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Anal. Chem. 1982, 5 4 , 1623-1627
(30) Rhim, W.-K.; Elleman, D. ID.: Vaughan, R. W. J . Chem. Phys. 1973, 58, 1772. (31) Mansfleld, P. J . fhys. Chim. 1971, 4 . 1444. (32) Schaefer, J.; Stejskal, E. 0.;Buchdahl, R. Macromolecules 1977, 70, 384. (33) Hatcher, P. G.; Breger, I. A.; Dennis, L. W.; Maclel, G. E. Prepr. Pap .-Am. Chem. SOC., Div. Fuel Chem., in press. (34) Maciel, G. E.; Szeverenyl, W. M.; Sullivan, M. J., to be submltted for publication. (35) Bloembergen, N. Physlca (Amsterdam) 1949, 15, 386. (38) Gerstein, B. C.; Chow, C.; Pembleton, R. G.; Wllson. R. C. J . Phys.
(42) Abragam, A. "The Prlnclples of Nuclear Magnetism"; Oxford University Press: London, 1961; p 378. (43) Farrar. T. C.; Becker, E. D. "Pulse and Fourler transform NMR"; Academlc Press: New York, 1971; p 57. (44) Noggle, J. H.; Shirmer, R. E. "The Nuclear Overhauser Effect"; Academlc Press: New York, 1971. (45) Farrar, T. C.; Becker, E. D. "Pulse and Fourier Transform NMR"; Academic Press: New York, 1971. (46) Schaefer, J.; SteJskal, E. 0.;Buchdahl, R. Macromolecules 1975, 8 , 291. (47) VanderHart, D. L.; Earl, W. L.; Garroway, A. N. J . M a p . Reson. 1961, 44, 381. (48) Szeverenyl, N. M.; Sulllvan, M. J.; Maciel, G. E., unpublished work. (49) Dlxon, T. W. J . Magn. Reson. 1981, 44, 220. (50) Tegenfeldt, J.; Haeberlen, U. J . Magn. Reson. 1979, 36, 453.
(37) Yokono, T.; Sanada, Y. Friel 1978, 57, 334. (38) Yokono, T.; Miyazawa, K.; Sanada, Y.; Marsh, H. Fuel 1979, 58, 896. (39) Qandy, D. W., Gulf Research and Development Co., private communlcatlon. (40) Retcofsky, H. L.: Stark, J. M.;Friedel, R. A. Anal. Chem. 1968, 40, 1899. (41) Retcofsky, H. L.; Hough, M. R.; Maguire, M. M.; Clarkson. R. B. "Advances in Chemistry Series"; Gorbaty, M. L., Ouchl, K.. Eds.; Amerlcan Chemical Society: Washington, DC, lg8l;No. 192, Chapter 4.
RECEIVEDfor review December 9, 1981. Acepted April 19, 1982. The authors are grateful for support of this work by the U.S.Department of Energy under Contract No. DEAT20-81LC10652 from the Laramie Energy Technology Center and Contract No. DE-AC22-79ET14940 from the Pittsburgh Energy Technology Center.
(28) Farrar, T. C.; Becker, E. D. "Pulse and Fourler Transform NMR"; Academic Press: New York, 1971; Chapter 2. (29) Waugh, J. S.; Huber, L. M.;Haeberlen, V. Phys. Rev. Lett. 1966, 20,
180.
-. .-... . .- .. - . - - -.
Chem 1077, R I , S A 5
Determination1 of Elements in National Bureau of Standards' Geological Standard Reference Materials by Neutron Activation Ana lysis Chrlstopher C. Graham, Mlchael D. Glaecock, James J. Carnl, James R. Vogt," and Thomas G. Spaldlng Research Reactor Facility, Un,iversity of Missouri, Columbia, Missouri 652 1 I
Instrumental neutron activcitlon analysts (INAA) and prompt gamma neutron activation slnalysis (PGNAA) have been used to determine elemental concentrations in twai recently issued National Bureau of Standards (NBS) Standard Reference Materlais (SRM's). The rersults obtained are in good agreement wlth the certlfled and lnformatlon values reported by NBS for those elements In each materlal for which comparisons are avallabie. Average concentratlons of 35 elements in SRM 278 obsidian rock and 32 elements in SRM 688 basalt rock are reported for comparison with results that may be obtained by other laboratories.
