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. S T P 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 enrichments pellets have different P5 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. T h e 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
783
'+OXY
NIL
W CI)
z
B
CI)
W [I: [I:
W
D
[I:
0
I
0 W [I:
L
NANOGRAMS INJECTED Figure 3.
Standard curves of ioxynil (A), MI1 (m), and IBA ( 0 )
ONTROL SOIL
I
4
I
I
8 1 MINUTES
2
1
Figure 1. Gas chromatograms of ioxynil, MII, and IBA added to soil and control soil
I
I
2.5 with 0.1N hydrochloric acid. The dilute acid solution was extracted once with 100-ml., and twice with 50-ml., portions of chloroform. The chloroform extracts were combined and transferred to a 500-ml. round-bottom flask and evaporated to dryness a t reduced pressure on a rotating evaporator at 30" C. The residues were esterified and analyzed according to the same procedure used for soil. A standard curve was prepared by adding 0, 1, 2, 3, and 4 ml. each of a lO-pg.-per-ml. standard acetone solution of ioxynil, M I I , and IBA to each of five 15-ml. graduated centrifuge tubes. The solvent was removed with the aid of a stream of air. Esterification and analysis were performed as described for the soil samples. RESULTS AND DISCUSSION
w
a
z
2
v)
W
CK
oWf
n [r
0
YCK
CONTROL WHEAT
C IGNITE INJECT
I
I
4 8 MINUTES
1
Figure 2. Gas chromatograms of ioxynil and IBA added to wheat and control wheat
784
ANALYTICAL CHEMISTRY
I n Figure 1 are gas chromatograms of soil equivalent to 20 mg. of soil to which 2.0 p.p.m. of ioxynil, M I I , and IBA were added before extraction. Also included in Figure 1 is a chromatogram of soil extract equivalent to 200 mg. of soil which was used as a control. It is apparent that chromatographic separation of the individual compounds is sufficient where no interfering peaks occur. Figure 2 shows a chromatogram of an extract of ground wheat equavalent to 1500 mg. of wheat to which 0.1 p.p.m. of ioxynil and ioxynil benzoic acid was added before extraction. Also shown is a chromatogram of ground wheat equivalent to 600 mg. of grain. Figure 3 shows typical standard curves for the three iodo compounds based on peak height. The sensitivities of the detector to ioxynil, M I I , and IBA given in terms of grams of iodine per second are 4.1 X 2.3 X 10-lo, and 3.9 X 10-10, respectively. This sensitivity is considerably less than that reported previously (3). The flow rate used in this work is 5.75 times as fast and
Table 1. Recovery of loxynil and Metabolites from Grain and Soil
Compound Ioxynil Ioxynil Ioxynil IBA IBA IBA MI1
Sample Wheat Oats
Soil Wheat Oats Soil Soil
Added, Recovery, p.p.m. 0.1 0.1 2.0 0.1
0.1
2.0 2.0
%
90.0 78.0 106.0 69.0 80.0 97.0 108.0
the applied microwave power is 30% less than that of McCormack et al. Detector response to n-nonane has been given as approximately an inverse logarithmic function of flow rate (3). These workers found that the response of ethyl iodide at 2062 A. increased with increasing microwave power, and at power settings above about 65%, it increased very sharply. The operating conditions chosen for this study-Le., flow rate, microwave power, and column temperature-were those which gave the most reproducible results with sufficient sensitivity. Table I lists the recovery levels for the three iodo compounds added before extraction to check soil, and the recovery levels for ioxynil and IBA added to ground wheat and oats before extraction. LITERATURE CITED
(1) Bache, C. A., Lisk, D. J., ANAL.
CHEM.37, 1477 (1965). ( 2 ) Gutenmann, W. H., Lisk, D. J., J . Assoc. O&. Agr. Chemists, in press. (3) McCormack, A. J., Tong, S. C. c., Cooke, W. D., ANAL. CHEM.37, 1470 (1965). (4) Powell, L. E., Plant Physiology 39, No. 5, 836 (1964). C. A. BACHE D. J. LISK Pesticide Residue Laboratory Cornel1 University Ithaca, N. Y.
