Page 122 - Illustrated Pocket Dictionary of Chromatography

LOOP 121

where L is the column length and t is the residence time of the com-
ponent in the column.

linear regression The process through which the slope and inter-
cept of a linearly correlated set of data are determined. One of the
techniques used is least squares.

linear velocity, u The rate at which the mobile phase moves
through a length of column. The linear flow rate is calculated from:

u = F A
e
where F is the flow rate, e is the column porosity, and A is the cross-
sectional area of the column tubing.

liquid chromatography (LC) A technique that utilizes a liquid
mobile phase to generate separations.

liquid-phase loading This term applies to the liquid stationary
phase that is present on a GC support that is used in a GLC separa-
tion. It is expressed as a weight percent:

% liquid loading = ( [ wt of liquid phase) ( wt of liquid phase
+ wt of support material)] ¥ 100

liquid-solid chromatography (LSC) See adsorption
chromatography.

loading (1) The amount of stationary phase adsorbed or bonded to
a support material. This is often expressed as a weight percent. (2)
The amount of sample injected onto a column is referred to as the
sample loading.

longitudinal diffusion A band-broadening effect that is the result
of the chemical potential gradient caused by the concentration dif-
ferences within the eluting sample band and the adjacent mobile
phase. It is part of the B term in the van Deemter and Knox equations.
loop A part of an injector that contains the sample before injection.
In some injectors the sample needle acts as the loop as well. Injector
loops can be internal or external to the body of the injector. Large
volumes (≥2mL) are typically external. Loops are constructed from
stainless steel and PEEK.