chromatography.

Liquid–solid chromatography: Same as adsorption chromatography.

Loadability: The maximum amount of analyte that can be injected onto a column that no longer permits the isolation of product at the desired level of purity or recovery level; important in preparative chromatography

Loading (phase loading versus sample loading): The amount of stationary phase coated or bonded onto a solid support. In liquid–liquid chromatography, the amount of liquid phase in milligrams of per gram of packing. In bonded-phase chromatography, the loading may be expressed in micromoles per square meter or percentage carbon (w/w). Also called coverage or surface coverage. An alternate and unrelated meaning is the amount of sample mass injected on an analytical- or preparative-scale column; preparative-scale columns often are operated in an overloaded condition for throughput reasons.

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

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