Sol–Gel Approach to in Situ Creation of High PH-resistant Surface-bonded o

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Journal of Chromatography A, 1062 (2005) 1–14 Sol–gel approach to in situ creation of high pH-resistant surface-bonded organic–inorganic hybrid zirconia coating for capillary microextraction (in-tube SPME) Khalid Alhooshani, Tae-Young Kim, Abuzar Kabir, Abdul Malik Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, SCA 400, Tampa, FL 33620-5250, USA Received 3 June 2004; received in revised form 25 October 2004; accepted 29 October 2004 Abstract A novel zirconia-based hybrid organic–inorganic sol–gel coating was developed for capillary microextraction (CME) (in-tube SPME). High degree of chemical inertness inherent in zirconia makes it very difficult to covalently bind a suitable organic ligand to its surface. In the present work, this problem was addressed from a sol–gel chemistry point of view. Principles of sol–gel chemistry were employed to chemically bind a hydroxy-terminated silicone polymer (polydimethyldiphenylsiloxane, PDMDPS) to a sol–gel zirconia network in the course of its evolution from a highly reactive alkoxide precursor undergoing controlled hydrolytic polycondensation reactions. A fused silica capillary was filled with a properly designed sol solution to allow for the sol–gel reactions to take place within the capillary for a predetermined period of time (typically 15–30 min). In the course of this process, a layer of the evolving hybrid organic–inorganic sol–gel polymer got chemically anchored to the silanol groups on the capillary inner walls via condensation reaction. At the end of this in-capillary residence time, the unbonded part of the sol solution was expelled from the capillary under helium pressure, leaving behind a chemically bonded sol–gel zirconia-PDMDPS coating on the inner walls. Polycyclic aromatic hydrocarbons, ketones, and aldehydes were efficiently extracted and preconcentrated from dilute aqueous samples using sol–gel zirconia-PDMDPS coated capillaries followed by thermal desorption and GC analysis of the extracted solutes. The newly developed sol–gel hybrid zirconia coatings demonstrated excellent pH stability, and retained the extraction characteristics intact even after continuous rinsing with a 0.1 M NaOH solution for 24 h. To our knowledge, this is the first report on the use of a sol–gel zirconia-based hybrid organic–inorganic coating as an extraction medium in solid phase microextraction (SPME). © 2004 Elsevier B.V. All rights reserved. Keywords: Capillary microextraction; In-tube SPME; Sol–gel extraction media; Sol–gel technology; Sol–gel zirconia poly(dimethyldiphenylsiloxane) coating; pH stability; Sample preconcentration; Gas chromatography; Hyphenated techniques; Polycyclic aromatic hydrocarbons; Aldehydes; Ketones 1. Introduction Solid phase microextraction (SPME) was developed in 1989 by Belardi and Pawliszyn [1] to facilitate rapid sample preparation for both laboratory and field analyses. It provided a simple and efficient solvent-free method for the extraction and preconcentration of analytes from various sample matri- ces. Corresponding author. Tel.: +1 813 974 9688; fax: +1 813 974 3203. E-mail address: [email protected] (A. Malik). In SPME, a sorptive coating (either on the outer surface of a fused silica fiber or on the inner surface of a fused sil- ica capillary) serves as the extraction medium in which the analytes get preferentially sorbed and preconcentrated. Poly- meric surface coatings are predominantly used in conven- tional fiber-based SPME [1–4] as well as in the more recently materialized in-tube SPME [5–8] also referred to as capil- lary microextraction (CME) [9]. A number of new polymeric coatings have recently been developed [10]. Besides poly- meric coatings, SPME fibers have also been prepared by us- ing nonpolymeric materials [11] or by gluing reversed-phase high-performance liquid chromatography (HPLC) particles 0021-9673/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2004.10.103

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  • Journal of Chromatography A, 1062 (2005) 114

    Solgel approach to in situ creation of high porgan g fo

    E)uzar

    er Aven

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    Abstract

    A novel zdegree of chwork, this pra hydroxy-tefrom a highwith a prope(typically 15to the silanoof the sol socoating on tdilute aqueosolutes. Theintact even azirconia-bas 2004 Else

    Keywords: CapH stability; S

    1. Introdu

    Solid ph1989 by Bepreparationa simple anand preconces.

    CorrespoE-mail a

    0021-9673/$doi:10.1016/jirconia-based hybrid organicinorganic solgel coating was developed for capillary microextraction (CME) (in-tube SPME). Highemical inertness inherent in zirconia makes it very difficult to covalently bind a suitable organic ligand to its surface. In the presentoblem was addressed from a solgel chemistry point of view. Principles of solgel chemistry were employed to chemically bindrminated silicone polymer (polydimethyldiphenylsiloxane, PDMDPS) to a solgel zirconia network in the course of its evolutionly reactive alkoxide precursor undergoing controlled hydrolytic polycondensation reactions. A fused silica capillary was filledrly designed sol solution to allow for the solgel reactions to take place within the capillary for a predetermined period of time30 min). In the course of this process, a layer of the evolving hybrid organicinorganic solgel polymer got chemically anchoredl groups on the capillary inner walls via condensation reaction. At the end of this in-capillary residence time, the unbonded partlution was expelled from the capillary under helium pressure, leaving behind a chemically bonded solgel zirconia-PDMDPShe inner walls. Polycyclic aromatic hydrocarbons, ketones, and aldehydes were efficiently extracted and preconcentrated fromus samples using solgel zirconia-PDMDPS coated capillaries followed by thermal desorption and GC analysis of the extractednewly developed solgel hybrid zirconia coatings demonstrated excellent pH stability, and retained the extraction characteristicsfter continuous rinsing with a 0.1 M NaOH solution for 24 h. To our knowledge, this is the first report on the use of a solgeled hybrid organicinorganic coating as an extraction medium in solid phase microextraction (SPME).vier B.V. All rights reserved.

    pillary microextraction; In-tube SPME; Solgel extraction media; Solgel technology; Solgel zirconia poly(dimethyldiphenylsiloxane) coating;ample preconcentration; Gas chromatography; Hyphenated techniques; Polycyclic aromatic hydrocarbons; Aldehydes; Ketones

    ction

    ase microextraction (SPME) was developed inlardi and Pawliszyn [1] to facilitate rapid samplefor both laboratory and field analyses. It providedd efficient solvent-free method for the extractioncentration of analytes from various sample matri-

    nding author. Tel.: +1 813 974 9688; fax: +1 813 974 3203.ddress: [email protected] (A. Malik).

