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Silica remains the most common support for HPLC
columns despite the more recent development of
alternative supports such as organic polymers and
zirconia. Since the introduction of silica supports
for HPLC approximately 30 years ago, the evolution
of silica manufacturing technology can be
described as having three generations. First genera-
tion silica (Type A) is synthesized from inorganic
sols. The second generation is base deactivated sili-
ca prepared by chemical treatment of Type A silica
to remove surface metal impurities. Third genera-
tion silica (Type B) is synthesized from an organic
sol starting material. Type B silica contains only
trace amounts (ppm levels) of metal impurities,
giving it attributes similar to those of base-deactivat-
ed silica without the chemical treatments needed to
remove metal impurities.
by Terry Reid, HPLC Chemist
Restek HPLC Columns
Three Generations of Silica Technology
✔ Pinnacle II™ silica—columns packed using Restek-manufactured silica.
✔ Ultra silica—similar pore size, but greater retention compared to
Pinnacle II ™ silica.
✔ Allure™ silica—largest surface area and greatest retention.
The evolution of silica from Type A to Type B was
largely driven by the desire for reversed phase sili-
ca supports that could analyze basic compounds
without mobile phase additives and without exces-
sive peak tailing. Because most HPLC analysts use
the reversed phase mode and a large proportion of
samples analyzed by reversed phase contain basic
analytes (e.g., most pharmaceuticals), base deacti-
vation of silica is an important issue. As a result,
many HPLC users prefer columns made from Type
B silica. However, many HPLC analysts still want to
buy columns made with Type A and/or base-deacti-
vated silica because they are using methods that
were developed with these types of columns. Also,
for some applications, first or second generation
silica can perform just as well as or even better
than Type B products. To satisfy all these needs,
Restek offers several lines of HPLC columns that
cover the three generations of silica.
In 2001 Restek introduced the Pinnacle II™ product
line, which is based on new Type A silica developed
and manufactured in our Bellefonte facility. The
Pinnacle II ™ products are very similar to our origi-
nal Pinnacle™ product line, but are controlled by
Restek’s in-house silica production. The analysis of
phenolic compounds in Echinacea using a Pinnacle
II ™ C18 column shows excellent performance for
neutral and acidic compounds (Figure 1).
Research is currently in progress to develop a sec-
ond-generation product from our Pinnacle II™ sili-
ca; one that will allow us to offer an alternative to
the well-established Pinnacle ™ Amine (base-deacti-
vated) product line.
The Ultra and Allure™ product lines are manufac-
tured from Type B silica, but differ in their pore
sizes. Ultra silica is 100Å while Allure™ silica is
60Å. Type B silica typically is higher in surface area
than Type A silica. The Ultra silica has a similar
pore size to Pinnacle and Pinnacle II™ silica but has
a much greater surface area, making it consider-
ably more retentive. Because of its smaller pore
size, the Allure™ silica provides even greater surface
area and greater retention than the Ultra silica. The
Allure ™ product line was developed for LC/MS
applications where it often is beneficial to have
maximum retention. A separation of an antibiotic
sample containing two basic compounds using an
Allure ™ C18 column is shown in Figure 2. Although
this is UV detection, the completely volatile mobile
phase is compatible with MS detection.
LC_0067
Figure 2
The Allure™ C18 column separates two basic
compounds using a mobile phase that is
compatible with MS detection.
Figure 1
The Pinnacle II™ C18 analysis of Echinacea
shows excellent performance for neutral and
acidic compounds.
Allure™ C18 (cat.# 9164565)
Dimensions: 150 x 4.6mm
Particle size: 5µm; Pore size: 60Å
Conditions:
Mobile phase: 10mM ammonium formate,
pH to 3.0 with formic acid:methanol
(50:50, v/v)
Flow: 1.0mL/min.; Temp.: ambient
Det.: UV @ 220nm
Sample:
Inj.: 10µL; Conc.: 100µg/mL
Solvent: water:methanol (1:1, v/v)
1. trimethoprim
2. sulfamethoxazole
3. naphthoate
Pinnacle II™ C18 (cat.# 9214565)
Dimensions: 150 x 4.6mm
Particle size: 5µm; Pore Size: 110Å
Conditions:
Mobile phase: A=0.1% phosphoric acid, B=acetonitrile
Time %A %B
0 90 10
13 78 22
14 60 40
14.5 60 40
15 90 10
20 90 10
Sample: Echinacea capsule
Inj.: 10µL
Conc.: 6.7mg/mL capsule
contents in sample diluent
Solvent: ethanol:water (70:30)
Sample temp.: 25°C
Flow: 1.5 mL/min.
Temp.: 35°C
Det.: UV @ 330nm
1. caftaric acid
2. chlorogenic acid
3. echinacoside
4. cichoric acid
1
2
3
2 min. 4 6 8 10
LC_0195
1
2 3
4
2 min. 2.5 5 7.5 10 12.5 15
Pinnacle II™ C18 5µm Columns
Length 4.6mm ID
50mm 9214555
100mm 9214515
150mm 9214565
250mm 9214575
Ultra C18 5µm Columns
Length 4.6mm ID
30mm 9174535
50mm 9174555
100mm 9174515
150mm 9174565
200mm 9174525
250mm 9174575
Allure™ C18 5µm Columns
Length 4.6mm ID
30mm 9164535
50mm 9164555
100mm 9164515
150mm 9164565
200mm 9164525
250mm 9164575
for moreinfo
including a complete product listing,
request lit. cat.# 59241, HPLC Columns
and Accessories Catalog.