Table 11. Determination of Copper by Substoichiometric Neutron Activation Analysis Cu reported: ppm Material Cu found,n ppm T-1 65.7 i 2.4 (3) 62(6) f 3 (2) llO(7); 114 f 4(8) w-1 104 116 f 10 (9) Sye-1 29.3 i 2.9(2) 23 (IO); 25 (11) PCC- 1 9.23 i 0.09(2) 10.4(12); 8 f 2(9) G- 1 12.8 i 1.2(2) 13(7) GR 358 i 19 (2) 345 (13) Allende meteorite 78.3 f 2.9 (3) ... Bowen’s kale 5.20 f 0.06 (2) 4.81 f 0.74 (14) 1R1 tobacco 70.1 =t11.6(2) ... Human blood serum 1.65 i 0.05 (2) ... Artificial mixture 0.0083 pg 0.0077 pg Artificial mixture 0.0427 pg 0.0446 pg a Figures in parentheses indicate the number of replicate determinations carried out. Figures in parentheses indicate the reference numbers.
matter (15). 1R1tobacco is an international cigarette tobacco standard manufactured and distributed by the University of Kentucky, Lexington, Ky. Our value of 70.1 ppm may be
compared with the values 76.7 (16), 32.4 (19, 17-32 (18), and 15-21 (19) ppm in various commercial tobaccos reported in the literature. The wide variation in the values is a result of the tobacco crops grown on different soils. In freezedried human blood serum, we found 1.65 ppm of copper. Earlier values for copper in human blood serum were 1.54 (20) and 2 (21) ppm. To find out the experimental limits of copper determination by this method, two artificial mixtures containing 0.0077 pg and 0.045 pg of copper were analyzed and the values found were 0.0083 pg and 0.043 pg, respectively. Five samples containing the same amounts of copper were extracted by the procedure given, and the replicate results were found to agree within f1.84 relative per cent at 95% confidence limits. Two samples and a standard can be analyzed by this method in 45 minutes after receiving the irradiated material in our laboratory. The radiochemical purity of the isolated 64Cuactivity was checked by measuring its gamma-ray spectra, beta maximum energy, and half-life, and in all cases the samples were found to be highly pure. Thus, the proposed method can be used for the determination of trace amounts of copper in geological or biological materials with good degree of precision and in a very short time.
( 6 ) C. 0. Ingamells and N. H. Suhr, Geochirn. Cosmochinz. Acta,
27, 897 (1963). (7) M. Fleischer, ibid., 33,65 (1969). (8) 0. Johansen and E. Steinnes, Talanta, 17, 407 (1970). (9) R. A. Schmitt, T. A. Linn, Jr., and H. Wakita, Radiochim. Acta., 13, 200 (1970). (10) N. M. Sine, W. 0. Taylor, G. R. Webber, and C . L. Lewis, Geochim. Cosmochim. Acta, 33, 121 (1969). (11) G. R. Webber, ibid., 29, 229 (1965). (12) F. J. Flangan, ibid., 33, 81 (1969). (13) M. Roubault, H. de La Roche, and K. Govindraju, Sei. Terre, 13, 379 (1968). (14) H. J. M. Bowen, in “Advances in Activation Analysis,” J. M. A. Lenihan and S. J. Thompson, Ed., Academic Press, London, 1968, Vol. 1. (15) B. Mason, “Meteorites,” John Wiley, New York, N.Y., 1962.
RECEIVED for review July 12, 1971. Accepted January 28, 1972. The authors are grateful t o the Council of Scientific and Industrial Research, Government of India, New Delhi, for financial assistance to one of them (R.A.N.). (16) R. C. Voss and H. Nicol, Lancet, 2, 435 (1960). (17) A. G. Souliotis, Analyst, 94, 359 (1969). (18) E. C. Cogbill and M. E. Hobbs, Tobacco Sei., 1,68 (1957). (19) W. K. Collins, G. L. Jones, J. A. Weybrew, and D. F. Matzienger, Crop Sei., 1,407 (1961). (20) C. C . Thomas, G . P. Terecho, and J. A. Sondel, Nucl. Appl., 3, 53 (1967). (21) A. Jacobsen, J. Nucl. Med., 2,289 (1961).
