U.S. patent application number 10/471388 was filed with the patent office on 2004-07-08 for high efficiency sol-gel gas chromatography column.
Invention is credited to Kabir, Abuzar, Malik, Abdul, Shende, Chetan.
Application Number | 20040129141 10/471388 |
Document ID | / |
Family ID | 32682581 |
Filed Date | 2004-07-08 |
United States Patent
Application |
20040129141 |
Kind Code |
A1 |
Malik, Abdul ; et
al. |
July 8, 2004 |
High efficiency sol-gel gas chromatography column
Abstract
A capillary column (10) includes a tube structure having inner
walls (14) and a sol-gel substrate (16) coated on a portion of
inner walls (14) to form a stationary phase coating (18) on inner
walls (14). The sol solution used to prepare the sol-gel substrate
(16) has at least one baseline stabilizing reagent and at least one
surface deactivation reagent resulting in the sol-gel substrate
(16) having at least one baseline stabilizing reagent residual and
at least one surface deactivating reagent residual. A method of
making the sol-gel solution is by mixing suitable sol-gel
precursors to form the solution, stablizing the solution by adding
at least one baseline stabilization reagent, deactivating the
solution by adding at least one surface deactivation reagent to the
solution, and reacting the solution in the presence of at least one
catalyst.
Inventors: |
Malik, Abdul; (Tampa,
FL) ; Kabir, Abuzar; (Tampa, FL) ; Shende,
Chetan; (Tampa, FL) |
Correspondence
Address: |
SMITH & HOPEN PA
15950 BAY VISTA DRIVE
SUITE 220
CLEARWATER
FL
33760
|
Family ID: |
32682581 |
Appl. No.: |
10/471388 |
Filed: |
March 8, 2004 |
PCT Filed: |
March 8, 2002 |
PCT NO: |
PCT/US02/07163 |
Current U.S.
Class: |
96/101 |
Current CPC
Class: |
G01N 2030/567 20130101;
G01N 30/56 20130101; B01J 2220/86 20130101; G01N 30/6078 20130101;
B01J 20/285 20130101; B01D 15/265 20130101; B01J 20/286 20130101;
B01J 20/28047 20130101; B01D 15/206 20130101; B01J 2220/54
20130101 |
Class at
Publication: |
096/101 |
International
Class: |
B01D 053/02 |
Claims
What is claimed is:
1. A capillary column comprising: a tube structure including inner
walls; and a sol-gel substrate coated on a portion of said inner
walls of said tube structure to form a stationary phase coating on
said inner walls, said sol-gel substrate including at least one
baseline stabilizing reagent residual and at least one surface
deactivation reagent residual.
2. The capillary column according to claim 1, wherein said at least
one baseline stabilizing reagent residual is selected from the
group consisting of residuals from
bis(trimethoxysilylethyl)-benzene, sol-gel active reagents with
phenyl-containing groups, and cyclohexane-containing groups.
3. The capillary column according to claim 1, wherein said at least
one surface deactivation reagent residual is selected from the
group consisting of 1,1,1,3,3,3-hexamethyldisilazane,
hydrosiloxane, and hydrosilane.
4. The capillary column according to claim 1, wherein said sol-gel
substrate is made from sol-gel precursors having the general
structure: 3wherein, Z=a precursor-forming element selected from
the group consisting of silicon, aluminum, titanium, zirconium,
vanadium, and germanium, alkyl moieties and their derivatives,
alkenyl moieties and their derivatives, aryl moieties and their
derivatives, arylene moieties and their derivatives, cyanoalkyl
moieties and their derivatives, fluoroalkyl moieties and their
derivatives, phenyl moieties and their derivatives, cyanophenyl
moieties and their derivatives, biphenyl moiety and its
derivatives, cyanobiphenyl moieties and their derivatives,
dicyanobiphenyl moieties and their derivatives, cyclodextrin
moieties and their derivatives, crown ether moieties and their
derivatives, cryptand moieties and their derivatives, calixarene
moieties and their derivatives, liquid crystal moieties and their
derivatives, dendrimer moieties and their derivatives, cyclophane
moieties and their derivatives, chiral moieties, and polymeric
moieties; and R.sub.1, R.sub.2, R.sub.3, and R.sub.4=R-groups that
are moieties selected from the group consisting of sol-gel-active
moieties, alkoxy moieties, hydroxy moieties, non-sol-gel-active
moieties, methyl, octadecyl, and phenyl.
5. The capillary column according to claim 4, wherein said alkoxy
groups are selected from the group consisting of a methoxy group,
ethoxy group, n-Propoxy group, iso-Propoxy group, n-butoxy group,
iso-butoxy group, and tert-butoxy group.
6. The capillary column according to claim 4, wherein said R-groups
are at least two moieties selected from the group consisting of
sol-gel active moieties, alkoxy moieties, and hydroxy moieties.
7. The capillary column according to claim 6, wherein remaining
said R-groups are moieties selected from the group consisting of
methyl, octadecyl, phenyl, and hydrogen.
8. The capillary column according to claim 1, wherein said sol-gel
substrate further includes a residual deactivation reagent selected
from the group consisting of polymethylhydrosiloxane and
hexamethyldisilazane.
9. The capillary column according to claim 1, wherein said tube
structure is made of materials selected from the group consisting
of glass, fused silica, alumina, titania, and zirconia.
10. A method of making a sol-gel capillary solution for placement
into a capillary column by: mixing suitable sol-gel precursors to
form a sol-gel solution; stabilizing the sol-gel coating by adding
at least one baseline stabilization reagent to the sol-gel
solution; deactivating the sol-gel coating by adding at least one
surface deactivation reagent to the sol-gel solution; and reacting
the solution in the presence of at least one catalyst.
11. The method according to claim 10, wherein said reacting step
further includes adding trifluoroacetic acid as the catalyst and
the additional catalyst is selected from the group consisting of
acids, bases or fluorides.
12. The method according to claim 10, including the step of adding
ammonium fluoride as an additional catalyst.
13. The method according to claim 10, including the step of
hydrothermally pre-treating the capillary column.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to analytical separation
technology and more specifically towards gas chromatography
separation systems based on sol-gel stationary phases having
improved performance characteristics.
[0003] 2. Background Art
[0004] The introduction of an open tubular column by Golay (Golay,
M. J. E., et al.,) about three decades ago, has revolutionized the
analytical capability of gas chromatography (hereinafter "GC").
More specifically, capillary GC has matured into a separation
technique that is widely used in various fields of science and
industry (Altgelt, K. H., et al.; Clement, R. E.; Berezkin, V. G.,
et al.; and Tebbett, I.). Capillary GC is a separation technique in
which the vapor phase of a sample in a gaseous, mobile phase passes
through a capillary tube whose inner walls contain a thin film of
an adsorbing or absorbing medium (i.e., stationary phase). Because
of differential interactions of the sample components with the
stationary phase, the individual components of the sample move
through the column with different velocities. This leads to the
physical separation of the sample components into individual
chromatographic zones as they move down the column with their
characteristic velocities. The separated components are detected
instrumentally as they are eluted from the column. Contemporary
technology for the preparation of open tubular columns is
time-consuming. It consists of three major, individually executed
steps (Poole, C. F., et al.): capillary surface deactivation
(Woolley, C. L. et al.), static coating (Bouche, J. et al.), and
stationary phase immobilization (Blomberg L. G.). Involvement of
multiple steps in conventional column technology increases the
fabrication time and is likely to result in greater
column-to-column variation. The column deactivation step is
critically important for the GC separation of polar compounds that
are prone to undergo adsorptive interactions (e.g., with the
silanol groups on fused silica capillary inner walls). In
conventional column technology, deactivation is usually carried out
as a separate step, and involves chemical derivatization of the
surface silanol groups. Various reagents have been used to
chemically deactivate the surface silanol groups (de Nijs; R. C.