    In SPME, a sorptive coating (either on the outer surfaceof a fused silica fiber or on the inner surface of a fused sil-ica capillary) serves as the extraction medium in which theanalytes get preferentially sorbed and preconcentrated. Poly-meric surface coatings are predominantly used in conven-tional fiber-based SPME [14] as well as in the more recentlymaterialized in-tube SPME [58] also referred to as capil-lary microextraction (CME) [9]. A number of new polymericcoatings have recently been developed [10]. Besides poly-meric coatings, SPME fibers have also been prepared by us-ing nonpolymeric materials [11] or by gluing reversed-phasehigh-performance liquid chromatography (HPLC) particles

    see front matter 2004 Elsevier B.V. All rights reserved..chroma.2004.10.103icinorganic hybrid zirconia coatin(in-tube SPM

    Khalid Alhooshani, Tae-Young Kim, AbDepartment of Chemistry, University of South Florida, 4202 East Fowl

    Received 3 June 2004; received in revised form 25 OctoH-resistant surface-bondedr capillary microextraction

    Kabir, Abdul Malik

    ue, SCA 400, Tampa, FL 33620-5250, USA

    4; accepted 29 October 2004

  • 2 K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114

    onto SPME fiber surface [12]. The sorbent coating plays afundamentally important role in the SPME analysis, and fur-ther development and growth of SPME will greatly dependon new breand coating

    Solgelsynthesis omild thermroom tempfacilitatesoperationallaboratoryand/or contsilica capimechanismcoating toappropriatebonding,thermal andventional cto create silmetal oxidprovides anto achieve eseparations

    Solgelable sorptiveither pureof this unihybrid solin the fieldtion. In thestationary pcoatings [1and co-wortion of a thmoieties onas open tubliquid chrotechnologytubular liquMalik andfor capillarphase micralso got innovel sorbesolid-phasefibers, solmance by[24] and ssolgel coabetween thwith the cosolgel SPMsensitivity,time [26].

    reported by Malik and co-workers [9]. In this format, alsoknown to as in-tube SPME, sample extraction was accom-plished using a solgel coating created on the inner surface

    used se solredomrial pcterisbilitiecominnarro

    , silicasorptidissoroces

    c pHolyticaa widin coologieell knal canionedrconial oxideinsolualso s

    eraturlent co othused

    brane-tensiv

    cles annarytly apfied fu[444

    rconiace-bone appof vie

    e highformezirconfor zirossiblers to

    lentlyreparael soride, a

    inatedd to thed viaolyticakthroughs in the areas of sorbent developmenttechnology [13].

    chemistry offers an effective methodology for thef macromolecular materials under extraordinarilyal conditions (typically at room temperature). Theerature operation, inherent in solgel chemistry,the material synthesis process by easing the

    requirements on equipment specification andsafety. This greatly simplifies the job to carry outrol solgel reactions within small-diameter fused

    llaries. The solgel approach provides a facileto chemically bind an in situ created solgel

    the inner walls of the capillary made out of ansolgel-active material. Thanks to this chemical

    solgel coatings possess significantly highersolvent stabilities [14] compared with their con-

    ounterparts. The solgel approach can be appliedica-based as well as the newly emerging transitione-based sorbents. Furthermore, solgel chemistry

    opportunity to create advanced material systemsnhanced performance and selectivity in analyticaland sample preconcentration [10,15].

    organicinorganic hybrid materials provide desir-e properties that are difficult to achieve by using

    ly organic or purely inorganic materials. Becauseque opportunity to achieve enhanced selectivity,gel materials have created a great deal of interestof microcolumn separations and sample prepara-recent past, silica-based organicinorganic hybridhases have been developed in the form of surface618] and monolithic beds [19]. In 1993, Dabriokers [20] developed a procedure for the prepara-in layer of silica gel with chemically bonded C18the inner walls of fused-silica capillaries for use

    ular columns in reversed-phase high-performancematography. Colon and Guo [21] used solgelto prepare stationary phase coatings for open-id chromatography and electrochromatography.co-workers introduced solgel coated columnsy GC [22] and solgel coated fibers for solid-oextraction [13,23]. Subsequently, other groupsvolved in solgel research aiming at developingnts for solid-phase microextraction [2428] andextraction [29,30]. Compared with conventional

    gel SPME fibers demonstrated superior perfor-exhibiting high thermal stability (up to 380 C)olvent stability [25]. This enhanced stability ofted fibers is attributed to the chemical bonding

    e solgel coating and the fiber surface. Comparednventionally prepared fibers, in many instances,

    E fibers showed better selectivity and extraction[26] less extraction time, [27] and extended life-Recently, solgel capillary microextraction was

    of a fTh

    are pmatecharapossishortis thetionstheirsilication pacidihydrwitharea

    technare w

    logicment

    Zimetacallyconiatempexcelare twbeingmem

    Expartistatiorecen

    modi(CE)of zisurfa

    Wpointto thbeentics,sors

    be pcurso

    cova

    the psolgbutoxtermliganplishhydrilica capillary.gel microextraction sorbents reported to dateinantly silica-based. In spite of many attractiveroperties (e.g., mechanical strength, surfacetics, catalytic inertness, surface derivatizations, etc.), silica-based materials have some inherentgs. The main drawback of silica-based sorbentsw range of pH stability. Under extreme pH condi--based materials become chemically unstable, andve properties may be compromised. For example,lves under alkaline conditions, and their dissolu-s starts at a pH value of about 8 [31]. Under highlyconditions, silica-based bonded phases becomelly unstable [32]. Therefore, developing sorbentse range of pH stability is an important researchntemporary separation and sample preparations. Transition metal oxides (zirconia, titania, etc.)own for their pH stability [33], and appear to bedidates for exploration to overcome the above-drawbacks inherent in silica-based materials.possesses much better alkali resistance than others, such as alumina, silica, and titania. It is practi-ble within a wide pH range (114) [3639]. Zir-hows outstanding resistance to dissolution at highes [40,41]. Besides the extraordinary pH stability,hemical inertness and high mechanical strengther attractive features that add value to zirconia foras a support material in chromatography [34] andbased separations [35].e research work has been done on zirconiad their surface modifications for use as HPLC

