U.S. patent application number 12/463156 was filed with the patent office on 2009-10-08 for tube structure with sol-gel zirconia coating.
Invention is credited to Khalid Alhooshani, Abdul Malik.
Application Number | 20090250349 12/463156 |
Document ID | / |
Family ID | 37994869 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090250349 |
Kind Code |
A1 |
Malik; Abdul ; et
al. |
October 8, 2009 |
Tube Structure with Sol-Gel Zirconia Coating
Abstract
The subject invention concerns zirconia-based hybrid
organic-inorganic sol-gel coating for optional use as a stationary
phase in capillary microextraction (CME), gas chromatographic (GC),
high performance liquid chromatography (HPLC), capillary
electrophoresis (CE), capillary electrochromatography (CEC) and
related analytical techniques. Sol-gel chemistry is employed to
chemically bind a hydroxy-terminated silicone polymer
(polydimethyldiphenylsiloxane, PDMDPS) to a sol-gel zirconia
network. In one embodiment, a fused silica capillary is filled with
a properly designed sol solution to allow for the sol-gel reactions
to take place within the capillary. In the course of this process,
a layer of the evolving hybrid organic-inorganic sol-gel polymer
becomes chemically bonded to the silanol groups on the inner
capillary walls. The unbonded part of the sol solution is expelled
from the capillary under helium pressure, leaving behind a
chemically bonded sol-gel zirconia-PDMDPS coating on the inner
walls of the capillary. Polycyclic aromatic hydrocarbons, ketones,
and aldehydes are efficiently extracted and preconcentrated from
dilute aqueous samples followed by GC separation of the extracted
analytes.
Inventors: |
Malik; Abdul; (Tampa,
FL) ; Alhooshani; Khalid; (Temple Terrace,
FL) |
Correspondence
Address: |
SALIWANCHIK LLOYD & SALIWANCHIK;A PROFESSIONAL ASSOCIATION
PO Box 142950
GAINESVILLE
FL
32614
US
|
Family ID: |
37994869 |
Appl. No.: |
12/463156 |
Filed: |
May 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11491786 |
Jul 24, 2006 |
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12463156 |
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10704766 |
Nov 10, 2003 |
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11491786 |
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60319680 |
Nov 8, 2002 |
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Current U.S.
Class: |
204/605 ;
210/198.2; 96/101 |
Current CPC
Class: |
B01J 20/3268 20130101;
B01J 20/3242 20130101; C23C 18/1254 20130101; C23C 18/1216
20130101; B01J 20/286 20130101; B01J 20/28047 20130101; B01J 20/285
20130101; B01J 2220/86 20130101 |
Class at
Publication: |
204/605 ;
210/198.2; 96/101 |
International
Class: |
B01D 15/08 20060101
B01D015/08; G01N 27/26 20060101 G01N027/26; B01D 53/02 20060101
B01D053/02 |
Claims
1. A sol solution coated column comprising: a) a vessel having a
bore, defining an inner surface of the vessel; and b) a
deactivated, sol-gel zirconia-polymer stationary phase coating
chemically bonded to the inner surface of the vessel; wherein said
chemical bond comprises a --Si--O--Zr-- bond.
2. The column of claim 1, wherein the zirconia is provided by
zirconium butoxide.
3. The column of claim 1, wherein the polymer is
dimethyldiphenylsiloxane.
4. The column of claim 1, wherein the vessel is a fused silica
capillary.
5. The column of claim 1, wherein the coating comprises a
zirconia-polydimethyldiphenylsiloxane coating, wherein said
zirconia is chemically bonded to said polydimethyldiphenylsiloxane
coating via a --Zr--O--Si-- bond.
6. A sol-gel coated column prepared according to the steps of: a)
providing a fused-silica capillary comprising a vessel having a
bore, defining an inner surface of the capillary; b) filling the
fused-silica capillary with a sol solution comprising: i) a sol-gel
precursor comprising a zirconia solution; ii) a stationary phase
coating; iii) a chelating reagent; and iv) a deactivating reagent;
dissolved in a solvent for a residence time sufficient for the sol
solution to evolve into a sol-gel stationary phase and to
chemically bond to the inner surface of the capillary, wherein said
chemical bond comprises a --Si--O--Zr-- bond; c) expelling any
residual sol solution; and d) conditioning the sol-gel coated
capillary; whereby a deactivated, sol-gel zirconia-polymer
stationary phase coated column is made.
7. The sol-gel coated column according to claim 6, wherein the
sol-gel precursor is a zirconium (IV) alkoxide.
8. The sol-gel coated column according to claim 6, wherein the
sol-gel precursor is zirconium (IV) butoxide.
9. The sol-gel coated column according to claim 6, wherein the
stationary phase coating is a silanol-terminated
poly(dimethyldiphenylsiloxane) copolymer, wherein said zirconia is
chemically bonded to said polydimethyldiphenylsiloxane coating via
a --Zr--O--Si-- bond.
10. The sol-gel coated column according to claim 6, wherein the
chelating agent is acetic acid, triethanolamine,
1,5-diaminopentane, acetylacetonate, acetoacetate, valeric acid, or
a combination of any of the foregoing.
11. The sol-gel coated column according to claim 6, wherein the
deactivating reagent is poly(methylhydrosilozane),
hexamethyldisilozane, or a combination of both.
12. The sol-gel coated column according to claim 6, wherein the
solvent is methylene chloride.
