Glossary of HPLC/LC Separation Terms

Feb 01, 2008
Volume 26, Issue 2, pg 118–168


Tailing: The phenomenon in which a normal Gaussian peak has an asymmetry factor greater than 1. The peak will have an extended trailing edge. Tailing is caused by packing sites that have both a stronger-than-normal retention for the solute and slower desorption kinetics. A typical example of a tailing phenomenon would be the strong adsorption of amines on the residual silanol groups of a low-coverage reversed-phase packing at intermediate pH values. Tailing also can result from injecting an excessive mass or sample, badly packed columns, excessive extracolumn volume, poor fittings, excessive detector volume, and slow detector response. See Figure 1.

Tailing factor: U.S. Pharmacopeia measure of peak asymmetry defined as the ratio of the peak width at 5% of the apex to twofold the distance from the apex to the 5% height on the short time side of the peak. Greater than unity for tailed peaks. See also asymmetry factor.

Temperature programming: Changing column temperature as a function of time during the separation. Rarely used in HPLC; if so, usually in a stepwise manner.

Ternary mobile phase: Mobile phase that is a mixture of three solvents or buffers.

Theoretical plate (N): A concept described by Martin and Synge. Relates chromatographic separation to the theory of distillation. Length of column relating to this concept is called height equivalent to a theoretical plate. See also HETP. Plates are calculated as N = 16(V R/w b)2 = 16 (t R/w b)2, where V R is the retention volume, w b is the width at the peak base, and t R is the retention time. See also N.

Thermally tuned tandem column chromatography: A form of LC in which two columns with distinctly different selectivities are placed in tandem and operated at two temperatures to optimize the resolution or analysis speed. Both columns use a common eluent, and the entire sample passes through both columns and is detected with a single detector. It is not a two-dimensional technique because each sample component provides only one peak.

Titania: An uncommon adsorbent used in adsorption chromatography.

t m : See migration time.

t M : Holdup time.

Tortuosity or tortuosity factor: A packed-column property that controls the inhibition of longitudinal diffusion of the solute as it diffuses along the column axis. The B term in the van Deemter equation is proportional to the tortuosity. See also B term, γ, and molecular diffusion term.

Total mobile-phase volume (V t ): The total volume of mobile phase in an SEC column. Also known as totally included volume. Same as V M .

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