2076 * ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978 (26) R. Woodriff, M. Marinkovic, R . A . Howald, and I. Eliezer, Anal. Chem., 49, 2008 (1977). (27) C. J. Pickford and G. Rossi, A I . Absorpt. News/., 14, 78 (1975). (28) A . Mubarak, L. Hageman, R. A Howald, and R. Woodriff, Soil Sci. SOC. Am. J . , in press. (29) D. J. Churella and T. R. Copeland, Anal. Chem., 50, 309 (1978). (30) R . E. Sturgeon, Anal, Chem., 49, 1255A (1977).
(31) R. D.
Ediger, A t . Absorpt. News/. 14,
127 (1975).
Received for review August 1, 1978. Accepted September 18, 1978. This work was supported by Grant No. CHE-74-15060 from the National Science Foundation.
Determination of Technetium by Graphite Furnace Atomic Absorption Spectrometry J. H. Kaye" and N. E. Ballou Physical Sciences Department, Battelle, Pacific Northwest Laboratories, Richland, Washington 99352
A detection limit of 6 X lo-'' g has been achieved for measurement of technetium by graphite furnace atomic absorption spectrometry. A commercially available, demountable, hollow cathode lamp was used and both argon and neon were used as fill gases for the lamp. The range of applicability of the method, when the unresolved 2614.23-2615.87 A doublet is used for analysis, is from 60 pg to at least 3 ng of technetium per aliquot analyzed.
Several highly sensitive analytical methods are now available for measurement of "Tc, as summarized in Table I. However, all of these except atomic absorption require a high degree of chemical purification prior to analysis. The most widely used measurement technique involves counting of the 0.292-MeV d ray of 99Tc ( 1 ) . In this case, excellent separation and purification of y9Tc from all other 3 contaminants is required. This can be difficult and laborious. In addition, no stable isotope exists for technetium which could be used as a carrier. 'The neutron activation analysis method (2--4)also yields high sensitivity, but the procedure for separating and purifying the technetium prior to activation is laborious and time consuming and very fast post-activation chemical separations must be performed to remove interferents which have half-lives close to that of looTc (15.8 s). Recently a mass spectrometric technique has been developed for analysis of 99rI'c( 5 ) . It provides a very low detection limit, on the order of 1.0 X 1 0 ~ g (0.02 pCi) or less. However, this method also requires extensive chemical separation and purification steps to remove interference from 99Ru and g'Mo. T h e latter interferes with measurement of the 97'I'c isotopic tracer which is used. A technique is needed which provides high sensitivity and yet does not require the extensive chemical steps which the aforementioned methods demand. One approach which can meet these requirements is atomic absorption analysis, since the technique is highly sensitive and yet very few elements interfere. An atomic absorption procedure for technetium was developed by Hareland e t al. (6). I t involves use of the acetylene-air flame and yields a sensitivity of 3 j g / m L of sample solution. However, as is the case with most atomic absorption procedures, this method calls for the use of a special hollow cathode lamp with a cathode containing technetium. The fact that such a lamp is not an off-the-shelf item has probably prevented much further development and application of this method. Now, de-
''
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Table I. Sensitive Analytical Yethods for \leasurement of Technetium method isotope dilution mass spectrometry neutron activation analysis p counting atomic absorption (acetylene-air flame) polarography spectrophotometry emission spectrometry infrared spectroscopy gravimetric methods X-ray fluorescence
detection limit, g
references
1x 9-20 x 10.''
2.7 x 4.5 x
lo-"
5 x 10-8 10- 6 -10-9 1 x 10-7 5 x 2x 1.8 x 10-5
a Assumes 5 m L required for analysis; reducing flame required.
--
mountable hollow cathode lamp systems are available a t a reasonable cost and preparation of a cathode containing technetium metal should be quite feasible. Determination of technetium by furnace atomic absorption spectrometry has not previously been reported. In this paper we describe the development of a method for sensitive analysis of technetium by furnace atomic absorption spectrometry as well as the preparation and evaluation of a technetium hollow cathode lamp. The measurement range for technetium by the method is presented.