    phases [42,43]. A number of reports have alsopeared in the literature on the use of zirconia-sed silica capillaries in capillary electrophoresis8]. However, the excessive chemical inertnessparticles remains a difficult hurdle to creatingded stationary phases.

    roached this problem from a solgel chemistryw. We took into consideration the fact that contraryinertness of zirconia particles that have already

    d and attained highly stable structural characteris-ium alkoxides are highly reactive solgel precur-conia. By using appropriate conditions, it should

    to utilize the reactivity of such zirconia pre-create organicinorganic zirconia materials withbonded organic ligands. In this paper, we reporttion of zirconia-based hybrid organicinorganicbents from a highly reactive precursor, zirconiumnd a solgel-active organic polymer (hydroxy-PDMDPS). The covalent bonding of the organice solgel zirconia network structure was accom-condensation reaction in the course of controlled

    polycondensation reactions taking place in the sol

  • K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114 3

    solution. Here, we demonstrate the outstanding performanceof the in situ created solgel zirconia-PDMDPS coating incapillary microextraction in hyphenation with open-tubulargas chroma

    2. Experim

    2.1. Equip

    All CMmadzu Moflame ioniztor. On-lining ChromLaboratoryVortex Genwas used fdients. A M(Accuratewas used t(if any) at 1320 FTIRused to acqterials. A Bsystem (Baobtain 16Inc., Austinlary GC colof fused sil(Fig. 1) waous samplehomebuilt,vice [49] wrinse the futraction caption from tand (d) purrinsing, coa

    2.2. Chem

    Fused-sa protectiPolymicrolene andmethanol)burgh, PA)hydrosiloxanophenonhydes (nohyde, and(PAHs) (nthrene, pyAldrich (Mpoly(dimet

    g. 1. Gr

    23%onenties In

    Prepa

    carefully designed sol solution was used to createoating. The key ingredients of the sol solution usedisted in Table 1. The sol solution was prepared in a

    polypropylene centrifuge tube by dissolving the fol-g ingredients in mixed solvent system consisting of

    ylene chloride and butanol (250L each): 1015Lrconium(IV) butoxide (80% solution in 1-butanol),g of silanol-terminated poly(dimethyldiphenylsiloxane)lymer, 70 mg of poly(methylhydrosiloxane), 10L of,3,3,3-hexamethyldisilazane, and 24L of glacialc acid. The dissolution process was aided by thor-

    vortexing. The sol solution was then centrifuged at0 rpm (15,682 g) to remove the precipitate (if any).

    top clear sol solution was transferred to a clean vialas further used in the coating process. A hydrother-treated fused silica capillary (2 m) was filled with the

    sol solution, using pressurized helium (50 psi) in the fill-urging device [49]. The sol solution was allowed to staye the capillary for a controlled period of time (typically0 min) to facilitate the formation of a solgel coating,ts chemical bonding to the capillary inner walls. Afterthe free portion of the solution was expelled from thelary, leaving behind a surface-bonded solgel coatingtography (CME-GC).

    ental

    ment

    E-GC experiments were performed on a Shi-del 14A capillary GC system equipped with aation detector (FID) and a split-splitless injec-

    e data collection and processing were done us-Perfect (version 3.5) computer software (JusticeSoftware, Denville, NJ). A Fisher Model G-560ie 2 system (Fisher Scientific, Pittsburgh, PA)

    or thorough mixing of various sol solution ingre-icrocentaur model APO 5760 microcentrifuge

    Chemical and Scientific Corp., Westbury, NY)o separate the sol solution from the precipitate3,000 rpm (15,682 g). A Nicolet model Avatar

    instrument (Thermo Nicolet, Madison, WI) wasuire infrared spectra of the prepared solgel ma-arnstead Model 04741 Nanopure deionized waterrnstead/Thermodyne, Dubuque, IA) was used to.0 M water. Stainless steel mini-unions (SGE, TX) were used to connect the fused silica capil-umn with the microextraction capillary, also madeica. An in-house-designed liquid sample dispensers used to facilitate gravity-fed flow of the aque-through the solgel microextraction capillary. A

    gas pressure-operated capillary filling/purging de-as used to perform a number of operations: (a)sed silica capillary with solvents; (b) fill the ex-illary with the sol solution; (c) expel the sol solu-

    he capillary at the end of solgel coating process;ge the capillary with helium after treatments liketing, and sample extraction.

    icals and materials

    ilica capillary (320 and 250m, i.d.) withve polyimide coating was purchased from

    Technologies Inc. (Phoenix, AZ). Naphtha-HPLC-grade solvents (methylene chloride,

    were purchased from Fisher Scientific (Pitts-. Hexamethyldisilazane (HMDS), poly (methyl-ane) (PMHS), ketones (valerophenone, hex-e, heptanophenone, and decanophenone), alde-nylaldehyde, n-decylaldehyde, undecylic alde-dodecanal), polycyclic aromatic hydrocarbonsaphthalene, acenaphthene, fluorene, phenan-

    rene, and naphthacene), were purchased fromilwaukee, WI). Two types of silanol-terminatedhyldiphenylsiloxane) (PDMDPS) copolymers

    Fi

    (withcompnolog

    2.3.

