US20090250349A1

US20090250349A1 - Tube Structure with Sol-Gel Zirconia Coating

Info

Publication number: US20090250349A1
Application number: US12/463,156
Authority: US
Inventors: Abdul Malik; Khalid Alhooshani
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-11-08
Filing date: 2009-05-08
Publication date: 2009-10-08
Also published as: US7407568B1; US8241476B1; US20070095736A1

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.

Description

CROSS-REFERENCE TO RELATED APPLICATION

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

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.
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.
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.
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 C₁₈moieties 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° 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.
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.
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

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.
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

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:

FIG. 1 is the gravity feed extraction system for capillary microextraction.

FIG. 2 is the homebuilt capillary filling/purging device.

FIG. 3 is a CME-GC analysis of PAHs using a sol-gel zirconia-PDMDPS coated capillary.

FIG. 4 is a CME-GC analysis of Aldehydesusing a sol-gel zirconia-PDMDPS coated capillary.

FIG. 5 is a CME-GC analysis of ketonesusing a sol-gel zirconia-PDMDPS coated capillary.

FIG. 6 is a CME-GC analysis of mixture of PAHs, aldehydes and ketones using a sol-gel zirconia-PDMDPS coated capillary.

FIG. 7 is extraction kinetics of aqueous undecylic aldehyde, heptanophenone, and ydroxyl on a sol-gel zirconia-PDMDPS microextraction coated capillary.

FIG. 8 a is CME-GC analysis of PAHs using a sol-gel zirconia-PDMDPS coated capillary before rinsing with NaOH.

FIG. 8 b is CME-GC analysis of PAHs using a sol-gel zirconia-PDMDPS coated capillary rinsed with NaOH for 24 hours.

DETAILED DESCRIPTION

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° C. to the final temperature (e.g., 300° 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.
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.
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° C. to 300° C., thereby forming a prepared column for sample preconcentration or analytical separation.

EXPERIMENT

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 ˜16.0 M Ω 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.
Fused-silica capillary (320-μm 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.).
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 I

Names, and Chemical Structure of the Coating Solution Ingredients for Sol-Gel Capillary

INGREDIENT	FUNCTION	CHEMICAL STRUCTURE

Zirconium (IV) butoxide	Sol-gel precursor

Silanol-terminated poly (dimethyldiphenylsiloxane)	Coating stationary phase

Methylene chloride	Solvent	CH₂Cl₂
Acetic Acid	Chelating	CH₃COOH
	reagent

Poly(methylhydrosiloxane)	Deactivating reagent

Hexamethyldisilazane	Deactivating reagent

The sol solution is prepared in a clean polypropylene centrifuge tube by dissolving the following ingredients in methylene chloride (1 mL): 10-15 μL of zirconium (IV) butoxide (80% solution in 1-butanol), 80-100 μL of silanol-terminated poly (dimethyldiphenylsiloxane) copolymer (PDMDPS), 80 μL of poly (methylhydrosiloxane) (PMHS), 10 μL of 1,1,1,3,3,3-hexamethyldisilazane (HMDS), and 2-4 μL 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° C. to 150° C. at 1° C. /min and held at 150° C. for 300 min. Following this, the conditioning temperature is raised from 150° C. to 320° C. at 1° C./min and held at 320° 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° C. at 4° 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.
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.
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° 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.
To perform capillary microextraction, a previously conditioned sol-gel extraction capillary (10 cm×320 μm 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° C. starting from 30° 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° 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° C. to 320° C. at rate of 20° C./min. Analyte detection is performed using a flame ionization detector (FID) maintained at 350° C.
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.
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.
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. β-diketones such as acetylacetonate and acetoacetate may also be used as chelating agents leading to the segregation of the β-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.
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.
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.
The hydrolysis of the zirconium (IV) butoxide precursor is represented by the following equation showing the hydrolysis of zirconium (TV) butoxide precursor.
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).
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.
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.
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.
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×0.32 mm i.d microextraction capillary; extraction time, 30 min (gravity fed at room temperature). Other conditions: 10 m×0.25 mm i.d. sol-gel PDMS GC column; splitless desorption; injector temperature rose from 30-300° C.: column temperature program from 30 to 300° C. at rate of 20° C./min; helium carrier gas: FID 350° C. Peaks: (1) Naphthalene (2) Acenaphthene (3) Fluorene (4) Phenanthrene (5) Pyrene (6) 2,3-Benzanthracene.
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 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_R
		(n = 4)	Peak area	Repeatability	t_R
Analyte		mean peak	repeatability	(n = 4)	Repeatability	Detection
Chemical	Analyte	area (aribitary	(n = 4)	mean t_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

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×0.32 mm i.d microextraction capillary; extraction time, 40 min (gravity fed at room temperature). Other conditions: 10 m×0.25 mm i.d. sol-gel PDMS column; splitless desorption; injector temperature rose from 30-300° C.: column temperature program from 30 to 300° C. at rate of 20° C./min; helium carrier gas: FID 350° 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%).
FIG. 5 shows a gas chromatogram illustrating CME-GC analysis of several ketones extracted from an aqueous sample. The extraction parameters are: 10 cm×0.32 mm i.d microextraction capillary; extraction time, 40 min (gravity fed at room temperature). Other conditions: 10 m×0.25 mm i.d. sol-gel PDMS GC column; splitless desorption; injector temperature rose from 30-300° C.: column temperature program from 30 to 300° C. at rate of 20° C./min; helium calTier gas: FID 350° 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%.
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×0.32 mm i.d microextraction capillary; extraction time, 40 min (gravity fed at room temperature). Other conditions: 10 m×0.25 mm i.d. sol-gel PDMS column; splitless desorption; injector temperature rose from 30-300° C.: column temperature program from 30 to 300° C. at rate of 20° C./min; helium carrier gas: FID 350° 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.
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×0.32 mm i.d microextraction capillary; wide rang of extraction timeOther conditions: 10 m×0.25 mm i.d. sol-gel PDMS GC column; splitless desorption; injector temperature from 30-300° C.: column temperature program from 30 to 300° C. at rate of 20° C./min; helium carrier gas: FID 350° 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 ≈13) for 24 h. Chromatograms in FIG. 8 a and 8 b show CME-GC analysis of five PAHs before (FIG. 8 a) and after (FIG. 8 b) zirconia-PDMDPS extraction capillary is rinsed with 0.1 M NaOH solution. The extraction parameters are: 10 cm×0.32 mm i.d microextraction capillary; extraction time, 30 min (gravity fed at room temperature). Other conditions: 10 m×0.25 mm i.d. sol-gel PDMS GC column; splitless desorption; injector temperature rose from 30-300° C.: column temperature program from 30 to 280° C. at rate of 20° C./min then from 280° C. to 300° C. at rate of 2° C./min; helium carrier gas: FID 350° 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 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 A₁	mean peak area A₂	\|(A₂-A₁)/A₁\| × 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

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%.
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.
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.

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° C. to 150° C. at 1° C. per minute and maintaining the temperature at 150° C. for 300 minutes, a second heating step comprising heating the capillary from 150° C. to 320° C. at 1° C. per minute and maintaining the temperature at 320° C. for 120 minutes; and a third heating step comprising heating the capillary from 40° C. to 320° C. at 4° 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° C. to 300° 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.