CONCLUSION
The results obtained from the investigations described here indicate that the ATd method gives an accurate saturates determination on both olefinic and nonolefinic heavy petroleum fractions, including bright stocks. Unlike most methods reported for the determination of saturates in heavy petroleum fractions, the A T h method is also applicable to mixtures of saturates containing olefins. For example, the AT.4 method is useful for the analysis of baturates in the heavy products from wax cracking. I n addition, the ATA technique is effective for the purification of high molecular
weight saturated hydrocarbons and for the purification of spectrometric grade saturated solvents. ACKNOWLEDGMENT
The authors express their appreciation to Frances J. Galbraith and to Harry Morgan for supplying the mass spectrometer and infrared analyses, respectively, and to Giovanni A. Bonetti for his discussions concerning the use of the nitration mixture for this application. LITERATURE CITED
(1) American Society for Testing Materials, Method D-1319-61T, Phila-
delphia, Pa.
( 2 ) Bonetti, G. A., Paper presented be-
fore Division of Petroleum Chemistry, ACS, Chicago Meeting, September 3-8, 1961. (3) Kahler, J. E., Rowlands, D. C., Brewer, J., Powell, W. H., Ellis, W. C., J. Chem. Eng. Data 5 ( l ) ,94 (1960). (4) Knight, H. S., Groennings, S., A N ~ L . CHEM.28, 1949 (1956). (5) Lipkin, 1LI. R., Hoffecker, W. A., Martin, C. C., Ledley, R. E., Zbzd., 20, 130 (1948). (6) Mills. I. W., Proc. A m . Petrol. Znst., ‘ k’ection’ZII 29M. 50 11949). (7) Schwartz, R. b., Brasseaux, D. J., ANAL.CHEM.30, 1999 (1958). (8) Snyder, L. R., Zbid., 34, 771 (1962). (9) Watson, A. T., Zbw!., 24, 507 (1952). RECEIVED for review November 24, 1964. Accepted March 15, 1965.
Direct Determination of Oxygen in Organophosphorus Compounds by Graphite-Pipe Reduction BEN D. HOLT Chemistry Division, Argonne National laboratory, Argonne, 111.
A novel approach to the carbonreduction method provides for the direct determination of oxygen in organophosphorus compounds with sufficient accuracy to aid in differentiating mixtures of high-molecular-weight organic phosphates, phosphonates, and phosphinates. Phosphorus-bearing decomposition products do not interact with the quartz container. Limitations on the upper operating temperature and on the texture and composition of the reducing carbon, that have characterized the conventional carbonreduction method, are greatly relaxed. The average recovery of oxygen obtained on a group of organophosphorus compounds containing 4 to 30% oxygen was with a relative standard deviation of about &0.5%.
loo.o%,
I
working with highmolecular-weight, organic phosphates, phosphonates, and phosphinates find a need for distinguishing among these compounds by some method other than carbon-hydrogenphosphorus determination and a potentiometric titration. For example, since the difference of one oxygen atom in the chemical compositions of trioctyl phosphate and dioctyl octyl phosphonate accounts for only about 47, of the total molecular weight. it would be informati\ e to measure the total oxygen content of an unknoun substance which might be one or the other of these compounds, or a mixture of the two. If the ineasurement is to be useful in this application, NVESTIGATORS
the relative error should be less than +I%. A fluorination method and a carbonreduction method were tested in this laboratory for the direct determination of oxygen in organophosphorus compounds. By the fluorination method, as reported by Sheft and Katz ( 5 ) ,a sample of the organic material was placed in a nickel vessel containing BrF2SbF6. The vessel was evacuated, disconnected from the vacuum line, and heated on a mechanical shaker for 4 hours at 500’ C. to fluorinate the sample and convert its oxygen to 02. The gas was Toeplerpumped through three cold traps to a calibrated volume for measurement and for subsequent mass spectrometric analysis. S o t only did this tedious procedure involve a rather corrosive reagent a t an elevated temperature, but the production of large quantities of HF caused the development of high pressures within the nickel vessel during the prolonged heating period. Considerable difficulties were experienced with valve leakage and moisture contamination. Cnder optimum operating conditions no more than one sample could be analyzed in one day. S i n e samples of tributyl phosphate were analyzed for oxygen by this method, the average recovery being 91%, with a relative standard deviation of +9%. One possible explanation for the low, erratic reiults was that some of the sample oxygen remained in the form of a volatile oxyfluoride even a t the conclusion of the 4-hour heating period. In 1952 Vnterzaucher (7‘) pointed out that the carbon-reduction method,
which has since been widely used in the direct determination of oxygen in many other organic compounds, was not applicable to the analysis of compounds containing phosphorus or fluorine. When these elements were present, the apparatus suffered damage and the results were unsatisfactory. *illthough during the past decade some improvements have been made in the carbonreduction technique, such as lowering the required temperature of the carbon bed by the addition of a platinum catalyst ( 4 ) and others (1-3)> there remains the need for a procedure by which oxygen can be successfully determined in organophosphorus compounds. A new technique was developed that yielded complete recoveries of oxygen in a series of organophosphorus compounds with a relative error of about +0.5%. It involved the use of a carbon-reduction bed contained in an induction-heated graphite pipe. The SiO, of the quartz reaction chamber as not directly exposed either to the corrosive vapors of the sample or to the hot reducing carbon of the graphite. h c cordingly, considerably more latitude was effected in the operating temperatures of the carbon bed.