13. The sol-gel coated column according to claim 6, wherein the
conditioning step comprises a first heating step comprising heating
the capillary from 40.degree. C. to 150.degree. C. at 1.degree. C.
per minute and maintaining the temperature at 150.degree. C. for
300 minutes, a second heating step comprising heating the capillary
from 150.degree. C. to 320.degree. C. at 1.degree. C. per minute
and maintaining the temperature at 320.degree. C. for 120 minutes;
and a third heating step comprising heating the capillary from
40.degree. C. to 320.degree. C. at 4.degree. C. per minute; wherein
the first heating step and the second heating step take place
sequentially; and wherein a cleaning step comprising rinsing the
capillary with a solvent precedes the third heating step.
14. The sol-gel coated column according to claim 6, wherein the
residence time of step b) comprises 10 to 15 minutes.
15. The sol-gel coated column according to claim 6, wherein the
residence time of step b) comprises 30 minutes.
16. The column of claim 1, wherein the column is a chromatographic
separation column.
17. The column of claim 1, wherein the column is an electrophoretic
column.
18. The sol-gel coated column according to claim 6, wherein step d
comprises heating the capillary at 250.degree. C. to 300.degree.
C.
19. The sol-gel coated column according to claim 6, wherein the
column is a chromatographic separation column.
20. The sol-gel coated column according to claim 6, wherein the
column is an electrophoretic column.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 11/491,786, filed Jul. 24, 2006, which is a continuation of
U.S. application Ser. No. 10/704,766, filed Nov. 10, 2003, now
abandoned, which claims the benefit of U.S. Provisional Application
Ser. No. 60/319,680, filed Nov. 8, 2002.
BACKGROUND OF THE INVENTION
[0002] Solid phase microextraction (SPME) was developed in 1989 by
Belardi and Pawliszyn to facilitate rapid sample preparation both
for the laboratory and field analysis. It provided a simple and
efficient solvent-free method for extraction and preconcentration
of analytes from various sample matrices. In SPME, a sorptive
stationary phase coating, (either on the outer surface of a fused
silica fiber or on the inner surface of a fused silica capillary)
actually serves as the extraction medium in which the analytes get
preferentially sorbed and preconcentrated. Polymeric surface
coatings are predominantly used in conventional fiber-based SPME as
well as in the newly materialized in-tube SPME, also referred to as
capillary microextraction (CME). A number of new polymeric coatings
have recently been developed. Besides polymeric coatings, SPME
fibers have also been prepared by using nonpolymeric materials or
by gluing reversed-phase HPLC particles onto SPME fiber
surface.
[0003] The stationary phase coating play a fundamentally important
role in the SPME analysis. Because the stationary phase coating is
the key component of the SPME device, further development and
growth of SPME will greatly depend on new breakthroughs in the
areas of stationary phase development and coating technology.
[0004] Sol-gel chemistry offers an effective methodology for the
synthesis of macromolecular material systems under extraordinarily
mild thermal conditions (often at room temperature) which greatly
simplifies the job to carry out sol-gel reactions within
small-diameter fused silica capillaries by eliminating the
procedural complications as well as the need for enhanced
technological and safety requirements for carrying out reactions
under elevated temperatures. Sol-gel process provides a facile
mechanism to chemically bind the in situ created sol-gel stationary
phase coatings to the inner walls of the capillary made out of an
appropriate sol-gel-active material. Due to this chemical bonding,
sol-gel coatings possess significantly higher thermal and solvent
stabilities compared with their conventional counterparts. Sol gel
chemistry has thus opened a whole new approach to column technology
for analytical separations and sample preconcentrations. The
sol-gel approach can be applied to create both silica-based
stationary phases as well as the newly emerging transition metal
oxide-based stationary phases. Furthermore, sol-gel chemistry
provides an opportunity to create advanced material systems and to
use their properties to achieve enhanced performance and
selectivity in analytical separations and sample
preconcentration.
[0005] Sol-gel organic-inorganic hybrid materials provide desirable
properties that are difficult to achieve using either purely
organic or purely inorganic materials. This opportunity is being
explored in the filed of microcolumn separations and sample
preparation through creation of hybrid organic-inorganic stationary
phases in the form of surface coatings and monolithic beds. In
1993, a procedure was developed for the preparation of a thin layer
of silica gel with chemically bonded C.sub.18 moieties on the
internal wall of fused-silica capillaries for reversed-phase
high-performance liquid chromatography. Colon and Guo in 1995
implemented sol-gel stationary phase for open tubular liquid
chromatography and electrochromatography. Malik and coworkers
introduced sol-gel coated column for capillary GC and sol-gel
coated fibers for solid-phase microextraction (SPME). Following
this, other groups also got involved in sol-gel research aiming at
developing novel stationary phases for solid-phase microextraction
and solid-phase extraction. Sol-gel SPME fibers demonstrated
superior performance compared with conventional fibers by
exhibiting high thermal stability (up to 360.degree. C.) and
solvent stability due to chemical bonding between the sol-gel
coating and the fiber surface. They also showed better selectivity
and extraction sensitivity toward various analytes, less extraction
time due to fast mass transfer and extended lifetime. Recently,
sol-gel capillary microextraction (CME) was reported by Malik and
coworkers. In this in-tube format, sample extraction was
accomplished using a sol-gel coating created on the inner surface
of a fused silica capillary.
[0006] The existing stationary phases are predominantly
silica-based. In spite of many attractive material properties
(e.g., mechanical strength, surface characteristics, catalytic
inertness, surface derivatization possibilities, etc.),
silica-based stationary phases have some inherent shortcomings. The
main drawback of silica-based stationary phases is the narrow range
of pH stability. Under extreme pH conditions silica-based
stationary phases become chemically unstable, and their stationary
phase properties are compromised. For example, silica dissolves
under alkaline condition, and their dissolution process starts at a
pH value of about 8. Under highly acidic pH conditions,
silica-based bonded stationary phases become hydrolytically
unstable. Therefore, developing stationary phases with a wide range
of pH stability is an important research area in contemporary
separation and sample preparation technologies. Transition metal
oxides (zirconia, titania, etc.) are well known for their pH
stability, and appear to be logical candidates for exploration to
overcome the above-mentioned drawbacks inherent in silica-based
stationary phases.
