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<br />i
<br />;:.. ;.v.aes-ss2
<br />
<br />s G ~n,ere~r+, r .. sC-:,,w; ' ~. - - ^. ^CC' of CiAV Snp~
<br />assn-..;. ;,. U. iJr: GOILns, Ui,.~ ,Pd3; '/~, .. ,p i 1-d8.
<br />(21 Duoooroll, Peter, Tozlcity to Fish of CyenYfes end Rehtee CDm•
<br />Do'JeC9. A P.nvie'n~. EPA~4aa /'_~90J 7, 1978.
<br />13) riYPnltleS In Water. I9d7 Ann,:a( goat o/ ASTM S»ndarW, A$TM:
<br />Phila0010h1a, PA, 1997; Vol. 7 t.i. x•2036-82. 01282-83. pp 119-t29.
<br />(4) OWIi)y Cnferle lav Warsr r8a91C+ora 8nok 1: U.S. EPA O111De D1 Water
<br />R(Ipl,at%J ~s ectl S'9rtlartlS: Ylashnplon, D.C.. 1886: EPA-440!5-86.
<br />001.
<br />161 Tereeenkar. Pfll; 45has, t3enpuly; DNpa, S, Malty. Anal. Glam.
<br />1989, 9d, 1584-1588. _
<br />(8) RaY• Rem @. Am, Leb. 1989, TD, 104-112.
<br />(71 Sekerka, 1.: Lochner, J. F, WAter Arra, 7979. 10. 179-489.
<br />I9) Ponbnol. Chrletel. S. Alt. J. Chem. 1984. 77. 133-137.
<br />(BI Nonomura, MekOto. Anal. Chem, 1e67, Sp. ?073-2078.
<br />(101 Pohlantlt ChrL!el S Ak. J. 6.nam„ 1985. ?d, :10-"~
<br />(tt7 JunpreiS, E. (srnnl ,; ,-ate. ~ e9 7.553-Se+
<br />(121 Jungrel9, ENIn; Am, Fanny, A r. coon. acre x971. do, t8r-ro?.
<br />113) L30ugen, D. Peter; Arpnan, gatlar: Brook sb8nk, Polar, A29I. Chem.
<br />1973, 59, 1845-1819.
<br />114) Kelatla, P. Nablh. /. Warsr POlWr, Confrd FeC. 19x9. 61, 358-358.
<br />(16) Plhler, B.; K0719. L. AnA/. Grim, Aeta 1990. 8d. 781-?81.
<br />(18) Zald, S. A,; Carey, J• Cyenkle ~rrd the Envhonmenr-Procee0:nps of
<br />a Cpnlerence; Beolechnlul Englnearln9 Proprem, Dept, 01 CwN EnpL
<br />nearkp, CSIh Fort Calllne. CO. 1985: V01, 2, pp 383-377.
<br />(17) O11no, S. Bue. Chem- Soc. JRn. 1987, 40, 1765-1175.
<br />(19) Mlriatt. J. L. GyenMe arq rho EnMronmenr-Procoodlnpa a/ a Confer-
<br />ence; CkaleGhnlCal Enginaerlnp Prrgrem, DODi. 01 Clvii Enpinoering.
<br />CSU: Fort CoIW1a, CO, 1995; Vol. 1, pp 85-81.
<br />RecervEn fnr review August 10, 1990. Accopred .January 4.
<br />1981.
<br />Kinetic Titration Method To Determine the Excited-State
<br />Concentration of a Photochemical Sensitizer
<br />I'. E. Poston and J. M. $errie'
<br />Department of Chemistry, University a( Utah, Salt Lake City, Utah 84112
<br />
<br />A noncomperatlve method to determine the excltad-trlplel-
<br />stata concentrallon of a photosenaltlcer fa described. TM
<br />method le based on the klnatlcs o} reactbn or quenching of
<br />the exched slate end avolda many o} the Umhatlana of eurraM
<br />techniques. Since the Illellmes of excltad lrlplat etalas of
<br />molecules In fluid aolullon era generally mlcroaeeonds ar
<br />longer, a dlMuslon-controlled quanchar In less than ml8lmaler
<br />concentrations can elgnlllcanlly Inlluenee the decay rats of
<br />the trljNet poputatlon. II Lhls small concentrellon of quencher
<br />la comparable to the Inltlal conoantratlon of excltad states,
<br />Then the klnatlca of Cho frlplsl-stela decay are na Wngar
<br />pseudo flrat order. Tlrls klnstlc behavior k exploited to pro-
<br />vlde a atmple, nonCOmperetlve tRrallon method for dstsrmlNrp
<br />exclted•trlplel-state concentrations. The rata conatanl for
<br />quenching need not be known In advance, and any method
<br />of monltoring the quenching klnellu can be used. The
<br />-echnlque Is evalualad In the present study la delermlltlrtg the
<br />excltad-lrlplat-slate concentration of ben:ophsnone by
<br />measuring the decay klnellcs o} phasphareaeence qusnehed
<br />by blacalyl.