M., et al.; Schomburg, G. et al.; Blomberg, L. et al.; and Lee, M.
L. et al.). Effectiveness of these deactivation procedures greatly
depends on the chemical structure and composition of the fused
silica surface to which they are applied.
[0005] Of special importance are the concentration and mode of
distribution of surface silanol groups. Because the fused silica
capillary drawing process involves the use of high temperatures
(.about.2,000.degree. C.), the silanol group concentration on the
drawn capillary surface can initially be low due to the formation
of siloxane bridges under high-temperature drawing conditions.
During subsequent storage and handling, some of these siloxane
bridges can undergo hydrolysis due to reaction with environmental
moisture. Thus, depending on the post-drawing history, even the
same batch of fused silica capillary can have different
concentrations of the silanol groups that can also vary by the
modes of their distribution on the surface.
[0006] Moreover, different degrees of reaction and adsorption
activities are shown by different types of surface silanol groups
(Lawrocki, J.). As a result, fused silica capillaries from
different batches or even from the same batch but stored and/or
handled under different conditions, cannot produce identical
surface characteristics after being subjected to the same
deactivation treatments. This makes surface deactivation a
difficult procedure to reproduce. To overcome these difficulties,
some researchers have used hydrothermal surface treatments to
standardize silanol group concentrations and their distributions
over the surface (Sumpter, S. R. et al.). This additional step
however, makes the time consuming column making procedure even
longer. Static coating is another time-consuming step in
conventional column technology. A typical 30-m long column can
require as much as ten hours or more for static coating. The
duration of this step can vary depending on the length and diameter
of the capillary, and the volatility of the solvent used.
[0007] To coat a column by the static coating technique, the fused
silica capillary is filled with a stationary phase solution
prepared in a low-boiling solvent. One end of the capillary is
sealed using a high viscosity grease or by some other means (Abe,
I. et al.), and the other end is connected to a vacuum pump. Under
these conditions, the solvent begins to evaporate from the
capillary end connected to the vacuum pump, leaving behind the
stationary phase that becomes deposited on the capillary inner
walls as a thin film. Stationary phase film of desired thickness
could be obtained by using a coating solution of appropriate
concentration that can be easily calculated through simple
equations (Ettre, L. S. et al.).
[0008] In static coating, two major drawbacks are encountered.
First, the technique is excessively time consuming, and not very
suitable for automation. Second, the physically coated stationary
phase film shows a pronounced tendency to rearrangements that can
ultimately result in droplet formation due to Rayleigh instability
(Bartle, K. D. et al.). Such a structural change in the coated
films can serve as a cause for the deterioration or even complete
loss of the column's separation capability.
[0009] To avoid these undesirable effects, static-coated stationary
phase films need to be stabilized immediately after their coating.
This is usually achieved by stationary phase immobilization through
free radical cross-linking (Wright, B. W. et al.) that leads to the
formation of chemical bridges between coated polymeric molecules of
the stationary phase. In such an approach, stability of the coated
film is achieved not through chemical bonding of the stationary
phase molecules to the capillary walls, but mainly through an
increase of their molecular size and consequently, through decrease
of their solubility and vapor pressure.
[0010] Such an immobilization process has a number of drawbacks.
First, polar stationary phases are difficult to immobilize by this
technique (Yakabe, Y., et al.). Second, free radical cross-linking
reactions are difficult to control to ensure the same degree of
cross-linking in different columns with the same stationary phase.
Third, cross-linking reactions can lead to significant changes in
the polymer structure and chromatographic properties of the
resulting immobilized polymer can significantly differ from those
of the originally taken stationary phase (Blomberg L. G.). All
these drawbacks add up to make column preparation by conventional
techniques a task that is difficult to control and reproduce
(Blomberg, L., et al.).
[0011] In order to overcome all of the above problems, a
preparation of a GC capillary column including a tube structure and
a deactivated surface-bonded sol-gel coating on a portion of the
tube structure forming a stationary phase was disclosed and claimed
in PCT Application PCT/US99/19113, published as WO 00/11463, to
Malik et al. The invention disclosed therein is for a structure for
forming a capillary tube, e.g., for gas chromatography, and a
technique for forming such capillary tube. The capillary tube
includes a tube structure and a deactivated surface-bonded sol-gel
coating on a portion of the tube structure to form a stationary
phase coating on that portion of the tube structure. The
deactivated sol-gel stationary phase coating enables separation of
analytes while minimizing adsorption of analytes on the separation
column structure. This type of column was a significant advancement
in the art, but it was recognized that certain improvements would
greatly enhance the performance of the sol-gel coated column.
[0012] One area of improvement deals with baseline stability. A GC
column is commonly operated under temperature-programmed conditions
whereby the temperature of the column is increased with time. As
the column temperature increases, the gas chromatography baseline
rises because of column bleed caused due to the formation of
volatile compounds from the stationary phase coating on the inner
surface of the capillary column. In GC columns with
polyslioxane-based stationary phases, the formation of volatile
cyclic compounds is favored by the flexibility of the polysiloxane
chains. One way to overcome or significantly reduce the
column-bleeding problem is to reduce the flexibility of the
polymeric structure of the GC stationary phase by incorporating
phenyl rings in the polysiloxane backbone. This reduces the
flexibility of polysiloxanes, and consequently, their ability to
produce cyclic volatiles through rearrangements. The selection of
the phenyl-containing reagent and the degree of substitution in the
polysiloxane backbone are both critical, and care must be taken so
that the stationary phase does not become too rigid. Otherwise,
chromatographic properties of the polymer (especially the mass
transfer properties) can be compromised. In an attempt to provide
increased baseline stability, Mayer et al. used
1,4-bis(hydroxydimethylsilyl)benzene to incorporate a phenyl ring
in the polydimethyldiphenylsiloxane structure by conducting its
reaction with diphenylsilanediol at 110.degree. C. for 48 hours.
This non-sol-gel process however, is inconvenient for two reasons.
First, the process is lengthy and carried out at elevated
temperature. Second, the 1,4-bis(hydroxydimethylsiyl)benzene
reagent used for the incorporation of the phenyl group provides a
polymer structure where the phenyl ring is directly bonded to
silicon atoms without any spacer groups and leads to a very rigid
polymer affecting its mass transfer properties and chromatographic
efficiency.
[0013] Accordingly, there is a need for an improved GC column
having improved baseline stability, higher efficiency, and reduced
conditioning time. Additionally, there is a need for a sol-gel GC
column having desired stationary phase film thickness and improved
retention characteristics that are capable of being fabricated into
long columns. The present invention describes a sol-gel
chemistry-based process that provides all of the above-mentioned
desirable column characteristics through a simple procedure carried
out under mild thermal conditions.
