reaction but also a later peak for desorbtion of the product. This would permit evaluation of the heat of reaction and qualitative identification of the reaction products. LITERATURE CITED
(1) Barrsll, E. M. 11, Rogers, L. B., ANAL.CHEM.34, 1101 (1962). ( 2 ) Blumberg, A,, J. Phys. Chem. 63, 1129 11959). (3) Borchardt, H. J., Daniels, F., J. Am. Chem. SOC.79, 41 (1957).
(4) Breger, I. A., Whitehead, W. L., Fuel 30, 247 (1951). (5) Ke, B., J. Polymer Sci. 49, 15 (1960). (6) Kissinger, H. E., ANAL. CHEM.29, 1702 (1957). (7) La?ge, N. A., “Handbook of Chemistry 10th ed., p .495, 585, Handbook Publishers, Inc., Jandusky, Oho, 1961. (8) Makenzie, R. C., “The Differential Thermal Investigation of Clays,” Mineralogical Society, London, 1957. (9) . , Mehlin. J. P.. IND.ENG.CHEM..ANAL. ED. 10, y36 (1938). (10) Morita. H., ANAL. CHEM.28. 64
(11) Morita, H., Rice, H., Ibid., 27, 330 (1955). (12) Shrine:, F. L., Fuson, R. C., “The S stematic tfdentification of Or anic dmpounds, 3rd ed., p. 19, &ley, New York. 1949. (13) Stone, ‘R. L., ANAL. CHEM. 32, 1582 (1960). (14) Vaeaallo, D. A., Harden, J. C., Ibid., 34, 132 (1962). (15) Vold, M. J., Ibid., 21, 683 (1949). RECEIVEDfor review October 23, 1961. Accepted April 20, 1962. Work sup-
ported in part b the U. s. Atomic Energy Cornmiasion undrer Contract AT(30-1)-905.
Determination of Perchlorate by Isotopic DiIutio n with Potassium Perchl o rate-Ch Io rine-36 J. K. JOHANNESSON’ Wellingfon City Council Laborafory, Wellington, New Zealand
b Perchlorate may be determined with accuracy by the radiochemical method of isotopic dilution of potassium perchlorate. The preparation of labeled potassium perchlorate is- described. Perchlorate may be determined in the presence of salts of volatile acids by removal of cations by ion exchange and evaporation in the presence of a small amount of added potassium ion. This method has been applied to its determination in sea water. No perchlorate was found in natural sea water within the sensitivity of the method.
U
electrolysis of sea water in connection with sewage treatment research, i t became necessary to determine the oxyacids of chlorine formed as a result of high anode current densities. The determination of perchlorate ion in the presence of sea water is difficult, and, accordingly, the investigation described here was undertaken. Due to lack of characteristic reactions, the perchlorate ion has presented difficulties in analysis. Nabar and &machandran (4) have recently reviewed the literature on this analysis and find that the methods fall into one of three main categories: reduction to chloride by wet reactions with determination of the chloride so formed; reduction to chloride by dry ignition reactions, again with the determination of the chloride produced; and the formation of insoluble compounds with substances SING
Present address, Seddon Memorial Polytechnic, Wellesley St., Auckland, New Zealand.