    Athe care lcleanlowinmethof zi85 mcopo1,1,1acetiough13,00Theand wmallyclearing/pinsid153and ithat,capilavity-fed extraction system for capillary microextraction.

    and 1418% contents of the diphenyl-containing) were purchased from United Chemical Tech-c. (Bristol, PA).

    ration of solgel zirconia-PDMDPS coating

  • 4 K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114

    Table 1Names, and chemical structure of the coating solution ingredients for solgel capillary

    Ingredient Function Chemical structure

    Zirconium(IV

    Silanol-termin mpone

    Methylene chAcetic acid

    Poly(methylh

    1,1,1,3,3,3-H

    within thepurging widitioned by1 C/min aconditionin1 C/min aillary was fchloride anWhile condhelium at 1into 10 cmillary micro

    2.4. Prepa

    PAHs, kor tetrahydsilanized glevel concelutions wit

    2.5. Gravimicroextra

    The gratraction (Fia Chromaflconsistinginside an accylindrical5% (v/v) so

    ernigbient

    al amoThe e

    emble

    Solg) butoxide Solgel precursor

    ated poly (dimethyldiphenylsiloxane) Solgel-active organic co

    loride SolventChelating reagent

    ydrosiloxane) Deactivating reagent

    examethyldisilazane Deactivating reagent

    capillary. The solgel coating was then dried byth helium. The coated capillary was further con-temperature programming from 40 to 150 C at

    nd held at 150 C for 300 min. Following this, theg temperature was raised from 150 to 320 C at

    nd held at 320 C for 120 min. The extraction cap-urther cleaned by rinsing with 3 mL of methylened conditioned again from 40 to 320 C at 4 C/min.

    by ovto amliberflow.reass

    2.6.itioning, the capillary was constantly purged withmL/min. The conditioned capillary was then cut

    long pieces that were further used to perform cap-extraction.

    ration of the samplesetones, and aldehydes were dissolved in methanolrofuran to prepare 0.1 mg/L stock solutions inlass vials. For extraction, fresh samples with ppbntrations were prepared by diluting the stock so-

    h deionized water.

    ty-fed sample dispenser for capillaryction

    vity-fed sample dispenser for capillary microex-g. 1) was constructed by in-house modification ofex AQ column (Kontes Glass Co., Vineland, NJ)of a thick-walled glass cylinder coaxially placedrylic jacket. The inner surface of the thick-walledglass column was deactivated by treating with alution of HMDS in methylene chloride followed

    To perfoditioned socapillary (1vertically cple dispenthen placedflow throuWhile passmoleculescoating resple flow th3040 minter this, theat 25 kPa foplaced twocapillary w6.5 mm ofinto the cofrom the owithin thecompletedend of the Gcapillary rent

    CH2Cl2CH3COOH

    ht heating at 100 C. The column was then cooledtemperature, thoroughly rinsed with methanol andunts of deionized water, and dried in a heliumntire Chromaflex AQ column was subsequentlyd.

    el capillary microextraction-GC analysisrm capillary microextraction, a previously con-lgel zirconia-PDMDPS coated microextraction0 cm 320m i.d. or 10 cm 250m i.d.) wasonnected to the bottom end of the empty sam-

    ser (Fig. 1). The aqueous sample (50 mL) wasin the dispenser from the top, and allowed to

    gh the microextraction capillary under gravity.ing through the extraction capillary, the analytewere sorbed by the solgel zirconia-PDMDPSiding on the inner walls of the capillary. The sam-rough the capillary was allowed to continue forfor an extraction equilibrium to be established. Af-microextraction capillary was purged with heliumr 1 min and connected to the top end of a vertically-way mini-union connecting the microextractionith the inlet end of the GC column. Approximately,the extraction capillary remained tightly insertednnector, as did the same length of GC columnpposite side of the mini-union facing each otherconnector. The installation of the capillary wasby providing a leak-free connection at the bottomC injection port so that top 9 cm of the extractionmained inside the injection port. The extracted

  • K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114 5

    analytes were then thermally desorbed from the capillary byrapidly raising the temperature of the injector (up to 300 Cstarting from 30 C). The desorption was performed over a8.2 min period in the splitless mode allowing the released an-alytes to be swept over by the carrier gas into the GC columnheld at 30 C during the entire desorption process. Such alow column temperature facilitated effective solute focusingat the column inlet. Following this, the column temperaturewas programmed from 30 to 320 C at rate of 20 C/min. Thesplit vent remained closed throughout the entire chromato-graphic run. Analyte detection was performed using a flameionization d

    3. Result a

    Capillarthe inner snumber ofSPME sucmechanicabreakage,the sorbenagainst mealso providthe microecoating onintact. Innway to persample disbacks of fiagitation dcontaminat

    The solhomogeneohas receivesample precellent conthat provedextraction m

    A generphase coatGC colum[22]. In theingredientsPDMDPS cZirconium(

    butoxi

    used as a solgel precursor and served as a source forthe inorganic component of the solgel organicinorganichybrid coating.

    The solgel Zirconia-PDMDPS coating presented herewas generated via two major reactions: (1) hydrolysis of asolgel precursor, zirconium(IV) butoxide; and (2) polycon-densation of the precursor and it hydrolysis products betweenthemselves and with other solgel-active ingredients in thecoating solution, including silanol-terminated PDMDPS. Thehydrolysis of the zirconium(IV) butoxide precursor is repre-sented by Scheme 1 [50].

    ondensation of the solgel polymer growing in closeity ofsurfa

    ng chme 2Amajors usinide) irs. Evously,meratwate

    ult touli an

    by disnt likesing thic moparentan alsnts. A8], tribeen uns. Inces onformaasingthe p

    rconiuchelatly thr

    Silanlymers) weemicaondenetector (FID) maintained at 350 C.