SUMMARY OF THE INVENTION
[0014] According to the present invention, there is provided a
capillary column including a tube structure having inner walls and
a sol-gel substrate coated on a portion of the inner walls of the
tube structure to form a stationary phase coating on the inner
walls. The sol solution used to prepare the sol-gel substrate has
at least one baseline stabilizing reagent and at least one surface
deactivation reagent. The resulting sol-gel substrate has at least
one baseline stabilizing reagent residual and at least one surface
deactivation reagent residual. The present invention further
provides for a method of making a sol-gel solution for placement
into a capillary column by mixing suitable sol-gel precursors, at
least one sol-gel-active organic polymer or ligand, at least one
baseline stabilization reagent to the sol-gel solution, at least
one surface deactivation reagent, and at least one sol-gel
catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other advantages of the present invention are readily
appreciated as the same becomes better understood by reference to
the following detailed description when considered in connection
with the accompanying drawings wherein:
[0016] FIG. 1 is a longitudinal, cross-sectional view of an
embodiment of a capillary column of the present invention;
[0017] FIG. 2 is drawing of an embodiment of the present invention,
more specifically, a filling and purging device for the preparation
of the capillary column of the present invention;
[0018] FIG. 3A. GC separation of Grob test mixture on a
sol-gel-coated PDMS column prepared using a sol solution containing
hydroxy-terminated polydimethylsiloxane, poly dimethyl (82-86%)
diphenyl (14-18%) siloxane, hydroxy-terminated
poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3,-hexamethyldisilazane, trifluoroacetic acid, and
bis(trimethoxysilylethyl)benzene, but no ammonium fluoride, wherein
the conditions are: 10-m.times.250-.mu.m-i.d. fused silica
capillary column; stationary phase, sol-gel PDMS; carrier gas,
helium; injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature programming from 40.degree. C. at
6.degree. C. minutes.sup.-1 with peaks (1) 2,3-butanediol, (2)
n-decane, (3) 1-octanol, (4) 1-nonanal (5) n-undecane, (6)
2,6-dimethylaniline, (7) methyl decanoate, (8) methyl undecanoate,
and (9) methyl dodecanoate;
[0019] FIG. 3B. GC separation of Grob test mixture on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3-hexamethyldisilazane, trifluoroacetic acid, and both
ammonium fluoride and bis(trimethoxysilylethyl)benzene, wherein the
conditions are: 10-m.times.250 .mu.m-i.d. fused silica capillary
column; stationary phase, sol-gel PDMS; carrier gas, helium;
injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature programming from 40.degree. C. at
6.degree. C. minutes.sup.-1 with peaks (1) 2,3-butanediol, (2)
n-decane, (3) 1-octanol, (4) 2,6-dimethylphenol, (5) 1-nonanal, (6)
n-undecane, (7) 2,6-dimethylaniline (8) methyl decanoate, (9)
dicyclohexylamine, (10) methyl undecanoate and (11) methyl
dodecanoate;
[0020] FIG. 4A. GC separation of Grob test mixture on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3-hexamethyldisilazane, trifluoroacetic acid, ammonium
fluoride but no bis(trimethoxysilylethyl)benzene, wherein the
conditions are: 10-m.times.250-.mu.m-i.d. fused silica capillary
column; stationary phase, sol-gel PDMS; carrier gas, helium;
injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature programming from 40.degree. C. at
6.degree. C. minutes.sup.-1and with peaks (1) 2,3-butanediol, (2)
n-decane, (3) 1-octanol, (4) 2,6-dimethylphenol, (5) 1-nonanal, (6)
n-undecane, (7) 2,6-dimethylaniline (8) methyl decanoate, (9)
dicyclohexylamine, (10) methyl undecanoate, and (11) methyl
dodecanoate;
[0021] FIG. 4B is a GC separation of Grob test mixture on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3-hexamethyldisilazane, trifluoroacetic acid, ammonium
fluoride, and bis(trimethoxysilylethyl)benzene with conditions
being 10-m.times.250-.mu.m-i.d. fused silica capillary column;
stationary phase, sol-gel PDMS; carrier gas, helium; injection,
split (100:1, 300.degree. C.); detector, FID, 350.degree. C.;
temperature programming from 40.degree. C. at 6.degree. C.
minutes.sup.-1; and with peaks (1) 2,3-butanediol, (2) n-decane,
(3) 1-octanol, (4) 2,6-dimethylphenol, (5) 1-nonanal, (6)
n-undecane, (7) 2,6-dimethylaniline, (8) methyl decanoate, (9)
dicyclohexylamine, (10) methyl undecanoate, and (11) methyl
dodecanoate;
[0022] FIG. 5A is a GC separation of Grob test mixture on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimethoxysilane,
trifluoroacetic acid, ammonium fluoride and
bis(trimethoxysilylethyl)benzene and
1,1,1,3,3,3-hexamethyldisilazane, with conditions being
10-m.times.250-.mu.m-i.d. fused silica capillary column; stationary
phase, sol-gel PDMS; carrier gas, helium; injection, split (100:1,
300.degree. C.); detector, FID, 350.degree. C.; temperature
programming from 40.degree. C. at 6.degree. C. minutes.sup.-1, and
with peaks (1) 2,3-butanediol, (2) n-decane, (3) 1-octanol, (4)
2,6-dimethylphenol, (5) 1-nonanal, (6) n-undecane, (7)
2,6-dimethylaniline, (8) methyl decanoate, (9) dicyclohexylamine,
(10) methyl undecanoate, and (11) methyl dodecanoate;
[0023] FIG. 5B is a GC separation of Grob test mixture on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimthoxysilane,
trifluoroacetic acid, ammonium fluoride and
bis(trimethoxysilylethyl)benzene but no
1,1,1,3,3,3-hexamethyldisilazane, with conditions being
10-m.times.250-.mu.m-i.d. fused silica capillary column; stationary
phase, sol-gel PDMS; carrier gas, helium; injection, split (100:1,
300.degree. C.); detector, FID, 350.degree. C.; temperature
programming from 40.degree. C. at 6.degree. C. minutes.sup.-1 and
peaks (1) 2,3-butanediol, (2) n-decane, (3) 1-octanol, (4)
2,6-dimethylphenol, (5) n-undecane, (6) 2,6-dimethylaniline, (7)
methyl decanoate, (8) methyl undecanoate, and (9) methyl
dodecanoate;
[0024] FIG. 6 is a GC separation of Grob test mixture on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3-hexamethyldisilazane, trifluoroacetic acid, ammonium
fluoride and bis(trimethoxsilylethyl)benzene, with conditions being
10-m.times.250-.mu.m-i.d. fused silica capillary column; stationary
phase, sol-gel PDMS; carrier gas, helium; injection, split (100:1,
300.degree. C.); detector, FID, 350.degree. C.; temperature
programming from 40.degree. C. at 6.degree. C. minutes.sup.-1; and
with peaks (1) 2,3-butanediol, (2) n-decane, (3) 1-octanol, (4)
2,6-dimethylphenol, (5) 1-nonanal, (6) n-undecane, (7)
2,6-dimethylaniline, (8) methyl decanoate, (9) dicyclohexylamine,
(10) methyl undecanoate, and (11) methyl dodecanoate;
[0025] FIG. 7 is a GC separation of PAHs on a sol-gel-coated PDMS
capillary column prepared using a sol solution containing
hydroxy-terminated polydimethylsiloxane, hydroxy-terminated poly
dimethyl (82-86%) diphenyl (14-18%) siloxane,
poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3-hexamethyldisilazane, trifluoroacetic acid, ammonium
fluoride and bis(trimethoxysilylethyl)benzene with conditions being
10-m.times.250-.mu.m-i.d. fused silica capillary column; stationary
phase, sol-gel PDMS; carrier gas, helium; injection, split (100:1,
300.degree. C.); detector, FID, 350.degree. C., temperature
programming from 80.degree. C. at 6.degree. C. minutes.sup.-1 and
with peaks (1) naphthalene, (2) acenaphthylene, (3) acenaphthene,
(4) fluorene, (5) phenanthrene, (6) o-terphenyl, (7) fluoranthene,
and (8) pyrene;
[0026] FIG. 8 is a GC separation of aniline derivatives on a
sol-gel-coated PDMS capillary column prepared using a sol solution
containing hydroxy-terminated polydimethylsiloxane,
hydroxy-terminated poly dimethyl (82-86%) diphenyl (14-18%)
siloxane, poly(methylhydrosiloxane), methyltrimethoxysilane,
1,1,1,3,3,3-hexamethyldisilazane, trifluoroacetic acid, ammonium
fluoride and bis(trimethoxysilylethyl)benzene, with conditions
being 10-m.times.250-.mu.m-i.d. fused silica capillary column;
stationary phase, sol-gel PDMS; carrier gas, helium; injection,
split (100:1, 300.degree. C.); detector, FID, 350.degree. C.;
temperature programming from 40.degree. C. at 6.degree. C.
