investigation of ethyl bridged hybrid organic/inorganic ... · test b: ph 12 (performed at 50 °c)...
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KDW 1 © 2002 Waters CorporationWaters
Investigation of Ethyl Bridged Hybrid Organic/Inorganic Particles for
Reversed-Phase HPLC Applications
Kevin Wyndham, John O'Gara, Kenneth Glose, Nicole Arpin, Bonnie Alden, Cheryl Boissel,
Pamela Iraneta, and Thomas Walter
HPLC 2002 Conference Montreal Canada
Poster No. 383 June 5, 2002
Waters Corporation
WA20266
KDW 2 © 2002 Waters CorporationWaters
Investigation of Ethyl Bridged Hybrid Organic/Inorganic Particles for Reversed-Phase HPLC Applications
HPLC 2002 Conference Montreal Canada
Poster No. 383 June 5, 2002
We have recently shown that great improvements in chromatographic stability toward high pH mobile phases can be achieved by using hybrid organic/inorganic packing materials. In this report, we take a close look at the synthesis and characterization of highly spherical ethyl bridged hybrids particles. We will examine the effects of using different molar concentrations of ethyl bridged hybrid alkoxysilanes has on the pore properties of these hybrid materials. We will also evaluate the reversed-phase chromatographic performance of these ethyl bridged hybrid packing materials, and compare these results with conventional silica-based packing materials.
Summary
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Hybrid Materials for RP HPLC
Low efficiency
Mechanically weak
Wide pH range
No tailing for bases
Polymeric (Organic)
Tailing peaks for bases
Limited pH range
Mechanically strong
High efficiency
Silica (Inorganic)
UndesirableDesirable
Hybrid Materials seek to combine the desirable attributes of silicaand polymeric materials, and limit the undesirable attributes
Neue, U. D.; et. al. Am. Lab., 1999, 31 (22), 36.Cheng, Y.-F.; et. al. LCGC, 2000, 18 (11), 1162.
KDW 4 © 2002 Waters CorporationWaters
Structure of Ethyl Bridged Hybrids
OSi
OSi
OSi
OSi
OSi
OSi
OSi
OSi
OSi
O
OH OH OH OH OH H2C CH2OH OH
O O O O O O O
OSi O Si
OSi
OSi
OSi
OSi
OSi
OSi
OSi
OH2C CH2 O O O O O O O
Si
SiO
O
O
OH
O
CH2H2C
H2CCH2
Wall
Surface
Increased mechanical stability of columnInternal bridging groups provide high interconnectivity
Increased base stability of columnInternal bridging groups provide hydrophobicity
Reduced USP peak tailing factorsSurface ethyl groups reduce surface silanol concentration
RP HPLC ConsequenceBridged Hybrid Attribute
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Synthesis of Bridged Hybrid Particles
! Explored different ratios inorganic and organic components and surface areas
! Can fully characterize Bridged Hybrids by %C, SEM, TGA, BET, NMR
! Other bridged silanes have been explored
Porous Hybrid Particles
CH2
SiEtOO
SiEtOOEtO
Si
Si
O
OO
O
O
nPolyethoxyoligosiloxane Polymer
CH2EtO
OH
CH2CH2
OEtSi
EtO OEtOEt
CH2SiEtO
OEtEtO
+
Tetraethoxysilane(Inorganic)
Bis(triethoxysilyl)ethane(Organic)
CH2
SiOEt
OEtOEt
Patent Pending
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Influence of Organic Content on Morphology
33 mol% Organic Component 20 mol% Organic Component
! Under standard conditions highly spherical particles were obtained for materials with ≤20 mol% organic component.
! Modified synthetic conditions must be used to prepare spherical particles with >30 mol% organic component.
KDW 7 © 2002 Waters CorporationWaters
Influence of Organic Content on Particle Properties
1850.761455.6%20 mol%
1830.731503.9%11 mol%
2220.721252.4%8 mol%
2710.71971.1%4 mol%
Pore Diameter
(Å)
Pore Volume (cc/g)
Surface Area
(m2/g)%C
Organic Content
Notes: %C determined by elemental analysis. Surface propertieswere determined by Nitrogen Sorption (BET Method).
! Higher organic content in Bridged Hybrids leads to greater carbon content and surface areas.
! Since 20 mol% is the highest organic content with desirable morphology, we explored this material in depth.
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Different Surface Areas of 20 mol% Organic Content Bridged Hybrids
Pore Diameter
Pore Volume
Surface Area 189 m2/g171 m2/g145 m2/g
148 Å150 Å185 Å
0.76 cc/g0.71 cc/g0.72 cc/g
BridgedHybrid C
BridgedHybrid B
Bridged Hybrid A
5 µm Bridged Hybrid
! We can prepare a variety of 20 mol% organic content Bridged Hybrids (sized 5 µm) with different surface areas, from modifications in the synthetic procedure.