    nd discussion

    y microextraction [9] uses a sorbent coating onurface of a capillary, and thereby overcomes adeficiencies inherent in conventional fiber-basedh as susceptibility of the sorbent coating to

    l damage due to scraping during operation, fiberand possible sample contamination. In CME,t coating is protected by the fused silica tubingchanical damage. The capillary format of SPMEes operational flexibility and convenience duringxtraction process since the protective polyimidethe outer surface of fused silica capillary remainser surface-coated capillaries provide a simpleform extraction in conjunction with a gravity-fedpenser (Fig. 1), and thus avoid typical draw-ber-based SPME, including the need for sampleuring extraction as well as the sample loss andion problems associated with this.gel process is a straightforward route to obtainingus gels of desired compositions. In recent years, it

    d increased attention in analytical separations andparations due to its outstanding versatility and ex-trol over properties of the created solgel materialsto be promising for use as stationary phases andedia.

    al procedure for the creation of solgel stationarying on the inner walls of fused silica capillaryns was first described by Malik and co-workerspresent work, a judiciously designed sol solution(Table 1) was used to create the solgel zirconia-oating on the fused silica capillary inner surface.IV) butoxide (80% solution in 1-butanol) was

    Scheme 1. Hydrolysis of zirconium(IV)

    Cvicinillarycoati(Sche

    Aterialbutoxcurso

    vigoragglowhendifficGanglemsolveexposphertransides creage[565haveactioreplaThedecre

    Inof zias a

    slowTwocopoblockbe chpolycde precursor.

    the capillary walls with silanol group on the cap-ce led to the formation of an organicinorganicemically anchored to the capillary inner walls

    ).obstacle to preparing zirconia-based solgel ma-

    g zirconium alkoxide precursors (e.g., zirconiums the very rapid solgel reaction rates for these pre-en if the solution of zirconium alkoxide is stirredthe rates of these reactions are so high that largeed zirconia particles precipitate out immediatelyr is added [51]. Such fast precipitation makes itreproducibly prepare zirconia solgel materials.

    d Kundu [52] addressed the fast precipitation prob-solving zirconium propoxide in a non-polar dry

    cyclohexane. The hydrolysis was performed bye coatings prepared from the solution to atmo-

    isture. Heating to 450 C was necessary to obtainfilms. The hydrolysis rates of zirconium alkox-

    o be controlled by chelating with ligand-exchangecetic acid [53,54], valeric acid [55], -diketonesethanolamine [59], and 1, 5-diaminopentane [56]sed as chelating reagents for zirconia solgel re-

    general, chelation occurs when the added reagente or more alkoxy groups forming a strong bond.

    tion of this bond reduces the hydrolysis rate bythe number of available alkoxy groups [60].resent work, we controlled the hydrolysis ratem butoxide by using glacial acetic acid [61]ing agent as well as a source of water releasedough the esterification with 1-butanol [62,63].ol-terminated poly (dimethyldiphenylsiloxane)s (with 23% and 1418% diphenyl-containingre used as solgel-active organic components tolly incorporated in the solgel network throughsation reactions with the zirconium butoxide

  • 6 K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114

    Scheme 2. Deactivation and shielding of solgel zirconia-PDMDPS coa

    precursor and its hydrolysis products. An IR spectrum ofthe pure co-polymers (the one with 23% phenyl-containingblock) is presented in Fig. 2A where a small stretching at3068 cm1 indicates the presence of phenyl groups.

    Fig. 2. IR spcopolymer wzirconia-PDM1418% diph

    This advcomponentformationthat can becoating on

    apillarkage aore, s

    hicknica cshrinthermand tectra representing: (A) pure silanol-terminated PDMDPSith 23% diphenyl-containing component; and (B) solgelDPS material prepared using PDMDPS copolymer with

    enyl-containing component.

    properties [hexamethyserved as dzation of ththe resultinwas to minpolar soluteloss, peakeffects. Insolgel zircvation reacthermal cocoating pro

    Hydrolyreagents arand constitsis. The conicon compoto publishefor ZrOSFig. 2B shomaterial prted surface using PMHS and HMDS.

    antageous chemical incorporation of an organicinto the solgel network is responsible for the

    of an organicinorganic hybrid material systemconveniently used for in situ creation of surfacea substrate like the inner walls of a fused sil-

    y. Besides, the organic groups help to reduce thend cracking of the solgel coating [64,65]. Fur-olgel process can be used to control the porosityess of the coating and to improve its mechanical

    66]. Poly (methylhydrosiloxane) and 1,1,1,3,3,3-ldisilazane that were used in the sol solution,eactivation reagents to perform chemical derivati-e strongly adsorptive residual hydroxyl groups ong solgel material. The purpose of these reactionsimize the strong adsorptive interactions betweens and the solgel sorbent that may lead to sampletailing, sample carry-over and other deleteriousthe presented method for the preparation of theonia coated microextraction capillary, the deacti-tions were designed to take place mainly duringnditioning of the capillary following the solgelcedure.tic polycondensation reactions for solgel-activee well established in solgel chemistry [6770],ute the fundamental mechanism in solgel synthe-densation between solgel-active zirconia and sil-unds is also well documented [7173]. According

    d literature data, [74,75] the characteristic IR bandi bonds is located in the vicinity of 945980 cm1.ws an IR spectrum of solgel zirconia PDMDPSepared by using a PDMDPS polymer containing

  • K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114 7

    Fig. 3. Scann DPS coated microextraction capillary. (A) Illustrates cross-sectionalview (1000) he coati

    approximathan that prat 954 cmthe prepare

    Metal-bcoating repIn the conpresence onumber ofducibility p

    Table 2Peak area andusing solgel

    Analyte

    Chemical clas

    PAHs

    Aldehyde

    Ketones

    rtion atakenplishsuita

    el conia code coing electron microscopic images of a 0.32 mm i.d. Solgel zirconia-PDMof roughened surface obtained by solgel coating process. (B) Illustrates t

    tely eight time higher amounts of the phenyl groupesented in Fig. 2A. The presence of the stretching1 indicates to the presence of ZrOSi bonds ind solgel material [74].ound hydroxyl groups on the created solgelresent strong adsorptive sites for polar solutes.