minutes.sup.-1 and with peaks (1) pyridine, (2) N-methylaniline,
(3) 2-ethylaniline, (4) 4-ethylaniline, (5) N-butylaniline;
[0027] FIG. 9 is a gas chromatogram demonstrating separation of a
Grob test mixture on a sol-gel-coated PEG column, wherein the
conditions are: 10-m.times.250-.mu.m-i.d. fused silica capillary
column; stationary phase, sol-gel polyethylene glycol (PEG);
carrier gas, helium; injection, split (100:1, 300.degree. C.);
detector, FID, 350.degree. C., temperature programming from
40.degree. C. at 6.degree. C. min.sup.-1; and with peaks (1)
n-decane, (2) n-undecane, (3) nonanal, (4) 2,3-butanediol, (5)
1-octane, (6) methyl decanoate, (7) dicylcohexylamine, (8) methyl
undecanoate, (9) methyl dodecanoate, (10) 2,6-dimethylaniline, (11)
2,6-dimethylphenol, and (12) 2-ethylhexanoic acid;
[0028] FIG. 10 is a gas chromatogram illustrating separation of
aniline derivatives on a sol-gel coated PEG column, wherein the
conditions are: 10-m.times.250-.mu.m-i.d. fused silica capillary
column; stationary phase, sol-gel polyethylene glycol (PEG);
carrier gas, helium; injection, split (100:1, 300.degree. C.);
detector, FID, 350.degree. C.; temperature programming from
65.degree. C. at 6.degree. C. min.sup.-1; and with peaks (1)
N,N-dimethylaniline, (2) N-methylaniline, (3) N-ethylaniline, (4)
2-ethylaniline, (5) 4-ethylaniline, and (6) 3-ethylaniline;
[0029] FIG. 11 is a gas chromatogram illustrating separation of
aldehydes on a sol-gel coated PEG column, wherein the conditions
are: 10-m.times.250 .mu.m-i.d. fused silica capillary column;
stationary phase, sol-gel polyethylene glycol (PEG); carrier gas,
helium; injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature programming from 75.degree. C. at
6.degree. C. min.sup.-1; and with peaks (1) nonylaldehyde, (2)
benzaldehyde, (3) o-toulaldehyde, (4) m-toulaldehyde, and (5)
p-toulaldehyde;
[0030] FIG. 12 is a gas chromatogram demonstrating separation of
ketones on a sol-gel coated PEG column, wherein the conditions are:
10-m.times.250-.beta.m-i.d. fused silica capillary column;
stationary phase, sol-gel polyethylene glycol (PEG); carrier gas,
helium; injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature programming from 80.degree. C. at
6.degree. C. min.sup.-1; and with peaks (1) 5-nonanone, (2)
butyrophenone, (3) valerophenone, (4) hexanophenone, and (5)
heptanophenone;
[0031] FIG. 13 is a gas chromatogram illustrating separation of
alcohols on a sol-gel coated PEG column, wherein the conditions
are: 10-m.times.250 .mu.m-i.d. fused silica capillary column;
stationary phase, sol-gel polyethylene glycol (PEG); carrier gas,
helium; injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature programming from 70.degree. C. at
6.degree. C. min.sup.-1; and with peaks (1) butanol, (2) pentanol,
(3) hexanol, (4) heptanol, and (5) octanol;
[0032] FIG. 14 is a schematic illustration of hydrolysis reactions
involved in the preparation of sol-gel PDMS coated columns
according to the present invention;
[0033] FIG. 15 is a schematic illustration of condensation
reactions involved in sol-gel PDMS stationary phase of the present
invention;
[0034] FIG. 16 is a schematic illustration of a condensation
reaction of the present invention occurring on a fused silica
capillary inner surface;
[0035] FIG. 17 is a schematic illustration of a deactivation of
residual silanol groups using hexamethyldisilazane (HMDS);
[0036] FIG. 18 is a schematic illustration of hydrolysis reactions
for the preparations of sol-gel PEG coated columns according to the
present invention;
[0037] FIG. 19 is a schematic illustration of a condensation
reaction of the present invention demonstrating the growth of a
sol-gel PEG polymer (A is a spacer group);
[0038] FIG. 20 is a schematic illustration of a growing sol-gel PEG
polymer being bonded to a silica surface;
[0039] FIG. 21 is a schematic illustration of a reaction of the
sol-gel PEG polymer bonded to a silica surface with
hexamethyldisilazane (HMDS) to form a deactivated sol-gel PEG
polymer coating bonded to the silica surface;
[0040] FIG. 22A is a scanning electron micrograph of a sol-gel PDMS
coating on the inner surface of a fused silica capillary column
(magnification 10,000.times.); and
[0041] FIG. 22B is a scanning electron micrograph of a sol-gel PEG
coating on the inner surface of a fused silica capillary column
(magnification 10,000.times.).
DETAILED DESCRIPTION OF THE INVENTION
[0042] Generally, the present invention is directed to a capillary
column and to a method of making the capillary column, wherein the
capillary column provides for a rapid and simple method for
simultaneous deactivation, coating, and stationary phase
immobilization in gas chromatography (hereinafter "GC"). To achieve
this goal, a sol-gel chemistry-based approach to column preparation
is provided that is a viable alternative to conventional GC column
technology. The sol-gel column technology eliminates the major
drawbacks of conventional column technology through chemical
bonding of the sol-gel stationary phase molecules to an interfacial
layer that evolves on the top of the original capillary surface.
More specifically, the present invention provides for a sol-gel GC
column having improved baseline stability, higher efficiency, and
reduced conditioning time. The present invention further provides
for a sol-gel GC column having desired stationary phase film
thicknesses and improved retention characteristics that are capable
of being fabricated into long columns as long as 30 meters or
longer. The present invention is useful for capillary systems as
well as any other chromatography system that employs the use of
polysiloxane-based, PEG-based, and other types of stationary phases
for separation.
[0043] The term "baseline stability" as used herein is defined as,
but is not limited to, a state wherein the formation of volatile
products due to the breakdown of the stationary phase at elevated
temperatures is hindered or prevented. More specifically, baseline
stability occurs when the stationary phase is prevented from
rearrangement so that the formation of low molecular weight
compounds is suppressed. This can be achieved through a reduction
of polymer chain flexibility by introducing a rigid phenyl group
into the polymer backbone.
[0044] The term "deactivation reagent" as used herein is defined
as, but is not limited to, any reagent that reacts with the polar
adsorptive sites (e.g., silanol groups) on the column inner surface
or stationary phase coating, and thereby prevents the stationary
phase coating within the column from adsorbing polar analytes. The
adsorptive interaction of the stationary phase with polar analytes
occurs because of the presence of silanol groups that are harmful
to polar compounds desired to be analyzed.
[0045] The present invention has numerous applications and uses.
Primarily, the present invention is useful in separation processes
involving analytes including, but not limited, to hyrdocarbons,
polycyclic aromatic hydrocarbons (PAHs), alcohols, aldehydes,
ketones, phenols, fatty acids, fatty acid methyl esters, amines,
and other analytes known to those of skill in the art. Accordingly,
the present invention is useful in chemical, petrochemical,
environmental, pharmaceutical applications, and other similar
applications.
[0046] The present invention has various advantages over the prior
art. The sol-gel chemistry-based novel approach to column
technology is presented for high resolution capillary GC that
provides a fast way of surface roughening, deactivation, coating,
and stationary phase immobilization--all carried out in a single
step. Unlike conventional column technology in which these
procedures are carried out as individual, time-consuming, steps,
the new technology can achieve all these just by filling a
capillary with a sol solution of appropriate composition, and
allowing it to stay inside the capillary for a controlled period,
followed by inert gas purging and conditioning of the capillary.
The new technology greatly simplifies the methodology for the
preparation of high efficiency GC columns, and offers an
opportunity to reduce the column preparation time at least by a
factor of ten. Being simple in technical execution, the new
technology is very suitable for automation and mass production.
