+
C6HsOs 2Fe(III) Fe(I1)
+
+ 2H+ + 2Fe(II)
CeHeOs
+ 3 ferz2-
+
Fe(II)(fer~)~~-
Thus for each ascorbic acid oxidized there are two chelates of Fe(II)(ferz), 4- produced yielding effective molar absorptivity of 55800 which is the determining factor in the limit of detection. Pure ascorbic acid in the amounts as low as 5 pg/25 ml and in the amounts greater than 10 pg/25 ml can easily be determined with a relative precision of *2% and *l%, respectively. In general the calculated absorbance values using iodimetric method and macro samples are higher by approximately 2 to 4 % as compared to the values obtained by the iron(II1)-ferrozine method. This discrepancy may be due t o the inhomogeneity of the sample, since in both cases fresh citrus fruit after centrifugation contains some cellular fragments. Sucrose, glucose, mannose, fructose, and formaldehyde do not interfere. Tartaric and citric acids chelate with iron(II1) and slow down the reaction of ascorbic acid. The interference of these acids is overcome by the addition
of aluminum ion. The analysis of commercial cranberry juice is unsatisfactory by the iron(II1)-ferrozine method, since the developed color changes with time. However, the absorbance values taken after a reaction time of 2 to 3 minutes seem to correspond to the ascorbic acid present in the cranberry juice. Oxalic acid in the amounts as high as 10 times that of iron(II1) has no effect. Phosphate in the amounts approximately 100 times that of iron(II1) does not interfere. Copper(II), cobalt(II), and nickel(I1) form chelates with ferrozine. Thus, in the presence of these ions the amount of ferrozine should be increased until there is no further change of the iron(I1)-ferrozine color intensity. In actual analysis, it is advisable to use an excess of ferrozine. Determination of ascorbic acid in the presence of iron(I1) can be achieved by passing the solution through a cation exchange resin and analyzing the eluent for the ascorbic acid.
RECEIVED for review May 24, 1971. Accepted August 20, 1971.
Cyanide Extraction and Electrodisposition of Trace Amounts of Radioactive Silver from Large Biological Samples V. F. Hodge and T.R. Folsom Scripps Institution of Oceanography, Uniuersity of California, San Diego, La Jolla, Calif. 92037
THESTUDY OF RADIOACTIVE silver in the marine biosphere was recently given new impetus when the long-lived nuclide losmAg(tliz= 127 yr) was found in the livers of several species of marine animals caught in 1964-1965 (1). It became apparent that if llomAg(fl/* = 253 d) could be measured along with losmAg,the ratio of these two nuclides might be useful in some cases in identifying the origin of the radiosilver. These nuclides may enter the biosphere as fallout from nuclear weapons or as pollution from nuclear generating stations or nuclear powered vessels. As part of a continuing study of radioactivity in the marine environment, attempts were made to measure, without chemical pretreatment, losmAgand l1ornAgin the livers of albacore tuna collected during the summers of 1968 and 1970. Although the available multiparameter NaI spectrometer can detect concentrations of the two silver nuclides as low as 1.0 =t 0.2 pCi/sample, other fallout activities such as 6oCoand 65Zn,which were generally present in the livers in relatively high amounts, interfered with the identification of the two silver isotopes in the low concentrations that were encountered. Therefore, a method was sought that would concentrate trace amounts of radiosilver from kilogram quantities of wet tissue without loss, and that would at the same time eliminate interferences from 6OCo and 6jZn. Wet ashing of large organic samples has been difficult because the process requires many gallons of acid and often weeks of regular attention. Dry ashing also had to be rejected since there are reports that silver can be lost at temperatures
as low as 100 “C (2). Therefore, we chose to utilize the complexing action of the cyanide ion that has long been exploited by the mining and electroplating arts. For example, very small amounts of fallout silver (on the order of 10-l6 mole) are readily recovered from kilogram amounts of fresh liver tissue by simply stirring the comminuted liver into a basic cyanide solution which contains a gram of silver ion, and then allowing about two days for the added silver t o exchange with the radioactive traces. The silver is then plated directly from the slurry onto platinum strips. The silver may be stripped from the platinum with nitric acid and finally collected as its chloride precipitate. Thus the radiosilver in a large organism can be readily concentrated into a small volume and brought close to a small detector such as a solid-state Ge(Li) detector. Moreover, this procedure is equally effective with slurries of fresh liver, liver long preserved in formalin, and also biological samples reduced at 250 “C to a black char.
(1) T. R. Folsom, R. Grismore, and D. R. Young, Nature, 227, 941 (1970).
(2) T. T. Gorsuch, “The Destruction of Organic Matter,” Pergamon Press Ltd., New York, N.Y., 1970, p 66.