such as methylene blue or copperpyridine complex, with colorimetric estimation of the loss of soluble reagent. The first two depend upon the determination of the chloride produced, hence any chloride originally present in excess means that the estimation depends on the difference between two large values, and further, precautions must be taken to ensure complete reduction. The colorimetric methods are affected by other ions such as sulfate or chlorate and, further, the complex between methylene blue and perchlorate is quite soluble, necessitating the preparation of standard solutions of much the same ionic strength and chemical constitution as the unknown solutions. The only sparingly soluble inorganic salts of perchlorate acid are those of potassium, ammonium, and rubidium. The solubility of potassium perchlorate is considerable, being about 1.5 mg. per 100 ml. a t 25’ C., (3); this is depressed by the presence of excess potassium or perchlorate ion, and by ethyl alcohol. I n the absence of other ions the precipitation of potassium perchlorate in the presence of a large excess of ethyl alcohol would serve for its gravimetric determination, but unfortunately salts such as potassium sulfate or chloride are also of low solubility in the presence of ethyl alcohol, and would be coprecipitated. The method presented in this paper uses an entirely different approach, the technique of isotopic dilution, a principle well established in the field of biochemical analysis (2). The basis of the method is that a known quantity of potassium perchlorate labeled with radioactive chlorine-36 of known activity, is added to the solution con-
taining the unknown quantity of perchlorate present as a potassium salt, the solution is then concentrated, cooled, and the precipitated potassium perchlorate is recrystallized and the radioactivity is measured and, if necessary, repeated a second time after another recrystallization. Conventional calculation for isotopic dilution analysis gives the amount of the original perchlorate. Only a portion of the potassium perchlorate need be obtained for find weighing and counting to determine the activity. The method gives excellent results in the presence of large excesses of chloride, sulfate, and nitrate. In all the work to be described, radiochemical technique and precautions against radiation ingestion hazards were observed ( 2 , 6 ) . The low levels of activity used are such that any well equipped chemical laboratory with good fume hoods may be used. EXPERIMENTAL PREPARATION OF LABELED POTASSIUM PERCHLORATE
The source of the radioactive chlorine-36 was the CIS-I as supplied by the Radiochemical Centre a t Amersham. This preparation was 1.87N HCl, with an activity of 116 /IC. per gram of chlorine and is stated to be better than 99% radiochemically pure. Five microcuries of the above preparation were added to 1 gram of potassium chloride in 25 ml. of water, two platinum electrodes each 2 x 2 cm. were inserted, and a direct current of 0.8 to 1.0 amp. passed for 8 hours. Five grams of potassium chlorate were then added and the electrolysis continued for another eight or more hours, when potassium perchlorate precipitated out a t the anode and hence fell to the bottom of the electrolysis vessel. The solution VOL. 34, NO. 9, AUGUST 1962
1 11 1
,
became hot during the above reactions and evaporation occurred, necessitating the addition of water from time to time. Following the completion of the electrolysis the solution was heated to dissolve precipitated potaasium perchlorate, water was added if necessary to effect complete solution, then allowed to cool, and the potassium perchlorate of high activity crystallized out. This was recrystalliaed twice. The original mother liquor and those from the recrystallizations of the high activity were combined, 5 grams of (unlabeled) potassium perchlorate were added, dissolved by heating, and crystalliEed out by cooling. After recrystallizing twice more, potamium perchlorate of a lower activity was obtained. The high activity material weighed 2 grams after the final recrystalhatiom and had an activity of approximately 1 IC. per gram which meant that 50 mg. counted under an end window Geiger-Muller tube gave approximately 7700 counts per minute (c.p.m.). The low activity material had an activity of about one tenth that of the above and 5 grams were obtained. Standard solutions of the above were prepared by dissolving an exactly known weight such as 1 gram in 100 ml. of water. Five milliliters of this solution thus contained 50 mg. of the labeled salt. MEASUREMENT OF RADIOACTIVITY
Chlorine-36 decays by emission of a beta particle of 0.714 m.e.v. energy and has such a long half life that no corrections for decay are necessary. All counts were made by use of a thin end window. (1.5 mg./cm.*) The standard curve of counts per minute us. weight was prepared by placing evenly distributed layers of the active potassium perchlorate in stainless steel planchets of 1 inch diameter, which were weighed empty and then weighed again after each addition of chemical; the number of counts per minute was measured and the results plotted as shown in Figure 1, for successive additions of the chemical. The natural activity of the potassium was negligibly small. The method of estimating the activity of the test sample was to measure the
Table I.
a
,
C.P.M..
12.1 21.5 35.0 54.6 73.0 81,l 96.6 121.2
2,077 3,400 5,470 8,410 10,200 11,600 13,600 15,700
number of counts per minute of a weighed sample when counted in the above manner, and to compare it with the counts per minute to be expected from the same weight of original labeled potassium perchlorate aa given by the standard curve. The validity of this is demonstrated by the figures given in Table I, where the ratios of counts from two lots of labeled potassium perchlorate of different activitieswere compared.
