Anal. C h e m . 1980, 52, 457-459
injection of the sample solution. Application. The VUV atomic absorption spectrometric method developed was applied to the NBS standard reference material, mercury in water (SRM 1641),and the fish homogenate (MA-A-2). Mercury in water was diluted 1000 times, a n d analyzed. T h e fish homogenate sample (ca. 1 g) was digested in a wet digestion system with a acid mixture (3 mL concd HNO,, 1 mL concd H2S04and 1 mL concd HC10J for about 15 h. The digested solution was diluted to 50 mL. The analytical results are summarized in Table 111. The data are almost consistent with the certified value of NBS and the value obtained at 253.7 nm, respectively.
457
J. Olafsson, Anal. Chim. Acta, 68, 207 (1974). K. Matsunaga, M. Nishirnura, and S. Konishi, Nature (London),258, 224 (1975). K. Fuwa, "Spectrochemical Methods of Analysis", J. D. Winefordner, Ed., Wiley-Interscience, New York. 197 1, pp 189-234. R. M. Dagnall, J. M. Mansfield, M. D. Silvester, and T. S. West, Nature (London), Phys. Sci., 235, 156 (1972). J. W. Robinson, P. J. Slevin, G. D. Hindman, and D. K. Wolcott, Anal. Chim. Acta. 81, 431 (1972). R. M. Daanall, J. M. Mansfield. M. C. Silvester, and T. S. West, Spectrosc. L e r t . , 6, 183 (1973). G. F. Kirkbright, T. S . West, and P. J. Wilson, Analyst(London),98, 49 (1973). J. Takahashi, K. Tanabe. H. Haraguchi, and K. Fuwa, Bunseki Kagaku, 27, 738 (1978). M. P. Stainton, Anal. Chem., 43, 625 (1971). T. R. Gilbert and D. N. Hume, Anal. Chim. Acta, 65, 461 (1973).
LITERATURE CITED (1) W. R. Hatch and W. L. Ott, Anal. Chem., 40, 2085 (1968). (2) J. E. Hawley and J. D. Ingle, Jr., Anal. Chem., 47, 719 (1975). (3) S. Yamazaki, Y. Dokiya, T. Hayashi, S. Toda, and K. Fuwa, Nippon Kagaku-kaishi. 8, 1148 (1977). (4) S. H. Omang, Anal. Chim. Acta, 53, 415 (1971).
RECEIVED for review May 29,1979. Accepted August 23,1979. This research has been supported by Grant-in-Aid for Environmental Science under grants No. 303022 and No. 303035 from the Ministry of Education, Science, and Culture, Japan.
Retention of Chromium by Graphite Furnace Tubes Claude Veillon," Barbara E. Guthrie,' and Wayne R. Wolf Human Nutrition Center, Nutrition Institute, United States Department of Agriculture, Building 3 0 7 , Room 2 75, Beltsville, Maryland 2 0 7 0 5
Using "Cr tracer techniques, a considerable amount of chromium was found to be irreversibly retained in graphite furnace tubes upon atomlzatiin. Both atomization temperature and sample matrix were found to be very influential in the amount retained. Pyrolytically-coated tubes retained less Cr than uncoated tubes. Considerable errors are likely if the method of additlons is not used. No Cr loss by volatilization was observed for indicated char temperatures up to 1300 OC.
Table I. Percentage of 51CrRetained in Graphite Tubes tube type and atomization temperature
EXPERIMENTAL Apparatus and Reagents. A commercially available graphite tube furnace and power supply (Model 2100, Perkin-Elmer Corp., Norwalk, Conn.) was used with both pyrolytically-coated and uncoated tubes. Radioactive chromium in the form of carrier-free Present address: Nutrition Department, Otago University, Dunedin, New Zealand. This article not subject to U.S. Copyright
'lCr standard
uncoated 2600 'C 2700 3 C
pyrolytic 2600 'C 2700 'C
During an investigation of human urinary chromium excretion using graphite furnace atomic absorption spectrometry (I),it became evident that some of the analyte was being "lost", and so was not available for measurement. Possible mechanisms for the apparent loss include carbide formation, matrix effects in the complex urine ash matrix (such as volatilization of the Cr as non-atomic species, or the formation of refractory compounds), diffusion losses through the graphite walls, mechanical losses during the dry or atomize modes, and losses which occur in the sample preparation procedure prior t o analysis. These various loss pathways, and the effect of furnace temperatures on these pathways, were investigated using "Cr solutions and rat urine containing endogenous 51Cr. The use of W r as a tracer in these studies permits one to unambigously and quantitatively measure and follow the Cr throughout the sample preparation and atomization processes. Considerable evidence of stable carbide formation was found. The atomization temperature was found to be very important, and large differences were observed depending upon the sample matrix used.