! These Bridged Hybrids are highly spherical, and have comparable characterization data (%C, SEM, TGA, NMR)
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C18-Surface Bonding of 5 µm Particles
3.0 µmol/m2
14.0 %
185 Å
0.72 cc/g
145 m2/g
5.6%
Bridged Hybrid A
3.2 µmol/m2
15.9 %
150 Å
0.71 cc/g
171 m2/g
5.7%
BridgedHybrid B
0.85 cc/g0.76 cc/gPore Volume
3.3 µmol/m23.0 µmol/m2C18 Coverage
19.8 %16.7 %Total %C
100 Å148 ÅPore Diameter
340 m2/g189 m2/gSurface Area
0.0%5.9%Particle %C
SilicaBridgedHybrid C
2. End Cap
1. C18 BondO Si
O
OOH
! Slightly lower surface coverages are expected for Bridged Hybrids due to reduced surface silanol concentrations
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Chromatographic Characterization
NH
HN O
O
Uracil
Naphthalene Acenaphthene
Butyl Paraben
Propranolol pKa = 9.6Amitriptyline pKa = 9.4
OH
O OC4H9
O
OH
NH2+
NH+
OC3H7
O
OC3H7
ODipropylphthalate
Mobile Phase: Flow Rate: Temperature:
65:35 Methanol / 20 mM KH2PO4 Buffer pH 7.01.4 mL/min, 4.6 x 150 mm23.4± 0.1 ºC
KDW 11 © 2002 Waters CorporationWaters
Comparison of C18-bondings on Bridged Hybrids and Silica
! Increased retentivity with higher surface area Bridged Hybrids! Bridged Hybrid C18 columns have similar selectivity as Silica C18 columns,
but better peak shape for basic analytes
10 20 30
Silica
Time (min)
V0
12 3 4
65 Bridged Hybrid A
Bridged Hybrid B
Bridged Hybrid C
V0. Uracil1. Propranolol2. Butylparaben3. Dipropylphthalate4. Naphthalene5. Acenaphthene6. Amitriptyline
KDW 12 © 2002 Waters CorporationWaters
Accelerated High pH Stability Tests
TEST A: pH 10 (Performed at 50 °C)
" Challenge: 50 mM NEt3, pH 10, 2 mL/min for 60 min# Wash Step: water (2 mL/min ) for 10 min, methanol (2 mL/min) for 10 min$ Test: Methanol / pH 7.0 K2HPO4 (65/35 v/v)% Return to 1 until column fails
Column failure:
TEST B: pH 12 (Performed at 50 °C)
" Challenge: 0.01 M NaOH, pH 12, 2 mL/min for 60 min# Wash Step: water (2 mL/min ) for 10 min, methanol (2 mL/min) for 10 min$ Test: 50% acetonitrile in water% Return to 1 until column fails
Defined as time (hrs) until >50% loss in plate number (N), or when column voided
KDW 13 © 2002 Waters CorporationWaters
High pH Stability Test A (pH10): Comparison of Bonded Silica and Bridged Hybrids
2030405060708090
100110
0 25 50 75 100 125 150
Time Exposed to pH 10 Buffer (hrs)
%O
rigin
al E
ffic
ienc
y (5
sig
ma)
B ridged Unbo ndedB ridged C 18Silica C 18 - B rand ASilica C 18 - B rand B
! C18-bonded and unbonded 20 mol% organic content Bridged Hybrid columns have an order of magnitude greater base stability than Silica C18
! Where Silica columns fail from rapid dissolution of SiO2, bonded phases on Bridge Hybrids may hydrolyze before dissolution of the particle
KDW 14 © 2002 Waters CorporationWaters
High pH Stability Test B (pH 12): Surface Area Contribution to Stability of Bridged Hybrids
R2 = 0.9274
R2 = 0.8668
0
20
40
60
80
100
120
140 150 160 170 180 190 200
Surface Area (m2/g)
Effi
cien
cy h
alf
life
pH 1
2 bu
ffer
(ho
urs)
Bridged C18
Bridged Unbonded
! Silica C18 columns fail within an hour on this test! C18-bonded and unbonded 20 mol% organic content Bridge Hybrid
columns last > 20h! General trends for Bridged Hybrid C18 columns:
↓ Surface Area ↑ Base Stability
KDW 15 © 2002 Waters CorporationWaters
Summary
! A variety of Bridged Hybrid material, with different surface areas and organic content can now be prepared
! Chromatographic Properties of 20 mol% organic content Bridged Hybrids C18 columns were assessed:! Similar selectivity as Silica C18 columns! Reduced peak tailing for basic analytes
! At least an order of magnitude higher column stability in high pH mobile phases
! Column stability toward high pH increases with decreasing surface area
Contact InformationKevin Wyndham