Columns prepared by the new technology provide significantly
superior thermal stability due to direct chemical bonding of the
stationary phase coating to the capillary walls. Enhanced surface
area of the columns, as evidenced by SEM results, provides a
sample-capacity advantage to the sol-gel columns. The new
methodology provides excellent surface deactivation quality, which
is either comparable with or superior to that obtained by
conventional techniques. This is supported by examples of high
efficiency separations obtained for polar compounds including free
fatty acids, amines, alcohols, diols, phenols, aldehydes and
ketones. The sol-gel column technology has the potential to offer a
viable alternative to existing methods for column preparation in
analytical microseparation techniques.
[0047] The present invention has numerous embodiments, depending
upon the desired application. As described below, the formation of
the various embodiments are intended for use in gas chromatography.
However, due to the vast applicability of the present invention,
the column and related methods thereof can be modified in various
manners for use in other areas of analytical separation
technologies. The principles of the present invention can also be
used to form capillary columns for use in liquid chromatography,
capillary electrochromatography, supercritical fluid
chromatography, and as sample preconcentrators where a compound of
interest is present in very small concentrations in a sample.
[0048] In one embodiment (FIG. 1), the present invention provides
for a capillary column 10 including a tube structure 12 having
inner walls 14 and a sol-gel substrate 16 coated on a portion of
the inner walls 14 of the tube structure 12 to form a stationary
phase coating 18 on the inner walls 14. The stationary phase
coating 18 is created using at least one baseline stabilizing
reagent and at least one surface deactivation reagent. The
stationary phase coating 18 is bonded to the inner walls 14 of the
tube structure 12. The surface-bonded sol-gel substrate 16 is
applied to the inner walls 14 of the tube structure 12 by use of an
apparatus as illustrated in FIG. 2 and the method described
herein.
[0049] The tube structure 12 of the capillary column 10 can be made
of numerous materials including, but not limited to alumina, fused
silica, glass, titania, zirconia, polymeric hollow fibers, and any
other similar tubing materials known to those of skill in the art.
Typically, fused silica is the most convenient material used.
Sol-gel chemistry in analytical microseparations presents a
universal approach to creating advanced material systems including
those based on alumina, titania, and zirconia that have not been
adequately evaluated in conventional separation column technology.
Thus, the sol-gel chemistry-based column technology has the
potential to effectively utilize advanced material properties to
fill this gap.
[0050] As for the sol-gel substrate, it has the formula: 1
[0051] wherein,
[0052] X=Residual of a deactivation reagent (e.g.,
polymethylhydrosiloxane (PMHS), hexamethyldisilazane (HMDS),
etc.);
[0053] Y=Sol-gel reaction residual of a sol-gel active organic
molecule (e.g., molecules with hydroxysilane or alkoxysilane
monomers, polydimethylsiloxane (PDMS), polymethylphenylsiloxane
(PMPS), polydimethyldiphenylsiloxane (PDMDPS), polyethylene glycol
(PEG) and related polymers such as Carbowax 20M, polyalkylene
glycol such as Ucon, macrocyclic molecules such as cyclodextrins,
crown ethers, calixarenes, alkyl moieties such as octadecyl, octyl,
a residual from a baseline stabilizing agent such as
bis(trimethoxysilylethyl)benzene,
1,4-bis(hydroxydimethylsilyl)benzene, etc.
[0054] Z=Sol-gel precursor-forming chemical element (e.g., Si, Al,
Ti, Zr, etc.)
[0055] l=An integer.gtoreq.0;
[0056] m=An integer.gtoreq.0;
[0057] n=An integer.gtoreq.0;
[0058] p=An integer.gtoreq.0;
[0059] q=An integer.gtoreq.0; and
[0060] l, m, n, p, and q are not simultaneously zero.
[0061] Dotted lines indicate the continuation of the chemical
structure with X, Y, Z, or Hydrogen (H) in space.
[0062] In the preparation of gas chromatography columns, it is
desirable to use sol-gel solutions to coat the walls of capillary
tube structures for the separation of analytes. These sol-gels are
prepared by standard methods known in the art and comprise both
polysiloxane and non-polysiloxane type gels. These include, but are
not limited to, polysiloxane-based gels with a wide range of
substituted functional groups, including: methyl, phenyl,
cyanoalkyl, cyanoaryl, etc. In addition, sol-gel polyethylene
glycols such as, but not limited to, PEG, Carbowax, Superox,
sol-gel alkyl, sol-gel polyalkylene oxides, such as Ucon, and other
sol-gels, such as sol-gel dendrimers can be modified by the instant
invention.
[0063] In order to achieve the desired sol-gels of the instant
invention, certain reagents in a reagent system were preferred for
the fabrication of the gels for the columns of the present
invention. The reagent system included two sol-gel precursors, a
sol-gel active polymer or ligand, a deactivation reagent, one or
more solvents and one or more a catalysts. For the purposes of this
invention, the precursors utilized for preparing the sol-gel coated
GC capillary columns of the present invention have the general
structure of: 2
[0064] wherein,
[0065] Z is the precursor-forming element taken from a group
including, but not limited to, silicon, aluminum, titanium,
zirconium, vanadium, germanium, and the like; and
[0066] R.sub.1, R.sub.2, R.sub.3, and R.sub.4 (i.e., "R-groups")
are substituent groups at least two of which are sol-gel-active,
wherein the sol-gel active groups include, but are not limited to,
alkoxy, hydroxy moieties, and the like. Typical sol-gel-active
alkoxy groups include, but are not limited to, a methoxy group,
ethoxy group, n-Propoxy group, iso-Propoxy group, n-butoxy group,
iso-butoxy group, tert-butoxy group, and any other alkoxy groups
known to those of skill in the art. If there are any remaining
R-groups, they can be any non sol-gel active groups such as methyl,
octadecyl, phenyl, and the like. It is preferred however, that
three or four of the R-groups are sol-gel active groups.
[0067] Typical non-sol-gel-active substituents of the
precursor-forming element (Z) include, but are not limited to,
alkyl moieties and their derivatives, alkenyl moieties and their
derivatives, aryl moieties and their derivatives, arylene moieties
and their derivatives, cyanoalkyl moieties and their derivatives,
fluoroalkyl moieties and their derivatives, phenyl moieties and
their derivatives, cyanophenyl moieties and their derivatives,
biphenyl moiety and its derivatives, cyanobiphenyl moieties and
their derivatives, dicyanobiphenyl moieties and their derivatives,
cyclodextrin moieties and their derivatives, crown ether moieties
and their derivatives, cryptand moieties and their derivatives,
calixarene moieties and their derivatives, liquid crystal moieties
and their derivatives, dendrimer moieties and their derivatives,
cyclophane moieties and their derivatives, chiral moieties,
polymeric moieties, and any other similar non-sol-gel active
moieties known to those of skill in the art.