APPARATUS
Figure 1 shows a diagram of the reaction chamber in which the sample was pyrolyzed and in which the resulting vapors were carried through hot carbon for the conversion of sample oxygen to carbon monoxide. VOL. 37, NO. 6, MAY 1965
e
751
GRAPHITE CUP 3/16" I D I 5116"O 0 GRAPHITE CHIPS >20 MESH GRAPHITE PIPE 3/8"1.D.1 Sl8"O.O. INDUCTION HEATING COIL BORON NITRIDE PIPE 5116"l 0 r l / 2 " 0 D
COOLING
1k r o
-$I4120
m A L v i t * i TRAIN
Figure 1 . Workable model of reaction chamber
The graphite sample cup, made from a spectrographic electrode cup (Type 204, United Carbon Products Co., Bay City, Mich.), was supported on a bed of graphite chips, packed in a 4-inch length of graphite pipe, 3/8-in~h i.d. by 5/8-inch 0.d. The graphite stock used for both the pipe and the chips was AUC-grade, extruded rod, supplied by National Carbon Co., Division of Union Carbide, New York, N. Y. The graphite pipe was connected by a threaded joint to a boron nitride section, 5/le-inch i.d. by l/z-inch o.d., fabricated from a 6-inch length of hot-pressed boron nitride rod supplied by Carborundum Co., Latrobe, Pa. The lower end of the boron nitride pipe was tapered to fit into the T 14/35 water-cooled borosilicate glass joint shown in the diagram. The graphite-BN pipe was enveloped by a vertical, quartz, closed-end tube that was supported in the 24/25 section of the water-cooled base. This envelope- provided a path for purified helium to flow up through the annular space between the graphite and quartz, down around the sample cup, through the hot zone of the bed of graphite chips, down through the BN pipe, and finally out to other components of the analytical train. A 31/2-inch extension of the 22-mm. quartz tubing beyond the end of the envelope served as both a handle, by which the envelope could be lifted out and replaced for adding samples, and a reservoir for liquid nitrogen. The reaction tube wm enclosed by a quartz chimney, supported in the 34/28 standard-taper joint of the water-cooled base. Dry nitrogen flowed up through the chimney and out to the atmosphere. Induction heating of the graphite pipe was effected by a five-turn work coil (13/4-in~hi.d., 1 1 / 4 inches high, fabricated from flattened 3/,-inch copper tubing) that was energized with lowvoltage, high-current power, supplied through a stepdown transformer from a 20-kw. generator (Model 1070, Induction Heating Corp., New York). This generator was capable of supplying considerably more power than was required for this application.
