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<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
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