counts on the sample cell. The average of these two 10-minute counts was then compared with the interspersed coniparison count. Table I1 gives the results of some typical determinations. ACKNOWLEDGMENT
Grateful acknowledgment is made to G. E. Gerhardt who designed and constructed the housing and associated circuity for the photomultiplier tube and furnished valuable assistance in overcoming many instrumental difficulties
which arose during the course of this work. LITERATURE CITED
(1) Audric, B. N., Long, J. V. P., Research
5,46 (1952). (2) Hayes, F. N., Nucleonics 12, S o . 3, 27 (1954). (3) Kallman, H., Furst, M., Sucleonics 8. KO. 3. 32 (1951). (4) Kafiman, H., 'Furst, AT., Phys. Rev. 79,857 (1950); 81, 853 (1951). (5) Kritchevsky, D., American Cyanamid Co., Pearl River, N. Y., personal communication. (6) McDonald, W. S., Turner, H. S., Chem. & Ind. 1952, 1001.
(7) Raben, XI. S., Bloembergen, K., Science 114,363 (1951). (8) Rosenthal, D. J., Anger, H. O., U. S. Atomic Energy Comm. UCRL-2320 (Aug. 21, 1953). (9) Weinberger, -4.J., Davidson, J. B., Ropp, G. A., -&SAL. CHEW28, 110 (1956). RECEIVED for review December 26, 1956. Accepted May 27, 1957. Presented in part, Meeting-in-Miniature of the Analytical Group, North Jersey Section, ACS, Xewark, K.J.,January 24,1955, and Section on Radiochemical Methods, XVth Congress of Pure and Applied Chemistry, Lisbon, Portugal, September 14,1056.
Modified Determination of Radium in Water F. B. BARKER
U. S. Geological Survey, Denver, Colo. L. L. THATCHER U. S. Geological Survey, Washington, D. C. The proposed method embodies a barium sulfate carrier precipitation, filtration through molecular filter membranes, and collection of activity after prescribed aging period. The method is sufficiently accurate and precise to indicate the potability of water and for use in general studies of radium in chemical hydrology. Amounts of radium as low as 0.1 ppc. can be detected by using 1-hour counting times. Radium-226 is used as the standard and the results indicate about 100 to 1 1 0 of the activity of the alpha-emitting radium isotopes as radium-223, radium-224, and radium226.
yo
C
interest in radioactivity in water has developed within the past sereral years. T o the public health official and the n-aterworks engineer, radioactivity in the water supply is important as a possible health hazard. To the industrial engineer, it is a variable n-hich may affect the quality of his industrial products. To the geologist and geochemist, it is a clue to subsurface conditions and processes. T o the hydrologist, radioactivity in water is a potential tool for the study of \T ater movement. Radium is a source of radioactivity in water. The isotope radium-226 is a member of the uranium series, radium228 and radium-224 are members of the thorium series, and radium-223 is a member of the actinouranium series. From the standpoint of health, radium-226 is the most important because of its very OXSIDERABLE
low permissible tolerance level in safe drinking water (IO), 40 ppc. per liter. However, from the geochemical and hydrological standpoint, the other isotopes are also of interest. Several methods suitable for determining radium in mater have been reported. The emanation method (2, 3, 8 ) has been used extensively and is capable of yielding very good results for the isotope radium-226; however, the equipment is expensive t o install and operate. Stehney (12) has determined both radium-226 and radium-224 in water by a modification of a method developed by Ames and coworkers ( I ) and revised by Russell, Lesko, and 8chubert ( I I ) , which involves doublecarrier precipitation followed by alpha counting. A simple barium sulfatecarrier precipitation method for determining radium in urine was reported by Harley and Foti ( 7 ) ) and a similar method vas described by Gubeli and Jucker ( 5 ) . The U.S. Geological Survey uses a modification of the method of Harley and Foti ( 7 ) for the routine determination of radium in natural waters. The method embodies a barium sulfatecarrier precipitation, filtration through a molecular filter membrane, and counting of activity after a prescribed aging period. Although this method is less accurate for some waters than more elaborate procedures, it requires less time of the technicians and less equipment. It is sufficiently accurate and precise to indicate the potability of water and for general studies of radium in chemical hydrology.
