Page 161 - Illustrated Pocket Dictionary of Chromatography

162 RAOULT’S LAW

Raoult’s law Relates the partial gas pressure at a given tempera-
ture for component A in a liquid, p A, as a function of its mole fraction
in the liquid, x A, and its pressure above its pure liquid form at that
temperature, P A:
p A = x P A
A
This is based on ideal gas behavior.
Rayleigh scattering In Rayleigh scattering, the incident and
emitted photons are the same. This creates a nonzero background for
fluorescence detectors.

reciprocation The process of the piston moving into and out from
the piston head. Many HPLCs operate with a spring-loaded piston in
contact with an eccentric cam. As the cam rotates, the piston is forced
into the piston head at a fixed rate. The flow rate is then a function of
the volume displacement and the rate of reciprocations/minute.

recovery The recovery of an analyte is calculated as the amount
of material reaching the detector as compared with the theoretically
expected amount and is usually expressed as a percentage:
recovery = [ { amount detected amount expected]} ¥ 100
] [
High recovery is a requirement for most method validations.
recycle The process of returning solvent from the effluent path to
the reservoir. Solvent consumption is a significant ongoing cost of LC
analyses. To conserve solvent, the detector output is used as a trigger
to start/stop the detector effluent into the reservoir. The triggers are
at the beginning and ending of a peak. For recycling to be effective,
the system must:

(1) be isocratic (i.e., the effluent composition matches the reservoir
composition) and
(2) not introduce contamination or gas into the mobile phase.
reduced plate height, h Calculated from the height equivalent
to a theoretical plate, H, and the particle diameter, d p as follows:
h = H d p
This parameter is used to compare the relative column efficiencies for
columns having packing materials with different particle size.