With the certification of SRM 1571 orchard leaves in 1972, the National Bureau of Standards began a program to produce Standard Reference Materials (SRM) for use in biological and environmental analytical chemistry. The purpose of this program is to provide mate:rials of known elemental composition in a wide variety of natural matrices for use in analytical development and quality a,ssurance ( I ) . The usefulness of these materials, however, is, often limited by the number of elementa that NBS is able to certify. Consequently, numerous investigators have, independently of NBS, published a large body of data on the elemental concentrations of the various SRMs, thus extending their usefulness to the scientific community. In 1981, NBS issued two new materials, SRM 688 basalt rock (2)and SRM 278 obsidian rock (3),both of which should prove to be extremely useful in applications involving geological materials. At the prtssent time, NBS has certified 14 elements in basalt rock and 1,B elements in obsidian rock. This
study is an attempt to extend the data on the elemental concentrations of these SRMs and is similar in nature to those studies conducted by Ondov e t al. ( 4 ) for SRM 1633 fly ash and by Germani et d.(5) for SRM 1632a bituminous coal and SRM 1635 subbituminous coal. The study presented here utilized different nuclear analysis methods and several analysts working independently.
EXPERIMENTAL SECTION INAA. All samples were freeze-dried for 24 h and stored in a desiccator prior to irradiation. The details of the irradiation procedures varied according to the experiment; but, in general, two types of irradiations were performed. For the determination of Na, Mg, Al, Ca, Ti, V, Mn and K, samples of approximately 100 mg were encapsulated in high density polyethylene vials and irradiated at a flux of 1 x 1014neutrons cm-2 s-l for periods of 6 and 10 s,2 and 5 min, and 1h. For the determination of Na, Ca, As, Br, Ba, La, Nd, Sm, Lu, Au, U, Sc, Cr, Fe, Co, Ni, Zn, Rb, Zr, Sb, Cs, Ce, Eu, Tb, Yb, Hf, Ta, and Th, samples of approximately 200 mg were encapsulated in quartz vials and irradiated in an automatically rotated position at a typical flux of 5 x l O l S neutrons cm-2 s-l for periods varying from 30 to 235 h. Following irradiation, samples and standards were carefully transferred and weighed into nonradioactive polyvials so that it was not necessary to make a correction for the activity of the irradiation container. The well-known geological standard materials (4,6-10) NBS SRM 1633, NBS SRM 1633a,USGS 6 2 , and USGS BCR-1 were used as multielement comparator standards and were treated in exactly the same manner as the samples. The newer USGS rocks ( I I , 1 2 ) RGM-1 and QLO-1 were analyzed along with the samples and standards for quality control. The data from the samples irradiated for 6 and 10 s were taken at constant decay times of 10 and 13 min, respectively. The 2and 5-min irradiations were permitted to decay for 10 h and the 1-h irradiation was pemitted to decay for -3 days. Mea-
0003-2700/82/0354-1623$01.25/00 1982 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 9, AUGUST 1982
Table I. Elemental Concentrations in SRM 688 Basalt Rock and SRM 278 Obsidian Rock as Determined by INAA SRM 688 basalt rock element Na(%) Mg (%) Al (%)
concn 1.39 i 0.12 3.9 i 0.8 8.54 f 0.39