Comparison of Neutron Activation Analysis and Other Analyses Procedures for Fish Samples N. D. Eckhoff,’ C. J. Pappas,2 and C. W. Deyoe2 Kansas State University, Manhattan, Kansas 66502 NEUTRON ACTIVATION ANALYSIS (NAA), well developed as a rapid, sensitive, and precise nondestructive methodology, is used routinely by many laboratories. Analysts employing the NAA technique with gamma-ray spectrometry use two analytical procedures principally : peak area, which is fast but imprecise, and least squares unfolding, which is precise but reasonably complex and time-consuming. In lieu of an ideal method-Le., fast and precise-to analyze large quantities of spectral data, we describe below a compromise method, used to process hundreds of fish samples for concentration estimates for K, Ca, Mn, C1, and Na. Department of Nuclear Engineering.
* Department of Grain Science and Industry. 1506
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
Not all the gamma-ray spectral data are needed for a precise, nondestructive analysis of a sample ( I ) . Because large quantities of data need not be manipulated, this area of interest (AOI) least squares method, which saves computer time may be used : Each channel of the complex gamma-ray spectrum is assumed to be a linear combination of the elemental concentration estimate times the value of that channel in the elemental reference gamma-ray spectrum plus a deviation value Y=Ab+e
(1)
(1) N. D. Eckhoff and P. F. Ervin, Nucl. Instrum. Methods, 97, 263-6 (1971).
Table I. Concentrations of Various Element in Three Fish Bone and Three Total Fish Ash Samples as a Function of Analysis Technique Ca, % P,” % Na, Z Mn,b ppm K, Z c1, % Fish Bone 1 AAc NAA-ld NAA-2J NAA-39 NAA-4h
14.87 14.62(SM)6 14.62(SM) 14.52(SM)
8.62 10.44(0.60)
Fish Bone 2 AA NAA-1 NAA-2 NAA-3 NAA-4
14.94 14.52(SM) 14.6qSM) 14.34(SM)
7.45 8.82(0.63)
Fish Bone 3 AA NAA-1 NAA-2 NAA-3 NAA-4
16.87 17.7qSM) 17.76(SM) 17.51(SM)
8.28 15.22(0.61)
Fish-Total Ash 1 AA NAA-1 NAA-2 NAA-3 NAA-4
4.34 4.58(0.09) 2.48(0.18) 4.58(0.09)
Fish-Total Ash 2 AA NAA-1 NAA-2 NAA-3 NAA-4 Fish-Total Ash 3 AA NAA-1 NAA-2 NAA-3 NAA-4
0.253(0.005) 0.253(0.@05) 0.251(0.O06) 0.432(0.004)
1.89(0.10) 1.89(0.10) 1.93(0.07) 0.42(0.004)
48.7(11,5) 48.7(11.5) 48.5(13.9) 64.6(9.4)
0.028(0.004) 0.028(0.004) 0.033(0.006)
0.316(0.005) 0.314(0.005) 0.310(0.006) 0,508(0.005)
1.12(0.12) 1.12(0.12) 1 .26(0.08) 0.35(0.005)
34.4(11.1) 34.1(11.6) 33.8(13.7) 39.9(9 .O)
0.044(0.004) 0.045(0.004) 0.047(0.006)
0.368(0.005) 0.365(0.004) 0.365(0.006) 0.436(0.009)
0.70(0.12) 0.81(0.13) 0.89(0.09) 0.43(0.004)
51.8(10.7) 51 .8(10.8) 51 .5(12.7) 50.7(7.8)
0.047(0.004) 0.048(0.004) 0.052(0.006)
3.06 3.12(0.56)
0.413 @.518(0.005) 0.509(0.005) 0.518(0.005) 0.509(0.005)
1.08 3.54(0.16) 2.68(0.16) 3.54(0.16) 1 .59(0.005)
23.6(0.7) 24.8(0.8) 23.6(0.7) 32.2(9.4)
0.298(0.005) 0.329(0.005) 0.298(0.005)
3.38 4.2q0.09) 6.65(0.17) 4.21(0.09)
2.21 3.16(0.47)
0.297 0.448(0.004) 0.429(0.004) 0.441(0.004) 0.357(0.004)
0.843 2.56(0.13) 1 .96(0.13) 2.6qO. 13) 0.72(0.004)
22.9(0.6) 23.5(0.7) 22.5(0.6) 30.1(7.1)
0.223(0.004) 0.259(0.004) 0.232(0.004)
2.23 3 .16(0.08) 6.01(0.18) 3.24(0.09)
1.28 2.75(0.40)
0.364 0.408(0.004) 0,392(0,003) 0.404(0.004) 0.380(0.004)
0,828 2.3q0.11) 1 .78(0.18) 2.40(0.11) 1.162(0.004)
17.9(0,5) 18,6(0.6) 17,9(0,5) 17.9(3.5)
0.229(0.004) 0,262(0.004) 0.234(0.004)
