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LC COLUMNS
USLC® Columns
Ultra Selective Liquid Chromatography™ Technology
Choose Columns Fast. Develop Methods Faster.
What is Ultra Selective Liquid Chromatography™ (USLC®) technology? This technique is the directed application of orthogonal
selectivity—the most influential factor affecting peak separation, or resolution—to provide the practicing chromatographer with the
best tools for choosing columns fast and developing methods faster. Through our extensive study of reversed-phase chromatography,
Restek created the widest range of selectivity in the industry using just four unique stationary phases: the USLC® column set. We also
defined a simple approach to choosing a column with the appropriate selectivity for any application.
Selectivity Drives Separations
Quickly and effectively resolve analytes by understanding and controlling selectivity through USLC® technology.
One of the most significant, yet least understood, steps of method development is finding the proper stationary phase for a
particular separation. As sample complexity increases, achieving adequate reso-
lution between matrix components and target analytes becomes more difficult.
Despite recent advancements in column format, such as sub-2-micron packings
and pellicular particles, resolution can still be difficult to obtain because, while
these formats can increase chromatographic efficiency and analysis speed, they do
not significantly influence resolution. Selectivity, as shown in Equation 1, is the
single most powerful factor affecting resolution, and it is largely dependent upon
stationary phase composition.
Real Diversity in Phase Chemistry
A small set of defined orthogonal columns means faster separations and more robust methods.
While numerous bonded phases are available for reversed-phase chromatography, many (e.g., C8 and C18) are similar and offer
only moderate changes in retention rather than significant differences in selectivity. Method development is less laborious and time-
consuming when you use a full range of column selectivities, including orthogonal phase chemistries like polar-embedded, phenyl,
and fluorophenyl columns. Restek has led the development of the unique USLC® column set across these phase classes to provide
analysts with a more effective range of column selectivities and innovative column chemistries for method development. The USLC®
column set (Figure 1) provides the widest range of reversed-phase selectivity available with just four columns and can be used to guide
proper stationary phase selection—the least understood yet most significant part of method development.
Restek®
USLC® Phase
(column class)
Aqueous C18(alkyl) Biphenyl (phenyl) IBD (polar embedded) PFP Propyl (fluorophenyl)
Ligand Type Proprietary polar modified
and functionally bonded C18
Unique Biphenyl Proprietary polar functional
embedded alkyl
Fluorophenyl
Properties • General-purpose with a well-
balanced retention profile.
• Compatible with 100%
aqueous mobile phases.
• Ideal for multi-component
LC-MS analyses.
• Increased retention for dipolar,
unsaturated, or conjugated
solutes.
• Enhanced selectivity when used
with protic (methanol) mobile
phase.
• Ideal for increasing sensitivity and
selectivity in LC-MS analyses.
• Increased retention for
acids and water-soluble
compounds.
• Compatible with 100%
aqueous mobile phases.
• Capable of both
reversed-phase and
HILIC separations.
• Increased retention for
both charged bases and
electronegative compounds.
• Capable of both reversed-
phase and HILIC separations.
• Ideal for increasing sensitivity
and selectivity in LC-MS
analyses.
18 IBD X3 Aqueous C18 Amino Silica Phenyl Phenyl Propyl Biphenyl Cyano
Si CH3
O
Si CH3 CH3
O
Si CH3 CH3
O
Si CH3 CH3
O
Si
OO O
Si CH 3
NH2
CH3
O
Si CH3
N
C
CH3
O
Si
OO O
OH
CH3 CH3
O
Si
OO
Si
P
P
alkyl chain
alkyl chain
Si CH3 CH3
O
C8
Si CH3 CH3
O
C18
Si CH3 CH3
O
C4
Si CH3 CH3
O
C1
Phenyl Aromax
Si CH3 CH3
O
Si CH3
Proprietary
CH3
O
Biphenyl
Si CH3 CH3
O
Aqueous C18
Si
OO
P
IBD
CH3 CH3
O
Si
P
PFP Propyl
Si CH 3
orthogonal selectivity to a C18 good choice for LC/MS HILIC compatible
CH3
O
F
F
F F
F
Cyano
Si CH3
N
C
CH 3
O
Silica
Si
OO O
OH
Amino
Si CH3
NH2
CH3
O
Aromatic Retention
Non Polar Retention
Aci ic Retention
Amino Silica Phenyl Phenyl Propyl Biphenyl Cyano PFP PFP Propyl
Si CH3 CH3
O
Si CH 3 CH3
O
i
3 3 Si CH3 CH3
O
Si CH3 CH3
O
i CH3
NH2
CH3 Si CH3
N
C
CH3
O
Si
OO O
OH
F
F
F F
F
F
F
F F
F
18 Amino Silica Phenyl Pheny Pr pyl Biphenyl Cya o FP PFP Propyl
Si CH3 CH3
O
i
3 Si CH3 CH3
O
Si CH3 CH 3 Si CH3 CH3
O
Si CH3
NH2
CH3
O
N
C
Si
O O
OH
F
F
F F
F
F
F
F F
F
Equation 1: Selectivity has the greatest
mathematical effect on resolution.
Selectivity (S) = 100 x 1-r2
S = 53.5
R = ¼ N x (k/(k+1)) x ( α-1)
E ciency Retention Factor Selectivity
RESTEK® USLC® Ultra Selective Liquid Chromatography™
slc
Figure 1: Restek® columns offer the widest range of unique and effective phase chemistries to aid the
chromatographer in choosing columns fast and developing methods faster.