[0007] What is needed, then, is an improved product and a method of
use of such product, for increasing the sample concentration
sensibility in Chromatographic and electrophoretic separation
techniques including but not limited to GC, HPLC, CZE, and CEC.
SUMMARY OF INVENTION
[0008] The present invention relates to zirconia-based stationary
phases for chromatographic separations and sample
preconcentrations. Zirconia has many unique properties that make it
attractive as a chromatographic support material. Zirconia's most
notable properties are: it's excellent chemical and pH stability,
inertness, and unique surface chemistry. In the present method,
sol-gel chemistry is used to exploit these properties by in situ
preparation of zirconia-based stationary phases within separation
columns and extraction tubes. The utility of the created columns
and extraction tubes are demonstrated by experimental results on
gas chromatographic separations obtained on sol-gel zirconia coated
capillary columns and capillary microextraction results obtained on
sol-gel zirconia-coated capillaries.
[0009] A sol solution coated column is developed. The column
comprising a vessel having a bore, and an inner surface, where the
sol solution molecules are chemically bonded onto the inner
surface. The sol solution is made from a stationary phase mixture
comprising zirconium solution, and an organic compound. A first
portion of the stationary phase is a thin layer, chemically bonded
to the inner surface of the capillary, and a second portion of the
stationary phase is a residual solution, which residual solution is
then expelled, leaving a prepared column for sample
preconcentration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a fuller understanding of the nature and objects of the
invention, reference should be made to the following detailed
description, taken in connection with the accompanying drawings, in
which:
[0011] FIG. 1 is the gravity feed extraction system for capillary
microextraction.
[0012] FIG. 2 is the homebuilt capillary filling/purging
device.
[0013] FIG. 3 is a CME-GC analysis of PAHs using a sol-gel
zirconia-PDMDPS coated capillary.
[0014] FIG. 4 is a CME-GC analysis of Aldehydesusing a sol-gel
zirconia-PDMDPS coated capillary.
[0015] FIG. 5 is a CME-GC analysis of ketonesusing a sol-gel
zirconia-PDMDPS coated capillary.
[0016] FIG. 6 is a CME-GC analysis of mixture of PAHs, aldehydes
and ketones using a sol-gel zirconia-PDMDPS coated capillary.
[0017] FIG. 7 is extraction kinetics of aqueous undecylic aldehyde,
heptanophenone, and ydroxyl on a sol-gel zirconia-PDMDPS
microextraction coated capillary.
[0018] FIG. 8a is CME-GC analysis of PAHs using a sol-gel
zirconia-PDMDPS coated capillary before rinsing with NaOH.
[0019] FIG. 8b is CME-GC analysis of PAHs using a sol-gel
zirconia-PDMDPS coated capillary rinsed with NaOH for 24 hours.
DETAILED DESCRIPTION
[0020] For the preparation of sol-gel-coated capillaries according
to this invention, a cleaned and hydrothermally treated
fused-silica capillary is filled with a specially designed sol
solution using a helium pressure-operated filling/purging device.
The key ingredients of the sol solution include appropriate amounts
of: sol-gel precursor such as zirconium (IV) butoxide; a stationary
phase coating such as silanol-terminated poly copolymer
(dimethyldiphenylsiloxane); a solvent such as methylene chloride; a
chelating reagent such as acetic acid; a deactivating reagent such
as poly(methylhydrosiloxane); or a deactivating reagent such as
hexamethyldisilazane. After filling, the sol solution is allowed to
stay inside the capillary for 10-15 minutes. During this time, an
organic-inorganic hybrid sol-gel network evolves in the sol
solution within the confined environment of the fused-silica
capillary, and a thin layer of the evolving sol-gel stationary
phase chemically bonds to the capillary walls as a result of
condensation reaction with the silanol groups on the capillary
inner surface. After the residence time, the residual sol solution
is expelled from the capillary under helium pressure. The
sol-gel-coated capillary is further purged with helium for 1 hour
and conditioned in a GC oven using temperature programming (from
40.degree. C. to the final temperature (e.g., 300.degree. C.) at 1
C./mm). The capillary is held at the final temperature under helium
purge. The final conditioning temperatures used for the two types
of sol-gel coatings are determined by their thermal stability. The
coated capillary is then rinsed with a suitable solvent (e.g.,
methylene chloride) and purged with helium. The column is ready to
use.
[0021] The sol-gel zirconia coated capillaries can be used either
as a separation column for chromatographic (HPLC or GC) and
electrophoretic (CE or CEC) techniques or as extraction micro tubes
for sample preconcentration (online or offline) of trace analytes
for subsequent analysis by GC, HPLC, SFC, CZE or CEC. For online
sample preconcentration and HPLC analysis of trace analytes, the
prepared coated capillary is installed in the HPLC as the injection
loop for sample extraction. While the dilute sample solutions are
injected into the loop, the analyte is extracted by the stationary
phase on the surface of the capillary. The sample solution is
allowed to reside inside the loop for some time until it reaches
the equilibrium. After removing the sample matrix from the
capillary, the extracted analytes are injected into the separation
column by using a mobile phase rich in organic component (e.g.,
acetonitrile). Low parts per billion level detection limits are
achieved in HPLC-UV/vis using sol-gel zirconia coated extraction
capillary. The GC separation of a natural gas sample into its
components in less than one minute are also conducted.
