DOC

Catalytic spectrophotometric determination of trace selenium in microemulsion after separation and enrichment by SDG

By Crystal Miller,2014-06-20 08:48
10 views 0
Catalytic spectrophotometric determination of trace selenium in microemulsion after separation and enrichment by SDG

    Catalytic spectrophotometric determination

    of trace selenium in microemulsion after

    separation and enrichment by SDG RAREMETALs

    Vo1.25,No.3,.1un2oo6,p.281

    Catalyticspectrophotometricdeterminationoftraceseleniumin

    microemulsionafterseparationandenrichmentbySDG

    LIHuizhi,ZHAIDiantang,andFANHng~u

    SchoolofChemistryandChemJctllEngineering,JinanUnJversity,Jinan250022,China (Received200505-09)

    Abstract:AnewcatalyticspectrophotometricmethodwasdevelopedforthedeterminationoftraceamountofSe(IV)in

    microemulsionmedium.1emethodisbasedonthecatalyticeffectoftracesofSe(IV)ontheoxidationof

    2',4'-dichlomphenylfluomne(p-CPF)bypotassiumbromatewithHNO3asanactivatorinthepresenceofnomonicmi.

    croemulsionmedium.Underoptimumconditions,thecalibrationgraphislinearintherangeof0.415gg?LofSeOV)at

    480nm.Thedetectionlimitachievedis9.86xl0-.L

    .SamplesweredissolvedandtheobtainedtraceSe(IV)was

    separatedandenrichedbysulphydryldextranegelfSDG).Themethodhasbeenappliedfordeterminationoftraceselenium

    withsatisfactoryresults.

    Keywords:analyticalchemistry;Se0V);catalyticspectrophotometric;microemulsionmedium;separation;enrichment

    1.Introduction

    Seleniumisbothamicronutrientandtoxicele. mentforlivingbeings,dependingontheconcentra

    tionleve1.1emetalplaysanimportantrolein physiologicalsystemsincludingnormalizationof sugarlevels.participationmvariousenzymesys

    ternsasaninhibitorandcofactorandcatalystatthe oxiclarionofvariousamines.Itisalsoanessential elementforcellgrowthatgg?Llevels.However,

    anexcessofseleniuminfoodorpharmaceutical preparationsishazardoustohumanhealth.There

    fore.itisnecessarytoestablishsensitiveandaccu

    rateanalyticalmethodsforquantitativedetermina- tionofselenium.

    Thereareseveralmethodsavailablefordetermi. nationofSe(IV)includingatomicabsorptionspec

    troscopy(AAS)[1,ICP_AES[2,flowinjection

    analysis(FIb),spectrofluorimetry[3,andspectro-

    photometry.Inroutineanalysis,spectrophotometric methodisversatileandeconomica1.especiallyfor developingcountries.However,themethodsmen

    tionodabovearetime.consumingorlesssensitive. Catalytickineticmethodshavereceivedconsider- ableattentionbecauseofthesignificantadvantages inthedeterminationofmanycomponentsinfface levels.Variouscatalytickineticmethodsforthede

    mrminationofSe(IV)inwatersystemshavebeen reported4-l1].Inmicroemulsionmedium,thereac

    tionbetween2',4'-dichlorophenylfluoroneC

    andpotassiumbromatehasneverbeenreportedfor Se(IV)determination.Microemulsionsaletranspar-

entortranslucent,homogeneousandthermody

    namicallystablesystemshavinglowviscositythat arecomposedofsurfactant,water,oilandcosurfac. rantatappropriateratios.Comparedwithamicellar system.microemulsionhaslowersurfacetension andstrongsolubilityinorganicandinorganicsub- stances12141.

    Inourwork.microemulsionwithTritonX100

    wasusedtoenhancethesensitivityandstabilityof anSe0V)2'.4'-dichlorophenylfluoronepotassium

    bromatenitricacidreactionsystem.Differentvari

    ablesthataffectthereactionsystemof

    2'I4'-dichlorophenylfluoronewithpotassiumbro. matecatalyzedbySe(IV)inmieroemulsionaswell asdetaileddescriptionofproceduresarepresented below.Tl1eproposedmethodishighlysensitive.se

    Correspondingauthor:LIHuizhiE-mail:chm_ lihz@ujn.edu.ca

282

    lective,andsimpleforthedeterminationoftrace Se(IV)afterseparationandenrichmentbysulphy

    dryldexlranegel(SDG)151.

    2.Experimental

    2.1.Apparatus

    Aspectrophotometer,Model722wasusedfor absorbancemeas~ements.Absorptionspeclrawere recordedonaModelUV3000Shimadzuspecffo-

    photometer.Conventional1.0cmquartzcellswere

usedintheseinstruments.AModelpHS3Cdigital

    pHmeterwithacombinedglasscalomelelectrode

    wasusedforpHmeasurements.

