Page 100 - Illustrated Pocket Dictionary of Chromatography

96 n-HEXANE

on silica—0.00; polarity index (P¢): 0.1; Hildebrand solubility parame-
ter (d): 7.4; solubility in water (20°C): 0.003%; water solubility in
heptane (20°C): 0.01%. Volatile and flammable.

CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3
Heptane
Heptane is used sparingly in GC as a sample solvent and in LC as a
normal-phase mobile-phase component because of its high cost rela-
tive to hexane. Although alkanes are considered very stable, they do
degrade over time when in contact with oxygen, heat, and light.

n-hexane Molecular weight: 86.2; boiling point: 68.7°C; refractive
index (20°C): 1.379; density (20°C): 0.66g/mL; viscosity (20°C): 0.31
o
cP; UV cutoff: 195nm; eluotropic strength (e ) on alumina—0.01, on
silica—0.00; polarity index (P¢): 0.1; Hildebrand solubility parameter
(d): 7.3; solubility in water (20°C): 0.014%; water solubility in hexane
(20°C): 0.01%. Volatile and flammable. Hexane is a solvent commonly
used as a sample solvent in GC and a mobile-phase component in LC
and TLC. It should be kept in mind that the commonly purchased high-
purity hexane is typically a mixture of approximately 85% n-hexanes
and 99.9% hexanes; in essence a C 6 hydrocarbon isomer blend.
Although alkanes are considered very stable, they do degrade over
time when in contact with oxygen, heat, and light.

CH 3 CH 2 CH 2 CH 2 CH 2 CH 3
Hexane

high-performance liquid chromatography (HPLC) A liquid
chromatography technique that uses columns packed with particles
that are 3–10mm in diameter. To generate constant flow through such
a packed bed requires that the mobile phase be forced through by a
pump, often at pressures exceeding 500psi. Smaller particle diame-
ters lead to higher efficiency and high-pressure mobile-phase delivery
to shorter analysis times.

high-performance thin-layer chromatography (HPTLC) A
technique based on the same principles as thin-layer chromatography
except using smaller particles (5–15mm) and an adsorbent thickness
of only ~150mm. In general, the reduced thickness of the adsorbent
generates a faster separation and the smaller particle diameter higher
efficiency.