REAGENTS
Standard Radium Solution. ,4 Kational Bureau of Standards radium226 gamma-ray standard, containing 1.0 x 10-7 gram of radium, is broken under approximately a liter of distilled water, and the solution is transferred t o a 2-liter volumetric flask. The broken ampoule is leached with 50 ml. of concentrated hydrochloric acid and washed with distilled water; the leach and washings are added to the original solution. Dilution t o 2 liters provides a stock solution containing 5 X 10-l' gram per ml. of radium. A working standard is prepared by diluting 10 ml. of the stock solution plus 10 ml. of concentrated hydrochloric acid to 500 nil. The usual precautions required when handling radioactive alpha emitters niust be observed to prevent the contamination of personnel and equipment. Barium Carrier Solution. TWOand a half grams of reagent grade barium chloride dihydrate are dissolved in 1 liter of distilled water. Ammonium Sulfate Solution. Four hundred grams of reagent grade ammonium sulfate are dissolved in 1 liter of hot distilled water; t h e solution is cooled and filtered. Sulfuric Acid Wash Solution. Concentrated sulfuric acid is diluted 1 t o 200; 0.15 gram of Aerosol OT, 10070 (American Cyanamid Co.) is added for each liter of solution. PROCEDURE
Water samples containing less than 350 mg. of calcium are diluted t o 1 liter in 2-liter beakers and the acidity of each is adjusted t o approximately p H 3 with hydrochloric acid. A 1-liter disVOL. 29, NO. 11, NOVEMBER 1957
0
1573
tilled water blank, and two standards consisting of 1 ml. and 5 ml. of the standard radium solution in 1 liter of distilled water are prepared with each set of samples. The solutions are heated to almost boiling, and 3 ml. of the barium chloride carrier is added to each. While stirring vigorously, 15 ml. of the ammonium sulfate solution is added. Stirring is continued intermittently for several minutes or until the barium sulfate precipitate begins to form. The precipitates are allowed to digest at room temperature for a t least 4 hours. The barium sulfate precipitates are collected quantitatively on black 47-mm. hydrosol-assay molecular filter membranes (available from the h'lillipore Corp., Watertown, Mass.) and washed with the sulfuric acid wash solution. Use of the black filter permits the analyst t o determine when the precipitate is distributed evenly. When the filters are sufficiently dry, they are cemented to nutrient pads supplied with each filter to prevent curling. The precipitate is allowed to age 10 to 12 days; this permits the growth of short-lived daughter activities to about 90% of equilibrium, thus increasing the counting rate. The activity on the filter disks is measured with an alpha-scintillation counter, and the radium content of the sample is determined by comparison with the standards. Amounts of radium as low as 0.1 p p c . can be detected in this manner by using 1-hour counting times.
Table I.
Ion Ca++
1574
ANALYTICAL CHEMISTRY
Concn., P.P.M. 270 210 480 200 290 5 ppc, /liter
S a+
c1so4- -
HCOaRa++
Table II. Effect of pH and Amount of Carrier Added upon Activity of Precipitate" carrier Activity of Ppt., C.P.H. pH 3 pH 5 Added, Mg. pH 1 0 40 2.8 231 515.513 528 4.2 491' 5 6 469 7.0 464 464,453 500 11 473 14 498 478,431 512 17 411 20 397 22 397 2 .i
224
-I
363 396 $63,271 184 222 213 149 122 137 0 Obtained from solution containing 5 p p c . per liter of radium-222. 28 56 84
Table 111. Comparison of Radium Carried from Test Solution with That from Distilled Water
DISCUSSION
Harley and Foti ( 7 ) found that 2 mg. of barium is sufficient to carry radium quantitatively from 200 ml. of solution and that pH has no significant effect in the range from pH 1 to pH 5 . Under slightly different conditions, however, Jucker and Treadwell (9) reported the amount carried is strongly dependent upon pH. To determine the effect of pH in analyses of natural ground waters by the modified method, a series of experiments was made with a synthetic sample of water having the composition given in Table I. The only conditions varied in the procedure were pH and amount of carrier. The results are given in Table 11. Statistical analysis of the data indicates no significant effect attributable to pH in the range investigated. However, the amount of barium carrier is significant a t the 1% level. Figure 1 illustrates this relationship at pH 3. The amount of radium carried from the synthetic sample was compared with that carried from the standard solutions used in the routine analysis. The results, given in Table 111, indicate no significant difference; hence, the use of distilled water standards is permissible. The various radium isotopes present in the precipitate are not measured with equal efficiency. The isotope radium-
Analysis of Solution Used in Lieu of Natural Waters
Test
Activity Activity in Test in Std., Soh, ppc./Liter ppc./Liter
Ratio of Counts in
Test Soh. to Counts in Std.