    Allreagentsusedwereofanalyticalpufftyunless specifiedotherwise.Solutionsweremadeindoubly distilledwater.AstockofSe(IV)(1.0mg?mL)was preparedandfurtherdilutionsasrequiredwereem- ployed.NonionicmicroemulsionoftritonX100was

    preparedaccordingtothemassratiooftritonX100:

    nbutanol:nheptane:H,O=5.5:3.3:0.8:90.4. 2'.4'-dichlorophenylfluoronesolutionpreparedin absoluteethano1.4.0×10广qmol?L:nitricacidsolu

    tion.1.2×10.mo1.Ll:potassiumbromatesolution, 2.0×10mo1.L.

    2.3.Recommendedprocedure

    3.0mLof0.1LLg.mL-Se(IV)solutionwas

    transferredintoa25mLtesttube,then3.0mLof 1.2×l0.mo1.Lnitricacid.5.0mLof4.0×10广q

    mo1.Ll2'.4'-dichlomphenylfluoronesolution.2.0 mLofnOM'onicmicroemulsionoftritonX100.and

    4.0mLof2.0×lmol?Lpotassiumbromateso

    lutionwereadded.Then,thevolumewasmadeupto 23mLapproximatelywithdoublydistilledwater andmixedwel1.Thesolutionwasheatedfor10min at80?0.5.Cinathermostatbath.Thesolutionwas dilutedtothemarkwithwatel"andshakenthor- oughly.Last,thesolutionwascooledtoroomtem

    peraturebyplacingunderrtmningtapwater,theab- sorbanceofthesolutioninthecatalyticsystem), inwhichSe(IV)wasadded,wasdeterminedat480

    nlTlagainstwaterbyusing1cmquartzcel1.A RAREMETALS,Vo1.25,No.iJun2006

    noncatalyticsystemwaspreparedinthesame manner,replacingSe(IV)solutionwithdoublydis

    tilledwater.Theabsorbanceofthenoncatalytic

    systemwaslabeledasA0.TheAAvaluewascalcu

    latedfromA0toAofthetwodeterminations. 3.Resultsanddiscussion

    3.1.Absorptionspectra

    2'.4'dichlorophenylfluoroneisadyethatcanbe oxidizedbyKBrO3.Intheexperiment,itwasfound tIlat2'.4'-dichlorophenylfluoroneWasslowlyoxi

    dizedbyKBrO1inacidmedia,whereastherateof oxidationsa'onglyincreasedinthepresenceoftrace amountsofSe(IV).Fig.1showstheabsorption spectraofcatalyticandnoncatalyticsystemsindif-

    ferentmedia.

    FromFig.1,itisfoundthattheabsorbanceof eachsystemreachesmaximumat480nlT1.Hence, 480nlTlWasselectedforfurtherstudies.

    Fig.1.Absorptionspectraofnon-catalyticandcata- lyticreactionsindifferentmediaagainstwater:(1) non-catalyticreactioninmicroemulsionoftritonX.100; (2)non-catalyticreactioninwater;(3)catalyticreac- lioninwater;(4)catalyticreactioninmicroemulsionof tritonX.100.Conditions:1.44×10mol?L_nitricadd;

    8.0×10r5mo1.1-12'.4'.diddorophenylfluorone;3.2×

    10-3mo1.L-Ipotassiumbromate;5.0mLofbuffersolu. 1ion(pH--3.2);2.0mLofnomomcmicroemulsionof tritonX-100and0.3lagofSe(IV)solution.

    3.2.Effectofthemountofpotassiumbromate Intermsoftheexperimentalprocedure,the

LlH.z.eta1.Catalyticspectrophotometricdeterminationoftraceseleniuminmicroemulsion

    after283

    amountofpotassiumbromateaddedwasvariedto findtheoptimumamountoftheoxidantKBrO.The resultisgiveninFig.2.ThereactionrateAAof noncatalyticandcatalyticreactionsincreasedupto 3.0mLandthereafteritremainedstableoverthe rangeOf3.07.0mL.Greateramountofthereagent decreasedthesensitivity.Thus,4.0mLofKBrO1 wasusedintherestofthestudy.

    33.Innuenceoftheamountofnitricacid

    Theinfluenceofnitricacid(1.2×10-mo1.L)

    asanactivatorwasstudiedinthevolumerangeof 1.05.0mL.Fi2.3indicatesthattheoxidationreac

    tionwasacceleratedobviouslybynitricacidandAA remainedconstantandreachedmaximumafterthe additionof2.0.4.0mLofnitricacid.T11us.3.0mL 0f1.2×l0mo1.Lnitricacidwasrecommended.

    /mL

    rag.2.EffectoftheamountofKBr03onthereaction. OtherconditionsarethesalneasthoseinFig.1. VHNO

    ,

    /mL

    rag.3.EffectoftheamountofHN03onthereaction. OtherconditionsarethesanleasthoseinFig.1.

3.4.Effectoftheamountofp-CPF

    Accordingtotheaboveprocedure,theeffectof theamountof2'.4'dichlorophenylfluomne(4.0×

    l0mol?L)wasstudiedbyvaryingthevolumeof 2',4'-dichlorophenylfluorone(Fig.4).Therateof catalyticandnoncatalyticreactionsacceleratedwith increasing2'.4'-dichlorophenylfluoronevolumeand forcatalyticreactiontheinfluencewasmorepro

    nounced.