Radioactive counts are subject to a statistical error which must be allowed for in aasessing the accuracy of a radiochemical method of analysis. Since the calculation of the amount of perchlorate is made by the equation: =
M,
(;
= 1)
where c.p.m. of the standard KC104 c.p.m. of the isolated KC104 of the same weight as for x m = weight of KC104in test solution ml = weight of standard KC104 added
x
y
= =
Then the standard deviation of the 2 quantity - is given by Y
C.P.M. from Standard Curve
% ' Deviation ab
ANALYTICAL CHEMISTRY
I 2M)
400 670 1,075 1,600 2,030 2,230
2E
5.19 5.14 5.13 5.29 5.05 5.24 5.28 5.19 Mean = 5.17
where a and b are, respectively, the standard deviations of x and y. Since all counts were made to 104, then the above standard deviation becomes X Y 0.014 for the work described in this paper. PROCEDURE FOR ESTIMATION OF PERCHLORATE
ACCURACY
This KClO, used, to prepare the standard curve.
11 12
IM PAN
Figure 1. Standard curve for weight of potassium perchlorate against counts per minute
Comparison of Potassium Perchlorate of Two Different Activities
Weight KClO,. KClO,, Mg.
1
Do Wg. O r LABLLLLD KIO, M SAMPLE
from Mean
-0.3 -0.7 -0.9 +2.3 -2.5 +1.3 +2.1 +0.3
I t is necessary for the composition of the test solution to be such that potassium perchlorate be the least soluble combination possible. Further any perchlorate present should have sufficient potassium available in solution to give the potassium salt. These requirements may be met by passing the test solution through an ion exchange column either in the hydrogen or potassium form, or where there is an excess of chloride and/or nitrate passage through the resin in the hydrogen form, followed by addition of enough potassium chloride to give potassium salts of the less volatile acids, and then evaporating to dryness. This procedure is described in detail under the analysis of seawater. Sulfate may be eliminated by ddition of a slight excess of barium chloride, filtering, and treating the filtrate by ion exchange as described under seawater. To a suitable volume of solution containing 100 to 300 mg. of potassium perchlorate are added 5 ml. of standard labeled potassium perchlorate (= 50.0 mg.), and the mixture is evaporated to incipient crystallization, poured into a borosilicate glass centrifuge tube, and allowed to cool and crystallize. After briefly centrifuging, the supernatant is removed, a small quantity of water added and the potassium redissolved by warming, followed by recrystallization upon cooling. Thk procedure is repeated to give a three-time recrystallized product, which
is then transferred to a weighed stainless steel planchet, dried, reweighed, and counted under the Geiger-Muller tube; the process does not take much time once experience has been obtained.
to obtain pure potassium perchlorate. If there is doubt about the purity of the salt it should bc recrystallized to constant activity. Typical results are shown in Table 11.
EXAMPLE OF TYPICAL ESTIMATION
DISCUSSION
Weight of KClO, Time for lo4 counts Counts per minute Corrected for background (y) C.P.M. from standard curve for 77.1 mg. (2) Weight of standard KCIO, added ( M I ) :If = 48 0
2200 (m - 1)
Standard deviation u
7 7 . 1 mg. 13.95 minutes 717 703 2200 4 8 . 0 nig. = 102 mg.
2200 703 0.014 X 48 = 2.1
= __ X
Thus ilcI = 102 f 4.2 1ng. for the 95y0 confidence limits ESTIMATION OF PERCHLORATE IN SEA WATER
To 250 ml. of sea water containing perchlorate are added 50.0 mg. of standard labeled potassium perchlorate and the mixture is then passed through .a cation exchange resin in the hydrogen form. A column 20 cm. by 1.5 cm. containing Amberlite IR 120 was used for the work described here. I t is important to realize that once the standard labeled potassium perchlorate has been mixed with the test solution, it is not necessary to obtain quantitative recovery of solutions, e k . since it is the activity of the final recrystallized product which is measured. The effluent from the column is treated with 2 ml. of saturated potassium chloride and then evaporated to dryness, the residue being recrystallized three times
Perchlorate may be determine readily by the radiochemical method of isotopic dilution using labeled potassium perchlorate, which method may be applied directly in the presence of a ten- or twentyfold excess of sulfate, chloride, or nitrate as potassium salts, but chlorate may interfere. Chlorate is however, readily eliminated by evaporating to dryness with concentrated hydrochloric acid. In general, a known quantity of labeled potassium perchlorate should be added to the unknown solution before conversion to potassium salts or elimination of interfering ions, so that any perchlorate which may be lost will not affect the activity of the h a 1 isolate. I t has been claimed by Bass Becking, Haldane, and Izard (1) that sea water contains naturally occurring perchlorate, but the experiments described in this paper show that the quantities present, if any, are very much less than those stated by the above authors. LITERATURE CITED
( 1 ) Bass Becking, L. G . M.,Haldane, A. D., Ieard, D., .I.‘ature 182, 645 1958). ( 2 ) Comar, C. L., “Radioisotopes in
Biology and hgriculture,” McCrawHill, Kew York, 1955. ( 3 ) Mellor, J. W., “A Com rehensive Treatise on Inorganic and ‘fheoretical
Table II.
