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Numerous HPLC
grade silica materi-
als currently are
available in the
marketplace, but
these silicas differ
greatly from one
manufacturer to
another. Some of the most important factors
affecting the selectivity of a substrate are sur-
face area, pore volume, and pore diameter dis-
tribution. We have determined these physical
properties of our new Viva™ 300 Ångstrom silica,
and have compared this silica to other commer-
cially available 300Å silicas.
Of the silicas tested, Viva™ 300Å silica shows the
largest available surface area and the greatest
percentage of pores narrowly distributed around
a mean diameter of 300Å (Table I). These charac-
teristics ensure greater accessibility to larger
molecules, relative to other materials. They also
are important because silicas with excessive
numbers of pores smaller than 200Å can become
more easily fouled with larger molecular weight
debris, and silicas with excessive numbers of
pores larger than 500Å can be impractically frag-
ile for conventional HPLC applications.
Figure 1 depicts a typical porous silica particle.
In general, as the number of pores in a silica
increase, surface area and pore volume
increase. Also, as
pore width increas-
es, pore volume
increases. For a
fixed pore volume,
materials having
the smallest pore
diameters have the
largest available
surface area (Table
II). While smaller
pores (e.g., 60Å)
maximize retention
of small molecules,
larger pores are necessary when analyzing high-
er molecular weight analytes, such as proteins
and peptides, because retention will be maxi-
mized if an analyte can enter into the pores of
the material. Theoretically, the more pores to
which an analyte has access, the longer the
retention. For analytes with molecular weights
greater than 3000, silica materials with pore
diameters in the 250-350Å range, or larger,
should yield the highest retention. In addition, a
narrow pore diameter distribution is desirable,
Viva™ HPLC Silica: Ideal for Separating
Large Molecules
New Wide Pore Silica, Designed and Manufactured by Restek
by Vernon Bartlett, HPLC Manager, Bruce Albright, HPLC Chemist,
and Rebecca Wittrig, Ph.D., HPLC Product Marketing Manager
• 67% of available surface area can interact with proteins, peptides, other large molecules.
• Larger surface area than other commercially available 300Å materials.
•Manufactured by Restek, quality controlled by Restek.
Turning Visions into Reality™
THE RESTEK ADVANTAGE
2005 vol. 1
New Viva™ 300Å Silica for Large Molecules . . . . 1-2
Parts for Dionex ASE® Systems. . . . . . . . . . . . . . . . 3
New Solid Phase ExtractionTubes for Nitrosamines. . 3
Combine Primary and Confirmation GC Analysis of
Organochlorine Pesticides . . . . . . . . . . . . . . . . 4-5
Restek Seminars for 2005. . . . . . . . . . . . . . . . . . . . 5
Superior Storage and Transfer of Sulfur
Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
Nine-Minute GC/MS Analysis of
Semivolatile Organics. . . . . . . . . . . . . . . . . . . . 8-9
High-Resolution GC/MS of Dioxin or Furan
Congeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Stable, Low-Bleed Rtx®-XLB Columns . . . . . . . . . . 11
Enhanced Rtx®-1PONA Column for Detailed
Hydrocarbon Analysis . . . . . . . . . . . . . . . . . . . . 12
New GC Column for PCB Congeners or Aroclor®
Mixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Fast GC/MS Analysis of Semivolatiles . . . . . . . . . 14
Unique GC Column for Rapid Analysis of
Semivolatiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
New Mixes: Chlorination Disinfection Byproducts
& Solvents, Halogenated Pesticides . . . . . . 16-17
GC/ECD Analysis of Chlorophenoxyacid
Herbicides . . . . . . . . . . . . . . . . . . . . . . . . . . 18-19
Injection Liners, O-Rings, Liner Seals; Injector
and Detector Parts . . . . . . . . . . . . . . . . . . . 20-21
Reliable Restek Connectors for Capillary GC . . . . 22
EZ No-Vent™ GC Column-MS Connector for
Varian Systems . . . . . . . . . . . . . . . . . . . . . . . . . 23
2005 Restek Catalog Available Now . . . . . . . . . . . 24
in this issue
because this can aid in separating closely related
analytes that differ only slightly in hydrodynam-
ic size (size in solution). In developing Viva™ sili-
ca, we found some “wide pore” materials do
not possess sufficiently large pore volume in
the pore diameter range needed for effectively
separating large molecules.
Figure 1 A typical
porous silica substrate:
as the number of pores
increase, surface area
and pore volume
increase.
Table II For a fixed pore volume, the smaller
the pores in a silica particle, the larger the sur-
face area.
Pore Diameter (Å) Surface Area (m2 /g)
60 300-600
100 150-300
200 75-150
300 50-75
500 30-40
1000 20-30
Table I Viva™ silica has the highest percentage of available surface area from 200-300Å pores,
allowing the greatest interaction with large molecules.
Total Surface Area % of Total Surface Area
Silica (m2/g) <200Å 200-300Å >300Å
Viva™ 300Å 128.0 2.5 67.3 30.2
(7) 300Å 51.8 65.6 18.5 15.9
(6) 300Å 87.2 53.6 22.2 24.2
(5) 300Å 105.8 56.3 22.3 21.4
(3) 300Å 83.5 40.5 24.5 35.0
(“B”) 200Å 231.5 66.1 33.1 0.8
(“B”) 300Å 118.1 8.3 34.3 57.4
new!
TurningVisions into Reality™ 20YEARS