    text of analytical microextraxtion or separation,

    distoto beaccom

    withsolgzircohydrif such groups is undesirable, and may lead to adeleterious effects including sample loss, repro-roblems, sample carryover problems, and peak

    retention time repeatability data for PAHs, aldehydes, and ketones extracted from aqzirconia-PDMDPS

    Peak area repeatability (n= 4)s Name Mean peak area (aribitary unit) R.S.D. (%)

    Naphthalene 11692.42 7.25Acenaphthene 23560.38 4.58Fluorene 30970.30 2.45Phenanthrene 09010.92 3.46Pyrene 55005.40 2.78Naphthacene 22378.12 5.42

    1-Nonanal 15910.25 1.291-Decanal 22908.98 5.45Undecanal 30413.15 5.08Dodecanal 32182.70 3.72

    Valerophenone 03712.88 3.10Hexanophenone 13780.88 1.24Heptanophenone 47398.87 1.24Decanophenone 83156.67 2.20Trans-chalcone 06546.25 5.57

    hexamethyof polymfor this pung thickness (10,000).

    nd tailing. Therefore, appropriate measures needto deactivate these adsorptive sites. This may beed by chemically reacting the hydroxyl groupsble derivatization reagents. Like silica-basedatings, the surface hydroxyl groups of solgelating can be derivatized using reactive silicon

    mpounds such as alkyl hydrosilanes [76,77] andueous samples using four replicate measurements by CME-GC

    tR Repeatability (n= 4) Detection limit(ng/mL)Mean tR (min) R.S.D. (%)

    15.32 0.11 0.5717.12 0.05 0.1617.73 0.12 0.0918.76 0.10 0.0620.22 0.22 0.0321.44 0.14 0.05

    15.27 0.03 0.3315.94 0.16 0.0816.61 0.10 0.1017.22 0.11 0.05

    16.79 0.06 0.9217.40 0.07 0.3318.19 0.27 0.0819.44 0.11 0.0219.82 0.03 0.57

    ldisilazane [78]. In this work, we used a mixtureethylhydrosiloxane and hexamethyldisilazanerpose: the underlying chemical reactions are

  • 8 K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114

    Fig. 4. CME-extraction captraction capillOther conditiodesorption; inture program350 C. Peaksthrene; (5) py

    schematicathe chemicbefore and

    One of tation of a s

    Table 3Capillary-to-csolgel zircon

    Name of the a

    UndecanalHexanophenoFluorenePhenanthreneGC analysis of PAHs using a solgel zirconia-PDMDPS coatedillary. Extraction parameters: 10 cm 0.32 mm i.d. microex-ary; extraction time, 30 min (gravity fed at room temperature).ns: 10 m 0.25 mm i.d. Solgel PDMS GC column; splitlessjector temperature rose from 30 to 300 C: column tempera-from 30 to 300 C at rate of 20 C/min; helium carrier gas: FID: (1) naphthalene; (2) acenaphthene; (3) fluorene; (4) phenan-rene; and (6) naphthacene.

    lly represented in Scheme 2 (A and B illustrateal structure of the solgel zirconia surface coatingafter deactivation respectively).he most important undertakings in CME is the cre-table, surface-bonded sorbent coating on the inner

    apillary and run-to-run peak area repeatability for mixture of PAHs, aldehydes, ania-PDMDPS coated extraction capillaries

    nalyte Peak area repeatability (n= 4)Capillary-to-capillary

    Mean peak area (aribitary unit) R.S.D. (%)47940.9 4.60

    ne 27538.4 1.6153250.7 5.4051399.9 4.91

    Fig. 5. CME-coated extractcroextractionature). Othersplitless desotemperature prier gas: FIDundecylic ald

    walls of aelectron micoated fuseThe SEM id ketones in four replicate measurements by CME-GC using

    Run-to-run

    Mean peak area (aribitary unit) R.S.D. (%)60364.2 4.0325055.5 2.1359485.7 2.1454867.9 2.84

    GC analysis of aldehydes using a solgel zirconia-PDMDPSion capillary. Extraction parameters: 10 cm 0.32 mm i.d. mi-capillary; extraction time, 40 min (gravity fed at room temper-conditions: 10 m 0.25 mm i.d. Solgel GC PDMS column;rption; injector temperature rose from 30 to 300 C: columnrogram from 30 to 300 C at rate of 20 C/min; helium car-350 C. Peaks: (1) nonylaldehyde; (2) n-decylaldehyde; (3)

    ehyde; and (4) dodecanal.fused silica capillary. Fig. 3 represents scanningcroscopic images of a solgel Zirconia-PDMDPSd silica capillary prepared in the present work.mages A and B were obtained at a magnification

  • K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114 9

    Fig. 6. CME-GC analysis of ketones using a solgel zirconia-PDMDPS coated extraction capillary. Extraction parameters: 10 cm 0.32 mm i.d. microextractioncapillary; extraction time, 40 min (gravity fed at room temperature). Other conditions: 10 m 0.25 mm i.d. Solgel PDMS GC column; splitless desorption;injector temperature rose from 30 to 300 C: column temperature program from 30 to 300 C at rate of 20 C/min; helium carrier gas: FID 350 C. Peaks: (1)valerophenone; (2) hexanophenone; (3) heptanophenone; (4) decanophenone; and (5) trans-chalcone.

  • 10 K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114

    of 1000 and 10,000, respectively. The microstructural de-tails revealed in these images clearly show that the createdsolgel zirconia coating possesses a porous make-up whichsubstantialtania coatin

    Solgelextraction oExperimencyclic aroPDMDPS

    CME-Gsample witmental dataa solgel zto-run repesolgel GCtion times (column useing a solge[22].

