Page 155 - Illustrated Pocket Dictionary of Chromatography

PUMP 155

functioning of a chromatographic system is often indicated through
the pressure generated at the head of the column. This is typically
referred to as head pressure (GC) or backpressure (LC). The pressure
is determined through the use of a pressure transducer situated
after the pump and before the injector. Common units of measure
for pressure are atmosphere (atm), bar, pounds per square inch (psi),
or Pascals (Pa).

1-propanol See n-propyl alcohol.

2-propanol See isopropyl alcohol.
n-propyl alcohol Molecular weight: 60.1; boiling point: 97.2°C;
refractive index (20°C): 1.3856; density (20°C): 0.80g/mL; viscosity
o
(20°C): 2.3cP; UV cutoff: 210nm; eluotropic strength (e ): on
alumina—0.82; polarity index (P¢): 4.3; Hildebrand solubility parame-
ter (d): 12.0; solubility in water (20°C): 0.04%; water solubility in n-
propyl alcohol (20°C): 0.009%. Extremely volatile and flammable.

CH 3 CH 2 CH 2 OH
n-Propyl alcohol

polytetrafluoroethylene (PTFE) A polymer of (CF 2CF 2) n that
has high chemical resistivity, low adhesiveness, elasticity, and a
wide useful temperature range. These characteristics make this
material ideal for routine low-pressure work in HPLC. The patented
®
trademark is Teflon . Note that PTFE is permeable to oxygen and
that this could be a problem when using an electrochemical detector
(depending on the operating applied potential) or in very low UV work
(<210nm).
pump A component of an LC system that generates the mobile-
phase profile and maintains (i.e., isocratic) or reproducibly alters (i.e.,
gradient) it throughout the course of a separation. Through its design
a pump ensures that solvent flow direction and rate are maintained
as invariant as possible. Pumps vary in delivery rate ranges from
0.01mL/min for microbore work to 5–10mL/min for GPC/SEC work
to >10mL/min for prep work. Pumps can be single piston (isocratic
work) or dual piston (or single piston and compensating piston for
gradient work).