EXPERIMENTAL Apparatus. An Instrumentation Laboratories (1.L.) Model 353 atomic absorption spectrophotometer with an I.L. Model 455 Graphite Furnace Atomizer was used for this study. Peak heights were determined from scans of relative absorbance vs. time obtained with an I.L. Model 114 recorder. Peak areas were determined by computer analysis of the same data. The demountable hollow cathode lamp used in this study was obtained from the Spectrogram Corporation, North Haven, Conn. A gas control system (Model LGC-1) from this same vendor was used to regulate the lamp fill-gas pressure over the range 0 to 20 Torr. To use the demountable hollow cathode lamp, certain modifications to the spectrophotometer were made as shown schematically in Figure 1. Light from the hollow cathode lamp passes through a quartz lens (Ll),which focuses the beam on the cuvette (C). A second quartz lens (L2) focuses the light at the entrance slit of the monochromator after the light is reflected at a right angle by means of a front surface mirror (M). C 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
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Figure 1. Schematic of optical system for "Tc measurements
,
3
,
I
OPERATING PRESSURE
0
1
2
INDICATED
I
OPERATING PRESSURE
3
4
5
PRESSURE, torr
Figure 2. Intensity of technetium lamp as a function of fill-gas pressure A special holder was fabricated so that the I.L. furnace atomizer could be used without modification. Minor modifications were made to the spectrophotometer in order to be able to operate the instrument in single beam mode. The instrument was also interfaced to a minicomputer system to permit convenient data acquisition, processing. and presentation. Reagents. Technetium-99 in solution form, as ammonium pertechnetate, was obtained from Amersham/Searle Corporation, Arlington Heights, Ill. Technetium solutions which varied in concentration from 0 to 287 X lo-'* g/pL were prepared by dilution of the primary standard with 1 M ",OH. The technetium cathode for the hollow cathode lamp was prepared by careful evaporation of 4.5 mg of technetium as ammonium pertechnetate solution in the well of a graphite cathode obtained from Spectrogram Corporation. The cathode was heated at 800 "C for 30 min in a stream of hydrogen gas to convert the technetium to the metallic form. Argon of 99.99% purity, and ultra-high purity neon obtained from Union Carbide Corporation, Linde Division, San Francisco, Calif., were used as lamp fill gases for this study. Check for Contamination. After the study was completed, the demountable hollow cathode lamp was disassembled and the lamp components were checked for r3 contamination. No activity was observed on any component except the cathode itself. An "absolute" (HEPA) filter was mounted on the exhaust port of the vacuum pump during this study as back-up protection in case any %Tc was released from the lamp cathode. h'o 8 activity was observed on this filter after the study. Procedure. The cathode containing the technetium was placed into the demountable lamp assembly, which was then evacuated. The lamp assembly was filled and evacuated three times with argon or neon and then evacuated to 0.2 Torr, as indicated on the LGC-1 panel meter. Then the gas pressure was adjusted to
the desired value. .4s shown in Figure 2, this is about 1.2 Torr (indicated) for argon and 3.4 Torr (indicated) for neon. A t a pressure just slightly below these values, the lamp intensity for the 261.4-nm Tc doublet line drops rapidly to zero. Helium was also tested as a fill gas, but since a wavelength scan through the 261.4-nm region did not reveal a peak due to the technetium doublet, no further studies were done with this gas. Scans of lamp intensity 1's. wavelength for argon fill gas over the range 255 to 270 nm show the 261.4-nni doublet peak as well as a peak at 260.9 nm to be due to technetium. Scans for neon fill gas are similar. Wavelength scans were also made in the vicinity of the 403.1- and 429.7-nm lines with argon fill-gas, since technetium absorbance lines have been reported at these wavelengths (6). Much lower absorbance readings were obtained when technetium solutions were analyzed at the 260.9-, 403.1-, or 429.7-nm wavelengths. These wavelengths would therefore be useful only for analysis of solutions containing rather high levels of technetium.
RESULTS AND DISCUSSION The first studies were made with argon gas a t 1.2-Torr pressure in the lamp. I t was found t h a t the optimum signal-to-noise ratio was obtained with a near-maximum lamp current of 20 mA, minimum amplifier gain, slit width at position 160 (entrance slit 160 pm, exit slit 200 pm, bandpass 0.43 nm), and with 620 1' to the photomultiplier tube. No significant improvement was found b y stopping t h e flow of gas through the cuvette chamber during the atomization cycle (pressurized mode). In a test of two different loadings of %Tc (2.3 and 4.5 mg) in the demountable hollow cathode lamp, a higher signal-to-noise ratio was observed with the larger 99Tc loading.
ANALYTICAL CHEMISTRY, VOL. 50, NO. 14, DECEMBER 1978
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40
1 I
> E
I
I
I
I
atures of approximately 2400, 2800,3100, 3300, and 3400 "C during the 10-s atomization step. Increasing peak heights resulted from the higher temperatures, with incomplete vaporization of technetium occurring a t the lowest temperature. A cuvette temperature of 3300 "C was chosen as a reasonable compromise between maximum peak height and long cuvette life.
I
114 pg 99Tc \
\
A
=
261.4 n m
I-
I
c3 W
ACKNOWLEDGMENT The authors thank Michael S. Rapids for helping t o set up
1 4i
5 a
and test the system.