    The repthe preparacoated capzirconia PDnew procedanalysis ofous sampleanalyte wareproducibpreparationin Table 3made on eapeak areasto-capillarycapillary-toRSD valuepounds usemethod, areproducib

    Fig. 5 ilhydes extrzirconia-PDtions of thThe extracSolgel zirfor 3040 mat room temcarcinogenenvironmenfects on pujor disinfecreaction becompoundsysis of tracand in drincompounds

    avoid undesirable adsorption that causes peak tailing. Solgelzirconia-PDMDPS coated capillary provided highly efficientextraction of the aldehydes, and the used solgel GC column

    ded excellent peak shapes which is also indicative ofquality of deactivation in the used solgel GC column.also demonstrates effective focusing of the analytes atolumn inlet after their thermal desorption from the mi-traction capillary. For the aldehydes, solgel CME-GCthe zirconia-PDMDPS coated capillary provided excel-repeatability in peak area (R.S.D. < 5%) and retention(R.S.D. < 0.16%).g. 6 shows a gas chromatogram illustrating CME-GCsis of several ketones extracted from an aqueous sam-

    . CME-gel zirco0 cmty fed ael PDM0 to 30C/min;laldehyxanophyrene; aly differs from that obtained by us for solgel ti-g [79].zirconia-PDMDPS-coated capillaries allowed thef analytes belonging to various chemical classes.

    tal data highlighting CME-GC analysis of poly-matic hydrocarbons using a solgel zirconia-coated capillary is shown in Fig. 4.C experiments were performed on an aqueoush low ppb level analyte concentrations. Experi-

    presented in Table 2 shows that CME-GC withirconia-PDMDPS coating provides excellent run-atability in solute peak areas (37%) and the usedcolumn provided excellent repeatability in reten-less than 0.2%). It should be pointed out that thed for GC analyses was also prepared in-house us-l method described by us in a previous publication

    roducibility of the newly developed method fortion of solgel hybrid organicinorganic zirconiaillaries was evaluated by preparing three solgelMDPS-coated capillaries in accordance with theure and following their performance in CME-GCdifferent classes of analytes extracted from aque-s. The GC peak area obtained for an extracteds used as the criterion for capillary-to-capillaryility which ultimately characterizes the capillarymethod reproducibility. The results are presented

    For each analyte, four replicate extractions werech capillary and the mean of the four measuredwas used in Table 3 for the purpose of capillary-reproducibility. The presented data show that the-capillary reproducibility is characterized by anof less than 5.5% for all three classes of com-d for this evaluation. For a sample preparationless than 5.5% R.S.D. is indicative of excellentility.lustrates a gas chromatogram of several free alde-acted from an aqueous sample using a solgel

    MDPS coated capillary. Here, the concentra-e used aldehydes were in 80500 ppb range.

    tion was carried out on a 10 cm 0.32 mm i.d.conia-PDMDPS coated microextraction capillaryin. The extraction of the analytes was performedperature. Aldehydes are known to have toxic and

    ic properties, and therefore, their presence in thet is of great concern because of their adverse ef-

    blic health and vegetation [80]. Aldehydes are ma-tion by products formed as a result of chemical

    tween disinfectant (ozone or chlorine) and organicin drinking water [81]. Therefore, accurate anal-

    e-level contents of aldehyde in the environmentking water is important [82]. Aldehydes are polar

    that are often derivatized [83] for GC analysis to

    provihighThisthe ccroex

    withlenttime

    Fianaly

    Fig. 7a solters: 1(graviSolgfrom 3of 20n-decy(6) he(10) pGC analysis of mixture of PAHs, aldehydes and ketones usingnia-PDMDPS coated extraction capillary. Extraction parame-

    0.32 mm i.d. microextraction capillary; extraction time, 40 mint room temperature). Other conditions: 10 m 0.25 mm i.d.S GC column; splitless desorption; injector temperature rose0 C: column temperature program from 30 to 300 C at ratehelium carrier gas: FID 350 C. Peaks: (1) napnthalene; (2)de; (3) undecylic aldehyde; (4) valerophenone; (5) dodecanal;enone; (7) fluorene; (8) heptanophenone; (9) phenanthrene;nd (11) naphthacene.

  • K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114 11

    ple. Like aldehydes, there was no need for derivatization ofthe ketones, either during extraction or GC analysis. Sharpand symmetrical GC peaks, evident from the chromatogram,show the effectiveness of the used CME-GC system, as wellas the practical utility of the mini-union metal connector pro-viding leak free connection between the extraction capillaryand the GC column. Excellent reproducibility was achieved inCME-GC of ketones using solgel zirconia-PDMDPS coatedcapillary as shown in Table 2. The peak area RSD% valuesfor ketones were less than 5.6% and their retention time re-peatability on used solgel PDMS column was characterizedby R.S.D. values of less than 0.27%.

    Fig. 7 shows a gas chromatogram illustrating CME-GCanalysis of an aqueous sample containing different classesof compounds including PAHs, aldehydes and ketones, andshows that the solgel zirconia-PDMDPS extraction capillarycan provide simultaneous extraction of polar and non-polarcompounds present in the aqueous sample, and demonstratesthe advantage over conventional SPME coatings that oftendo not allow such effective extraction of both polar and non-polar analyte from the same sample.

    In capillary microextraction technique, the amount ofanalyte extracted into the sorbent coating depends not onlyon the polarity and thickness of the coated phase, but also onthe extractiextraction oand undecyon a solcapillary. Taqueous saequilibriumshorter thanand undecyis because

    Fig. 8. Extracand fluorene olary. ExtractioOther conditiodesorption; inprogram from350 C.

    higher affinity toward the non-polar PDMDPS-based solgelzirconia coating than toward water. On the other hand,heptanophenone and undecylic aldehyde, being more polarand hydrophilic than fluorene showed a slower extraction bythe coated non-polar solgel zirconia-PDMDPS sorbent.

    Solgel zirconia-PDMDPS coating showed high pH sta-bility, and retained excellent performance after rinsing with0.1 M NaOH (pH 13) for 24 h. Chromatograms in Fig. 9a andb show CME-GC analysis of four PAHs before (Fig. 9a) andafter (Fig. 9b) zirconia-PDMDPS extraction capillary wasrinsed with 0.1 M NaOH solution.