[0022] The sol-gel-coated capillary is a small diameter cylindrical
vessel having a bore, and an inner surface, where the sol-gel
polymeric molecules are chemically bonded onto the inner surface.
The sol solution comprises a mixture of zirconium precursor (e.g.,
zirconium alkoxide) and an organic compound, where the solution
undergoes the following procedure: sol solution forms a thin layer,
chemically bonded to the inner surface of the capillary, leaving
behind a residual solution; The residual solution is then expelled;
the capillary is heated in an oven within a temperature range of
250.degree. C. to 300.degree. C., thereby forming a prepared column
for sample preconcentration or analytical separation.
EXPERIMENT
[0023] All CME-GC experiments are performed on a Shimadzu Model 14A
capillary GC system equipped with a flame ionization detector (FID)
and a split-splitless injector. On-line data collection and
processing are done using ChromPerfect (version 3.5) computer
software (Justice Laboratory Software, Denville, N.J.). A Fisher
Model G-560 Vortex Genie 2 system (Fisher Scientific, Pittsburgh,
Pa.) is used for thorough mixing of various sol solution
ingredients. A Microcentaur model APO 5760 microcentrifuge
(Accurate Chemical and Scientific Corp., Westbury, N.Y.) is used to
separate the sol solution from the precipitate (if any) at 13,000
rpm (15,682 g). A Barnstead Model 04741 Nanopure deionized water
system (Barnstead/Thermodyne, Dubuque, Iowa) was used to obtain
.about.16.0 M .OMEGA. water. Stainless steel mini-unions (SGE
Incorporated, Austin, Tex.) are used to connect the fused silica
capillary GC column with the microextraction capillary, also made
of fused silica. An in-house-designed liquid sample dispenser (FIG.
1) is used to facilitate gravity-fed flow of the aqueous sample
through the sol-gel microextraction capillary. The sample dispenser
of FIG. 1 has a screw cap 10 at the top and a screw cap 50 below
the column. An acrylic jacket 30 surrounds the deactivated glass
column 20, containing the sample 40. The sample 40 contains the
analytes of interest at room temperature. A polypropylene ferrule
70 connects the screw cap 50 and a plastic nut 80. A peek tubing 60
surrounds the fused silica extraction capillary 90. A homebuilt,
gas pressure-operated capillary filling/purging device (FIG. 2) is
used to rinse the fused silica capillary with solvents, to fill the
extraction capillary with the sol solution, to expel the sol
solution from the capillary at the end of sol-gel coating process,
and to purge it with helium after performing operations like
rinsing, coating, and sample extraction. The device of FIG. 2, a
fused silica extraction capillary 35 is positioned in contact with
the pressurization chamber 65, which is also in contact with the
coating solution vial 75. A threaded detachable cap 85 is threaded
onto the chamber 65. For the purging process, a gas flow inlet 15
with a flow control valve 25 is attached, in connection with the
extraction capillary 35. The gas flow outlet 55 on the opposite end
of the inlet is also attached, having a flow control valve 45.
[0024] Fused-silica capillary (320-.mu.m i.d.) with an outer
protective polyimide coating may be purchased from Polymicro
Technologies Inc. (Phoenix, Ariz.). Naphthalene and HPLC-grade
solvents (methylene chloride, methanol) may be purchased from
Fisher Scientific (Pittsburgh, Pa.). Hexamethyldisilazane (HMDS),
poly (methylhydrosiloxane) (PMHS), ketones (valerophenone,
hexanophenone, heptanophenone, and decanophenone), aldehydes
(nonylaldehyde, n-decylaldehyde, undecylic aldehyde, and
dodecanal), polycyclic aromatic hydrocarbons (PAHs) (naphthalene,
acenaphthene, ydroxyl, phenanthrene, pyrene, and
2,3-benzanthracene), may be purchased from Aldrich (Milwaukee,
Wis.). Silanol-terminated Poly (dimethyldiphenylsiloxane) copolymer
(PDMDPS) may be purchased from United Chemical Technologies, Inc.
(Bristol, Pa.).
[0025] A sol solution is used to create the coating. As seen in
Table I, the key ingredients of the sol solution used are: a
sol-gel precursor such as zirconium (IV) butoxide; a stationary
phase coating such as silanol-terminated poly copolymer
(dimethyldiphenylsiloxane); a solvent such as methylene chloride; a
chelating reagent such as acetic acid; a deactivating reagent such
as poly(methylhydrosiloxane); or a deactivating reagent such as
hexamethyldisilazane.
TABLE-US-00001 TABLE I Names, and Chemical Structure of the Coating
Solution Ingredients for Sol-Gel Capillary INGREDIENT FUNCTION
CHEMICAL STRUCTURE Zirconium (IV) butoxide Sol-gel precursor
##STR00001## Silanol-terminated poly (dimethyldiphenylsiloxane)
Coating stationary phase ##STR00002## Methylene chloride Solvent
CH.sub.2Cl.sub.2 Acetic Acid Chelating CH.sub.3COOH reagent
Poly(methylhydrosiloxane) Deactivating reagent ##STR00003##
Hexamethyldisilazane Deactivating reagent ##STR00004##
[0026] The sol solution is prepared in a clean polypropylene
centrifuge tube by dissolving the following ingredients in
methylene chloride (1 mL): 10-15 .mu.L of zirconium (IV) butoxide
(80% solution in 1-butanol), 80-100 .mu.L of silanol-terminated
poly (dimethyldiphenylsiloxane) copolymer (PDMDPS), 80 .mu.L of
poly (methylhydrosiloxane) (PMHS), 10 .mu.L of
1,1,1,3,3,3-hexamethyldisilazane (HMDS), and 2-4 .mu.L of acetic
acid. The dissolution process is aided by thorough vortexing. The
sol solution is then centrifuged at 13,000 rpm (15,682 g) to remove
the precipitates (if any). The top clear sol solution is
transferred to a clean vial and is further used in the coating
process. Using pressurized helium (50 psi) in the filling/purging
device, a hydrothermally treated fused silica capillary (200 cm) is
filled with the clear sol solution, allowing it to stay inside the
capillary for a controlled period of time (typically 30 min). After
that, the free portion of the solution is expelled from the
capillary, leaving behind a surface-bonded sol-gel coating on the
capillary inner walls. The sol-gel coating is then dried by purging
it with helium. The coated capillary is further conditioned by
temperature programming from 40.degree. C. to 150.degree. C. at
1.degree. C. /min and held at 150.degree. C. for 300 min. Following
this, the conditioning temperature is raised from 150.degree. C. to
320.degree. C. at 1.degree. C./min and held at 320.degree. C. for
120 min. The extraction capillary is further rinsed with 3 mL of
methylene chloride to clean the coated surface and conditioned
again from 40 to 320.degree. C. at 4.degree. C. /min. While
conditioning, the column is constantly purged with helium at 1
mL/min. The conditioned capillary is then cut into 10 cm long
pieces that are further used to perform capillary
microextraction.