\
1 M NH40H
LITERATURE CITED 0 1
0
I
I
I
1
2
4
6
8
(1) (2) (3) (4) (5)
10
TIME, sec Figure 3. Signal intensity vs. time for sample containing 114 pg of '?c, neon fill gas
(6)
Either argon or neon seems to be satisfactory for filling the demountable lamp. However, neon gives a somewhat lower noise level and a n absorption signal about 1.8 times greater than does an argon-filled lamp. Figure 3 is an example of the recorder output for a typical measurement with a neon-filled cathode containing 4.5 mg 99Tcand a sample size of 114 pg "Tc. Calibration curves for both argon and neon were linear over the ranges studied, Le., 0-914 pg 99Tc for argon and 0-2900 pg T c for neon. The relationship found between peak height and quantity of technetium is given by the expressions h = 0.095~:for argon and h = 0 . 1 5 1 ~ for neon, where h is the peak height in milliabsorbance units and w is the weight of 99Tc in picograms. For the case of argon, the milliabsorbance values were determined from an average of three peak height measurements at each of three different concentrations of T c . For neon, an average of three measurements at each of six different concentrations of 99Tc was taken. The detection limit for technetium is about 60 pg when a neon-filled lamp is used. Detection limit is herein defined as the quantity of technetium which yields a peak-height value that is twice the standard deviation of the blank value. Peak height values were determined for cuvette temper-
(7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (2 1) (22) (23) (24)
N. W. Golchert and J. Sedlet, Anal. Chem., 41, 669 (1969). G. Boyd and Q. Larson, J . Phys. Chem., 60, 707 (1956). S. Foti, E. Delucchi, and V. Akamian, Anal. Chim. Acta, 60, 261 (1972). S. Foti, E. Delucchi, and V. Akamian, Anal. Chim. Acta, 60, 269 (1972). J. H. Kaye, M. S. Rapids, and N. E. Ballou, "Determination of Picogram Levels of Technetium-99 by Isotope Dilution Mass Spectrometry" in "Proceedings of Third International Conference on Nuclear Methods in Environmental and Energy Research". Columbia, Mo., in press. W. A. Hareland, E. R. Ebersole, and T. P. Ramachandran, Anal. Chem., 44, 520 (1972). G. Boyd, J . Chem. Educ., 36, 3 (1959). L. Astheimer and K. Schwoachare, J . Electroanal. Chem., 15, 61 (1967). A. K. Lavrukhina and A. A. Pozdnyakov, "Analytical Chemistry of Technetium, Promethium, Astatine and Francium", Humphrey Science Publishers, Ann Arbor, Mich.. 1970. R. Villarreai, M.S. Thesis, University of Idaho, Moscow, Idaho, 1967. C. Crouthamel, Anal. Chem., 29, 1756 (1957). 0. Howard and C. Weber, Anal. Chem., 3 4 , 530 (1962). F. Miller and H. Zittel, Anal. Chem., 35, 299 (1963). F. J. Miller and P. F. Thomason, Anal. Chem., 32, 1429 (1960). F. J. Miller and P. F. Thomason, Anal. Chem., 33, 404 (1961). R. Colton et ai., U.K.At. Energy Auth. Rep., AERER 3746 (1961). M. AI-Kayssi. R. J. Magee, and C. L. Wilson, Talanta, 9, 125 (1962). F. Jasim, R. J. Magee, and C. L. Wilson, Talanta, 2, 93 (1959). F. Jasim, R . J. Magee, and C. L. Wilson, Talanta, 4, 17 (1960). W. Meggers, Spectrochim Acta. 4, 317 (1951). J. W. Cobble, "Technetium", in "Treatise on Analytical Chemistry", Part 11. Section A, Volume 6, Interscience Publishers, New York, 1964. R. J. Magee and M. AI-Kayssi, Anal. Chim. Acta, 27, 469 (1962). F. Jasim, R. J. Magee, and C. L. Wilson, Microchim Acta, 5-6, 721 (1960). S. G. Metcalf, Anal. Chim. Acta, 93, 297 (1977).
RECEIVEDfor review May 8, 1978. Accepted September 5 , 1978. This paper is based on work performed under the United States Department of Energy. formerly Energy Research and Development Administration, Contract EY-76C-06-1830.
Low-Temperature Positive Secondary Ion Mass Spectrometry of Neat and Argon-Diluted Organic Solids Harry T. Jonkman and Josef Michl" Department of Chemistry, University of Utah, Salt Lake City, Utah 84 7 72
Robert N. King and Joseph D. Andrade Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84 7 72
Secondary ion mass spectrometry of neat solid propane, n-pentane, benzene, toluene, and of propane imbedded in an argon matrix were observed at temperatures varying from 10 to 110 K and show fragmentation patterns similar to those known from ordinary electron impact mass spectrometry. The effects of the nature and energy of the primary probe ion and of the sample temperature were investigated. The analytical potential of the method, e.g., for reactive species trapped in inert matrices, is noted.
In the course of work with heat-sensitive involatile organic 0003-2700/78/0350-2078$01 O O / O
and biological materials and with highly reactive species isolated in inert matrices, it frequently appears desirable to complement other spectroscopic methods by mass spectral data. Since in these instances the species of interest cannot be easily transferred to the gas phase without change, standard mass spectrometry is of little direct use and methods such as field desorption ( I ) have been investigated. In recent years, a limited amount of exploratory work on organic solids using plasma desorption mass spectrometry (PDMS) ( 2 , 3) and secondary ion mass spectrometry (SIMS) (4-18) has been performed in several laboratories and appears t o show considerable promise. C 1978 American Chemical Society
