the points formed a curve rather than a straight line. A titration curve for 51.0 pg. of lead in the presence of 497 pg. of mercury(I1) is shown in Figure 2c. The end point for lead is obtained by using the intersection of the straight line and the curved line. Both cadmium and mercury(I1) form dithizonates, but not under the conditions of the procedure. -1. blank titration with mercury(I1) present in the solution also gave a line curving upwards. As soon as dithizone was added to this blank, there was visual evidence of the presence of excess dithizone, indicating that no mercury(11) dithizonate was formed. The chloroform layer was somewhat off-color as might be esperienced when there is mild osidation of some of the dithizone. KO discernible effect on either the titration curve or the recovery of lead was noticed with copper(II), silver, cobalt ( I I ) , zinc, nickel(II), manganese(II), calcium, iron(I1) , iron(II1) , aluminum, phosphate, sulfate, acetate, carbonate, or chloride when these were present a t a weight approsimately ten times that of lead. LITERATURE CITED
( 1 ) Bambach. K.. Burkev. R. E.. IND.
ENG.CHEM.,A?;AL. ED.-14, 904(1942). (2) Clifford, P. A., J . h s o c . Oflic. Agr. Chemists 26, 26 (1943). (3) Clifford, P. A,, Wichmann, H. J., Zbid., 19, 130 (1936). ~
(01 Figure 2.
(bl ML. TITRANT (0.0001 15M D I T H I Z O N E )
(cl
Titration of lead in presence of other metals (0)
51.0 pg. Pb; 501 fig. Sn(ll) pg. TI 51.0 fig. Pb; 497 pg. Hg(ll)
(bl 51.0 pg. Pb; 501 (c)
(4) Fischer, H., Leopoldi, G., 2. Anal. Chem. 119, 182 (1940). (5) Griffing, M. E., Rozek, A., Snyder, L. J., Henderson. S. R.. ANAL.CHEM. 29, 190 (1957). (6) Henderson, S. R., Snyder, L. J., Zbid., 31, 2113 (1959). ( 7 ) LeGoff, P., Tremillion, B., Bull. SOC. C h i m . France 1964, 350. (8) Sandell, E. B., “Colorimetric,, Determination of Traces of Metals. 3rd ed., p. 566, Interscience, New ’York, 1959. (9) Zbid., p. 142. (10) Ibid., p. 571. ( 1 1 ) Snyder, L. J., ANAL. CHEM. 19, 684 (1947). (12) Wilhite, R. N., Underwood, A. L., Zbid., 27, 1334 (1955).
(13) Willoughby, C. E., Wilkins, E. S., Jr., Kraemer, E. O., IND.ENG.CHEM., ANAL.ED. 7, 285 (1935).
R. A. J O N E S ~ ANTONSZCTKA Department of Chemistry University Of Detroit Detroit, 48221
Present address, Ethyl Corp. Research Laboratories, Ferndale, Mich. 48220
Division of Analytical Chemistry, 150th hleeting, ACS, Atlantic City, N. J., September 1965.
Determination of Fission Product Xenon Distribution in Uranium Ceramics by Isotope Dilution and Mass Spectrometry SIR: We have developed a method of determining the distribution of stable fission product xenon in highly irradiated UOz or UC fuel elements that is accurate to =+=3%. The existing method (4) was accurate to f 10 to 25% and required samples that were too large to allow detection of sharp irregularities in the xenon concentration gradient. The increased accuracy and sensitivity result from an improved sampling technique and an improved method of determining the xenon content of the samples. Previously samples had been taken by picking rough pieces of broken ceramic from appropriate locations in the fuel, but now they are ultrasonically drilled from precisely selected sites as -1- x 5-mm. cores. Although the ceramic is often shattered during nuclear reactor operation, the pieces are held in place by a metal sheath that forms an integral part of the fuel element. Our method involves bonding the fractured but restrained ceramic with epoxy resin followed by ultrasonic drilling of a series of
~ 4 0 - m g .samples. The exact location of each site is recorded on Polaroid film. I n the earlier method the quantity of fission product xenon was determined by pressure measurement of the separated and purified gas, but now it is found by isotope dilution with natural xenon followed by mass spectrometry. EXPERIMENTAL
Sampling. Hot-cell handling equipment was required for sampling t h e irradiated fuel including remote manipulators, a machinist’s table and vise, viewing equipment, photographic equipment, a listening device, a power hacksaw, a grinder, and a Mullard 60-watt ultrasonic drill. The drill consisted of a generator, drill head, and special drill-tip, all mounted on a bench stand. The generator was a n oscillator-amplifier system with frequency adjustable between 16 and 24 kc./second. A tuning control on the generator was used t o adjust the frequency to the resonant frequency of the drill head and tip. The drill head consisted of a transducer and a 9 : l