[0068] In addition to the above mentioned and preferred precursors,
other precursors can be used with the present invention. These
precursors include, but are not limited to, a chromatographically
active moiety selected from the group of octadecyl, octyl,
cyanopropyl, diol, biphenyl, and phenyl. Other representative
precursors include, but are not limited to, Tetramethoxysilane,
3-(N-styrylmethyl-2-aminoethylamino)-propyltrimet- hoxysilane
hydrochloride, N-tetradecyldimethyl(3-trimethoxysilylpropyl)amm-
onium chloride,
N-(3-trimethoxysilylpropyl)-N-methyl-N,N-diallylammonium chloride,
N-trimethoxysilylpropyltri-N-butylammonium bromide,
N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride,
Trimethoxysilylpropylthiouronium chloride,
3-[2-N-benzyaminoethylaminopro- pyl]trimethoxysilane hydrochloride,
1,4-Bis(hydroxydimethylsilyl)benzene,
Bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane,
1,4-bis(trimethoxysilyl- ethyl)benzene,
2-Cyanoethyltrimethoxysilane, 2-Cyanoethyltriethoxysilane,
(Cyanomethylphenethyl)trimethoxysilane,
(Cyanomethylphenethyl)triethoxysi- lane,
3-Cyanopropyldimethylmethoxysilane, 3-Cyanopropyltriethoxysilane,
3-Cyanopropyltrimethoxysilane, n-Octadecyltrimethoxysilane,
n-Octadecyldimethylmethoxysilane, Methyl-n-Octadecyldiethoxysilane,
Methyl-n-Octadecyldimethoxysilane, n-Octadecyltriethoxysilane,
n-Dodecyltriethoxysilane, n-Dodecyltrimethoxysilane,
n-Octyltriethyoxysilane, n-Octyltrimethoxysilane,
n-Ocyidiisobutylmethoxy- silane, n-Octylmethyldimethoxysilane,
n-Hexyltriethoxysilane, n-isobutyltriethoxysilane,
n-Propyltrimethoxysilane, Phenethyltrimethoxysilane,
N-Phenylaminopropyltrimethoxysilane, Styrylethyltrimethoxysilane,
3-(2,2,6,6-tetramethylpiperidine-4-oxy)-prop- yltriethoxysilane,
N-(3-triethoxysilylpropyl)acetyl-glycinamide,
(3,3,3-trifluoropropyl)trimethoxysilane,
(3,3,3-trifluoropropyl)methyldim- ethoxysilane,
3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltrimethoxy-
silane, 3-mercaptopropyltriethoxysilane,
mercaptomethylmethyldiethoxysilan- e,
3-mercaptopropylmethyldimethoxysilane,
3-mercaptopropyloctadecyldimetho- xysilane,
3-mercaptopropylloctyldimethoxysilane, 3-mercaptopropylcyanoprop-
yldimethoxysilane, 3-mercaptopropyloctadecyldiethoxysilane, and any
other similar precursor known to those of skill in the art.
[0069] The deactivation reagents include, but is not limited to,
hydrosilanes, polymethylhydrosiloxlanes, polymethylphenyl
hydrosiloxanes, polymethyl cyanopropyl hydrosioloxanes, and any
other similar deactivation reagent known to those of skill in the
art. The primary catalyst includes, but is not limited to,
trifluoroacetic acid, any acid, base, fluoride, and any other
similar catalyst known to those of skill in the art.
[0070] According to the present invention, in addition to the
above-mentioned materials, the performance of the sol gel
stationary phase is improved by the addition of at least one
baseline stabilizing reagent and at least one additional surface
deactivation reagent to the sol solution. The baseline-stabilizing
reagent prevents rearrangement of the sol-gel polymeric stationary
phase and formation of volatile compounds at elevated temperature.
In order to do so, the baseline-stabilizing reagent incorporates
with the phenyl ring in the polymer backbone structure at room
temperature using a sol-gel process. The baseline-stabilizing
reagent includes, but is not limited to,
bis(trimethoxysilylethyl)-benzene (BIS), phenyl-containing groups,
cyclohexane containing groups, and any other similar sol-gel active
stabilizing reagent known to those of skill in the art. In one
embodiment, the baseline-stabilizing reagent is used in conjunction
with methyltrimethoxysilane (a sol-gel percursor), and two sol-gel
catalysts (trifluoroacetic acid and ammonium fluoride). First the
sol-gel reactions are carried out for ten minutes using
trifluoroacetic acid as the primary catalyst. After this, a second
sol-gel catalyst is used to improve the condensation process for
the sol-gel coating and its bonding with the capillary inner
surface. The second sol-gel catalyst includes, but is not limited
to, ammonium fluoride, base, fluoride, and any other similar
catalysts known to those of skill in the art. It is known that
under acidic conditions the hydrolysis reaction proceeds faster to
produce primarily linear polymeric structure, but the
polycondensation reaction remains slow. The addition of fluoride
increases the polycondensation reaction rate.
[0071] Finally, a surface derivatization reagent is added as a
secondary deactivation reagent, which includes, but is not limited
to, 1,1,1,3,3,3-heaxmethyldisilazane, any hydrosilane, and any
other similar surface deactivation reagents known to those of skill
in the art. The sol-gel reactions involved in the formation of the
polysiloxane structure described herein, incorporation of phenyl
ring, and chemical bonding of the polymer to the column inner walls
are illustrated in FIGS. 14-21 for sol-gel PDMS and sol-gel
PEG.
[0072] The preparation of the sol-gel coating includes the steps of
providing the tube structure, providing a sol-gel solution
including one or more sol-gel precursors, an organic material with
at least one sol-gel active functional group, one or more sol-gel
catalysts, one or more deactivation reagents, and a solvent system.
The sol-gel solution is then reacted with a portion of the tube
(e.g., inner surface) under controlled conditions to produce a
surface bonded sol-gel coating on the portion of the tube. The free
portion of the solution is then removed from the tube under
pressure, purged with an inert gas, and is heated under controlled
conditions to cause the deactivation reagent to react with the
surface bonded sol-gel coating to deactivate and to condition the
sol-gel coated portion of the tube structure. Preferably, the
sol-gel precursor includes an alkoxy compound. The organic material
includes a monomeric or polymeric material with at least one
sol-gel active functional group. The sol-gel catalyst is taken from
the group consisting of an acid, a base and a fluoride compound,
and the deactivation reagent includes a material reactive to polar
functional groups (e.g., hydroxyl groups) bonded to the sol-gel
precursor-forming element in the coating or to the tube
structure.
[0073] The specific steps for fabrication starts with the cleaning
and hydrothermal treatment of a fused silica capillary. Then, the
preparation of the sol-gel solution utilizing the above precursors
is done. Next, the inner walls of the hydrothermally treated
capillary column are coated with the prepared sol-gel solution.
Finally, conditioning of the sol-gel coated capillary tube is
performed.
[0074] Referring now to FIG. 2, the selected capillary column 10 is
filled with the prepared sol-gel solution utilizing the device 20
as illustrated in FIG. 2. The device 20 includes a metallic
cylindrical pressurization chamber 22 and a bottom cap 24. The
bottom cap is removably attached to a distal end thereof by a
screw-threaded portion 34. It is understood that any attachment
mechanism can be used to secure the bottom cap 24 to the distal
portion of the chamber 22. A proximal end of the chamber 22 has a
second sealing mechanism 36 with an outlet mechanism 26, generally
in the form of a cross or any other suitable shape as desired,
extending therefrom. This outlet mechanism 26 has outwardly
extending portions 38, 40, 42 with outlet valves 28, 30 contained
within the radially extending portions or arms thereof. The
upwardly extending portion of the outlet means 26 has a capillary
column 10 extending therefrom, which is removably inserted through
the upwardly extending arm of the outlet device.
[0075] As previously mentioned, the sol-gel solution of the present
invention utilizes various sol-gel precursors. In one embodiment,
the sol-gel solution is prepared by mixing two solutions together
that are each prepared in separate polypropylene vials. The first
solution contains hydroxy-terminated polydimethylsiloxane (PDMS),
hydroxy-terminated polydimethyldiphenylsiloxane (PDMDPS),
polymethylhydrosiloxane (PMHS) and methylene chloride. The second
solution is methyltrimethoxysilane,
bis(trimethoxysilylethyl)-benzene, 1,1,1,3,3,3-hexamethyldisilazane
(HMDS) and methylene chloride. These two solutions are then admixed
by vortexing and separated from the ensuing precipitate by
centrifugation. The supernatant is carefully pipetted out and
placed in another vial for insertion into the filling and purging
device. This is accomplished by unscrewing the cap 24, inserting
the vial and then replacing the cap 24 to provide an airtight seal.
If necessary, Teflon tape or other suitable adhesive mechanism can
also be used in the sealing of the cap 24. In addition, airtight
sealing mechanism 44 is in communication with the arm member
extending upwardly from the cross-like member and connecting means
46 extending from the radially extending arms.
