other authors (Table 11), yield standard deviations of a similar magnitude-e g , ratio E/B = 1.53 I 1.15 (75%). F/C = 1.31 A 1.12 (85%),G / D = 0.72 f 0.67 (93%). We should not assign great significance a priori to the fact that our sensitivities are between others' values for Eo = 25 MeV and Eo = 30 MeV. Our distance sample-converter is greater (15 c m ) , and our electron beam intensity double (-210 PA) theirs. However, these features result in opposite effects. Moreover, the general agreement of sensitivity ratios is quite important, because it implies activation trends for our system, parallel with those of thintarget, low-& facilities, for the whole range of giant resonance energies ( k = 10 to 30 MeV). T h a t is, it suggests reasonably similar bremsstrahlung spectrum shapeswithin said range-for the ORELA and conventional facilities (2, 4, 6), as we had expected from Figure 1. Table I1 shows, finally, that our sensitivities agree best
with Lutz's results. The latter were obtained from a comprehensive table (2, 4 ) which lists calculated sensitivities for 76 photon reactions on 59 elements for electron beam energies Eo = 25, 30, and 35 MeV. With reasonable approximation, the average ratios of Table I1 can be used to estimate sensitivities for our PAA system, from Lutz's table, for elements and reactions not included in our work.
ACKNOWLEDGMENT We thank J. A. Harvey and H . A . Todd for their continuous interest in our work, and ORELA's operators for smooth scheduling and conduction of our bombardments. Received for review September 12. 1973. Accepted November 12, 1973. Oak Ridge National Laboratory is operated by the Union Carbide Corporation for the U.S. Atomic Energy Commission.
Determination of Lead in Paint with Fast Neutrons from a Californium-252 Source George J. Lutz Activation Analysis Section. Analytical Chemistry Division, National Bureau of Standards, Washfngton. D.C. 20234
Several decades ago in the United States, it was common practice to paint the interior walls and woodwork of dwellings with a formulation of paint containing large amounts of lead. This has created a tragic health problem, particularly in some of the larger cities, causing lead poisoning of children in certain susceptible age groups who have ingested this lead-bearing paint which has peeled or chipped off from the walls. The detection and alleviation of this hazard depends upon reliable chemical determinations of lead in suspected areas. Currently, screening of suspected paints is oriented to the detection of those containing greater than -0.5% of lead. The accurate determination of lead a t this level is not particularly difficult by a variety of methods, but they usually require time consuming manipulations such as dissolution prior to measurement, although Rasberry (I) has studied portable X-ray fluorescence analyzers developed specifically for use in screening, in situ, wall paint for lead. A purely instrumental activation analysis, particularly if it could be accomplished with a relatively inexpensive irradiation source would appear t o have merit. It would dispense with lengthy chemical treatments and would have the potential for largely automating the determination. This paper describes the evaluation of a small 252Cf source for this determination. T h e element californium was first synthesized by Thompson et al. (2) in 1950. Californium-252 is currently manufactured by irradiating plutonium targets in a nuclea r reactor. Starting with 239Pu, the heaviest isotope available in large quantities, the production of 252Cf requires a series of 13 neutron captures. Current production is about 1 gram per year. The isotope has a half-life of 2.65 years. It decays both by CY particle emission and by spontaneous ( 1 ) S. D. Rasberry, Appl. Spectrosc.. 27, 102 ( 1 9 7 3 ) . (2) S . G . Thompson, K . Street, J r . , A . Ghiorso, and G . T Seaborg, Phys. Rev., 7 8 , 298 (1950).
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fission. The neutron output from spontaneous fission of 1 gram of 252Cf is 2.34 X 10l2 per second. T h e unmoderated neutron spectrum of 252Cf is roughly the same as that of 235U.Relative to ( a , n ) isotopic neutron sources, 252Cf sources have smaller dimensions and less radioactive material. They require less space for decay helium and, for practical purposes, rarely require cooling. They are also competitive on a cost per neutron basis with other radioisotope neutron sources (3). Ricci and Handley ( 4 ) aptly considered their system utilizing this isotope for laboratory activiation analysis a "portable, maintenance-free, quasi-reactor."