A
1
1 1 1
0.98 1.08 1.02
C
5
5 5
1.00 0.92 0.99
Av. ratio
226 with its short-lived daughter products yields 8.0 alphas per minute per micromicrocurie after an aging period of 11 days. The isotopes radium-223 and radium-224 together with their daughter products yield 8.9 alphas per minute per micromicrocurie after the same aging period and are, therefore, measured with an efficiency of 110% relative to the radium-226 standard. The isotope radium-228 does not produce appreciable alpha activity during the aging time; therefore, it is not measured by this procedure. To relate the amount of radium in the precipitate a t time of counting to that in the sample a t the same time, any differences in the growth and decay of activity must be known. Growth or decay of radium-226 is negligible because of its long half life; therefore, it remains constant in both systems. The growth or decay of radium-224 is controlled in part by the amount of its parent thorium-228 present. Fleck (4) found that thorium-234 is carried almost quantitatively with barium sulfate precipitated from acid solution. If this is also true for thorium-228, the amount of radium-224 will be the same in both the precipitate and the water sample a t the time of counting. The amount of radium-223 is partially controlled both by the thorium-227 and actinium-227 present. The thorium isotope is probably carried almost quantitatively by the barium sulfate precipitate. Actinium may be carried quantitatively by barium sulfate (6),but the amount carried under the conditions of this method has not been determined. However, variations in the amount of actinium carried by the barium sulfate would not have a large effect upon the total alpha activity due to radium because of the low relative abundance of the actinium series. Thus, the alpha activity due to radium in the precipitate a t the time of counting is essentially the same as that due to ra-
6o *
0
>r
;zoo-
i
* 4
loot
Figure 1. Dependence of activity of precipitate upon amount of barium carrier
dium in the water sample a t the same time. Carrying of other radionuclides on the barium sulfate precipitate may cause positive errors. Factors that determine the relative amount of interference are: natural abundance, half life, growth of daughter activities, and the efficiency of carry. Apparently the most troublesome substances are the thorium isotopes; about 4 pgc. of these would be reported as 1 bpc. of radium. The degree of interference of other radionuclides in natural waters, and methods for minimizing it, are being studied. This method is not as accurate as the emanation or double carrier precipitation procedures for the determination of specific activity of radium-226. However, the accuracy of a single carrier precipitation is sufficient for many studies; also, when many determinations are required, it has the decided advantages of simplicity of procedure and economy. For example, in studying water supplies for conformance with
potability standards, the tendency for positive error attributable to the method is not a serious drawback. I n studies of water quality in relation to hydrology, a method is needed that n-ill give consistent and comparable results for a series of samples even though the measured property is not purely and entirely attributable to a single substance. For example, strontium interferes in the calcium determination, as do various anions in the bicarbonate determination. Consequently, the single carrier precipitation method has been adopted for routine determination of radium in natural waters by the C.S. Geologcal Survey. LITERATURE CITED
(1) Ames, D. P S ISedlet, J., Anderson, H. H., Kohman, T. P., “The
Transuranium Elements.” Natl. Nuclear Energy Ser., ’IV-l4B, G. T. Seaborg, J. J. Katz, W. M. Manning, eds., pp. 1700-16, McGraw-Hill, New York, 1949. (2) Curtiss, L. F. Davis F. J., J.