[0027] PAHs, ketones and aldehydes are dissolved in methanol to
prepare 0.1 mg/L stock solutions in silanized glass vials. For
extraction, fresh samples with ppb level concentrations are
prepared by diluting the stock solutions with deionized water.
[0028] A gravity-fed sample dispenser for capillary microextraction
may be constructed by in-house modification of a Chromaflex AQ
column (Kontes Glass Co.) consisting of a thick-walled glass
cylinder coaxially placed inside an acrylic jacket. The inner
surface of the thick-walled glass column is deactivated by treating
with a 5% v/v solution of HMDS in methylene chloride followed by
overnight heating at 100.degree. C. The column is then cooled to
ambient temperature, thoroughly rinsed with methanol and liberal
amounts of deionized water, and dried in a helium flow. The entire
Chromaflex AQ column is subsequently reassembled.
[0029] To perform capillary microextraction, a previously
conditioned sol-gel extraction capillary (10 cm.times.320 .mu.m
i.d.) is vertically connected to the bottom end of the empty sample
dispenser. The aqueous sample (50 mL) is then placed in the
dispenser from the top, and allowed to flow through the extraction
capillary under gravity. While passing through the extraction
capillary, the analyte molecules are sorbed by the sol-gel
zirconia-PDMDPS coating residing on the inner walls of the
capillary. The extraction process is continued for 30-40 min for
equilibrium to be established. After this, the microextraction
capillary is purged with helium at 25 KPa for 1 min and connected
to the top end of a two-way mini-union connecting the
microextraction capillary with the inlet end of the GC column.
Approximately 6.5 mm of the extraction capillary resides in the
connector, and the same length of GC column from other side of the
connector. The installation of the capillary is completed by
providing a leak-free connection at the bottom end of the GC
injection port so that top 9 cm of the extraction capillary
remaines inside the injection port. The extracted analytes are then
thermally desorbed from the capillary by rapidly raising the
temperature of the injector (up to 300.degree. C. starting from
30.degree. C.). The desorption is performed over a 8.2 min period
in the splitless mode whereby the released analytes are swept over
by the carrier gas into the GC column held at 30.degree. C. during
the entire injection process, facilitating effective solute
focusing at the column inlet. The split vent remains closed
throughout the entire chromatographic run. On completion of the
injection process, the column temperature is programmed from
30.degree. C. to 320.degree. C. at rate of 20.degree. C./min.
Analyte detection is performed using a flame ionization detector
(FID) maintained at 350.degree. C.
[0030] Capillary microextraction (in-Tube SPME) uses a stationary
phase coating on the inner surface of a capillary to overcome a
number of deficiencies inherent in conventional fiber-based SPME
such as coating scraping, fiber breakage, and possible sample
contamination. In this format, the stationary phase coating is
protected by the fused silica tubing against mechanical damage. The
in-tube format also provides flexibility and convenience to the
microextraction process since the protective polyamide coating on
the outer surface of fused silica capillary remains intact. Inner
surface-coated capillaries provide a simple way to perform
extraction in conjunction with a gravity-fed sample dispenser (FIG.
1), and thus avoids typical drawbacks of fiber-based SPME,
including the need for sample agitation during extraction and
sample loss and contamination problems associated with this.
[0031] In the present application, a sol solution is used to create
the sol-gel zirconia-PDMDPS coating. Zirconium (IV) butoxide (80%
solution in 1-butanol) is used as a sol-gel precursor. It serves as
a source for the inorganic component of the sol-gel
organic-inorganic hybrid coating, and delivers it through
hydrolytic polycondensation reactions. It also provides active
hydroxyl groups to facilitate its chemical bonding to other
sol-gel-active ingredients of the sol solution within the
capillary, as well as to the silanol groups of the fused silica
surface.
[0032] A major obstacle to preparing zirconia-based sol-gel
materials using zirconium alkoxides (e.g., zirconium butoxide) is
the rapid rate of sol-gel reactions undergone by zirconium
alkoxides. Even if the solution of zirconium alkoxide is stirred
vigorously, the rate of these reactions is so high that large
agglomerated zirconia particles precipitate out immediately when
water is added. Such fast precipitation makes the reproducible
preparation of zirconia sol-gel materials difficult to achieve. The
fast precipitation problem may be addressed by dissolving zirconium
propoxide in a non-polar dry solvent like cyclohexane. The
hydrolysis is performed by exposure of the coatings prepared from
the solution to atmospheric moisture. The hydrolysis rate of
zirconium alkoxide can also be controlled by chelating with
ligand-exchange reagents like acetic acid and valeric acid. The
addition of acetic acid modifies the structure of zirconium
alkoxide by replacing the alkyl group by acetyl group, which slow
down the reactivity of alkoxide toward water. .beta.-diketones such
as acetylacetonate and acetoacetate may also be used as chelating
agents leading to the segregation of the .beta.-diketone ligands on
the surface of the growing particle, with subsequent particle
growth restricted to those sites not occupied by the chelating
ligands. Triethanolamine and 1,5-diaminopentane have also been
investigated as chelating agents for zirconia sol-gel
reactions.
