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F{I~II; ~- ~~an~nh IE` IhJC TEL ~30:,-'9?-56.-' <br />~~ <br />I.ITERATU~CITED <br />Mau 04 9! `~~8 No .004 P.U3 <br />Anal. Chem. 1981. 63, 688-892 <br />(1) Von Michaelis, Hans. Cyanlee aM fha Envkompnt-PloroedMpe dl <br />e Conlarelwa: fAeoteahnioal Englnaering Program, Dept. of CNII Enp4 <br />nearing, csu: Fort Collin., co, lees; vol. 1, po 61-ea. <br />(2) DuodOrotl, Peter, ToxlClry to Flah Df Cyandea end ReNtee COm• <br />pountls. A Review. EPA-140/5.80.37, 1876. <br />(3) Cyanides In Wetar. 1987 Annual Bodr o/ AS1M Standards, ASTM: <br />PhNadelpMa. PA, 1887, Vol. 51,2, D•2D38-82, 01282-93, pp 118-128. <br />({) puemy CrlHrle for Weta /BBe IC7oAY B,70k); U.S. EPA Olflde of Water <br />Ropul911ona end $tandartls: Waahlnplon, D.C.. 1888: EPA-440/5-86• <br />oDl. <br />(6) Tareaenker. PAI; Aahea, Oanguy; Durpa, S. Malty. Anal. Chem. <br />1898, SB, 1684-1688. <br />{8) Roy. Rpm 9. Am. Leo. 1988. 1p, 104-112. <br />l7) 9ekerke. I.; L9thner, J. F. Wafer Rea. 7978, lo, 478-483. <br />(B) Pohbnel, Chrlalel. 9. Alr. J. Chem. 7884, 97, 139-737. <br />(D1 Nonomura, Mekclo. Anal. Chem. 1887, B8, 2073-2078. <br />ft01 Pohlandl, chTtal. B. Ah. /. Che .1806. 98, t10-11{. <br />(17)JunprPU, E. ISrneI J. GMm, 1961, .687-SB{. <br />(12) Jungrals, Ervin; Aln, Fanny. Adel. kn. Acfe 1977. BB, 181-182. <br />(19) Ctduleen, D. Pater; Afphen, Baser: rookabenk, Paler. Anal. them. <br />7872, bB, 1C 46-ta{9. <br />(141 Nelade, P. N~- :. Wafer PDUuI. ¢onlyd Fed. 1968. Bf, 950-358. <br />(16) Plhler, B.: V -Anal. Chlm. A a 1880, BB. 151-281. <br />(18) Zekll, S. A.: l.nbr. J GyanNe end fnvkronmenr-Pidceednps of <br />e Cpnle/tlnce, OculachMCel Enpbe ring Pr ram, Dept. of Clvll EnpF <br />nearing, CSU Con Conlns. CO. 19 6: Vol. 2, pp 963-377. <br />(17) Otlno, S. Buy GYiBrn. SoC. Jpn. 1 7, 4p, 1765-1776. <br />(1B) MutaB, J~ t. CynnMe and the Envron ant-FYCCaedlnys pl B Conler- <br />ence; 60oledhnitel Englnearing Pr ram, papt, of Civil Erpinoerinp, <br />C6lP Fort COIIinc, CO, 7986; Vol ~pp 86-81. <br />RecetvEn for review August 10, 1180. Accepted .January 4, <br />1881. <br />Kinetic Titration Method To Determine the Lxcited-State <br />Concentration of a Photochemical Sensitizer <br />P, E. Poston and J. M. Harries <br />Department o/ Cftemiatry, Uniuereity of Utah, Salt fake City, Utah 84112 <br />..i.. . <br />A noncomperetlva method io determine the exclted-trlplet- <br />slate concsntrallon of a photosen9ltlxer Is described. Ths <br />method le based on the klnatlcs of reactbn or qu9nehlnp of <br />Iho excMad slate end avoids many o} the M1ltetbns Of eurtaM <br />tachnlques. Since the Illatlma9 0l sxclted triplet stales of <br />molecules In tluld eolutlon are generally microseconds or <br />longer, a dlHusloncontrolled quencher M lass Than ml9lmoler <br />concentrations can elgnlflcanlly Inllusnc9 the decay rats of <br />the triplet poputstlon. 1/ this email concentrstlon of quencher <br />la comparable to the Initial concenlratlon of sxclted elates, <br />then the klnatlcs of the Irlplel-state decay ere no longer <br />pseudo f1r91 order. Thla kinetic behavior Is 9xplolted to pro. <br />olds a aknple, nonoomparatlve iRratlon method for dstsrminllrp <br />exclted•Irlplel-slet9 concentratlene. The rata eonatent for <br />quenchtnq need not be known In advance, and any method <br />of menltorlnq the quenehlllg klnatlcs can be usstl. The <br />technique Is evaluated In the present study for delerminlrtg the <br />sxclted-triplet-state concenlratlon of benxophenona by <br />measluing the decay klnsllc9 0} phosphorescence quenched <br />dy blecalyl. <br />In order to accurately dotennine the quantum yields of <br />phoG)inil.inted reactions nr molar properties of excited states, <br />it is necessary to know the concentration of photoexcited <br />muleculos. Concentrations of excited states can be estimptad <br />from the absorption cross section, excited state lifetime, and <br />grntln(1-elate concentration of a species together With the <br />axcilation optical power, beam spot size, and pul6e (luratinn. <br />These estimates can he inaccurate, however, due to spatial <br />inhumogeneily of rho excimtion beam or depletion of the <br />gtuund•state population, neither of which pre easily chnrac- <br />terizad. Determining excitad•lriplet-state concentrations is <br />perticulorly difficult, because yields of intersystem sassing <br />are getlarally not known with Accuracy. <br />Terhniyuee for obtaining cottcentrntione, molar ab;orp- <br />tivities, or yuentum yields of formation of triplet excited states <br />fall generally intq two classes, compnralive and nuncvmpp- <br />rptivo methods. Comparative meth s to estimate triplePatate <br />molar ebsorlltivities (])are typic y based on trilrlet-triplet <br />energy transfer from a standard xcited triplet donor; rho <br />decrease in the optical absorptio by the donor (having a <br />known Tl --'1'a absorptivity) is co related with the increase <br />in absorption by the acceptor to btein the acceptor molar <br />absorptivity (2). The method also es that all of rho aceaptor <br />Iropulatin» arises from energy tran ter from the donor, which <br />may ha dif(icult to assure. Uncert inties also arise Cram the <br />molar Absorptivity of the donor or i r photoproducl. and from <br />any yield of donor photoprnduct tl al ie nut quenched by t.17e <br />acceptor (1). By use of thD values f'f••T molar absorplivrty <br />thus obtained, cmparative metho scan also be used Co de• <br />torlnirle in[ersystern crossing yial s (3). Here, rile triplet <br />concentration of the unknown is a imatod from its'1='t pb• <br />sorption and emnppred to that of standard having known <br />triplet yield slid absorptivity. Far he result. to be 1•al: !, the <br />triplet states tnust not absorb the xciting light (4) an': '. <br />pletion of the ground stale must o negligible (ol. <br />'I'n ovoid some of the uncertni ties and assumptions of <br />cntnparative motltoLls, naneompa live mothocls fur deter- <br />mining triplet•elate populations an molar absorptivitiea have <br />been developed (G). These methn s do nut rely ol7 i»tertno- <br />lecular interactions such a6 ollargy i afar nor do they rwr~ -~ <br />knowledge of the motor absorpti ity or triplet yield r <br />standard. For example, triplet•swW COncentrntions and tool..: <br />absorpt.ivities curt be determined y direct phululysis of nn <br />unknown while eimultoneously m asuring the triplot•slale <br />absurptiol And the loss of ground-9 Ale absorption. Tn order <br />to obtain excited-stale cuncenirati ns, the methvd requires <br />either a spectral region whore the raulld stale absorbs free <br />of Qtly triplet-state absorption or an isnhvstic point where rile <br />molar absnrptivities of the ground d excited smtcs ore equal <br />(7). Other noncumparative motho s are haled on the pho• <br />lol,ysis kinetics for generating oxc led triplet states (E, R). <br />Methods that do not. require prior knowledge of the triplet <br />yield or molar absorptivity are bas d either on the intensit• <br />dependence of saturation by excitpt on pulses that are long. <br />than the singlet lifetime (91 or un the Lime dependence of <br />triplet-smt9 saturation using a rhop~od crrntinuous excitation <br /> <br />0003• 700/917d363.OBBBS02.50/a $~ 1981 gmerlcan Chemical Soclary <br />