<br />In order to accurately determine the quantum yields of
<br />phatoinitialed ronCtions or meter properties of excited stales,
<br />it i5 necesssry W know the concentration of phoWexcited
<br />molecules. Concentrations of excited states can be estimated
<br />from the absurptintt doss section. excited state lifetime, and
<br />gmuud-slate concentration oC a apecias together wile the
<br />excitation c,ptii~nl power, beam spot size, end autos cluratinn.
<br />These escirnates can he inaccurate, however, due to spatial
<br />inhomogeneily of the excitation beset or deplelier. -r t'::'
<br />gruund•scat.e population, neither oC which are ee_+;; •.::;a:r.
<br />teri2ed. llelenniuing excitad•lriplet•stote cunrr::r. ~. ,. ~~ .
<br />particularly diffmult, because yields of inter=gater~ ..: ~~.- r.
<br />ate gear:rally not kuuwn with accuracy.
<br />Techulyurs fnr Ohtsmiug antcentratim:.
<br />tivities. nr quantun yields of fnrmatmn :,f :, :: ., .
<br />I'sIl generally into two classes, u~mpnrati',, .....
<br />rativo methods. Comparative metlhods w estimate triplePatate
<br />molar absorj>tivities (1) are typically based on triplet-triplet
<br />energy teanafcr from a stsndard excited triplet donor; the
<br />decreosa ire the optical absorption by the donor (having e
<br />Itnown Tt -1'n absorptivity) is Correlated with the increase
<br />in absorption by the acceptoriq obtain the acceptor motor
<br />absorptivity (2)- The method asaUmee that all of the at:etrpt.or
<br />population arier9 from energy Lrnhsfer from the donor, which
<br />may ba dlf(icult to assure. Unceftaintics also arise from the
<br />molar absorptivity of the donor of iLg photoproducl and from
<br />any yield of donor (dhoWprnduct that ie not quenched by the
<br />acceptor (1). $y use of the values of T••T molar absorptivity
<br />thus obtained, comparative methods cart also be used to de-
<br />termine intersystem crossing yields (3). Hero, the triplet
<br />concentration oC Lhe unknown is Cstimatod from its'1='T ab•
<br />sorption and compared to that of a Standard b9ving known
<br />triplet yield a»d absorptivity. For the results tp be valid, the
<br />triplet states must not absorb thk exciting light (4) and dc-
<br />pletion of the ground state must ho negligible (5).
<br />Tn ovoid some of the uncertnlrlties and assumptions of
<br />comparative motho<ls, noncompt}rative methods fot deter-
<br />mining triplet•atale populations etYd molar ab9orptivitiea have
<br />been davaloped (6). These methods do not rely on intermo-
<br />lecular intamctions such as allergy jransfcr nor do they require
<br />knowledge of the molar absorptivity or triplet yield of a
<br />standazd. For example, triplet•stato concentrations attd molar
<br />absorpi.ivities con be determined Eby direct photolysis of an
<br />unknown while simultaneously trloosuring the triplot•state
<br />ab9urptinn and the loss of ground-ptate absorption- In order
<br />to obtain excited•statr cunrentratiuns, Cho method requires
<br />either a spectrsl region whore ihe.ground state absorbs free
<br />of nnv triplet-state absorption qr an isnheFtlC Auint where the
<br />;tc„rpti~'ilirs ~tf 5',e ground mrri excited states ore equal
<br />t: ,. ~ t .ar nonuomparative methods are hosed i,tt the pho•
<br />:: .;nto-~tc=_ tr.r .ascot+.~ t•~.Crted triplet states (G, H).
<br />- - - :: f!:at :..:;..r -~mii-~ trio? knowledge of the triplet
<br />.- ~ ~ .. ~~•.I ri;her nn flee intensi c;
<br />.. . _..-`I ~:~n pulsrc roar are innget
<br />__ ... ..,:t~~ .'~:..; ..n the lime dependence of
<br />' •~ :~ _ , ,i;~ppod [mttiuuous excitation
<br />
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