[0033] In the present application, the hydrolysis rate of zirconium
butoxide was controlled by glacial acetic acid, which served as a
chelating agent as well as a source of water released slowly
through the esterification with 1-butanol. Silanol-terminated poly
(dimethyldiphenylsiloxane) copolymer is used as a sol-gel active
organic ligand, which is chemically incorporated into the sol-gel
network through polycondensation reactions with hydrolysis products
of the zirconium butoxide precursor. This advantageous chemical
incorporation of an organic component into the sol-gel network
leads to the formation of an organic-inorganic hybrid material
system that can be conveniently used for in situ creation of
surface coating on a substrate like the inner walls of the fused
silica capillary. The organic groups also help to reduce the
shrinkage and cracking of the sol-gel coating. Furthermore, sol-gel
process can be used to control the porosity and thickness of the
coating and to improve its mechanical properties. The poly
(methylhydrosiloxane) (PMHS) and 1,1,1,3,3,3-hexamethyldisilazane
(HMDS) serve as deactivating reagents to perform derivatization
reactions mainly during thermal conditioning of the sol-gel
stationary phase following the coating procedure.
[0034] One of the most important undertakings in CME is the
creation of a surface-bonded stable stationary phase coating on the
inner walls of a fused silica capillary. The sol-gel
Zirconia-PDMDPS coating presented here is generated via two major
reactions: (1) hydrolysis of a sol-gel precursor, zirconium (IV)
butoxide, and (2) polycondensation of the precursor and it
hydrolysis products. Condensation of these reactive species between
themselves and with the other sol-gel-active ingredients in the
coating solution, including silanol-terminated PDMDPS, lead to the
formation of an organic-inorganic hybrid polymer that are
ultimately chemically bonded to the capillary inner walls through
condensation with the silanol groups residing on the capillary
inner surface.
[0035] The hydrolysis of the zirconium (IV) butoxide precursor is
represented by the following equation showing the hydrolysis of
zirconium (TV) butoxide precursor.
##STR00005##
[0036] Hydrolytic polycondensation reactions for sol-gel-active
reagents are well established in sol-gel chemistry, and constitute
the fundamental mechanism in sol-gel synthesis. The condensation
between sol-gel-active zirconia and silicon compounds is also well
documented. One of the possible routes of polycondensation
reactions is represented in the following reaction showing
condensation reactions leading to the formation of zirconia based
hybrid organic-inorganic material with chemically incorporated
poly(dimethyldiphenylsiloxane).
##STR00006##
[0037] The silanol groups on the inner surface of the fused silica
capillary can also undergo condensation reaction forming a chemical
anchor between the fused silica capillary surface and the sol-gel
polymeric network evolving in the close vicinity of the surface.
This is illustrated in the following reaction showing chemical
anchoring of sol-gel zirconia-PDMDPS coating onto the fused silica
capillary inner walls via condensation reactions.
##STR00007##
[0038] Strong adsorptive interactions, typical of zirconia surface
with polar solutes, can be moderated by surface derivatization and
shielding. Like silica-based sol-gel coatings, the surface hydroxyl
groups of sol-gel zirconia coating can be derivatized using
reactive silicon hydride compounds such as alkyl hydrosilanes and
hexamethyldisilazane (HMDS). In this work, a mixture of
polymethylhydrosiloxane (PMHS) and hexamethyldisilazane (HMDS) was
used for this purpose: the underlying chemical reactions are
schematically represented in the following reaction showing
deactivation and shielding of sol-gel zirconia-PDMDPS coated
surface using PMHS and HMDS.
##STR00008##
[0039] Such a surface bonded sol-gel polymeric stationary phase can
be created by simply filling a fused silica capillary with the
properly designed sol solution, and allowing the solution to stay
inside the capillary for a short period (e.g., 10-30 min), and
subsequently expelling the liquid content of the capillary under an
inert gas pressure. Sol-gel zirconia-PDMDPS-coated capillaries
allow the extraction of analytes belonging to various chemical
classes.
[0040] Experimental data illustrating CME-GC of polycyclic aromatic
hydrocarbons (PAHs) using a sol-gel zirconia-PDMDPS coated
capillary is shown in FIG. 3. Extraction parameters are: 10
cm.times.0.32 mm i.d microextraction capillary; extraction time, 30
min (gravity fed at room temperature). Other conditions: 10
m.times.0.25 mm i.d. sol-gel PDMS GC column; splitless desorption;
injector temperature rose from 30-300.degree. C.: column
temperature program from 30 to 300.degree. C. at rate of 20.degree.
C./min; helium carrier gas: FID 350.degree. C. Peaks: (1)
Naphthalene (2) Acenaphthene (3) Fluorene (4) Phenanthrene (5)
Pyrene (6) 2,3-Benzanthracene.
[0041] CME-GC experiments are performed on an aqueous sample with
low ppb level analyte concentrations. Experimental data presented
in Table II shows that CME-GC with a sol-gel zirconia-PDMDPS
coating provides excellent run-to-run repeatability in solute peak
areas (3-7%) and the used GC column provided excellent
repeatability in retention times (less than 0.2%).