[0076] Prior to the insertion of the vial 32 into the chamber 22,
the valves 28, 30 are closed and then the capillary column 10 is
inserted into the chamber 22 via the outwardly extending portion of
the cross-like member 26 such that it is in contact with the
sol-gel solution contained in vial 32. A gas pressure is selected
depending on the size of the capillary to be filled and this
pressure is applied to an inert gas applied to the chamber 22 by
opening the valve 28. The sol-gel is then pushed up from the vial
32 into the capillary 10, completely filling the extent thereof.
When the sol-gel solution overflows from the distal end of the
capillary 10, the inlet valve 28 is closed and the outlet valve 30
is then opened to release the excess pressure from the chamber
22.
[0077] The solution is allowed to reside inside the full extent of
the capillary column 10 for a desired length of time, according to
the thickness of coating to be formed on the inner walls 14 of the
tube structure 12 of the capillary column 10, and the sol-gel
reactions take place within the capillary column 10. These
reactions include chemical bonding of the inner walls 14 of the
tube structure 12 with the components of the sol-gel by virtue of
the silanol groups in the polymeric network reacting with the
silanol groups of the silica tube structure 12. This reaction forms
an immobilized sol-gel surface coating integral with the inner
walls 14 of the tube structure 12. The now filled capillary is then
subjected to further processing.
[0078] After the reaction period for the sol-gel solution is
completed, the outlet valve 30 is closed and the inlet valve 28 is
opened to allow for an inert pressurized gas to be again introduced
into the capillary 10. Prior to this gas introduction, the cap 24
is opened to remove the vial 32, leaving the chamber 22 without any
members other than the distal end of capillary 10 extending
thereto. This gas purging allows the excess sol-gel solution, which
has not yet bonded to the capillary walls to be purged from the
capillary 10 via its distal end. Purging with the inert gas also
removes any residual solvent or other volatiles from the capillary
10.
[0079] Final conditioning of the capillary 12 is accomplished by
sealing the ends of the capillary after it is removed from the
device 20 by use of any known sealing means such as an
oxy-acetylene torch. A programmed system of heating is then applied
to the capillary and then the seals are removed to allow for
solvent rinsing after which a final programmed temperature drying
with simultaneous inert gas purging is performed. The column thus
prepared is ready then for use.
[0080] The above discussion provides a factual basis for the use of
the column and related method described herein. The methods used
with a utility of the present invention can be shown by the
following non-limiting examples and accompanying figures.
EXAMPLES
[0081] The following examples specifically provide for the specific
methods and materials utilized with the present invention.
[0082] Materials:
[0083] Fused silica capillary (250 .mu.m i.d.) can be obtained from
Polymicro Technologies Inc. (Phoenix, Ariz., USA). HPLC-Grade
tetrahydrofuran (THF), methylene chloride, and methanol were
purchased from Fisher Scientific (Pittsburgh, Pa., USA).
Tetramethoxysilane (TMOS, 99+%), poly(methylhydrosiloxane) (PMHS),
and trifluoroacetic acid (containing 5% water), were purchased from
Aldrich (Milwaukee, Wis., USA) Hydroxy-terminated
poly(dimethylsiloxane) (PDMS), methyl-trimethoxysilane (MTMS) and
trimethylmethoxysilane (TMMS) were purchased from United Chemical
Technologies, Inc. (Bristol, Pa., USA). Ucon 75-H-90,000 polymer
was obtained from Alltech (Deerfield, Ill., USA).
[0084] Gas chromatographic experiments have been carried out on a
Shimadzu Model 14A capillary GC system. A Jeol Model JSM-35
scanning electron microscope has been used for the investigation of
coated surfaces. A homemade capillary filling device has been used
for filling the capillary with the coating sol solution using
nitrogen pressure. A Microcentaur Model APO 5760 centrifuge has
been used to separate the sol solution from the precipitate. A
Fisher Model G-560 Vortex Genie 2 system has been used for thorough
mixing of various solution ingredients. A Barnstead Model 04741
Nanopure deionized water system was used to obtain 17.8 M.OMEGA.
water.
Example One
[0085] The inner surface of an appropriate length of a fused silica
capillary is cleaned by sequentially rinsing with 5 ml each of the
following solvents:
[0086] (a) methylene chloride;
[0087] (b) methanol; and
[0088] (c) deionized water.
[0089] The capillary is then purged with a flow of helium, or any
other inert gas, for 5 minutes leaving behind a thin coating of
deionized water on the inner surface of the capillary. The two ends
of the capillary are then sealed with an oxy-acetylene flame. The
sealed capillary was then heated by programming the temperatures
from an initial value of 40.degree. C. to a final value of
300.degree. C. at a rate of change of 4.degree. C. per minute, and
allowing the thermal treatment at the final temperature to continue
for approximately 120 minutes. The capillary was allowed to cool
down to room temperature, and then the ends are cut open. The
capillary was then purged again with an inert gas, the flow rate
being 1 ml per minute while being simultaneously heated at the same
programmed temperature as delineated before.
[0090] Two solutions were then prepared in separate polypropylene
vials:
1 (1) Solution 1: (a) Hydroxy-terminated Polydimethylsiloxane
(PDMS) 0.025 g (b) Hydroxy-terminated Polydimethyldiphenylsiloxane
0.025 g (PDMDPS) (c) Polymethylhydrosiloxane (PMHS) 25 .mu.l (d)
Methylene chloride 600 .mu.l (2) Solution 2: (a)
Methylteimethoxysilane (MTMS) 5 .mu.l (b)
bis(trimethoxysilylethyl)-benzene 10 .mu.l (c)
1,1,1,3,3,3-hexamethyldisilazane (HMDS) 10 .mu.l (d) methylene
chloride 280 .mu.l
[0091] The solutions were then mixed together by thorough
vortexing. This was followed by the addition of 50 .mu.l of
trifluoroacetic acid (containing 5% water) and vortexed again.
Further, a 20 .mu.l volume of a methanolic solution of ammonium
fluoride (20 mg/ml) was added to the mixture. The precipitate was
separated out by centrifugation and the supernatant was carefully
pipetted out and transferred to a clean vial. This final sol-gel
solution was then further used to coat the capillary column.
[0092] The pre-treated capillary tube was then filled with the
sol-gel solution and allowed to sit for a selected residence time
(e.g. 10-30 minutes). This allowed the sol-gel polymer to be formed
in the sol solution and get bonded to the inner walls of the
capillary. The excess, unreacted sol-gel solution was then expelled
from the capillary under helium or other inert gas pressure,
leaving the surface-bonded coating on the inner surface of the
capillary tube. Volatiles and residual solvents or sol-gel solution
were then purged off the tube using helium or other inert gas for
30-60 minutes.
[0093] Both ends of the now coated and gas-filled capillary were
sealed and then heated by use of a programmed temperature sequence.
This sequence was as follows, but other modifications of this are
within the scope of the present invention:
[0094] (1) Heating from 40.degree. C. to 150.degree. C. at
1.degree. C. per minute with an incremental change with a hold time
of 5 hours at 150.degree. C.
[0095] (2) Heating the column from 150.degree. C. at programmed
sequential increments to a final temperature of 350.degree. C. or
any other temperature suitable for the selected sol-gel matrix.
This heating was allowed to continue for a hold time of
approximately 60 minutes.
[0096] (3) Opening of the ends of the column.
[0097] (4) Rinsing of the column with a selected solvent mixture,
e.g. 1:1 v/v methylene chloride/methanol mixture.
[0098] (5) Drying of the coated capillary under helium purge and
further temperature programming conditions; e. g., 40.degree. C. to
350.degree. C. at 6.degree. C. per minute.
[0099] The column was then ready for use in chromatographic
analysis. In order to test the efficacy of the columns of the
present invention, several columns were prepared with and without
the preferred reagents of the present invention.