EXPERIMENTAL The iiBS 252Cf facility consists of 8 sources of 75 gg each a t the time of these experiments. The sources are mounted in a 90- x 90- X 210-cm high aluminum tank filled with demineralized water. The source configuration is shown in Figure 1. The purpose of the octagonal source array is to produce a neutron flux as homogeneous as practical at the sample irradiation position. Since the stable isotopes of lead do not undergo nuclear reactions with thermal neutrons useful for analytical purposes. the sources are moved as close as possible to the central pneumatic tube to enhance t'ast neutron reactions. The fast neutron flux is approximately 5 x 10; n.'cm2-sec. Samples are packaged in a polyethylene snap cap vial of 1-cm diameter and 2.S-cm length. This is placed in a larger polyethylene vial with spacers to ensure that the sample is in the position of maximum neutron flux. A compressed air pneumatic transfer system transfers the samples to the irradiation position and return. Preliminary experiments involved irradiating and counting a few grams of lead for various lengths of time. Three nuclear reactions were detected. These are shown in Table I. The threshold of the reaction 2"O'Pb(n,2n)2"3Pbis about 7.3 MeV and the yield even with long irradiation times is inadequate for analytical purposes. The inelastic scattering reactions. however. yielded sufficient activity to warrant further investigation although, because ( 3 ) J. L. Crandall. isotop. Radiat. Techno/..70, 306 (1970). ( 4 ) E Ricci and T. H. Handley. Ana/. Chem., 42, 378 (1970).
200
SAMPLE, A T IRRADIATION POSITION HIGH DENSITY LINEAR POLYETHYLENE
I
I
I
I
1
AI SOURCE HOLDER
’
I POSITIONING PINS
Pb-207m 1064 keV
J
SIDE VIEW
01
0
I
I
1
I
20
40
60
83
1 100
CHANNEL NUMBER
Figure 2. Nal(TI) spectrum of paint sample irradiated for 3 seconds, counted for 6 seconds-recycled 20 times small polyethylene vials. Cadmium sheet of about 1-mm thickness was wrapped around the vials to minimize thermal neutron reactions, and these were packaged in the larger vials with polyethylene spacers. Standards of lead salts were similarly packaged. Because of the intrinsic stability of the isotope source, flux monitors were not necessary. Samples were irradiated for 1-2 hours and, after transfer to a clean counting vial, were examined with a KaI(T1) detector and a multichannel analyzer. Only a few experiments were required to show that (n,p) reactions on stable titanium isotopes yielding scandium radionuclides had sufficiently high yields that the photopeaks of the lead isotopes could not be resolved with the NaI detector. With a Ge(Li) detector, however, all three gamma-ray lines of 204mPbcould be adequately resolved. The elements titanium, iron, barium, calcium, magnesium, copper, silicon, strontium, and zinc, possible major and minor constituents in a paint sample, were irradiated and counted under the same conditions as the paint samples, and it was determined that they would not interfere with the lead activity measurement. The zo7Pb(n,n’)207mPbreaction was examined by irradiating the paint samples for about 3 seconds and, after allowing for about 2 seconds return, counting for 6 seconds with two 4-inch X 4-inch NaI(T1) detectors. Because the transit time of the samples from irradiation source to detectors exceeded two half-lives of the isotope produced, it was necessary to recycle the sample a number of times to build up adequate counting statistics. The precision of timing of sample return for this short-lived isotope was marginal and results are not as reliable as with the 2”4mPb isotope. A NaI spectrum of the SRM paint cycled 20 times is shown in Figure 2.
