Page 21 - Illustrated Pocket Dictionary of Chromatography

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back diffusion Occurs in gas chromatography when the injector
septum no longer seals after an injection. This allows air and air-borne
contaminants into the system and leads to ghost peaks.
back flush A technique used to effectively clean an LC column
from materials that have deposited on the head of the column. This
involves reversing the direction of solvent flow in the column and
using a very strong solvent to elute the adsorbed material from the
head of the column. Effective back flushing requires the use of a
strong mobile phase. Note that this may involve a number of steps,
especially if a mobile phase with salt-based buffers is used. In any
case, never have the back flush effluent go through the detector; pump
the effluent directly to waste. Also, for columns that have received
long-term use back flushing may be detrimental because the reversed
flow may cause a weakened packing bed structure to collapse.

backpressure The measure of the resistance to flow through a
chromatographic system. Barring any constriction at the point of
entry of the mobile phase into the system, the backpressure is a
measure of the pressure of the system at the top of the column. In
general, decreased particle size and increased mobile-phase viscosity
increase the system backpressure. Common units of pressure are
atmospheres, bars, pounds per square inch (psi), or pascals (Pa).
band Term used to describe the analyte envelope as it moves
through the stationary phase.
band broadening During the course of the elution process all the
factors that contribute to widening the analyte envelope are termed
band broadening. Band broadening is a function of phase-transfer
processes, extra column volumes, and diffusion phenomena. The
larger the band broadening effects, the less efficient the system.

bandwidth (1) Bandwidth, t w, describes the width of the analyte
envelope, along the length of the column or plate, as it elutes from
the column; bandwidth is analogous to peak width for the eluted
sample that has passed through the detector. (2) Defines the range of

Illustrated Pocket Dictionary of Chromatography, by Paul C. Sadek.
ISBN 0-471-20021-2 Copyright © 2004 John Wiley & Sons, Inc.
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