Example Two
[0100] Preparation of Columns With and Without Ammonium
Fluoride
2 Solution 1 (for column without ammonium fluoride): PDMS 0.025 g
Polydimethyldiphenylsiloxane in 200 .mu.l methyl chloride 0.025 g
PMHS 25 .mu.l Methyl chloride 400 .mu.l Solution 2 (for column
without ammonium fluoride): M-TMOS 5 .mu.l BIS 10 .mu.l HMDS 10
.mu.l Methylene chloride 310 .mu.l
[0101] As before, the two solutions were combined and introduced
into a fused silica capillary tube and post-treated according to
the method above. A GROB test mixture was then run.
3 Solution 3 (for column with ammonium fluoride): PDMS 0.025 g
Polydimethyldiphenylsiloxane in 200 .mu.l methylene chloride 0.025
g PMHS 25 .mu.l Methylene chloride 400 .mu.l Solution 4 (for column
with ammonium fluoride): M-TMOS 5 .mu.l BIS 10 .mu.l. HMDS 10 .mu.l
Methylene chloride 310 .mu.l
[0102] Again, solutions 3 and 4 were mixed together, however, in
addition 50 .mu.l TFA (5% water), 20 .mu.l of methanolic ammonium
fluoride were added after the initial mixing and centrifuging.
Another test solution was run on this column after the final
treatment steps.
[0103] Results of comparison studies of columns prepared without
and with the ammonium fluoride are illustrated in FIGS. 3A and
3B.
Example Three
[0104] Preparation of Columns With and Without BIS
4 Solution 1 (with BIS): PDMS 0.025 g Polydimethyldiphenylsiloxane
with 0.025 g 200 .mu.l methylene chloride PMHS 25 .mu.l Methylene
chloride 400 .mu.l Solution 2 (with BIS): M-TMOS 5 .mu.l BIS 10
.mu.l HMDS 5 .mu.l Methylene chloride 285 .mu.l
[0105] The vials were admixed as above and after centrifuging for
10 minutes, the ammonium fluoride catalyst is added to the mixture.
The column was prepared by the method presented before.
5 Solution 3 (without BIS): PDMS 0.025 g
Polydimethyldiphenylsiloxane in 0.025 g 200 .mu.l methylene
chloride PMHS 25 .mu.l Methylene chloride 400 .mu.l Solution 4
(without BIS): M-TMOS 5 .mu.l HMDS 5 .mu.l Methylene chloride 285
.mu.l
[0106] As above, the columns was prepared according to the
procedure outlined before.
[0107] Both columns were tested using a GROB test mixture and the
resulting spectra are shown in FIGS. 4A and 4B. The column with the
BIS component clearly shows improved baseline stability and better
peak resolution.
Example Four
[0108] Columns Prepared With and Without HMDS
6 Solution 1 (with HMDS): PDMS 0.025 g Polydimethyldiphenylsiloxane
in 0.025 g 200 .mu.l methylene chloride PMHS 25 .mu.l Methylene
chloride 400 .mu.l Solution 2 (with HMDS): M-TMOS 5 .mu.l BIS 10
.mu.l HMDS 5 .mu.l Methylene chloride 285 .mu.l Solution 3 (without
HMDS): PDMS 0.025 g Polydimethyldiphenylsiloxane in 0.025 g 200
.mu.l of methylene chloride PMHS 25 .mu.l Methylene chloride 400
.mu.l Solution 4 (without HMDS): M-TMOS 5 .mu.l BIS 10 .mu.l
Methylene chloride 290 .mu.l
[0109] The columns were again prepared by the methods already
disclosed, including the addition of the ammonium fluoride catalyst
step. The results of the spectra of GROB test solution runs are
shown in FIGS. 5A and 5B. Again, the addition of the HMDS gave
improved results.
Example Five
[0110] Optimized Solution
7 Solution 1: PDMS 0.025 g Polydimethyldiphenylsiloxane in 0.025 g
300 .mu.l methylene chloride PMHS 25 .mu.l Methylene chloride 300
.mu.l Solution 2: M-TMOS 5 .mu.l BIS 10 .mu.l HMDS 10 .mu.l
Methylene chloride 280 .mu.l
[0111] The columns were prepared according to the already disclosed
method.
[0112] As can be seen from the above examples and Table 1, the
columns of the instant invention demonstrated a reproducibility in
results both run-to-run and column-to-column.
[0113] Throughout this application, various publications, including
United States patents, are referenced by author and year and by
patent number. Full citations for the publications are listed
below. The disclosures of these publications and patents in their
entireties are hereby incorporated by reference into this
application in order to describe more fully the state of the art to
which this invention pertains.
[0114] The invention has been described in an illustrative manner,
and it is to be understood that the terminology used is intended to
be in the nature of words of description rather than of
limitation.
[0115] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is,
therefore, to be understood that within the scope of the appended
claims, the invention can be practiced otherwise than as
specifically described.
8TABLE 1 Retention Time and Retention Factor Reproducibility Data
Obtained on three Sol-Gel Coated PEG colum in 5 Replicate Runs Peak
RSD RSD # NAME tr SD % k SD % COLUMN NUMBER 1 1 n-Hexadecane 2.38
0.02 0.71 3.4 0.03 0.94 2 Methyl Undecanoate 4.48 0.09 1.96 7.37
0.10 1.34 3 1-Decanol 2.79 0.00 0.14 3.72 0.01 0.24 4 n-Octadecane
3.63 0.05 1.38 5.72 0.09 1.63 5 2,6-Dimethylphenol 3.15 0.02 0.67
4.8 0.04 0.92 6 2-Ethylhexanoic acid 6.1 0.14 2.21 10.3 0.25 2.42 7
Hexanophenone 10.12 0.13 1.30 17.75 0.24 1.37 8 Eicosane 18.43 0.41
2.25 33.13 0.76 2.29 COLUMN NUMBER 2 1 n-Hexadecane 1.93 0.01 0.31
2.26 0.01 0.40 2 Methyl Undecanoate 2.49 0.00 0.16 3.22 0.00 0.12 3
Dicyclohexylamine 2.64 0.03 1.14 3.48 0.06 1.72 4 1-Decanol 2.79
0.00 0.14 3.72 0.01 0.24 5 n-Octadecane 3.81 0.00 0.10 5.45 0.01
0.15 6 2,6-Dimethylphenol 4.22 0.00 0.09 6.15 0.00 0.07 7
2-Ethylhexanoic acid 4.87 0.00 0.08 7.25 0.01 0.11 8 Hexanophenone
6.94 0.01 0.12 10.70 0.00 0.00 9 Eicosane 8.23 0.01 0.12 12.92 0.02
0.15 COLUMN NUMBER 3 1 n-Hexadecane 1.50 0.01 0.80 1.55 0.02 1.35 2
Methyl Undecanoate 1.72 0.01 0.70 1.92 0.02 1.09 3
Dicyclohexylamine 1.78 0.01 0.56 2.01 0.02 0.75 4 1-Decanol 2.29
0.06 2.53 2.89 0.10 3.49 5 n-Octadecane 2.56 0.00 0.00 3.33 0.00
0.00 6 2,6-Dimethylphenol 2.86 0.01 0.42 3.84 0.02 0.52 7
2-Ethylhexanoic acid 3.84 0.02 0.44 5.50 0.03 0.51 8 Hexanophenone
4.53 0.02 0.33 6.67 0.03 0.39 9 Eicosane 6.01 0.05 0.83 9.18 0.09
0.94 GC separation of polarity test mixture(TC WAX) on three
sol-gel coated PEG columns prepared in the same way, using sol
solutions containing different amounts of sol-gel ingredients;
column, 10-m .times. 0.25 mm-i.d. fused silica capillary column;
stationary phase, Polyethylene glycol PEG; carrier gas, helium;
injection, split (100:1, 300.degree. C.); detector, FID,
350.degree. C.; temperature, 150.degree. C.
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