752
ANALYTICAL CHEMISTRY
A diagram of the complete analytical train is shown in Figure 2. To the left of the reaction chamber, the supply of purified helium is represented by a silicon-oil manostat, a purification tube for the removal of COz and moisture, and a tube containing uranium turnings at 600" C. for the more complete removal of oxygen-containing impurities. Hinge connectors, shown on either side of the reaction chamber, facilitated vertical movement of the chamber within the fixed work coil. Each constructed of two pairs of 18/7 ball joints and one pair of 10/18 standard-taper joints, these 5l/*-inch hinges permitted the chamber (mounted on an appropriate aluminum-rod support) to be raised and lowered by a lab jack through a range of about 4 inches. To the right of the reaction chamber in Figure 2 are shown the components of the analytical train that served to isolate and measure the sample oxygen which emerged from the graphite bed as carbon monoxide in the helium stream. The gas mixture was conducted through a cold trap (- 196' C.), containing glass wool, for the removal of condensable gases and particulate matter, such as red phosphorus particles, carbon dust, etc. Sext, passing through the Schutze oxidizing reagent (Iz06,impregnated in silica gel) (6), the CO was quantitatively converted to COz, in which form it was collected and measured in the capillary cold trap of the open-well, capillary manometer. The vacuum line consisted of a manifold, a tilting McLeod gauge, a liquidnitrogen cold trap (with appropriate isolating stopcocks) and a mechanical pump, such as a Cenco Hyvac 7 (Central Scientific Co., Chicago). A positive pressure, equivalent to a &inch head of silicon oil, was maintained through the train up to the inlet, grooved stopcock of the capillary manometer. This stopcock throttled the rate of carrier gas flow throughout the train and into the vacuum system. PROCEDURE
Maintain the between-run, standingby condition of the analytical train at the time of starting an analysis as follows. Close the inlet, grooved stopcock to the capillary manometer and orient all other stopcocks so that manostatic pressure is maintained throughout the train, with helium gently bubbling out of the manostat. Dry nitrogen is flowing through the chimney a t 5 liters per minute and jets of compressed air are directed on the outer surface of the chimney near the work coil to dissipate heat accumulated from the previous run. The lower edge of the work coil is inch above the upper edge of the boron nitride section of pipe. Turn the stopcock a t the lower end of the reaction chamber to direct the helium out through the small (siliconoil) bubbler a t a moderate rate. Lift out the 22-mm. quartz envelope with one hand; remove the sample cup from the graphite bed with clean, 10-
MANOSTAT
Figure 2.
b
MANOMETER
Analytical train
inch tweezers in the other hand; and immediately return the envelope to its position in the 24/25 standard-taper joint. Place the cup in a small, glass, covered holder (made from a 12/18 standard-taper joint) and leave it to sit in the microbalance room for 10 minutes. Obtain the combined weight of the capsule and the covered holder before and after dispensing a sample containing about 2 mg. of oxygen (by micropipet, if liquid). Lift the envelope and replace the cup in the graphite pipe. Immediately reseat the envelope securely in the 24/25 joint and allow the helium to flush through the reaction chamber, and out the bubbler, for one minute. Fill the upper section of the envelope with liquid nitrogen and allow it to boil away during the succeeding steps of the procedure. Submerge the capillary-manometer U-tube in liquid nitrogen. Turn the stopcock at the lower end of the reaction chamber t o direct the helium stream toward the analytical train. By slightly opening the grooved stopcock on the inlet side of the manometer, establish a flow rate of 40 cc. per minute through the train. (This rate can be conveniently set by a previously calibrated position of the mercury column in the manometer.) Set the power control of the induction heating generator to a position which, by previous experiment, would be expected eventually t o raise the temperature of the graphite pipe t o about 1800' C. Turn on the power. After 15 seconds of such accelerated warm-up, reduce the power control to a position that will maintain the outer surface temperature a t about 1400' C. After about minute, increase the gas flow to 150 cc. per minute (as indicated by a predetermined mark on the manometer scale), and after 3 minutes, begin to lower the reaction chamber assembly so that the 1400' zone of the graphite bed may be shifted upward toward the sample cup. Lower the assembly continuously (or a t 1-minute intervals) at a rate such that the elevation drops by 1 inch during the first 5 minutes of heating and 2 inches during the first 8 minutes. Continue heating in this position for 2 minutes and then return the reaction chamber to its original position. Shut off the power
and continue the carrier gas flow for 4 additional minutes. Close the inlet stopcock on the manometer. When the mercury column has returned to its zero position, rotate the exit stopcock through 180" so that the volume of the hollow plug (from which the oblique cross tube has been removed) is included in the calibrated volume of the manometer. Remove the liquid nitrogen from the U-tube and read the CO, pressure a t room temperature. From a calibration chart of the manometer read the equivalent amount of oxygen and calculate the oxygen content of the sample. To establish the procedural blank, follow the entire procedure with an empty sample cup. This includes removal of the cup to the microbalance room.