K @) Ca (%) 8.2 f 0.6 Sc (pprn) 36.1 f 0.9 Ti (%) 0.70 f 0.07 V (ppm) 235 i 25 Cr (pprn) 328 f 1 5 0.118 i: 0.007 Mn (%) 7.23 i 0.19 Fe(%) Co (pprn) 47.5 f 1.5 NI (ppm) 123 f 29 Zn (PPm) As (pprn) 2.68 f 0.54 Br ( P P ~ Rb ( P P ~ ) Zr (ppm) 58.6 ?: 8.7 Sb (pprn) 0.466 i 0.207 c s (PPm) Ba (ppm) 197 f 33 La (ppm) 7.54 f 0.93 Ce (pprn) 10.1 f 3.9 Nd (ppm) 9.95 i 1.08 Sm (pprn) 2.09 f 0.22 Eu (ppm) 0.919 i: 0.048 Tb(ppm) 0.462 i 0.025 Yb ( p p q 1.86 i: 0.27 Lu (pprn) 0.342 i 0.057 Hf (ppm) 1.58 f 0.14 Ta (pprn) 0.246 f 0.058 Au (ppb) 0.9 i 0.4 Th ( P P ~ ) U (pprn) 0.34 f 0.08
Table 11. Concentrations in SRM 688 Basalt Rock and SRM 278 Obsidian Rock as Determined by PGNAAa
SRM 278 obsidian rock no. of detns
concn
B( P P ~ ) Na (%) Mg (%I Si (%) C1 (ppm) K (PPm) Ca (%) Ti (%) Mn (%) Fe (%) Sm (ppm) Gd (ppm)
i
0.26
31
7.43 f 3.42f 1 5 0.75 f 21 5.24 f
0.57 0.34 0.12 0.14
4 15 10 37
17 4 10
3.46
element
no. of detns
8 10
22 6.34 f 0.93 15 0.040 f 0.005 20 1.52 i 0.05 17 1.85f 0.18 17 54.0 f 2.5 7 5.06 f 1.29 2.61 i 0.62 1 3 0 f 12 5 2 8 5 i 16 3 1.61 f 0.13 4.92 f 0.34 17 1080f 58 22 35.4 i 2.5 10 59.4 f 6.8 5 28.2 f 1.0 27 5.69f 0.62 27 0.764 f 0.056 22 1.14 0.10 20 4.54 0.86 15 0.836 f 0.050 16 8.82 f 0.73 17 1.23 f 0.19 8 1.6 I: 0.8 12.8 f 0.3 1 4.82 f 0.35
25 16 37 37 37 27 16 36 29 23 31 56 51 29 8
56 45 33 44 43 45 45 32 41 44
surements on the longer irradiations were taken after 4-10 days and again after 9-17 weeks. All counts were performed by using a large coaxial Ge(Li) detector (-17% efficient, with 1.79-keV resolution). Additional measurements from two of the long irradiations were taken with a low-energy photon spectrometer (LEPS). Both detector systems were coupled to an automatic sample changer (13) and a 4096-channel Nuclear Data 6620 analyzer system. The data were stored on disk and later reduced by the peak-fitting program PEAK (14,15) and a modified version of the vendor-supplied NAA program (16,17). The computer-generated output was then checked for accuracy and completeness. The complexity of the spectra, however, made it necessary to reduce some of the spectral data by hand. A more complete description of the irradiation and counting conditions and nuclear parameters can be found elsewhere (18). PGNAA. Prompt y-ray neutron activation analysis (PGNAA) was also utilized to determine the elemental concentrations in both SRMs. PGNAA is accomplished by observing the y-ray emitted during irradiation. The excitation energy of the nucleus formed by neutron capture is released by emission of "prompt" s) following neutron y-rays which are emitted immediately capture. The Research Reactor's PGNAA facility utilizes a horizontal reactor beamport with a thermal neutron flux of 5 X lo8 neutrons cm-2 s-l at the sample position. The emitted prompt y-rays, with energies as great as 11 MeV, are measured with a large coaxial Ge(Li) detector (-19% efficient, with 1.85-keV resolution). The Ge(Li) detector is surrounded by a large NaI(T1) annulus which permits suppression of the Compton continuum. Heavy borated
~
a
SRM 688 basalt rock concn 0.88 f 0.14 1.05 f 0.07 5.7 f 0.4 9.3 f 0.2 24.6 f 0.6 0.17 f 0.01 7.9 f 0.2 0.72 f 0.02 0.112 f 0.006 7.23 f 0.17 2.31 I: 0.08 2.82 i 0.08
SRM 278 obsidian rock concn 25.2 f 0.4 2.6 f 0.2 7.8 f 0.2 36.6 f 1.3 640 i: 90 3.44 f 0.08 0.60 t 0.10 0.145 f 0.009 0.043 f 0.007 1.32 f 0.17 5.66 f 0.10 5.34 f 0.08
Results of nine determinations.
