Numerous HPLC
grade silicamateri-
als currently are
available in the
marketplace, but
these silicas differ
greatly from one
manufacturer to
another. Some of themost 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
amean diameter of 300Å (Table I).These charac-
teristics ensure greater accessibility to larger
molecules, relative to othermaterials.They also
are important because silicaswith excessive
numbers of pores smaller than 200Å can become
more easily fouledwith largermolecularweight
debris, and silicaswith 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
porewidth 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 necessarywhen analyzing high-
ermolecular weight analytes, such as proteins
and peptides, because retentionwill bemaxi-
mized if an analyte can enter into the pores of
thematerial.Theoretically, themore pores to
which an analyte has access, the longer the
retention. For analyteswithmolecular weights
greater than 3000, silicamaterialswith pore
diameters in the 250-350Å range, or larger,
should yield the highest retention. In addition, a
narrow pore diameter distribution is desirable,
Viva
™
HPLCSilica: Ideal forSeparating
LargeMolecules
NewWide Pore Silica, Designed andManufactured by Restek
by Vernon Bartlett, HPLCManager, Bruce Albright, HPLC Chemist,
and RebeccaWittrig, Ph.D., HPLC Product MarketingManager
•67% of available surface area can interact with proteins, peptides, other largemolecules.
•Larger surface area than other commercially available 300Åmaterials.
•Manufactured by Restek, quality controlled by Restek.
Turning Visions into Reality™
THE
RESTEK
ADVANTAGE
2005
vol.1
NewViva
™
300ÅSilica for LargeMolecules . . . .
1-2
Parts for Dionex ASE
®
Systems. . . . . . . . . . . . . . . .
3
NewSolidPhaseExtractionTubes forNitrosamines. .
3
CombinePrimary andConfirmationGCAnalysis of
OrganochlorinePesticides . . . . . . . . . . . . . . . .
4-5
Restek Seminars for 2005. . . . . . . . . . . . . . . . . . . .
5
Superior Storage andTransfer of Sulfur
Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . .
6-7
Nine-MinuteGC/MSAnalysis of
SemivolatileOrganics. . . . . . . . . . . . . . . . . . . .
8-9
High-ResolutionGC/MS of Dioxin or Furan
Congeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
Stable, Low-BleedRtx
®
-XLBColumns . . . . . . . . . .
11
EnhancedRtx
®
-1PONAColumn for Detailed
HydrocarbonAnalysis . . . . . . . . . . . . . . . . . . . .
12
NewGCColumn for PCBCongeners or Aroclor
®
Mixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
Fast GC/MSAnalysis of Semivolatiles . . . . . . . . .
14
UniqueGCColumn for RapidAnalysis of
Semivolatiles . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
NewMixes: ChlorinationDisinfectionByproducts
&Solvents, HalogenatedPesticides . . . . . .
16-17
GC/ECDAnalysis of Chlorophenoxyacid
Herbicides . . . . . . . . . . . . . . . . . . . . . . . . . .
18-19
Injection Liners, O-Rings, Liner Seals; Injector
andDetector Parts . . . . . . . . . . . . . . . . . . .
20-21
ReliableRestek Connectors for CapillaryGC . . . .
22
EZNo-Vent
™
GCColumn-MSConnector for
Varian Systems . . . . . . . . . . . . . . . . . . . . . . . . .
23
2005Restek CatalogAvailableNow . . . . . . . . . . .
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 largemolecules.
Figure1
A typical
porous silica substrate:
as thenumber of pores
increase, surfacearea
andporevolume
increase.
Table II
For a fixedporevolume, the smaller
thepores ina silicaparticle, the larger the sur-
facearea.
PoreDiameter (Å)
Surface Area (m
2
/g)
60
300-600
100
150-300
200
75-150
300
50-75
500
30-40
1000
20-30
Table I
Viva™ silicahas thehighest percentageof available surfacearea from200-300Åpores,
allowing thegreatest interactionwith largemolecules.
Total Surface Area
% of Total Surface Area
Silica
(m
2
/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 intoReality
™
20
YEARS