IRRADIATION POSITION
TOP V I E W
Figure 1. 252Cfsource configuration of the difficulty of precisely timing the transit time to the detector for the short-lived 2”7mPb, this reaction received only a cursory study. Work was concentrated on three paint samples. Two of them were the ‘‘coarse’’ and “fine” fractions of a paint which had been scraped off the window sash of a home undergoing renovation. T h e sample had been crushed with a mortar and pestle. Material passing through a No. 40 mesh sieve and retained on a No. 100 mesh sieve was designated “coarse,” material passing through the No. 100 mesh sieve was denoted “fine.” The third sample was a mixture of paints from various sources which was carefully ground and homogenized. This material has had its lead content certified by the National Bureau of Standards and the material is available as Standard Reference Material 1579 ( 5 ) . It is referred to in this paper as “SRM paint.” The reaction 204Pb(n,n’)204mPb was studied first. Samples of paint weighing approximately 1.7 grams were encapsulated in the
RESULTS AND DISCUSSION Table I. N u c l e a r R e a c t i o n s o f L e a d Observed with U n m o d e r a t e d N e u t r o n s of 252Cf Reaction
204Pb(n,2n)203Pb 204Pb (n,n’)204Pb 207Pb(n,n’)207mPb
Fksults on the determination of lead in the three paints are shown in Table 11. Samples “coarse” and “fine” were also analyzed by nondestructive photon activation analy-
Product half-life
Prominent product gamma-rays MeV
52 hr 67 min 0 . 8 sec
0.279, 0 . 4 0 1 0.375, 0.899, 0.912 0.570, 1.064
(5) B. Greifer. E. J. Maienthal, T. C. Rains, and S. D. Rasberry, “Development of NBS Standard Reference Material .No. 1579, Powdered Lead-Based Paint,” Nat. Bur. Stand. ( U . S . ) Spec. Pub/. 260-45, March 1973. Available from Superintendent of Documents, U.S. Government Printing Office,Washington, D.C. 20402.
Table 11. C o m p a r i s o n of * W f N e u t r o n A c t i v a t i o n A n a l y s i s with O t h e r M e t h o d s in the D e t e r m i n a t i o n of L e a d in Paint 252Cf
Activation 20’Pb(n,nf)207Pb, results, yo
Paint sample
*04Pb(n,n’)m4~Pb,results,
“Coarse”
3.8, 3.5, 3 . 7
-3
“Fine”
7.2, 7 . 4
-8
SRM Paint
10.7, 10.6, 1 1 . 7 , 1 1 . 4
Other methods and results, yo
Photon activation, 3.3,3.5 Photon activation, 7.6, 7.3, 7.2 Polarography and atomic absorption, 11.87 ( 5 )
ANALYTICAL CHEMISTRY, VOL. 46, NO. 4 , A P R I L 1974
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sis. SRM paint was analyzed by polarography and atomic absorption. The reasonably good agreement between 252Cf activation analysis and t h e other methods demonstrates t h e reliability and utility of the isotope source technique for this determination. Irradiation for 2 hours with the 600-/.~g 252Cf source followed by 100 minutes of counting with a 60-cm3 Ge(Li) detector yields about 7 counts of the 204mPb isotope per milligram of lead. For a paint sample weighing 1.5 grams, the lower limit of determination would be of the order of 1%. As noted, analysis of the Ge(Li) spectrum of those elements likely to be major or minor constituents of paint indicates that they will not interfere in t h e quantitation of the gamma ray lines of 204mPb.Self-shielding effects due to the matrix are expected to be negligible since the nuclear reaction involves fast neutrons and a paint sample is
unlikely to contain appreciable amounts of neutron moderating elements. T h e results presented here indicate that with a 252Cf source of several tens of milligrams and the 60-cm3 Ge(Li) detector, t h e determination of -1% of lead in a sample of 1-2 grams of paint could be accomplished with a 15-minUte irradiation and 15-minute counting. T h e potential exists for largely automating the irradiation and counting of a large number of samples. Hence, it would appear possible that although the initial cost of equipment for this determination would be greater than for alternate methods, the speed and adequate reliability of the isotope source method would make it economically competitive. Received for review August 23, 1973. Accepted November 13, 1973.
Colorimetric Determination of N-Arylhydroxylamineswith 9-ChIoroacridine Richard E. Gammans, James T. Stewart, and Larry A. Sternson' The Bioanalytical Laboratory, Department of Medicinal Chemistry, School of Pharmacy. The Univers/ty of Georgia. Athens, Ga. 30602
During the metabolic conversion of certain aromatic amines to excretable conjugates in the endoplasmic reticulum of liver cells, N-arylhydroxylamines are formed ( I ) which have been implicated in t h e chemical carcinogenesis ( 2 ) displayed by such compounds. Few analytical procedures are available for t h e rapid detection and assay of such aromatic hydroxylamines. Boyland and Nery (3) detected 1-3 bg/ml of N-phenylhydroxylamine colorimetrically by complex formation with either salicylidenearylamine N-oxides and ferrocyanide or pentacyano-ammine ferroate in aqueous solutions. Qualitative identification of arylhydroxylamines by thin-layer chromatography with the use of various spray reagents has also been described ( 4 ) . In addition, some gas chromatographic determinations of arylhydroxylamines have been reported (5, 6). T h e interaction of N-arylhydroxylamines with 9-chloroacridine to give highly-colored solutions has been observed in our laboratory. In this paper, we describe a new colorimetric method for determining microgram quantities of arylhydroxylamines with 9-chloroacridine.