Table 111. Summary of Concentrations for SRM 688 Basalt Rock and Comparison to NBS Valuesa this work 0.88 f 0.14 1.39 i 0.12 5.7 f 0.4 9.1 i: 0.2 24.6 f 0.6 0.17 f 0.01 7.9 i 0.3 36.1 i 0.9 0.72 f 0.02 235 i 25 328f 15 0.115 i 0.007 7.23 f 0.19 47.5 I: 1.5 123 i 29 2.68 i: 0.54 58.6 i 8.7 0.466 f 0.207 197 i 33 7.54 i 0.93 10.1 i 3.9 9.95 i 1.08 2.31 i 0.08 0.919 f 0.048 2.82 f 0.08 0.462 i 0.025 1.86 f 0.27 0.342i 0.057 1.58 f 0.14 0.246 i: 0.058 0.9 i 0.4 0.34 i 0.08
NBS ( 2 ) b
1.59 f 0.02 (5.1) 9.188 i: 0.048 22.6 f 0.1 0.155 f 0.006 (8.70) (38.1) 0.701 f 0.006 (250) 332f 9 0.106 i 0.001 7.239 f 0.028 (49.7) (150)
(200) (13.3) (2.79) (1.07) (0.448) (2.09) (0.34) (1.6) (0.37)
a All values reported by NBS have been converted from the oxide to the element through the use of gravimetric factors ( 2 9 ) . All values in parentheses are supplied by NBS as informational values and are not certified.
polyethylene and lead shielding surrounds both detectors. A more complete description of the PGNAA facility can be found elsewhere (19). Samples of approximately 1g were sealed in a Teflon bag and irradiated for 12 h. SRM 1633a was used as a comparator standard and treated in exactly the same manner as the samples. A Ti wire monitor was used to correct for any flux variations and pure element standards were utilized as quality control. As mentioned elsewhere (19-21), the precision and accuracy of PGNAA can be superior to INAA for certain elements, in that it is possible to irradiate as long as is necessary in order to obtain
ANALYTICAL CHEMISTRY, VOL. 54, NO. 9, AUGUST 1982
1625
Table IV. Summary of Cloncentrations for SRM 278 Obsidian Rock and Comparison t o NBS and Literature Values'" element
this work
NBS ( 3 ) b
25.2 i 0.4 3.46 j 0.26 7.8 i 0.2 36.6 j 1.3 640 i: 90 3.44 0.10 0.68j 0.11 5.24 3 0.14 0.145 i 0.009 6.34 i 0.93 0.040 f 0.005 1.52 2 0.05 1.85 3 0.18 54.0 3 2.5 5.06 i 1.29 2.61 3 0.62 130i: 12 2 8 5 i 16 1.61 A 0.13 4.92 * 0.34 1080 f 60 35.4 2 2.5 59.4 A 6.8 2 8 . 2 ~1.0 5.66 A 0.10 0.764 i: 0.056 5.34 2 0.08 1.14 i: 0.10 4.54 A 0.86 0.836 f 0.050 8.82 f 0.73 1.23 i 0.19 1.6 f 0.8 12.8 * 0.3 4.82 % 0.35
(25Y 3.59 i 0.04 7.489 i 0.079 34.15 i 0.06
Ahmad et al. ( 2 2 ) 3.90 i 0.23
3.45 % 0.02 0.703 i 0.001 (5.1) 0.147 % 0.004 (6.1) 0.040 i 0.002 1.43 i 0.01 (1.5) (55)
4.23
t
0.13
4.16
f
0.21
6.79 -+ 0.44 0.0409 i: 0.0015 1.14 i 0.23 2.04 i 0.22 4.68 i 0.13 2.66 f 0.2 143.17 f 2.63
127.5 i 0.3
1.7 i 0.4 5.12 % 0.44 885 i 54 27.59 * 0.38 56.5 f 1.9
(1.5) (5.5) (1140) (62.2) (5.7)C (0.84) (5.3)C (4.5) (0.73) (8.4) (1.2)
0.82 i 0.03 37.74 f 1.5 1.23 i: 0.03 3.58 i: 0.25 0.745 f 0.31 6.41 i 0.24 1.32 i 0.18
12.4 i 0.3 4.58 i 0.04
12.27 i 0.77 4.204 i 0.284
(1.0)
'" All values reported by NBS have been converted from the oxide to the element through the use of gravimetric factors These NBS inforAll values in parentheses are supplied by NBS as informational values and are not certified. (29).
mation values are based on University of Missouri work and are acknowledged on the certificate. ~
- -~
~~
good counting statistics. PGhlAA also eliminates the timing errors inherent in the measurement of short-lived nuclides and often offers several y-rays for each element.