TABLE-US-00002 TABLE II Peak Area and Retention Time Repeatability
Data for ppb Level Concentrations of PAHs, Aldehydes, and Ketones
Obtained in Four Replicate Measurements by CME-GC Using Sol-Gel
Zirconia-PDMDPS Peak area repeatability t.sub.R (n = 4) Peak area
Repeatability t.sub.R Analyte mean peak repeatability (n = 4)
Repeatability Detection Chemical Analyte area (aribitary (n = 4)
mean t.sub.R (n = 4) limit Class Name unit) RSD (%) (min) RSD (%)
ng/mL PAHs Naphthalene 11692.42 7.25 15.32 0.001 0.57 Acenaphthene
23560.38 4.58 17.12 0.001 0.16 Fluorene 30970.30 2.45 17.73 0.001
0.09 Phenanthrene 09010.92 3.46 18.76 0.100 0.06 Pyrene 55005.40
2.78 20.22 0.220 0.03 2,3- 22378.12 5.42 21.44 0.140 0.05
Benzanthracene Aldehyde 1-Nonanal 15910.25 1.29 15.27 0.030 0.33
1-Decanal 22908.98 5.45 15.94 0.160 0.08 Undecanal 30413.15 5.08
16.61 0.100 0.10 Dodecanal 32182.70 3.72 17.22 0.110 0.05 Ketones
Valerophenone 03712.88 3.10 16.79 0.060 0.92 Hexanophenone 13780.88
1.24 17.40 0.070 0.33 Heptanophenone 47398.87 1.24 18.19 0.270 0.08
Decanophenone 83156.67 2.20 19.44 0.110 0.02 Trans-Chalcone
06546.25 5.57 19.82 0.030 0.57
[0042] FIG. 4 illustrates a gas chromatogram of several free
aldehydes extracted from an aqueous sample using a sol-gel
zirconia-PDMDPS coated capillary. The extraction parameters are: 10
cm.times.0.32 mm i.d microextraction capillary; extraction time, 40
min (gravity fed at room temperature). Other conditions: 10
m.times.0.25 mm i.d. sol-gel PDMS column; splitless desorption;
injector temperature rose from 30-300.degree. C.: column
temperature program from 30 to 300.degree. C. at rate of 20.degree.
C./min; helium carrier gas: FID 350.degree. C. Peaks: (1)
Nonylaldehyde (2) n-decylaldehyde (3) Undecylic aldehyde (4)
Dodacanal. Here, the concentrations of the used aldehydes are in
the range of 80-500 ppb. Aldehydes are known to have toxic and
carcinogenic properties, and therefore, their presence in the
environment is of great concern because of the adverse effects
these compounds have on public health and vegetation. Aldehydes are
major disinfection by-products formed as a result of chemical
reaction between disinfectant (ozone or chlorine) and organic
compounds in drinking water. Accurate analysis of trace-level
contents of aldehyde in the environment and in drinking water is
important due to their carcinogenic activities and other adverse
health effects. Aldehydes are polar compounds, and are often
derivatized for GC analysis to avoid undesirable adsorption that
causes peak tailing. Sol-gel zirconia-PDMDPS coated capillary
provided highly efficient extraction of the aldehydes, and the used
sol-gel GC column provided excellent peak shapes demonstrating high
quality of deactivation in the used sol-gel GC column. This is also
indicative of effective focusing of the analytes at the column
inlet after their desorption, as well as the excellent performance
of the used sol-gel PDMS GC column. For the Aldehydes, sol-gel
CME-GC with the zirconia-PDMDPS coated capillary provides excellent
peak area repeatability with RSD value (less than 5%) and retention
time (less than 0.16%).
[0043] FIG. 5 shows a gas chromatogram illustrating CME-GC analysis
of several ketones extracted from an aqueous sample. The extraction
parameters are: 10 cm.times.0.32 mm i.d microextraction capillary;
extraction time, 40 min (gravity fed at room temperature). Other
conditions: 10 m.times.0.25 mm i.d. sol-gel PDMS GC column;
splitless desorption; injector temperature rose from 30-300.degree.
C.: column temperature program from 30 to 300.degree. C. at rate of
20.degree. C./min; helium calTier gas: FID 350.degree. C. Peaks:
(1) Valerophenone (2) Hexanophenone (3) Heptanophenone (4)
Benzophenone (5) Trans-Chalcone (6) Decanophenone. Like aldehydes,
there is no need for derivatization of the ketones, either during
extraction or GC separation. Sharp and symmetrical GC peaks,
evident from the chromatogram, show the effectiveness of the used
CME-GC system, as well as the practical utility of the mini-union
metal connector providing leak free connection with negligible dead
volume between the extraction capillary and the GC column. It also
implies effective focusing of the analytes at the column inlet
after their desorption. Excellent reproducibility is achieved in
CME-GC of ketones using sol-gel zirconia-PDMDPS coated capillary as
shown in Table 2. The peak area RSD % values for ketones are less
than 5.6% and their retention time repeatability on used sol-gel
PDMS column is characterized by RSD values of less than 0.27%.