Weight KC104 Taken, Mg. 50
100 200 400 100 200
100 200
Recovery of Added Potassium Perchlorate
Weight KC104 ReOther covered, Substances Mg.
250 250
seawater No. 1 . 250 ml. fresh 253
250
from 100%
Recovery
52.0 101 199 396 1 g. KCl 101.5 1 g. KC1 206 1 g. KNOa 99 1 g. each KC1 202
KNOI KzSOi 250 ml. sea- 105 water 250 ml. sea- 254 water (old sample sea water) 250 ml. fresh 245
100
Deviation
+4 +l -1 -1 +1.5
+3
-1 +1
seawater No. 2.
Fresh seawater samples were taken 50 miles apart on the coast of Wellington, New Zealand, August 1960. Chemistry,” Vol. 11, p. 395, Longmans, Green, New York, 1937. (4) Nabar, G. M., Ramachandran, C. It., ANAL.CHEM.31, 263 (1959). ( 5 ) Sherwood, R. J., A short course in Radiological Protection. Atomic Energy Research Establishment, Publ. L101, Her Majesty’s Stationery Office, 1959.
RECEIVED for review August, 30, 1961. Accepted April 6, 1962.
Determination of Iron and Uranium in High Purity Lead Foil by Neutron Activation Analysis P. A. BENSON, W. D. HOLLAND, and R. H. SMITH‘ Tracerlab, Inc., a Division of Laboratory for Eledronics, Richmond, Calif.
b The sensitivity of neutron activation analysis for Fe and U was extended by employing more sensitive detection methods, more rigorous decontamination chemistry, and higher neutron fluxes. Uranium was determined by measuring the Nppm activity arising from the decay of U539. Iron was determined by measuring simultaneously the Fe& and FeSgactivation products. The lead foils contained 0.56 to 3.0 p.p.m. iron and 0.91 to 0.020 p.p.b. uranium. Minimum sensitivity was calculated to be 0.02 p.p.m. iron and 0.006 p.p.b. uranium in 100 mg. of the foil. No error arose from the interfering reaction of Coa(n,p)Fe69.
T
HE DETERMINATION of iron and uranium in various materials by activation analysis has received considerable attention. Smales (8) and Stewart and Bentley (9) have determined uranium by measuring the fission fragments or fission product activities arising from the activation of the naturally occurring uranium isotope, U*36. Mahlman and Leddicotte (6) have measured the Npzss produced from the activation of the isotope U2= and the subsequent decay of Uzasaccording to the following nuclear reaction
8-
8‘
U*”(n,y)U*ag+Npfa +Pula (1) ’
The thermal neutron cross section for this reaction is 2.97 barns. The yradiations from the decay of Np239 were measured with a ?-well counter. Atchison and Beamer (1) and Kant, Cali, and Thompson (6) measured the beta activity from FeS9, while Iredale (4) measured the T-rays from that nuclide using a scintillation spectrometer. Iron, however, yields two radioactive isotopes on irradiation, arising from the reactions Fe“( n,y)Fess -& Mn66 l.
(2)
Present address, General Atomic Di-
viaion, General Dynamics, San Diego,
Calif.
VOL 34, NO. 9, AUGUST 1962
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