RESULTS A:ND DISCUSSION Concentrations. Concentrations of elements in basalt rock and obsidian rock as determined by INAA art3 listed in Table I. The reported values are the means of thle individual determinations for each element. The reported error limits are the standard deviation of the means which are generally greater than the uncertainties in counting statistics. All individual determinations were subjected to a standard Chauvenet's criterion outlier rejlection routine (.22),resulting in rejection of approximately 3% of all the determinations for basalt rock and 5% of all determinations for obsidian rock. Table I1 lists the elemental concentrations obtained by PGNAA. PGNAA provided additional data for nine elements determined by INAA (Na, M g , Al, K, Ca, Ti, n h , Fe, and Sm) and unique data on four otlher elements (B, Si, C1, and Gd). There is some disagreemenit between elements measured by both techniques which are discussed below. Tables I11 and IV list the combined results of the current study. In addition, the NBS certified and informational values and other available literature values are presented. Where both INAA and PGNAA debermine values for a given element, a weighted average is reported. In these cases, the weighting factor is the number of replicates divided by a2. Treatment of Specific Elements. Sodium. In the specific case of Na there is a significant difference between the results
~-
~
~
.~
reported by both methods. INAA is judged to be superior for Na determination because of the very large interference with B which is encountered by the most sensitive prompt y-ray for Na. Therefore, the INAA values were adopted in Tables I11 and IV. Magnesium. Determination of Mg in rocks by INAA is hampered by the major activities generated by 24Naand 28Al. In addition, the spectral interference from S6Mnforces determination of Mg via the much less sensitive 1014-keV y-ray. There were only four determinations of Mg made by INAA in basalt rock and the mean value is significantly lower than the NBS informational value. Measurements by PGNAA were less difficult to obtain. As a result, the PGNAA value, which is only slightly higher than the NBS value, was adopted. There were no determinations for Mg in the obsidian rock by either technique. Aluminum. A common problem in the analysis of silicate materials for aluminum by NAA is the 2aSi(n,p)28A1 reaction. Because of this primary interference, a correction is necessary, which is typically based on the activity of 28A1produced in a sample of pure silicon. Due to the increased uncertainty introduced by this method, it was decided not to attempt it but rather to report the data only to two significant figures, Iron. Measurements of Fe in obsidian rock by INAA were consistently higher than the NBS certified value. There are no known interferences which could explain these results. The PGNAA value in obsidian rock was lower than the NBS value but within the range of uncertainties. The PGNAA value for
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 9, AUGUST 1982
Fe involves a significant background subtraction to the extent of about 10% of all counts in the obsidian rock and much smaller correction for the basalt rock. Although the problem with Fe in obsidian rock could not be resolved, the INAA values were adopted for both SRM's. Nickel. The classical INAA approach to the determination of nickel is via the 68Ni(n,p)68Coreaction (23,24) which requires epithermal neutrons (-2% of the total flux). The W o activity was measured in this study with the resulting value being slightly lower than the NBS value. Further studies of these materials, involving a variation of INAA (25,26),indicate the value reported for Ni in basalt rock in this study is indeed low. Ni could not be determined in the obsidian rock. Zinc. It is difficult to measure Zn in samples with an approximately crustal abundance of Zn and Sc, primarily due to a spectral interference of the 1115-keV @Zny-ray from the 1120-keV y-ray of %3c. In this study, the obsidian rock with a Zn/Sc ratio of approximately 11 was easily measured; whereas, the basalt rock with a Zn/Sc ratio of approximately 1.5 encountered significant spectral interference, leading to a much greater error in the determination of Zn. Although a value 105 25 ppm was obtained, subsequent studies of the basalt rock following a 10-month decay indicate that the value is