    As is evident from Fig. 9, the extraction performance of thesolgel zirconia-PDMDPS capillary remained practically un-changed after rinsing with NaOH as it can be seen in Table 4.

    CME-extractiapillary 0.25tion tim

    0.25 mperatu80 C acarrie

    nthreneon time. Fig. 8 illustrates the kinetic profile for thef fluorene (a non-polar analyte), heptanophenonelic aldehyde (both are moderately polar analytes)gel zirconia-PDMDPS-coated microextractionhe CME experiments were carried out using

    mples of individual test analytes. The extractionfor fluorene reached in 10 min, which is muchextraction equilibrium time for heptanophenone

    lic aldehyde (both approximately 30 min). Thisfluorene exhibits hydrophobic behavior that has

    tion kinetics of aqueous undecylic aldehyde, heptanophenone,n a solgel zirconia-PDMDPS microextraction coated capil-n parameters: 10 cm 0.32 mm i.d. microextraction capillary;ns: 10 m 0.25 mm i.d. Solgel GC PDMS column; splitlessjector temperature from 30 to 300 C: column temperature30 to 300 C at rate of 20 C/min; helium carrier gas: FID

    Fig. 9.microtion c10 cmextrac10 mtor tem30 to 2heliumphenaGC analysis of PAHs using a solgel zirconia-PDMDPS coatedon capillary: before (a) and after (b) rinsing the microextrac-with 0.1 M NaOH solution for 24 h. Extraction parameters:

    mm i.d. microextraction capillary; coating thickness 0.3 mm,e, 30 min (gravity fed at room temperature). Other conditions:m i.d. Solgel GC PDMS column; splitless desorption; injec-

    re rose from 30 to 300 C: column temperature program fromt rate of 20 C/min then from 280 to 300 C at rate of 2 C/min;r gas: FID 350 C. Peaks: (1) acenaphthene; (2) fluorene; (3); and (4) pyrene.

  • 12 K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114

    Table 4Peak area repeatability data for ppb level concentrations of PAHs before and after extraction capillary treated with 0.1 M NaOH

    Name of theanalyte

    Peak area repeatabilitybefore rinsing with0.1 M NaOH

    Peak area repeatabilityafter rinsing withNaOH

    Relative change in peak area

    Mean peak area A1 (aribitary unit) Mean peak area AAcenaphthene 30380.91 29432.76Fluorene 35425.63 33428.86Phenanthrene 47547.31 46525.33Pyrene 33884.61 35636.56

    Fig. 10. CME-GC analysis of PAHs using a commercial coated capillarywith 0.25 mm coating thickness: before (a) and after (b) rinsing the mi-croextraction capillary with 0.1 M NaOH solution for 24 h. Extraction pa-rameters: 10 cm 0.25 mm i.d. microextraction capillary; extraction time,30 min (gravity fed at room temperature). Other conditions: 10 m 0.25 mmi.d. Solgel GC PDMS column; splitless desorption; injector temperaturerose from 30 to 300 C: column temperature program from 30 to 280 C atrate of 20 C/min then from 280 to 300 C at rate of 2 C/min; helium carriergas: FID 350 C. Peaks: (1) acenaphthene; (2) fluorene; (3) phenanthrene;and (4) pyrene.

    For coming a 10 cmPDMDPS-The resultssensitivity amicroextraous (Fig. 1

    Thesezirconia-batage over ccoatings haillary microsamples, othe extracti

    4. Conclu

    Solgelsorbent cotion. Princchemically(polydimetwork in thalkoxide pcontrolledfirst time, sin capillaryzirconia-PDstability: itunchanged13) for 24out simplyextraction canalytes wemal desorptemperaturdiverse ranPDMDPSlimits wereCME-GC-Fcoated mrun-to-runarea R.S.D0.1 M |(A2A1)/A1| 100 (%)

    2 (aribitary unit)3.125.642.155.17

    parison, the same experiment was conducted us-piece of a conventionally coated commercial

    based GC column as the microextraction capillary.are shown in Fig. 10. A drastic loss in extractionfter rinsing the conventionally coated silica-based

    ction capillary with 0.1 M NaOH solution is obvi-0).data suggest that the created hybrid solgelsed coatings have significant pH stability advan-onventional silica-based coatings, and that suchve the potential to extend the applicability of cap-extraction and related techniques to highly basic

    r analytes that require highly basic condition foron and/or analysis.

    sion

    zirconia-based hybrid organicinorganicating was developed for use in microextrac-iples of solgel chemistry was employed tobind a hydroxy-terminated silicone polymer

    hyldiphenylsiloxane) to a solgel zirconia net-e course of its evolution from highly reactiverecursor (zirconium tetrabutoxide) undergoinghydrolytic polycondensation reactions. For theolgel zirconia-PDMDPS coating was employed

    microextraction. The newly developed solgelMDPS coating demonstrated exceptional pH

    s extraction characteristics remained practicallyafter rinsing with a 0.1 M solution of NaOH (pH

    h. Solventless extraction of analytes was carriedby passing the aqueous sample through the solgelapillary for approximately 30 min. The extractedre efficiently transferred to a GC column via ther-

    tion, and the desorbed analytes were separated bye programmed GC. Efficient CME-GC analyses ofge of solutes was achieved using solgel zirconia-capillaries. Parts per trillion (ppt) level detection

    achieved for polar and non-polar analytes inID experiments. Solgel zirconia-PDMDPS

    icroextraction capillaries showed remarkablerepeatability (R.S.D. < 0.27%) and produced peak. values in the range of 1.247.25%.

  • K. Alhooshani et al. / J. Chromatogr. A 1062 (2005) 114 13

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    Sol-gel approach to in situ creation of high pH-resistant surface-bonded organic-inorganic hybrid zirconia coating for capillary microextraction (in-tube SPME)IntroductionExperimentalEquipmentChemicals and materialsPreparation of sol gel zirconia-PDMDPS coatingPreparation of the samplesGravity-fed sample dispenser for capillary microextractionSol gel capillary microextraction-GC analysis

    Result and discussionConclusionReferences