(24) D. E. On and F. A. Gunther, J. Assoc. Off.Anal. Chem., 49,669 (1966). (25) G. Voss and H. Geissbuhler, Meded. Rvksfac. Landbouwwet., 32, 877 (1967). (26) G. Voss, Bull. Environ. Contam. Toxicob, 3, 339 (1968). (27) D. E. Ott and F. A. Gunther. J. Assoc. Off. Anal. Chem... 51., 698 11968) (28) D. E. On, J. Agric. Food Chem., 18, 874 (1968). (29) W. D. Hormann. G. Formica, K. Ramsteiner, and D. 0.Eberle, J. A ~ Off. Anal. Chem.. 55, 1031 (1972). ~
(30) B. Karlhuber, K. Ramsteiner, W. D. Hormann, and W. Simon, J. Chromatogr.,84, 387 (1973).
I
~RECEIVED ~ ~ for. review
August 1,1974. Accepted January 17,
1975.
Elemental Concentrations in the National Bureau of Standards’ Environmental Coal and Fly Ash Standard Reference Materials J. M. Ondov,‘ W. H. Zoller, llhan Olrneq2 N. K.
and G. E. Gordon
Department of Chemistry, University of Maryland, College Park, MD 20742
L. A. Rancitelli and K. H. Abel Battelle Pacific Northwest Laboratories, Richland, WA 99352
R. H. Filby and K. R. Shah Nuclear Radiation Center, Washington State University, Pullman, WA 9 9 163
R. C. Ragaini Radiochemistry Division. Lawrence Livermore Laboratory, Livermore, CA 94550
The four participating laboratories measured the concentrations of 37 elements in NBS standard coal (SRM 1632) and 41 in fly ash (SRM 1633). Most of the measurements were done by instrumental neutron activation analysis, which was done by each of the laboratories. In addition, one laboratory used instrumental photon activation analysis and another counted the natural radioactivity to determine concentrations of K, Th, and U. The results obtained are in good agreement with the values given by NBS for the twelve elements in each material for which both they and we have values. For most elements for which comparisons can be made, the interlaboratory dispersion of results obtained in this work is much less than was obtained in a recent roundrobin analysis of these materials by many laboratories using a variety of techniques. Average concentrations for the 37 elements in the coal standard and 41 elements in the fly ash standard are presented for comparison with results that may be obtained by other laboratories.
In view of the increasing national concern about toxic elements in the environment, there is a clear need for accurate, reliable analytical methods for the measurement of concentrations of a wide range of trace elements in complex matrixes such as atmospheric particulate material, pollution source materials such as coal, fly ash and oil, and natural waters and sediments. In recognition of the acute need for accurate techniques, the Environmental Protection Agency (EPA) has organized interlaboratory comparisons of several techniques as applied to the analysis of various types of environmental samples. As reported by von Lehmden et al. ( I ) ,samples of coal, fly ash, residual fuel oil and gasoline were homogenized and portions of each distribut-
* Present address, Lawrence Livermore Laboratory, Livermore, CA 94550. Present address, Ankara Nuclear Research Center, Ankara, Turkey. Present address, Department of Chemistry, Middle East Technical University, Ankara, Turkey. 1102
ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
ed to nine laboratories for independent analyses for up to 28 elements by six analytical methods. Results from the interlaboratory comparison clearly indicate the need for improved methods. Although the nine laboratories selected for participation had “in-depth analytical experience in the determination of trace components in environmental materials,” results from the various methods and laboratories for most elements showed enormous variations far outside the quoted limits of uncertainty ( I ) . In summarizing the results for the 28 elements, von Lehmden et al. ( I ) stated that: 1)for eight trace elements in coal, fly ash and residual oil and three in gasoline, reported concentrations varied by more than one order of magnitude in each material; 2 ) reported concentrations for five additional elements varied by more than an order of magnitude in two different matrices; and 3) agreement was within an order of magnitude in all four matrices for only seven of the 28 elements. Clearly, better control of analytical methods is needed! As a further step in the comparison of analytical methods, the National Bureau of Standards (NBS), in cooperation with EPA, made up a set of four environmental standards for coal, fly ash, fuel oil, and gasoline. The standards were made by collecting samples of each material and combining and homogenizing them. The coal samples, for example, were obtained from the coal supplies used by five steam-electric plants. Most of the fly ash was obtained from those same plants. These are not the same standards as those used in the study described by von Lehmden et al. (I). The coal and fly ash standards (designated as Standard Reference Materials SRM 1632 and 1633, respectively) are now available from the Office of Standard Reference Materials of NBS. Portions of the standards were distributed to about eighty-five laboratories that analyze one or more of these standard materials. During late 1972, about fifty laboratories submitted results of their analyses to NBS. Simultaneously with these “round-robin” measurements, the staff of the NBS Analytical Chemistry Division made its own analyses of the standards in preparation for certification of the samples as Standard Reference Materials.