EXPERIMENTAL
Cyanide Extraction. All samples were ground in a Waring Blendor with sufficient water to achieve efficient blending action. For example, 2 kg of wet albacore liver tissue yielded approximately 5 liters of blended material. To this slurry, which was contained in an 11-liter polyethylene bucket, approximately 300 ml of 5M NaOH were added to bring the pH to 9. Then, 2 liters of a cyanide mixture were added. (Caution: All procedures involving cyanide were carried out
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
381
Table I. Efficiency of Cyanide Extraction of lWmAgand llomAg from Charred and Wet Tissue pCi/sample” Before Recovered Weight, g Nuclide extraction in AgCl Sample 1970 Sea Hare (mollusc) 60 ‘OK 0 2023 i 60 (whole bodies charred) 58Co 0 1040 =t10 0 60Co 82 f 3 1 l0rnAg 123 i 2 120 i 4 1970 Hawaiian* Yellowfin
100
tuna (wet liver)
40K
60Co 65Zn l08rnAg ll0rnAg
6
in a well drafted hood and with plastic gloves.) This solution was prepared from 2 liters of deionized H 2 0 , 1.5 grams of AgN03 (B&A Analyzed), 5 ml of 5M NaOH, and 1 lb of K C N (B&A Reagent, ACS) in that order. Enough deionized water was added to bring the total volume t o 10 liters. The final pH, as measured with Hydrion paper, was 12. This mixture was loosely covered and allowed to stand for 2 days in a hood, during which time the slurry was stirred occasionally with a plastic rod. At the end of 2 days, 2 thin platinum sheets, each having a n effective area of about 200 cm2,were inserted as electrodes into the liver mixture. A current density of approximately 0.5 mA/cm2 was applied, and essentially all of the silver was plated out in about 5-6 hours. The cathode was stripped of its silver in 100 ml of 1 : 1 concentrated HNOs (Baker Analyzed Reagent) :deionized water. After the silver had been removed (2-5 min), the electrode was placed in 100 ml of a 1 : 1 H N 0 3 rinse. The stripping solution and the rinse solution were combined and diluted with 200 ml of deionized water. Based on the weight of silver plate, a 10% excess 1 M NaCl (B&A Reagent, ACS) was added with magnetic stirring. The AgCl was collected by filtering with a Millipore filter apparatus onto a 1.5 p , 47 mm diameter filter disk (OHWP 047 00). The AgCl plus filter disk was transferred to a 2-inch Millipore plastic petri dish and counted. To test all reagents for 1osmAgand IIOmAg, 8 lb of KCN, 8 grams of AgN03, and 200 ml of 5M NaOH were dissolved in 10 liters of deionized water. After setting 2 days, the Ag was plated out and converted to AgC1. N o radiosilver was detected. Counting Techniques. All samples were counted for 1000-4000 min on a 47-2-dimensional sodium iodide gamma ray spectrometer. The absolute activities in the samples were determined by making comparisons with point sources of losmAgand llornAgthat had been calibrated against the prime standard of this laboratory (137Cs No. 107), which has been intercalibrated with standards of several other laboratories
RESULTS AND DISCUSSION
Samples of sea hare (Aplysia californica) that contained IlomAg,T O , and 6OCo in amounts easily measurable without chemical treatment were used t o test the efficiency of the basic cyanide procedure. One kilogram of wet sea-hare tissue was (3) T. R. Folsom and K. Saruhashi, J . Radiaf. Res. (Japan), 4, 39 (1963).
382
... ... 99 f 7 101 f 6
= 1.0.
F I ,
JAN. 64
, , 66
68
70
YEAR Figure 1. Variations in the mean concentrations of five different radioactive nuclides in liver tissue collected from N. Pacific albacore caught near San Diego a t four different periods ( 4 )
(3).
Destruction of Cyanide Waste. Cyanide solutions were destroyed by adding a 5 % solution of NaOCl (common bleach) until an excess of hypochlorite was detected and remained for hour.
102 3= 4
...
12.7 + 0 . 2 9 . 1 =k 0 . 2
8-L
1
...
... ...
0 0 0
195 i 17 6.7 i0.4 77 + 4 12.9 i 0 . 9 9 . 0 =k 0.5
f one counting standard deviation. 1lomAg/losmAg corrected to the date of collection (Dec. 9, 1970) is 12.6 pCii12.7 pCi
43 extracted,
charred at 250 “C t o obtain approximately 100 grams of char and counted in the 4n-2D spectrometer. The char was then extracted and the resulting AgCl precipitate counted; only llornAgwas present. The first entry in Table I shows that the recovery of llornAgwas quantitative, within counting errors. In another test, the wet liver of a 210-lb albacore, found t o contain exceptional amounts of both losmAgand llornAg,was used t o determine the efficiency of the cyanide leaching process. In addition to the silver nuclides, this large albacore had also concentrated relatively high amounts of WOand
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2 , FEBRUARY 1972
Table 11. Activities of 1mrnAgand llornAgFound in Livers of 1968 and 1970 Albacore by Cyanide Extraction Date pCi/sample* pCi/kgc Collected Countedd Preserved Wet wt”, kg loemAg 1 l0rnAg l08rnAg 1IOrnAg 10 Sept 68 25 Aug 70
22 Apr 71 Formalin 1.670 15 May 71 Frozen 6.050 a Original wet wt. =k one counting standard deviation. 108mAgratio = 1.1.