velocity transformer on which the drill tip was mounted. The drill tips used were as shown in Figure 1. Each tip, machined from cold-rolled steel, could be used for only one or two cores before it became too worn for further use. The drilling abrasives were 300-mesh silicon carbide in water for uranium dioxide and 300mesh boron carbide in oil for uranium carbide. A 1-inch section of fuel element was prepared for drilling by vacuum impregnation with epoxy resin according to the method of Rubin (Y),as modified by Ridal and Bain (6). The bonded section was then polished and drilled. Adequate drilling pressure was maintained by a counterbalance. Maximum drilling speed was obtained by listening to the sound of the drill by means of a microphone at the drilling site, and adjusting the frequency to produce maximum hissing. The drilling was watched through a periscope. Dense uranium dioxide could be penetrated at the rate of 0.25 cm. per hour. After drilling, the pellet face was washed free of slurry and the core was VOL 30, NO. 6, MAY 1966
781
4(
I
1
t
Figure 1.
\
I
10.65 o/cc. 1.06; wt
I -I
u*35
x'
Drill tip
dropped into a small polyethylene container by restarting the drill. The exact location of each core was calculated from Polaroid photographs of the pellet face taken through the periscope or stereomicroscope. Occasionally, due to brittleness of uranium dioxide and radiation damage to the epoxy impregnant , pellet surfaces crumbled after a few drillings, so the core positions were photographed after each second drilling. Isotope Dilution, Dissolution, and Purification. The fission product xenon content of the sample core was prepared for stable isotope dilution analysis in a conventional vacuum line evacuated by a mercury diffusion pump. Cooled charcoal traps were provided for selective adsorption and condensation of the xenon and contaminating gases, and two stainlesssteel calcium vapor induction furnaces were used for primary and final purification. il gas volume measuring section incorporating an accurate n!tcLeod gauge and appropriate calibrated gas proportioning chambers was also provided for the preparation of exact volumes of natural xenon. The sample core was placed in a dissolving flask, which was then attached to the apparatus by a standard taper joint, and the entire apparatus was evacuated to a t least torr. The dissolver was cooled with liquid nitrogen and 5 ml. of concentrated nitric acid was added slowly so that the acid was frozen before it could react with the sample. Evacuation was continued until the pressure was again 10-5 torr. An accurately known volume of pure natural xenon, which normally was twice the estimated volume of fission product xenon in the sample, but never less than 1 X ml. STP, was valved into the liquid nitrogen cooled dissolver. The volume of natural xenon added was calculated from the initial and final equilibrium pressure readings of the calibrated volume from which it was frozen. The final reading was always about 5 X 10-4 torr. The dissolver was then heated to 100' C. until the sample was completely dissolved. The time required varied between 20 minutes and 5 hours, depending upon the density of the sample. 782
\
ANALYTICAL CHEMISTRY
X
0
When the dissolution was complete, the dissolver was cooled with dry ice in trichloroethylene. The noncondensable gases were exposed to hot calcium vapor a t 700" C. which removed most of the oxides of nitrogen and water vapor. The gases still remainingmostly xenon, krypton, and argonwere adsorbed on activated charcoal cooled in liquid nitrogen in a part of the vacuum line which was then isolated from the dissolver. The gases were treated with another hot calcium furnace and readsorbed on activated charcoal a t liquid nitrogen temperature. The liquid nitrogen refrigerant was replaced with dry ice in trichloroethylene and the argon and krypton were allowed t o migrate t o a colder trap. The xenon was then pure enough (usually better than 95%) for mass spectrometric analysis. M a s s Spectrometric Analysis. The mass spectrometer ( 2 ) used to measure xenon abundances had a 90" magnetic sector with a radius of curvature of 15 cm. Ionization was by electron bombardment and ion collection was in the standard Faraday cup. The volume of the separated xenon was never smaller than 1 X 10-2 ml. STP which was sufficient to give a steady signal of 5 X amp. for the more abundant xenon isotopes for well over an hour. Between six and 11 scans of the xenon mass numbers from 129 to 136 were recorded and measured for each sample. The mass numbers of the natural xenon isotopes are 124, 126, 128, 129, 130, 131, 132, 134, and 136. Fission product xenon that is more than a few
Y
X
0
weeks old consists of mass numbers 131, 132, 134, and 136 only. KO detectable quantity of fission products Xe12Qis present because its precursor, 1129, has a half life of 1.6 X 107 years. The amount of fission product xenon was calculated from the equation
x
= y
(i -
I).