Results of NBS analyses and the round-robin studies were discussed a t a symposium held a t the National Environmental Research Center, Research Triangle Park, NC, in May 1973. For many of the elements measured, there were surprisingly wide variations of concentrations reported by the participating laboratories, far outside the uncertainties usually quoted for the techniques used. For this reason, it is clear that the standards are badly needed so that laboratories can check their procedures for the elements they claim to be able to measure, much as the geochemical community uses the U S . Geological Survey’s standard rocks as a check of laboratory procedures. Most of the NBS analyses were performed on about twenty elements of primary interest to EPA, most of them being known or suspected toxic elements. The Bureau’s certifications for these elements are undoubtedly quite reliable. However, many laboratories would like to be able to use the standards for a much wider range of elements. In trying to determine the origins of atmospheric particulate matter, for example, it is of considerable value to determine concentrations of a wide range of elements in air-filter samples and various source materials (2). T o extend the utility of these much needed standards, we report the results of our analyses of the coal and fly ash standards for about forty elements. All of the analyses were done by completely instrumental nuclear techniques: instrumental neutron and photon activation analysis (INAA and IPAA, respectively) and, for naturally radioactive K, T h , and U, direct y-ray counting. These methods have the advantage that they have no chemical manipulation that might add contaminants, fail to dissolve some portions of the samples, or lose volatile species (although care must be taken to prevent the loss of elements such as Hg and Br that can form volatile species during irradiation). Furthermore, the projectiles used (thermal neutrons or high-energy y-rays) have long ranges in the sample material as do the observed y-rays (mostly above 100 keV), so there is little chance of matrix effects. About the only errors involved in these procedures are those caused by statistical fluctuations of count rates, by pipetting of standard solutions to make u p elemental monitors for the irradiations, by flux variations within the irradiation container, and by variations of positioning of samples during counting.
EXPERIMENTAL University of Maryland. The standards were analyzed by INAA using methods quite similar to those previously described (3).The standards were irradiated along with monitors containing known amounts of each element a t a flux of l O I 3 n/cm2 sec in the NBS reactor. Irradiations of 30-sec duration were used for observation of species with half lives 1 3 8 min; 5-min irradiations for 38 min < t 1 / 2 1 1 5 hr; and 4-hr irradiations for longer-lived products. Sample sizes for coal and fly ash were 100 and 25 mg for the short irradiations and 200 and 100 mg for the 4-hr irradiations, respectively. Monitors containing each element to be determined in an irradiation were made by pipetting aliquots of standard solutions onto 5.5-cm diameter Whatman No. 1 filter material. These standards were irradiated simultaneously with the samples. For most elements, the monitors were checked by irradiating them simultaneously with weighable amounts of the pure elements or their compounds. Concentrations of several elements were determined by IPAA using bremsstrahlung produced by 35-MeV electrons from the NBS linac by the methods previously described ( 4 , 5 ) . In this case, samples of about 1 gram were irradiated along with Ni flux monitors which are used to correct for the variation of bremsstrahlung with position. Elemental flux monitors consisting of weighed primary standards were then irradiated in identical vials along with Ni flux monitors. Spectra of y-rays from irradiation products formed by both methods were obtained with a 55- or 65-cm.’ Ge(Li) detector coupled with a 4096-channel analyzer. The full-width a t half maximum (FWHM) of the peak produced by 1332-keV y-rays from the
decay of 6oCo was typically 2.0 to 2.2 keV. Results of our analyses of the coal and fly ash are listed in the second columns of Tables I and 11, respectively. The errors attached to our values are either the standard deviation of the several determinations or our estimate of the uncertainty of the measurement, whichever was the larger. Estimates of the uncertainties of the INAA determinations include a 13% error in preparation of the elemental monitors (dilution and pipetting errors), and uncertainties in counting statistics, which ranged from
