Table V.
Decontamination Factors
Cobalt Thorium Uranium Radium Cerium Promethium Radium Cesium Ruthenium Strontium Actinium Zinc Zirconium-niobium Iron Manganese Lead
>103 200 > 103 > 103 103 20 >io3
> 103 >io3 > 103 > 103 >io3 >io3 >io3
> 103 >io3
however, promethium occurs at levels much lower than strontium. The author has reported, for instance, that in steer bone, the promethium content is only 1% of the strontium-90 content (1). Should a sample be analyzed where a high promethium content is suspected, its interference can be easily overcome. By counting the sample through 30 mg. per sq. cm. of aluminum absorber, the promethium count can be reduced by a factor of 100. However, especially if a 2~ internal flow counter is used, this will result in a significant loss of yttrium counts because nearly all of the backscattered yttrium-90 radiation will also be absorbed. A better tech-
nique would be t,o increase the acid strengt'h in t'he EHPA washing steps from 0.5X to 0.8L11 hydrochloric acid. The yttrium recovery will only be reduced to 92%, but the promethium decontamination factor will be increased to 400. Yttrium-91, if present, can be different'iat'ed from yttrium-90 by either absorption or decay. .A far better solution is to extract the solution twice with EHPh to remove all ytt,riuiii nuclides, and then set the solution aside for a measured period of time for fresh yttrium-90 ingrowth. Two extractions will remove more than 99.9% of any yttrium initially present without loss of a measurable amount of strontium. The sensitivity of the procedure is, of course, a function of the background and geometry of the detection equipment being used, and is dependent upon the reagent' blank as well. With a geometry of 35 to 40%, a background of 1 c.p.m., and a reagent blank of 0.1 c.p.m., as little as IO-'* Curie of strontium-90 can be determined. ;is described, the procedure considers only the analysis of bone ash. It, has been successfully applied to other biological ashes, including food ash and plant ash, with no procedural alteration other than the methods used in dissolving the sample.
ACKNOWLEDGMENT
The author expresses his appreciation to Joseph Rivera of the U. S. Atomic Energy Commission Health and Safety Laboratory for furnishing some of the samples. LITERATURE CITED
(1) Eisenbud, Ll.> Petrow, H. G., Dosimetric hspects of Radium Poisoning, Ann. Rept., AEC Contract AT(30-112896,September 1964. ( 2 ) Kauffman, P. E., Matuszek, J. M.,
c.s.
Jr., Ninth Annual Meeting of the Health Physics Society, Cincinnati, Ohio, June 14-18, 1964. (3) Peppard, 1). F., >lason, G. W., Maier, J. L., Driscoll, W. J., J . Inorg. Sucl. Chem. 4, 1334 (1957). (4) Peppard, L). F., .\lason, G. W., Aloline, S. W., Ibid., 5 , 141 (1957). (5) Petrow, H. G., Allen, R. J., . ~ N A L . CHEM.33, 1303 (1961). ( 6 ) Ibid.,35, 747 (1963). (7) Petrow, H. G., Cover, .4.,Schiessle, U . J., Parsons, E., Ibid., 3 6 , 1600 (1964). HEKRYG. PETROW A. J. Lanza Research Laboratories Institute of Environmental AIedicine New York University Tuxedo, N. Y. RESE.4RCH supported in part by the Division of Biology and Medicine of U. S. A4tomic Energy Commission Contract AT(30-1) 3086 and Sational Cancer Institute Contract C h 06989 and ES00014.