urine ash so 1ut io no 58
45
i i
44
i
28
r
3 (8)c
69 ( 2 )
5 (9) 9 1:s) 5 l(3)
32 ( 2 )
Urine samples from rats which were injected subcutaneously with "CrCI,. Samples were dried (60 "C, 125 Torr), oxygen plasma ashed (400-W rf, 1 Torr 0,)and dissolved in 0.1 M HCI. "CrCI, in 0.1 M HCI. Number in parentheses indicates number of tubes i n each group. 51CrC13(New England Nuclear, Boston, Mass.) was used to spike test solutions, and was incorporated into rat urine by subcutaneous injection of adult male CD Sprague-Dawley rats (Charles River Breeding Laboratories, Boston, Mass.). Samples, standards, graphite tubes, and sample containers were measured by y emission spectrometry (Model 1185, Searle Analytic, Inc., Des Plaines, Ill.). All reagents were the same as those used for previous Cr analyses in urine ( 1 ) . Procedures. Labeled samples of 20-50 FL were injected into the furnace in the normal manner ( 1 ) and processed through various cycles. A t appropriate intervals, the tubes were removed and counted. For the sample preparation procedure studies, the porcelain crucibles were similarly counted. All spiked solutions were monitored, and compared to the initial 51Crstock solution to compensate for isotopic decay over the experimental time frame. By spiking with sufficient label to yield relatively high count rates, excellent counting statistics ( < I % )were obtained with counting times of a few minutes. Total counts at each step were checked to be certain that the label was accounted for, and care was taken in the placement of tubes and crucibles, and the volume of solutions, in the counting tubes to minimize any geometric effects on the measured counts. Counting rates were tens of thousands of counts per minute, corresponding to something on the order of lo-" g of jlCr, depending on the specific activity of the isotope. This is comparable
Published 1980 by the American Chemical Society
458
A N A L Y T I C A L CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
Table 11. Percentage of 5’Cr Retained in Graphite Tubes upon Repeated Atomizationa pyrolytic
Table 111. Percentage of ”Cr from Rat Urine Retained in Graphite Tubesa
uncoated
urine H:O1 + direct‘ HNO,d ~
t u b e type and
1st atomization sampleb
44
st an da r d 2nd atomization sample
standard 3rd atomization sample standard 4th atomization sample
standard
i
9‘
40 i 9 29
41
39
37 i 3 31
z
conditions
58, 3
69
32
9
28 37 t 9 27
i
pyrolytic char 800 ” C atomize 2700 “ C uncoated atomize 2700 ’C
3
57
33i 2 49
a 1st atomization at 2600 “ C for 9 s; all others at 2 7 0 0 “ C for 9 s. No additional sample after 1st atomization. Same solutions as in Table I. ‘ Mean i SD, 8 tubes for
samples, 2 tubes for standards.
to the amounts measured in urine analysis.