a The phosphorus estimators were obtained by a total activity calculation from 32P spectra obtained after a two-week decay. For comparison other results were obtained using colorimetry. * The concentration of manganese is given in pg/gm (ppm). AA is atomic absorption. NAA-1 = neutron activation analysis using the correct weighting matrix. e SM = indicates the standard deviation was less than 0.01. (Note all quantities in parentheses are standard deviations.) f NAA-2 = neutron activation analysis using the spectrum from fish bone 1 as the weighting matrix. NAA-3 = neutron activation analysis using the spectrum from total fish ash 1 as the weighting matrix. * NAA-4 = a neutron activation analysis using the correct weighting matrix but after samples were allowed to decay approximately one day.
where Y
=
A
=
b
=
e
=
( m X I> vector of the complex gamma-ray spectrum, (m n, matrix Of the reference gamma-ray spectra, (n X I> vector of elemental concentration estimates, (m X I> deviation vector.
Applying the least squares criterion, with proper weighting, results in the following for b: b
=
(ATWA)-I(ATWY)
(2)
where AT = transpose of A ,
(n X n) diagonal weighting matrix composed of the inverse of the variances of Y . The estimators, b, are only shape sensitive t o W (2). That W
is, only one inverse of ATWA is needed to form the estimators for many samples, provided each sample yields a similarly shaped gamma-ray spectrum. The variances association with the estimators, b, take this approximate form: u2(b) A r dia(ATWA)-l
(3)
where the average ratio of the variance of the Y vector to the variance used to form W dia(AT WA)-I = the diagonal elements of the inverse matrix. To circumvent recurring electronic shifts in gamma-ray spectra and methods of compensation, the area of interest (AOI) method was modified thus: r
=
=
(2) N. D. Eckhoff, “Optimal Neutron Activation Analysis,” Diss. Abstr., 29, No. 9, March 1969.
1. The peak regions of interest of each reference spectrum were extracted from the total gamma-ray spectrum. 2. Each region was formed by combining two channels of the region before the peak channel; using the peak channe1 as one bin; and combining two channels after the ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
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peak channel. Therefore, each peak region consisted of three bins. 3. Similarly, the peak regions of interest of each complex spectrum were extracted and combined into bins. (If the electronic shifts are small, no mathematical compensation is needed to align the complex and reference spectra.) EXPERIMENTAL
Apparatus. The Kansas State University TRIGA Mark I1 nuclear reactor was used to irradiate six fish samples. A 25-cc Ge(Li) semiconductor detector connected to a T M C 4096 multiparameter analyzer was used to collect gamma-ray spectra from each of the fish samples. The atomic absorption analyses were performed using a Jarrell-Ash Model 82-50 flame emission atomic absorption spectrophotometer. Reagents. No special preparation was necessary for the neutron activation analysis procedure. However, the fish samples were frozen prior to irradiation. Other portions of these six fish samples were ashed using a dry ash procedure. This dry ash was dissolved in 5 ml of 6N hydrochloric acid and diluted to 100 ml using deionized water. The diluted samples were analyzed for minerals on the Jarrell-Ash atomic absorption unit. Phosphorus was determined on the diluted sample colorimetrically using a Beckman Model 109200 Du-3 spectrophotorpeter. Procedure. All six fish samples were irradiated simultaneously for two minutes at a neutron flux of approximately 2.9 X 10” n/cm2 sec. After allowing from a 2- to 15-minute decay period, each spectrum was collected for 2 minutes. To determine the phosphorus content, each sample was allowed approximately a 2-week decay time and a bremstrahlung (from the pure p- emitter 32P)spectrum was collected for a 10-minute period. A time series of these bremstrahlung spectra was collected over a week period to confirm the presence of 3zPby half life comparison. RESULTS AND DISCUSSION