atom fraction, natural Xe134 atom fraction, fission product Xe134 where
x
= ml. STP of fission product xenon, y = ml. STP of natural xenon, S = ratio of natural XeIz9 to natural Xe134 M = ratio of Xe129 to Xe134 in the mixture of natural and fission product xenon
The atom fraction of Xe134was calculated from the abundances of Xe131, Xel32, Xelo4, and Xe136 relative to Xel*9 in the mixture minus the respective natural xenon relative abundances. These abundances were calculated relative to the abundance of XelZ9 in the mixture because it is the most abundant natural xenon isotope that is not contaminated with a fission product. The value of the atom fraction of fission product Xe134 is dependent upon the irradiation history of the sample. Uranium Analysis. The uranium content of the dissolved sample was determined by a spectrophotometric procedure (1) using potassium thiocyanate.
RESULTS A N D DISCUSSION
The analysis of five UOz drill cores, 1.3 mm. in diameter and 4.8 mm. long, which were irradiated under as similar conditions as possible, gave a n average result of 0.206 i 0.005 ml. STP xenon k)ergram of uranium. The relative standard deviation was =k2.6%. This result agreed with the concentrat'ion of fission product xenon calculated from P 3 5 depletion measurements, which was 0.205 =k 0.012 ml. S T P per gram of uranium. The amount of fission product xenon determined was about 8 X 10-3 nil. STP and the uranium content was approximately 40 mg. The smallest amount. of fission product xenon that causes a significant (2%) change in the 1291134 ratio of 1 X lo-* nil. STP of natural xenon is 8 X 10-6 ml. Volumes smaller than 1 X ml. cannot be handled routinely in the mass spectrometer, so that 8 X ml. of fission product xenon is the lower limit of the method as described here. Examples of the application of the method in determining the detailed ra-
dial distribution of fission product xenon in UOz fuel elements are given in Figure 2, where the concentrations of fission product xenon are plotted against calculated operating temperatures within each of three U 0 2 fuel pellets. The pellets have different P5 enrichments and irradiation times, and one is less dense than the others. These elements are only -1 cm. from surface to center, so that 100 C". on the graph are equivalent to a radial distance of -0.07 em. If greater sensitivity is required, the use of an electron multiplier ion detector, dilution with isotopically pure XelZ8(S), or a mass spectrometer operated in the static mode ( 5 ), should be considered, so that even smaller cores could be analyzed. However, our procedure provides a simple, accurate method for routine use in multiple-sample fission product distribution studies. ACKNOWLEDGMENT
The technical assistance of William Cherrin, R. W. Mills, J. A. Schruder,
and R. C. Styles is gratefully acknowledged. LITERATURE CITED
(1) Currah, J. E., Beamish, F. E., ANAL. CHEY.19, 609 (1947). (2) Graham, R. L., Harkness, A. L.,
Thode, H. G., J . Sci. Znstr. 24, 119 11947). (3,11Hayden, R. J., Inghram, M. G., Mass Spectroscopy in Physics Research," p. 189, Sational Bureau of Standards Czrcular 5 2 2 (1953). (4) Morgan, W. W., Hart, R. G. Miller, F. C., Olmstead. W. J.. Talanta 6. 275
(1960).
( 5 ) Reynolds, J. H., Rev. Sci. Znstr. 27, 924 ~ 1 9 , X ~ . ( 6 ) nidal,. k., Bain, A. S., Can. Sucl. Tech. 1, N o . 2, 39 (1961). ( 7 ) Rubin, B., Westinghouse Atomic Power
Div.Rept. WAPD-TM-264(1961).
I. H. CROCKER R. G. HART' Chalk River Nuclear Laboratories Atomic Energy of Canada Limited Chalk River, Ontario, Canada
Present address, Whiteshell Nuclear Research Establishment, Atomic Energy of Canada Limited, Pinawa, Manitoba, Canada.