RESULTS T h e retention of chromium in t h e graphite furnace tubes following atomization was investigated. These data are shown in Table I, for a 51CrC13standard in 0.1 M HC1, and a 0.1 M HC1 solution of the ash from oxygen plasma ashed rat urine, at two atomization “temperatures” in both pyrolytically-coated and uncoated tubes. A new tube was used for each measurement. The samples were dried (“DRY” mode) a t 150 “C for 30 s and ashed (“CHAR” mode) a t 1300 “C for 30 s prior to the atomization step. The tubes were counted a t the end of each step to ascertain that no loss of jlCr had occurred. It should be pointed out that the “temperatures” quoted are those indicated by the meter on the furnace power supply. This is basically a measurement of current through the graphite tube. Consequently, the accuracy will depend primarily upon the dimensions of the tube (compared to those used to calibrate the system). Repeatability from tube to tube is determined primarily by t h e uniformity of the tube dimensions. T h e data in Table I illustrate two important points: (a) a large difference in the amount of Cr retained occurs for an indicated atomization temperature change of only 100 “ C (750 “C), but no losses of exogenous jlCr added to control tissues. They attribute the volatile fraction to “glucose tolerance factor” (6). Tuman et al. ( 7 ) reported a volatile chromium fraction in brewers yeast which they measured indirectly. In contrast, Jones et al. (8) showed no losses of j’Cr from endogenously labeled brewers yeast with oven-drying, lyophilization, wet digestion (even with high levels of chloride), or dry ashing up to 700 “C. Essentially identical results were obtained by Koirtyohann and Hopkins (9) for liver and blood samples from rats endogenously labeled with W r . Kumpulainen (10) found no losses of 51Crupon dry ashing endogenously labeled brewers yeast a t 550 “C. Consequently, we investigated several sample preparation and analysis procedures with respect to the retention of 51Cr by the graphite tube and containers, and other possible loss mechanisms which might occur prior to analysis. These data are shown in Table 111. If there is a volatile form of Cr in rat urine, it is undetectable in an 800 “C char step. Likewise, solutions of ashed urine, untreated urine, and urine pretreated with H N 0 3 / H 2 0 2give similar retentions in the graphite tubes. Earlier interpretations of some observations by furnace atomic absorption as representing volatile Cr appear to be inaccurate. We believe that these interpretations were caused by failure of the background correction systems used to fully correct for the background when urine is run directly ( I ) , and/or attributable to the differences in Cr retention by the furnace tube when urines are compared to essentially matrix-free standard solutions (e.g., Tables I and 11). We next investigated various steps in the sample preparation and analys s procedures normally used in urinary Cr determinations ( I ) . Nonquantitative aspects of the procedure were assessed directly, using the 51Crlabeled urine as a tracer. Table IV shows data relating to possible loss of Cr during the “char” mode. For char temperatures of 1300 “C or less, no loss of Cr was observed. Above this temperature, the Cr loss becomes progressively greater. T h e effect of atomization temperature and time on Cr retention within the graphite tube is shown in Table V.
Anal. Chem. 1980, 52, 459-463
Table IV. Effect of Char Temperature and Time on Cr Retention within the Graphite TubeQ indicated temperature, “ C
char time, s
1000-1300 1400 1400
30-90
100
30
97 94 95 92
1500 1500
1600 1600 1700 1700
”Cr retained, 5%
60 30 60 30 60 30 60
87 84
69 65
a Uncoated tubes. Each timeitemperature pair represents the mean of 2 tubes.
Table V. Effect of Atomization Temperature and Time on Cr Retention within the Graphite Tubea indicated temperature, “ C 2300 2400 2500 2600 2700
”Cr retained, 7c atomize atomize 9s 15 s 50
69 57 52
40
35
48 45
33
a Uncoated tubes. Each measurement represents the mean of 2 tubes.
T h e sample preparation procedure used for urinary Cr analysis involves several steps (1). Aliquots of urine are placed in porcelain crucibles, dried under vacuum and heat, oxygen-plasma ashed, treated with HzOz,followed by an additional drying and ashing. T h e ash is then dissolved in HC1 and this solution is analyzed. Looking a t each of these steps using the 51Crlabeled urine, the following observations were made: (a) Drying in the vacuum oven resulted in no losses. Retention for 10 samples was 99 f 1%. (b) The first oxygen plasma ashing resulted in no losses. Retention for 10 samples was 100 f 170.(c) After the addition of H,Oz, a second drying, a n d a second ashing, no losses were observed. Recovery of t h e 51Cr was 100 f 1%. (d) When the HCl was added to
459
dissolve the ash, essentially complete recovery was obtained.
