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149
HPLC COLUMNS
Column Select ion
Multiply units in the left-most column by the conversion factors listed in the columns to the right.
e.g.,
10 psi x 0.068 = 0.68atm
10 bar x 29.5300 = 295.300 inches Hg
HPLC Pump Pressure Conversion Table
Pressure
psi
atm
kg/cm
2
torr
kPa
bar
inches Hg
1 psi = 1
0.068
0.0703
51.713
6.8948
0.06895
2.0359
1 atm =
14.696
1
1.0332
760
101.32
1.0133
29.921
1 kg/cm
2
=
14.223
0.967
1
735.5
98.06
0.9806
28.958
1 torr =
0.0193
0.00132
0.00136
1
0.1330
0.00133
0.0394
1 kPa =
0.1450
0.00987
0.0102
7.52
1
0.0100
0.2962
1 bar =
14.5038
0.9869
1.0197
751.88
100
1
29.5300
1 in Hg =
0.49612
0.0334
0.0345
25.400
3.376
0.03376
1
Figure 3
Restek stationary phases and recommended uses.
Alkyl Phases
• General purpose reversed phase columns rely on dispersive
interaction to separate molecules.
• Elution order is hydrophilic to hydrophobic; increased chain
length increases retention.
Modified Alkyl Phases
• Alkyl phases with modified bonding chemistry to increase polarity.
• Columns are compatible with 100% aqueous mobile phases.
• Rely on dispersive interaction with additional hydrogen bonding.
• Aqueous columns show balanced retention and are a great
starting point for method development.
• Polar embedded IBD columns provide good peak symmetry for
bases and offer orthogonal selectivity to a C18.
• IBD phases are capable of mixed mode mechanisms and can
operate in both reversed phase and HILIC modes.
Phenyl Phases
• Phenyl columns rely on dispersive and pi-pi (
π
-
π
) interactions.
• Enhanced retention and selectivity are seen with aromatic,
conjugated molecules, and compounds containing electron
withdrawing ring substituents.
• Biphenyl and Aromax columns show more interaction and
greater aromatic retention and selectivity, relative to
conventional phenyl and phenyl-hexyl phases.
Polar Phases
• Polar phases rely on aromatic and dipole interactions.
• Cyano and PFP Propyl phases show increased retention for
aromatic compounds and charged bases.
• PFP Propyl phases are commonly used for increased retention
of ionic and basic compounds.
• Amino columns are commonly used for the analysis of saccharides.
• Silica columns are used for normal phase and HILIC separations.
Si
CH
3
CH
3
O
C8
Si
CH
3
CH
3
O
C18
Si
CH
3
CH
3
O
C4
Si
CH
3
CH
3
O
C1
Non Polar Retention
Phenyl
Aromax
Si
CH
3
CH
3
O
Si
CH
3
Proprietary
CH
3
O
Biphenyl
Si
CH
3
CH
3
O
Aromatic Retention
Aqueous C18
Si
OO
P
IBD
CH
3
CH
3
O
Si
P
Acidic Retention
PFP Propyl
Si
CH
3
CH
3
O
F
F
F
F
F
Cyano
Si
CH
3
N
C
CH
3
O
Silica
Si
OO O
OH
Amino
Si
CH
3
NH
2
CH
3
O
orthogonal selectivity to a C18
good choice for LC/MS
HILIC compatible
Legend
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Mar 2011
