Page 153 - Illustrated Pocket Dictionary of Chromatography

PRECOLUMN 153

Reactor coils such as this are used to (1) give a long enough time to allow for a
chemical reaction to go to completion before reaching the detector and/or (2) be
placed in a heating bath or irradiation chamber to initiate or increase the reaction
rate.

pounds per square inch, psi A unit of measure for backpres-
sure in a chromatographic system, where 14.5psi = 1atm = 760torr.

pre-adsorbent A thick 2 to 4cm band of material running along
the bottom of a thin-layer chromatography plate. It is made from an
inactive material. The pre-adsorbent therefore allows for higher
sample loading with no chromatography occurring before the active
sorbent phase. An added benefit is that as the sample moves from the
pre-adsorbent layer to the active sorbent the sample band is sharp-
ened, resulting in a more efficient separation.
precision A measure of how reproducibly a method generates the
same result for replicate determinations. The overall precision of a
method consists of the precision of the sample preparation step, the
analysis step, and the data processing step.

precolumn Generally placed between the outlet check valve of the
pump and the pressure transducer. It has the same bonded phase iden-
tity as the analytical column. It is used to protect the analytical column