EXPERIMENTAL Apparatus. Spectra and absorbance measurements were made with a Perkin-Elmer Spectrophotometer. Model 202, and a Bausch and Lomh Spectronic 20 colorimeter. Reagents. 9-Chloroacridine was obtained from Eastman Organic Chemicals. N-Phenylhydroxylamine, p-chlorophenylhydroxylamine, and p-tolylhydroxylamine were synthesized by the method reported by Smissman and Corhett (7). CyclohexylhyAuthor to whom corespondence should he directed. C. C . Irving, J . Bioi. Chern., 239, 1589 ( 1 9 6 4 ) . J. A. Miller, J. W . Cramer, and E. C. Miller, Cancer Res.. 20, 950 (19 6 0 ) .
E. Boyland and R. Nery, Anaiyst ( L o n d o n ) ,89, 95 (1964) J. Booth and E. Boyland, Biochem. J., 91, 362 ( 1 9 6 4 ) . H. B. Hucker. Drug Metab. Disposition. 1, 322 ( 1 9 7 3 ) . A . H . Beckett and S. AI-Sarra], J . Pharm. Pharmacal.. 24, 916 (1972). E. E. Smissrnan and M. D. Corbett, J. Org. Chern., 37, 1847 (1972). A N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 4 , A P R I L 1974
droxylamine was prepared by reduction of cyclohexanone oxime ( 8 ) by the procedure of Feuer e t al. ( 9 ) . The melting points of the synthesized compounds were in agreement with literature values (10, 1 2 ) . All other chemicals were commercially available and were utilized as received. Fresh solutions of arylhydroxylamines were prepared daily by dissolving weighed amounts in 9570 ethanol. Solutions of 9-chloroacridine were prepared immediately before use hy dissolving weighed amounts in ethanol and were kept refrigerated. Procedure. A quantity of a n ethanolic solution of arylhydroxylamine was placed in a n appropriate volumetric flask. An ethanohc solution containing an approximate 10-fold excess of 9-chloroacridine was added to the flask. The solution was acidified with 10% v/v aqueous hydrochloric acid, shaken briefly, and allowed to stand a t room temperature for 5 minutes. Ethanol was added to volume so that the final concentration of arylhydroxylamine in the flask was equal to or greater than 1 X 10--5M.The absorhance was measured at 450 n m and the measurements were corrected for reagent blanks in the procedure.
RESULTS AND DISCUSSION 9-Chloroacridine interacts with an arylhydroxylamine in the analytical procedure to yield a highly-colored yelloworange solution. The absorption curve in the visible spectrum for a n analytical solution of A'-phenylhydroxylamine shows an absorption maximum a t 450 nm. Preliminary data have revealed that the reaction yields a nucleophilic addition product similar to the one reported for primary aromatic amines (12). Further work on the identification of the compound formed between arylhydroxylamines and 9-chloroacridine is under way in our laboratory. In comparing absorption curves of the colored solutions obtained with equimolar concentrations of the various arylhydroxylamines, it was noted that p-chlorophenylhyA . I . Vogel, " A Textbook of Practical Organic Chemistry." 3rd ed.. John Wiley, New Y o r k , N Y.. 1966. p 344 H . Feuer,*B F. Vincent, and R S Bartlett, J Org Chem.. 30. 2877
(1965). A . Lapworth and L Pearson J Chem. Soc.. 119. 765 ( 1 9 2 1 ) . R. D. Haworth and A . Lapworth, J. Chem Soc.. 119. 768 (1921) J. T . Stewart. T D. Shaw, and A . B. Ray. A n a / . Chem.. 41, 360 (19 6 9 ) .