Fluorescence Analysis for Traces of Naphthace ne in Anthracene SIR: Assay of trace impurities in anthracene purified by zone refining for growth of single crystals requires methods sensitive to levels below 1 p.p.m. impurity. The fluorescence of anthracene and of anthracene-naphthacene mixtures has been studied (1, 2 , 5-8, 11-13, 1 7 ) . Saphthacene, a major impurity in anthracene, may be determined by fluorescence. Saphthacene fluorescence arises not from direct excitation of the low concentration of naphthacene present, nor from absorption of energy from anthracene emission (8, 1 1 ) . I n solid solutions the anthracene host absorbs the exciting energy and transfers it to naphthacene by sensitized fluorescence (11, 16), or by excitation migration (4-6, 8). When molecules of the two species are separated beyond crystal lattice distances either upon fubion or by a solvent, the energy transfer cannot occur so readily as in the solid solution. EXPERIMENTAL
Apparatus. A Farrand spectrofluorimeter equipped with a 150-watt Xenon arc lamp, a n R C h IP28 photomultiplier and two monochromators was employed for all measure-
586
ANALYTICAL CHEMISTRY
ments. T h e phototube was connected by a microammeter to a Varian G-10 strip recorder. Reagents. Anthracene was prepared from anthraquinone by t h e method of Fieser (3) and was purified by recrystallization and zone refining. Naphthacene (Matheson Coleman & Bell No. 9082) was used without further purification. All solvents used were spectroquality grade. Procedure. Standard solutions of anthracene and naphthacene in isopropyl alcohol were mixed in proportions to prepare 39 qolutions, each containing 0.50 mg. per ml. of anthracene, and with naphthacene content ranging from 0.6 to 4360 p.p.m. of the anthracene , content. These standard mixtures, in 4-ml. portions, were diluted with 125 ml. of isopropanol to give clear solutions. Rapid addition of 125 ml. of distilled water to 4-id. portions of the standard mixtures produced colloidal dispersions. Fluorescence measurements were made with the exciting monochromator, adjusted for peak fluorescence, at 365 mp. Tyndall and Rayleigh types of emission (10) do not present a problem in the system. L-denfriend (15) and Parker and Reese (9, 10) have discussed instrumental errors in fluorescence analysis. In the present work,
the instrument was used at constant slit width and excitation energy was kept constant. No correction for phototube response was made because quantitative measurements were made at selected, fixed wavelengths. RESULTS AND DISCUSSION
Emission peaks for anthracene occur a t 405 mp (maximum), 430, and 450 mp; for naphthacene in anthracene at 510 mp (maximum), 540, and 575 mp. The results are qualitatively similar to those described for dilute solutions (1, 1 1 , 1 3 ) . Typical spectra for colloidal suspensions are presented in Figures 1 and 2. Colloidal Spectra. From 0.6 to 300 p.p.m. naphthacene, anthracene fluorescence a t 405 mp decreases and that of naphthacene a t 510 mp increases, as measured by the height of the emission peak (Table I). Above 300 p.p.m. napthacene, self-quenching of naphthacene emission is observed. This is caused by interaction betwsen naphthacene molecules a t the higher concentrations. Color of the colloidal suspensions changes much more noticeably than does that of the solid in either single crystal or polycrystalline form.
8 i
t
07
96 Range xlo
05
04
s :O 3 L C
u >02 -m 0 E
01
Figure 1. Typical fluorescence emission spectra of colloidal suspensions of naphthacene and anthracene
0 472
490
510 Wavelength
530
- Millhmlc r o n s
550
570
52
Figure 2. Fluorescence emission spectra at high recording sensitivity
Table I.
Fluorescence of Colloidal Suspensions of Naphthacene and Anthracene
Naphthacene concn., p.p.m. In anthracene 0.6 6 8 ill 13 1 16 5 39 8 53.1 146 29
_. -1
727 1090 2180 2420 2780 3200 3780 4360 Pure naphthacene
Anthracene, 1 4 0 6 mp 7.20 8.04 8 40 6 20 5 68 4 09 4.00 1.98 1.24 0 65 0 50 0 374 0 370 0.37 0.345 0.342 0.29 0.00
Naphthacene, Islo mp 0.187 2.10 2.90 2.99 3.24 5.27 5.69 9.79 11.3 9.90 10.18 9.42 8.3 8.2 8.33 7.05 6.88 0.00
Intensity ratio,
R
=
Zslo/Z405
0 026 0 262
0 345 0 482 0 571 1 30 1 42 4 94 9 11 15 2 20 3 25 2 22 4 22 1 24 1 20 6 23 0 0 00
Observed colors blue-violet blue-violet blue blue blue-green blue-green green green green green green green green green green green green none
Table 111.
5
Kaphthacene content, p.p.m. 0 60
4
22 4
5
74 7
No. of replications
-5
291
- Peak intensity, 405 rnp Range Mean Std. dev. 6 57 22 f 0 67 8 3 f 0 56 5 46 4 826 18 f 0 26 2 45 2 022 69 f 0 116 1 31 1 211 49
With the colloidal suspension technique, the blue anthracene fluorescence at 405 mh is spectrometrically measurable up to 4360 p.p.m. naphthacene. This contravenes Sloan’s statement ( I 4 ) that, at 0.3 p.p.m. naphthacene, the anthracene fluorescence is completely extinguished.
Table II.