Determination of Iodinated Herbicide Residues and Metabolites by Gas Chromatography Using the Emission Spectrometric Detector SIR: RIcCormack, Tong, and Cooke ( 3 ) developed a sensitive, selective,
emission spectrometric detector for use with gas chromatography. Compounds emerging from the column passed into an intense microwave-powered argon discharge in which fragmentation and excitation occurred. Emission of characteriqtic lines and bands were spectrometrically monitored and recorded. The method was applied to the analysis of residues of several organophosphorus insecticides in a variety of samples by measurement of the 2535.65 atomic phosphorus emission (1). LlcCormack et al. (3) observed a sensitive atomic iodine line a t 2062 A. with a sensitivity of gram of iodine per second for methyl iodide. I n the present work, the same equipment was used for analysis of the herbicide ioxynil (3,5-diiodo-4hydroxybenzonitrile) and two possible metabolites, 3-iodo-4-hydroxybenzonitrile (hfII) and 3,5-diiodo-4-hydroxybenzoic acid (IB-4) in wheat, oats, and soil. EXPERIMENTAL
Apparatus. The equipment used was identical t o t h a t described earlier (1) except that measurement of the 2062 A. atomic iodine line was made. The column was borosilicate glass, U-shaped, 4-mm. i.d. and 2 feet long. The packing was 5y0 S.E. 30 on 8CL100 mesh acid-washed Chromosorb W. Tempera-
tures of the column and flash heater were 160" and 230" C., respectively, and argon (120 cc. per minute) was the carrier gas. A microwave power setting of 55y0 was used. Procedure. T h e following procedure was used for extraction and analysis of ioxynil, IBA, a n d RlII in soil. Twenty-five grams of soil together with 75 ml. of acetone and 1 ml. of orthophosphoric acid were blended in a semimicro blender jar for 2 minutes. The soil slurry was then filtered through S and S 595 filter paper into a 200-ml. round-bottom flask fitted with a 24/40 standard taper joint. The flask was placed on a rotating evaporator and taken to near dryness a t 30" C. undw reduced pressure. The sample was then diluted with 50 ml. of distilled water and transferred to a 125-ml. separatory funnel equipped with a Teflon stopcock. The flask was rinsed once with 25 ml. of redistilled chloroform and this solution was added to the separatory funnel. The funnel was gently shaken and the lower chloroform layer was removed. The dilute acid solution was extracted twice more with 25-ml. portions of chloroform. The chloroform extracts were combined in a 100-ml. volumetric flask and the flask was filled to the mark with additional solvent. An appropriate aliquot, usually up to 50 ml., was taken for analysis and evaporated to dryness under vacuum on a rotating evaporator. The residue was quantitatively transferred to a 15-ml. graduated centrifuge tube with a few mil-
liliters of ether and again taken to dryness with a stream of air. The possible residues of ioxynil, 1111, and I U d were esterified with diazomethane by the micromethod of Powell (4, except that tube number 3 contained only 2 ml. of 10% anhydrous methanol in methylene chloride. The reaction with diazomethane converted ioxynil and hf I1 to the corresponding methyl ethers ( 2 ) and IBA to 3,5-diiodo4-methoxymethylbenzoate. Following esterification, the solvent was evaporated to near dryness and then diluted to 1 ml. with diethyl ether. Appropriate aliquots up to 20 pl. were then injected into the gas chromatograph. The procedure below was used for extraction and analysis of ioxynil and I B d in oats and wheat. Fifty grams of ground grain together with 100 ml. of 0.LV HC1 and 200 ml. of benzene were blended for 2 minutes. One hundred milliliters of saturated sodium sulfate were added and the entire mixture was blended for an additional 2 minutes. The resulting slurry was transferred to two 250-ml. centrifuge bottles and centrifuged for 10 minutes a t 2000 r.p.m. The benzene layer wa3 aspirated off and transferred to a 1000-ml. separatory funnel. The aqueous slurry was returned to the blender and the extraction repeated with an additional 200 ml. of benzene. The combined benzene extracts were extracted once with 100 ml. of 2% sodium bicarbonate and twice with 50-ml. portions of the bicarbonate solution. The bicarbonate extracts were combined and adjusted t o a pH of about VOL. 30, NO. 6, MAY 1966
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