[0044] FIG. 6 shows a gas chromatogram illustrating CME-GC analysis
of an aqueous sample containing different classes of compounds
including PAHs, aldehydes and ketones, and indicates that the
sol-gel zirconia-PDMDPS extraction capillary allowed simultaneous
extraction of polar and nonpolar compounds present in the aqueous
sample, and shows the advantage over conventional SPME stationary
phase that often do not allows such effective extraction of both
polar and nonpolar analyte from the same sample. The extraction
parameters are: 10 cm.times.0.32 mm i.d microextraction capillary;
extraction time, 40 min (gravity fed at room temperature). Other
conditions: 10 m.times.0.25 mm i.d. sol-gel PDMS column; splitless
desorption; injector temperature rose from 30-300.degree. C.:
column temperature program from 30 to 300.degree. C. at rate of
20.degree. C./min; helium carrier gas: FID 350.degree. C. Peaks 1)
Napnthalene (2) n-Decylaldehyde (3) Undecylic aldehyde (4)
Valerophenone (5) Dodacanal (6) Hexanophenon (7) Fluorene (8)
Heptanophenone (9) Phenanthrene (10) Pyrene (11) 2,3
Benzanthracene.
[0045] In capillary microextraction technique the amount of analyte
extracted into the stationary phase depends not only on the
polarity and thickness of the stationary phase, but also on the
extraction time. FIG. 7 illustrates the extraction profile of
ydroxyl (a nonpolar analyte), heptanophenone and undecylic aldehyde
(both are moderately polar analytes) on a sol-gel
zirconia-PDMDPS-coated microextraction capillary. The extraction
parameters are: 10 cm.times.0.32 mm i.d microextraction capillary;
wide rang of extraction timeOther conditions: 10 m.times.0.25 mm
i.d. sol-gel PDMS GC column; splitless desorption; injector
temperature from 30-300.degree. C.: column temperature program from
30 to 300.degree. C. at rate of 20.degree. C./min; helium carrier
gas: FID 350.degree. C. The extractions are carried out using
aqueous samples of individual analytes. The extraction equilibrium
for ydroxyl reached in 10 min, which is much shorter than
extraction equilibrium time for heptanophenone and undecylic
aldehyde (both approximately 30 min). This is because ydroxyl
exhibits hydrophobic behavior that has higher affinity toward the
nonpolar PDMDPS-based sol-gel zirconia stationary phase coating
than toward water. On the other hand, heptanophenone and undecylic
aldehyde, being more polar and hydrophilic than ydroxyl showed a
slower extraction by the stationary phase coating.Sol-gel
zirconia-PDMDPS stationary phase shows high pH stability, and
retains excellent performance after rinsing with 0.1 M NaOH (pH
.apprxeq.13) for 24 h. Chromatograms in FIG. 8a and 8b show CME-GC
analysis of five PAHs before (FIG. 8a) and after (FIG. 8b)
zirconia-PDMDPS extraction capillary is rinsed with 0.1 M NaOH
solution. The extraction parameters are: 10 cm.times.0.32 mm i.d
microextraction capillary; extraction time, 30 min (gravity fed at
room temperature). Other conditions: 10 m.times.0.25 mm i.d.
sol-gel PDMS GC column; splitless desorption; injector temperature
rose from 30-300.degree. C.: column temperature program from 30 to
280.degree. C. at rate of 20.degree. C./min then from 280.degree.
C. to 300.degree. C. at rate of 2.degree. C./min; helium carrier
gas: FID 350.degree. C. Peaks: (1) Naphthalene (2) Acenaphthene (3)
Fluorene (4) Phenanthrene (5) Pyrene. The extraction performance of
the capillary for PAHs remain practically unchanged after rinsing
with NaOH as it can be seen in Table III.
TABLE-US-00003 TABLE III Peak Area and Retention Time Repeatability
Data for ppb Level Concentrations of PAHs before and after
extraction capillary treated with 0.1 M NaOH Peak area Peak area
repeatability after repeatability after rinsing with 0.1 M rinsing
with 0.1 M Relative change NaOH NaOH in peak area mean peak area
A.sub.1 mean peak area A.sub.2 |(A.sub.2-A.sub.1)/A.sub.1| .times.
100 Analyte Name (aribitary unit) (aribitary unit) (%) Naphthalene
43165.9 43648.6 1.12 Acenaphthene 68272.7 65207.3 4.49 Fluorene
54598.0 50979.7 6.63 Phenanthrene 78111.5 76608.4 2.00
[0046] Sol-gel zirconia-based hybrid organic-inorganic stationary
phase coating is developed for use in microextraction. Principles
of sol-gel chemistry were employed to chemically bind a
ydroxyl-terminated silicone polymer (polydimethyldiphenylsiloxane,
PDMDPS) to a sol gel zirconia network in the course of its
evolution from highly reactive alkoxide precursor undergoing
controlled hydrolytic polycondensations reactions. For the first
time, sol-gel zirconia-PDMDPS coating is employed in capillary
microextraction. The newly developed sol-gel zirconia-PDMDPS
coating demonstrated exceptional pH stability and its extraction
characteristics remained practically unchanged after rinsing with a
0.1 M solution of NaOH (pH=13) for 24 h. Solventless extraction of
analytes may also be carried out by passing the aqueous sample
through the sol-gel extraction capillary for approximately 30 min.
The extracted analytes are efficiently transferred to a GC column
via thermal desorption, and the desorbed analytes are separated by
temperature programmed GC. Efficient CME-GC analyses of analytes
belonging to various chemical classes are achieved using so-gel
Zirconia-PDMDPS capillaries. Parts per trillion (ppt) level
detection sensitivities are achieved for polar and nonpolar
analytes. Sol-gel zirconia-PDMDPS coated microextraction capillary
shows remarkable run-to-run and repeatability and produces peak
area RSD values in the range of 1.24-7.25%.
[0047] It will be seen that the objects set forth above, and those
made apparent from the foregoing description, are efficiently
attained and since certain changes may be made in the above
construction without departing from the scope of the invention, it
is intended that all matters contained in the foregoing description
or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
[0048] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the
invention herein described, and all statements of the scope of the
invention which, as a matter of language, might be said to fall
therebetween.
* * * * *