cerous ion, in tlie absence of a n y int,erfering species, may be determined with a n accuracy of *57', by comparing its fluorescence intensity with that of a cerous sulfate standard. ;It higher crrous ion cencentrations, ,self-quenching apparently becomes important. Ceric ions presumahly deerewe cerous ion fluorescence by 'ilmrhing some of the exciting and emitted light. Calculations of the factor Q, the ratio of Ce(II1) fluorescence n tlie al)\ence and presence of Ce(IV ' , hayet-l on the Ce(IT') molar absorptivitie- a t 234 and 360 mp agree fair])- r w l l n-it11 the experimental results. FOY2 constant' ceric ion concentration Q i, independent, within tlie ~~sl)erimental error, of cerous ion conw itration over the range 3 X to lo-' gram ion per liter (Table 11). - i t ~~JJIW C't,!,III! conrentrations there is . ~ i irviclcnce ~ to suggest t,hat Q iiicrw-e- 4qnificaiitly. Log Q increahes linearly lr-itli increaqing Ce(IT7) concentration m.er tliP range 0.2 to 3.0 X g:r:iin iiin ]lei lit'er (Table 111). The equation log Q = 3760 [Ce(IV)] niay be deriwd i'ronl the average of the log Q ' [ C ' F ( I T J j ratios. I X n g this equation nitliin the limit? tievrilied. rerow iori c~riicc~ntratirlnof
Regarding the application of thia method to the analysis of Ce(II1) In the preyenre of cpecies other than Ce(IV), it should be noted that a n y substance 14 hich abiorbs near 250 or 350 mp mill reduce Ce(I11) fluorescence. The effect of each iubbtance present sould hai e to be in1 e+gated before proceeding nith the anal? +.
Table 111.
Dependence of Q on [Ce(lV)]
[WIy)1
gram ions 0 0557 0 0696 0 0774 0.167 0.268 0,228 0,260 0.301 0.323 0.307 0.353 0.330 0.39" 0.374 0.417 0,446 0.433 0 . 720 0 . 731 0.703 0.924 1 .OS6 1.076
0 0 0 0 0 0 0 0 0 0 0 0 0
145 188 242 484 676 686 728 773 790 821 872 879 977 1 02 .~ 1.07 1.15 1.16 1 85 1.94 1.94 2.42 2.89 2.89 ~
3h40 3 700
:3200 3450 3060 3320
LITERATURE CITED
:3580
1 ) (;reenhaus, H.
I