9.9 f 0.2 26.0 i 0 . 2
0.76 i 0 . 3 1 14.7 f 0 . 2
Sample activity/kg on date of collection.
65Zn. A 100-gram sample of the liver tissue was counted in the wet state for 2500 min and the silver was then extracted using the cyanide procedure. Entry number two in Table I 3hows that both silver nuclides were quantitatively removed in this case also. It may also be seen that the activity ratio remained unchanged during the procedure; this suggests that n o contamination occurred. Because of the success obtained in leaching radiosilver from wet tissue, the problem of measuring losrnAgand llomAgin the 1968 and 1970 albacore liver samples was then undertaken. The cyanide leaching process was applied t o 1.6 kilograms of livers preserved in formaldehyde since 1968 and six kilograms of frozen 1970 livers. Results are found in Table 11. To ensure that all of the radiosilver had been removed, a second batch of silver carrier was added to the liver slurries, equilibrated, and plated out. The AgCl precipitates from these “second extractions” were devoid of measurable amounts of either silver isotope. Figure 1 shows the variation of 65Zn, W o , 54Mn,llornAg, and losrnAgin livers of a specific population of albacore tuna caught in the summers off San Diego from 1964-1970 ( 4 ) . Without the cyanide extraction procedure, only upper limits of the 1968 and 1970 silver concentrations might have been reported. Thus the cyanide extraction procedure appears t o provide a convenient means by which 1osmAg and llomAg (4) T. R. Folsom, D. R. Young, V. F. Hodge, and R. Grismore,
Paper presented at the Third National Symposium on Radioecology, Oak Ridge, Tenn., May 1&12, 1971.
6 . 0 2~ 0 . 2 4.3 & O.lc d
8.7 f 3.6 4 . 8 i O.lc
4000 min counts.
11OmAg/
concentrations might be followed for many years to come in fish livers and other marine organisms. During the last few years, losmAg/llornAg ratios have been measured in a large number of marine fish and squid. The interpretations of these ratios from an oceanographic point of view, in which reference is made to several possible sources of silver nuclides from nuclear tests, are discussed elsewhere (1,5,6). Experiments are now under way in this laboratory in the hope of removing other gammaemitting nuclides from wet tissues by similar methods. ACKNOWLEDGMENT
The authors thank T. Otsu of the National Marine Fisheries Service, Honolulu, for supplying the Hawaiian samples ; D. R. Young, Southern California Coastal Water Research Project, Los Angeles, for the 1968 albacore samples; and P. Butram of the Westgate Cannery, San Diego, for the 1970 albacore samples.
RECEIVED for review June 21, 1971. Accepted August 25, 1971. This work was conducted under the financial support of the U.S. Atomic Energy Commission, Contract No. AT(04-3)-34, P.A. 71-15, and the U.S. Office of Naval Research Contract No. U S N N00014-69-A-0200-6011. (5) T. R. Folsom and D. R. Young, Nature, 206, 803 (1965). (6) R. Grismore, T. R. Folsom, V. F. Hodge, and D. R. Young, unpublished work, Scripps Institution of Oceanography, 1971.
Determination of Traces of Uranium by Radioisotope Energy Dispersive X-Ray (EDX) Analysis C. C. Bertrand and
T.A. Linn, Jr.
Metal Mining Diuision-Research Department, Kennecott Copper Corporation, Salt Lake City, Utah 841 I I
DIRECT DETERMINATION of traces of uranium in aqueous solutions by fluorimetric or spectrophotometric techniques is often precluded by interferences from diverse cations, especially iron (111) ( I , 2). Chemical separations, such as solvent extraction or ion exchange, are necessary to remove interferences and concentrate the uranium to meet sensitivity requirements (3-5). Our purpose required a more rapid (1) J. E. Currah and F. E. Beamish, ANAL.CHEM., 19, 609 (1947). (2) C. W. Sill and H. E. Peterson, ibid., p 646. (3) G. Alberti and A . Saini, Anal. Cliim. Acfa, 28, 536 (1963). (4) F. G. Sherif and A. M. Awad, ibid., 26, 235 (1962). ( 5 ) W. J. Maeck, G. L. Booman: M. C. Elliott, and J. E. Rein. ANAL.CHEM., 31, 1130 (1959).
and simple procedure for the determination of traces of uranium in a variety of aqueous samples. In addition, a versatile method was needed, which could be easily adapted for use at remote field laboratory sites. A rapid precipitation for the collection of uranium for radiochemical assay has been reported, which offers quantitative recovery of uranium (6). The separation utilizes barium sulfate as a collector for uranium (IV), and certain other 111- and IV-valent cations, in the presence of potassium (7, 8). The incorporation of radioisotope E D X analysis for (6) C. W. Sill and R. L. Williams, ANAL.CHEM., 41, 1624 (1969). (7) C. W. Sill and C. P. Willis, ibid., 36, 622 (1964). (8) Ibid., 38, 97 (1966).
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