For 5 samples, acid was added and the crucibles were allowed to stand for 0.5 h in the normal manner. T h e sample was removed and the crucibles were rinsed several times with water. T h e 51Cr remaining in the crucibles was 2.4 i= 1.8%. In light of our recent findings (11) regarding the background correction capabilities of earlier commercial atomic absorption spectrometers, and the Cr retention problems reported herein, it is not surprising that conflicting and erroneous urinary Cr values have appeared in the literature. Likewise, the “volatile fraction” reported in the past is quite possibly related to these phenomena. These retention data emphasize the need for precise temperature control in the furnace, a rapid heating rate to the final atomization temperature, and the important role played by the sample matrix. Considerable errors are possible when samples and standards with different matrices are compared. Pyrolytically-coated tubes are advantageous for Cr analyses. We found no evidence of loss of chromium by volatilization during analytical or sample preparatory steps.
LITERATURE CITED (1) 6.E. Guthrie, W. R. Wolf, and C. Veillon, Anal. Chem., 50, 1900-1902 (1978). (2) Y. Talmi and G. H. Morrison, Anal. Chem., 44, 1455-1466 (1972). (3) B. V. L-Vov, Spectrochim. Acta, Part B , 33, 153-193 (1978). (4) T. R. Ryan and C. R. H . Vogt, J . Chromatogr., 130,346-350 (1977). (5) D. Shapcott. K. Khoury, P. P. Demers, J. Vobecky. and Jos. Vobecky, Clin. Biochem., I O , 178-180 (1977). (6) K. Schwarz and W. Mertz, Arch. Biochern. Biophys., 85, 292-295 (1959). (7) R. W . Tuman, J. T. Bilbo, and R. J . Doisy, Diabetes, 27, 49-56 (1978). (8) G. 8.Jones, R. A . Buckley, and C . S.Chandler. Anal. Chim. Acta, 80, 389-392 (1975). (9) S.R. Koirtyohann and C. A. Hopkins, Ana/yst(London), 101, 870-875 (1976). (IO) J. Kumpulainen, Anal. Chim. Acta, 9 1 , 403-405 (1977). (11) C. Veillon, W. R. Wolf, and B. E . Guthrie, Anal. Chem., 51, 1022-1024 (1979).
RECEIVED for review July 31, 1979. Accepted November 30, 1979. B.E.G. was supported in part by a U S . Public Health Service International Research Fellowship (No. 1F05 T W 02529-01). Presented in part a t the Federation of Analytical Chemistry and Spectroscopy Societies 6th Annual Meeting, Philadelphia, Pa., September 1979. Specific manufacturer’s products are mentioned herein solely to reflect the personal experiences of the authors and do not constitute their endorsement nor that of the Department of Agriculture.
Candoluminescence Emission for the Determination of Bismuth, Manganese, and Antimony Saadi M. Dhaher and Zuhair M. Kassir” Chemistry Department, College of Science, University of Basrah, Basrah, Iraq
A candoluminescence emission technique is developed by shaping the matrix material (CaO-CaSO,) in the form of a rod 5 mm in diameter and 1-2 cm long. The activator (7.5 pL) is applied to the surface of the rod tip and exposed to nnrogen diluted hydrogen flame. Conditions were studied to obtain the best emission which lasts for 30 min or more. Workable calibration curves for bismuth (5-375 ng), manganese (4-75 ng), and antimony (4-40 ng) were obtained.
Candoluminescence is known to be the emission from certain metal oxides that contain trace metal ions as activators when exposed t o hydrogen flame. 0003-2700/80/0352-0459$01 .OO/O
Many workers studied the emission of flame-excited oxides. The early work on the subject was reviewed by Minchin ( I ) , and recently Ivey (2) reviewed the emission of solids heated in flames or excited by gases containing free radicals or excited molecules. The phenomenon was used by Donau (3)and Neunhoeffer ( 4 ) for qualitative analysis. Belcher et al. (5-7) established the possibility of using candoluminescence emission for quantitative determination of elements at trace level using calcium hydroxide-caldium sulfate as a matrix. The matrix in a homogeneous paste was inlaid into the aperture of a hexagonal steel screw. The method was applied for the determination of bismuth (6),manganese @), praseodymium and C 1980 American Chemical Society