Fluorescence of Isopropanol Solutions of Naphthacene and Anthracene
Naphthacene concn., Ant hrap.p.m. in cene, anthracene ZlOs mp 0 6 0 93 53 1 1 62 219 0 94 2180 3 26 Pure naphthacene 0 00
Naphthacene, 1 5 1 0 mp 0 00 0 00 0 03 0 13 0 00
Intensity ratio, R = 1510/1445
0,00 0.00
0.032 0.037 0.00
Observed colors blue-violet blue blue blue none
Reproducibility of Analyses
Peak intensity, 510 m p Range Mean Std. dev. 0 170 188 f 0 019 0 22 3 36 f 0 84 2 764 63 4 77 3 68f 0 82 5 80 10 4 9 51f O 81 11 3
Range 0 0256 0 0262 0 5460 749 1 822 25 6 959 18
Ratio, Z610/1401 Mean Std. Dev. 0 0260
f 0 00037
0 608
1 0 094
1 94
f 0 18
7 94
f 0 84
VOL. 37, NO. 4, APRIL 1965
587
Clear Solution Spectra. T h e results sumniarized in Table I1 confirm the reported insensitivity to naphthacene content. At concentrations higher than 2180 p.p.m., some emission is noted at 510 mp, but its intensity bears no significant relationship to the naphthacene content. Quantitative Evaluation of Colloidal Spectra. Figure 3 presents a plot of intensity ratio R = Isio/1405 as a function of added naphthacene content. The relationship is linear in the range of 10 to 300 p.p.m. naphthacene. Fluorescence of the “pure” standard anthracene indicated the presence of naphthacene by an intensity ratio of 0.026. On the assumption that linearity of R should hold even at low naphthacene content, the linear portion of the curve was extrapolated. The extrapolation suggested that 0.6 p.1i.m. napthacene was present in the standard. When all of the observations were rectified for this additional 0.6 p.p.m. naphthacene in the original material, all of the experimental points coincided closely with the predicted line. This line was fitted to the equation C = 28.1 R106, where C is naphthacene content, p.p.m. in anthracene. Above 300 p.p.m. naphthacene, self-quenching causes increasing deviations from the line. Reproducibility of Results. Experimental data on the fluorescence intensities, I, display considerable scatter a t constant composition. Bowen and Lawley (1) showed that the intensity varies with the amount of crystal surface, hence is affected by the particle size in microcrystalline suspensions of anthracene. Smaller particles with greater specific surface showed greater emission intensity. Variations in the size of the colloidal particles can thus be expected to produce variations in intensity. However, Table I11 shows that the use of the intensity ratio, R , considerably improves the reproducibility of the results because changes in specific surface appear to influence both emission peaks in the same way. Figure 2 indicates that the colloidal method shown here is sensitive to much less than 1 p.p.m. of naphthacene in anthracene, and readily distinguishes between samples differing by as little as 0.175 1i.p.m. naphthacene. Impurities other than naphthacene, emitting in the 510-mfi region could interfere mith the results, but such have not been found in the anthracene studied or in commercial samples of anthracene from other sources.
588
ANALYTICAL CHEMISTRY
tlook
/r c
i
4
._ c 10
cor
I
LITERATURE CITED
(1) Bowen, E. J., Lawley, P. D., .Yature 164, 572 (1949). (2) Czorny, B., “Electrical and Optical Properties of Organic Semiconductors,” Newark College of Engineering (1963). (3) Fieser, L. F., “Experiments in Organic Chemistry,” 3rd ed., pp. 159-64, I). C. Heath and Co., Boston, 1955. (4) Franck. J.. Teller. E.. J . Chem. Phus. 6. 861 (1938). (5) ‘Furst; hl., Kallmann, H. P., Brown, F. H., Zbid., 26, 1321-2 (1957). (6) Ganguly, S. C., ‘Yature 151, 673 I
,
ij -194.1) ”-_,.
(7) Lipsett, F. R., Dekker, A. J., Can. J . Phys. 30, 165-73 (1952). (8) Northrop, U. C., Simpson, O., Proc. Rou. SOC. (London) A234. 136-49 (1656). 9 ) Parker. C. A., Iteese, W.T., Analyst 85, 587 (1960). 10) Ibid., 87. 83-111 (1962). 11) Pringshem, P., “Fluorescence arid Phosphorescence,’ ’ 1st ed., Interscience, New York. 1949. 12) Sangster, R . C., Irvine, J. W., J . Chem. Phys. 24, 670 (1956). 13) Shpol ‘ski, E. T. S.,Ilena, A. A,, Bazilevich, V. Y . j Doklad. Akad. LYauk
I
I
1 1 1 1 1 1
S S S R 62, 227-30; (1948); C. A. 43, 498a (1943). (14) Sloan, G. J., “Physics and Chemistry of the Organic Solid State,” Fox, Labes, and Weissberger, eds., 1-01. 1, p. 192, Interscience, New York, 1963. (15) Ldenfriend, S., “Fluorescence Assay in Biology and Medicine,” Academic Press, Xew York, 1962. (16) Tan Duuron, B. L., Chern. Rea. 63, 325-51 (1963). (17) Van Duuren, B. L., Bardi, C. E., ANAL.CHEM.35, 2198-202 (1963).
SAULI. KREPS MELVISDRL-IK BOHDAN CZORXY~ Newark College of Engineering Department of Chemical Engineering 323 High St,. Newark 2, N . J. Financial assistance of the Newark College of Engineering Research Founda t,ion, Inc., which made this work possible, is gratefully acknowledged. 1 Present address, Semiconductor and hlaterials Division, Radio Corp. of America, Somerville, N. J.