Table I presents the results of neutron activation, atomic absorption, and colorimetric analyses of three fish bone and three total fish ash samples. Atomic absorption or colorimetric results for all samples and for all elements were unavailable. Additionally, the NAA results for Mn and C1 are
presented for completeness. Other analyses results for these two elements were not available for comparison. The NAA results for Ca illustrate the importance of the weighting factor matrix to obtain the proper estimate. Using a spectrum with a large amount of Ca as the weighting factor to estimate Ca in a spectrum with a significantly smaller amount of Ca would produce inaccurate estimates. The converse apparently is not true for Ca. The results for Na, K, Mn, and C1 appear to be unaffected by the choice of weighting factors. Atomic absorption and NAA results for Ca are comparable, the maximum deviation being 31 % and the average deviation, 11 %. Other comparisons, though not so good, in general are reasonable. It should be noted that by allowing approximately a 1-day decay period, K can be estimated more accurately by NAA. The time series bremstrahlung spectra revealed a half life of approximately 14 days. The comparison of the phosphorus results is fair. This NAA procedure phosphorus is under further investigation. The time savings for computation, using the approximate weighting factor matrix, were as follows: NAA-1 = 0.32 minutes/sample NAA-3 = 0.14 minutes/sample which gives a time savings ratio, SR (NAA-l/NAA-3), of 2.286. CONCLUSIONS
The results given in Table I and the very significant time savings ratio strongly suggest the use of the approximate weighting factor, case NAA-3, for the analysis of these fish samples. RECEIVED for review December 13, 1971. Accepted March 15, 1972. Financial support of the Kansas Agricultural Experiment Station, Manhattan, is gratefully acknowledged. Contribution No. 12, Department of Nuclear Engineering and Contribution No. 778, Department of Grain Science and Industry have been assigned this work.
Determination of Trace Quantities of Uranium in Biological Materials by Neutron Activation Analysis Using a Rapid Radiochemical Separation Donald A. Becker and Philip D. LaFleur Activation Analysis Section, Analytical Chemistry Division, National Bureau of Standards, Washington, D.C. 20234
WHENTHE NEED AROSE to analyze a new biological Standard Reference Material for trace quantities of uranium, the technique of neutron activation analysis was employed. A search of the literature revealed a large number of nuclear techniques including direct a-counting ( I , 2), delayed neutron counting (1) E. E. Campbell, B. M. Head, and M. F. Milligan, U S . At. Energy Comm. Rept., LA-1920, June 1955. (2) E. B. Kurtz, Jr., and R. Y. Anderson, ibid., AECU-3177, March 1956. 1508
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
(3), fission track counting (41, and nuclear activation techniques utilizing the 239Npdaughter of 239U (5,6), several different fission products from the fission of 23sU(7-9), and a (3) s. *miel, ANAL. CHEM.,34, 1683 (1962), 14’) B. s. CarDenter and C. H. Cheek, ibid., 42,121 (1970). (5) D. N. Edgington, Int. J . Appl. Radiat. Isotopes, 18,11(1967).
f6) M. Picer and P. Strohal. Anal. Chim. Acta, 40,131 (1968). i7) G . Buzzelli, ANAL.C H E M . ,1405(1965). ~~, (8) N. Ikeda, K. Kimura, N. Hasebe, and H. Shoji, Radiochim. Acta, 12,72 (1969). (9) A. A. Smales, Analyst (London),77,778 (1952).