    InFig.4.themaximumandconstant?Avalue

    wasobtainedbetween4.0and6.0mLof4.0×1

    mo1.L?2'.4'dichlorophenylfluorone.Hence,an additionof5.0mLwasselectedforfurtherstudies. p/inL

    F.4.Effectofthemountofp-CPFonthereaction. OtherconditionsarethesameasthoseinF.1. 3.5.Reactiontime.rateconstant,andhalf-life Undertheoptimumcondition,theinfluenceof reactiontimeonbothcatalyticandnon..catalyticre.. actionswasexaminedcarefully.Theresultsshowed thatthe?AvalHebetweennon-catalyticandcatalytic reactionshadalinearrelafionshipwithtime(from 510min).Thecorrespondinglinearregression equationwascalculated:

    AA=0.04|63t(min)+0.O162f,=0.996).

    Therefore,thereactiontimeselectedwas10min. Therateconstantandthehalf-lifewereobtainedas follows:

    ,

:

    0.04

    

    63

    :

    

    .72×104-1K//1S.:——=.X.

    60

    f:

    :4.89min.

    ;i2k

284

    3.6.Reactiontemperatureandapparentacfiva- tionenergy

    Undertheconditionsdescribedabove.theinflu. enceoftemperatureoncatalyticandnon-catalytic reactionswasinvestigatedandtheresultsshowed thatthesensitivityincreasedquicklyupto45.C. Between50_90.C.thereactionrateincreasedline. arlywithincreasingtemperature.Inordertoensure highsensitivityandmakeexperimentalmanipula- tioneasier,80.Cwasthusselectedforallexperi. ments.Accordingtoareportedmethod,usingAr- rheniusequation,alinewasconstructedbyploRing

    lg?Aversusl/(isthetemperature)attem-

    peraturebetween50and90.Canditslinearregres- sionequationwasexpressedas

    1

    lgAA=4.53x10l3.26(r=0.9984).

    1

    Then,fromitsslope,theapparentactivationen- ergycalculatedwas

    =4.53×103×8.314×2.303:86.74kJ/mo1.

    3.7.Calibrationgraph,precision,detectionlimit,and themethodofterminatingreaction

    Afteroptimizationoftheexperimentalparame- ters,aseriesofstandardSe(IV)solutionsweretested. Alinearcalibrationgraphwasobtainedinthecon. cenffationrangeof0.004-0.015Bg?mE-ofSe(IV). Thecorrespondingregressionequationwasas follows:

    RAREMETALS,"Co1.25,No.Jun2006

    AA=31.05c~.+0.03432(r=0.9975),

    wherecse"istheconcen~ationofSe(IV)ex. pressedinlag?mL.

    Thestandarddeviation)was1.02×l0ob-

    tainedfromaseriesofllreplicatedeterminationsof theblanks.Thedetectionlimit(c)ofthemethod calculatedfromtheequationc=3s/awas9.86×

    l旷…g?L,wherecisthedetectionlimitandais theslopeofthelinearcalibrationequation. Intheexperiment,themethodoffixedtimewas usedtoindicatetheamountsofreactant.Catalytic reactionshouldbeterminatedimmediatelyafterthe fixedtimewasreached.Thenabsorbancewas measuredatintervalsofl0min.andtheresult showedthatAAwasinvariablein2h.Henceitcould

    beconcludedthat,oncethesystemwascooleddown toroomtemperaturebyflowingwater,thereaction wouldbeterminatedimmediately.

    3.8.Eftandeliminationofcoexistentions Standardsolutionscontaining0.2BgSe4+and variouscoexistentionswereprepared.Witharela. tiveerroroflessthan?5%.thetolerancelimitsfor

    variouscoexistentionsareshowninle1. FromTablel,Na,l<,SOft-,F-,P,C1-,NO3-,

    Zn,,Ag,v5+,HandY(Tolerance:

    20.100LLg)donotinterferethedetermination.The slightlyinterferingionsofpd2,C,La3+,Cun, Bi3+,

    4+

    ,

    Au3+,

    Sb3+,,

    Ru3+,

    Ca2+andMg2+

    (Tolerance:2.0-10Bg)andtheseriouslyinterfering Table1.Toleranceamountofcoexistingionsindetermining8.0Pg.L-mSe4+lag?L-

    CoexistingionsBeforeseparatingAfterseparatingCoexistingionsBeforeseparatingAfters

    eparating

    Na.K240040000Cl-.Zn40Do40000

    SO42000040000NO3,Ca2,Mg4004OOOO

    F32002O000Tr"8032000

    Pd20o800oAu,Sb3+4OO4OOO

    Co20.02O000Ni.8.0800o

    Mn8.020O00Fle"4.0l200o

    Cr32040000Hg,Ag8004000

Report this document

For any questions or suggestions please email
cust-service@docsford.com