Research S a t l . Bur. Standards 31, 181 (1943). (3) Evans, R. D., Rev. Sci. Znstr. 6,
aa / i o 9 5 1 “ Y
\ A Y ” V , .
(4) Fleck, A , , J . Chem. SOC.103, 381 (1913). (5) Gubeli, o., Jucker, H.1 Helv. Chime Acta 38,485 (1955). (6) H ~ F. T,, ~“Actinide~ xle-
ments,” Natl. Nuclear Energy Ser., IV-148, G. T. Seabor and J. J. Katz, eds., p. 34, Mc8rawHill, New York, 1954. (7) Harley, J. H., Foti, S.,Nucleonics 10, No. 2 , 4 5 (1952). ( 8 ) Hursh, J. B . , J . Am. Water Works
Assoc. 46,43 (1954). ( 9 ) Jucker, J., Treadwell, W. D., Helv. Chim. Acta 37,.2002 (1954) ( l o ) Sational Committee on Radiation Protection, Natl. Bur. Standards Handbook, No. 52 (1953). (11) Russell, E. R., Lesko, R. C., Schubert, J., Nucleonics 7, No. 1, 60 (1950). (12) Stehney, A. F., Acta Radiol. 43, 43 (1955).
RECEIVEDfor review October 22, 1966. Accepted August 1, 1957. Division of
Water, Sewage, and Sanitation Chemistr.y, 130th Meeting, ACS, Atlantic City,N. J . , September 1956.
Determination of Uranium in Natural Waters L. L. THATCHER
U. S.
Geological Survey, Washington, D.
C.
F. B. BARKER
U. S. Geological Survey,
Denver, Colo.
b The fluorophotometric determination of uranium was studied to develop a procedure applicable to the routine analysis of waters. Three grams of the high carbonate flux are used in a dilution procedure with spiking. Because of the comparatively high reflectivity of this large disk and the low uranium concentration, a correction for nonquenched light is required. A formula is developed to compensate for the effect, an electrical fusion device is described, and the problem of fixing uranium in waters is discussed.
B
of widespread interest in uranium prospecting, disposal of reactor wastes, and determination of natural uranium background levels, the U. S. Geological Survey has undertaken a study of the distribution of uranium in natural waters. For studies of this type, a convenient, inexpensive, and reliable method of analysis is required. The well known fluorophotometric determination of uranium provides the closest available approach to these requirements. The method is sufficiently sensitive to permit direct deterECAUSE
mination with the solid residue from only 10 ml. of water, and the tolerance to interfering or quenching constituents is such that purification of the sample is seldom required. I n general, a combination of Price’s dilution and spiking techniques (6)to minimize and evaluate quenching is satisfactory for routine analysis. Although a fusion step utilized in the procedure requires careful control of temperature, the operations involved are not complex and can readily be mechanized to minimize the human element. Fields and Pyle ( I ) have discussed some of the advantages of the fluorophotometric method for water analysis. Because of convenience in handling, especially for routine analysis, the high carbonate flux introduced by Grimaldi has been used in the analytical program. This type of flux solidifies into a disk with a matte white surface which has a comparatively high reflectivity. A small percentage of incident light in the fluorophotometer strays through the secondary filter and is measured by the photomultiplier tube. Several fluorophotometers of widely divergent design, including two models which protect the
photomultiplier tube from stray light by a system of optical stops, have been tested, and no design has been found that completely eliminates the reflected light. Several combinations of secondary filter elements effected no improvement over the customary combination of a 9780 and 3484 type. It appears that a comparatively high reflected light value is an inherent characteristic of the high carbonate flux. It has, therefore, been necessary to consider the fluorophotometric readings in the uranium determination to consist of two light components, the reflected light and the fluorescent light, The latter component may be quenched, while the reflection component is considered not to be affected by quenching metals. Both of these light components enter into the blank value and a formula has been developed which corrects for them. Pure sodium fluoride, which solidifies with a comparatively rough surface interlaced with a network of cracks, gives a lower blank reading because of less reflected light. The sensitivity is also slightly superior. Comparative tests with blanks and 0.1-7 uranium standards gave readings of 20 (blank) VOL. 2 9 , NO. 1 1 , NOVEMBER 1957
1575
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