Table 1.
Oxygen Results on Organophosphorus Compounds by the Method in Its Present Form
Recovery, yo Compound 99.8 Diphenyl phosphinic arid 100.1 ( 14.7Yc 0) 99.3 101 0 99.8 Av. 100 0 i 0 6, Y.D. Ilioctyl phosphinic acid (1l.0YG0) Tributyl phosphate 99 6 (24.0% 0 ) 99 8 100 7 99 8 2-Ethylhexyl chloromethyl phosphonate 99 7 Av. 99 9 f 0 4, S.D. (19.8% 0) Compound Dibutyl phosphate (30.5% 0 )
f 29/26
(1
GLASS
)-BOROSILICATE -CI,SED I
QUARTZ
:(.
99.7 100.3 100 2 Av. 100 1 1ou 7 101 0 99 5
Av. 100 4
GRAPHITE PIPE
3 / 8 ' I O x5/8"0D.
no.
1 2
GRAPHITE C U P
I
GRAPHITE CHIPS
f WATER-CWLEO REACTION C H A M B E R
PURlFlE HELIUM
1
Figure 3. chamber
3 4 5 6 7
8
-ATING COIL
-ANALYTICAL TRAIN
First model of
reaction
These results pointed to some sort of loss or retention (or both) of the sample oxygen. I t was presumed that sample loss might have occurred by too rapid decomposition of the sample, and/or that retention of pyrolysis vapors of the sample might have been effected by back-diffusion out of the graphite pipe for deposition on the cold surfaces of the water-cooled quartz wall. Before attempting any remedial revisions of the apparatus or procedure, however, known quantities of CO, were injected into the helium stream, a t a point preceding entry into the reaction chamber, as tests of the over-all performance of the apparatus. Surprisingly, these tests revealed that the l/s-inch-thick walls of the graphite pipe were permeable to the helium steam and to the injected C02. As a result, about 5Oy0 of the COz flowed through the lower portion of the pipe,
6 4
0 0 1
8 1
7
Table II. Oxygen Results of Tributyl Phosphate Using All-Graphite Reduction Pipe
Sample
DISCUSSION
Reaction Chamber Design. For the reader who may contemplate the use of a reaction chamber similar in design t o earlier models t h a t were tested in this investigation, the following discussion points out some of t h e difficulties t h a t were encountered. Figure 3 shows a diagram of the first model. It had an all-graphite pipe, supported by a 14/35 standard-taper joint in a water-cooled reaction chamber. The 29/26 joint a t the top (used only for the introduction or removal of the pipe) was sealed with Apiezon IT, black wax. The sample cup, threaded to a graphite rod, was conveniently withdrawn and replaced through the KO. 9 O-ring joint. Inasmuch as excess helium from the manostat flushed out a t this point during sampling operation, the blank was negligibly affected by exposure of the opened reaction chamber to the air. The average recovery obtained on the first group of seven samples of sucrose analyzed in this reaction chamber was 97.6y0. Twelve samples of tributyl phosphate were then analyzed, producing the results shown in Table 11. The recoveries were characterized not only by incompleteness but also by sluggishness. Even after three heating cycles, the average recovery was only 96%, with rather poor precision.
r'
100 99 100 Av. 100 Tri-n-octyl phosphine oxide 100 (4.1470 0 ) 99 99 Av. 99
RESULTS
In Table I the results obtained on a group of organophosphorus compounds are listed. The average net recovery of oxygen was 100.070, with a relative standard deviation of about *o.570. Results on some nonphosphorus organic compounds that were obtained during a developmental stage of the method, using an earlier-design reaction chamber, are presented under "Discussion." The normal blank value that persisted with these analyses was about 0.025 mg. of oxygen. This amounted to about 1% of the total oxygen measured per analysis.
Recovery,
9 10 11 12
yo Recovery in heating cycle First Second Third 91 93 93 90 91 95 95 90 93 94 96 92 94 89 97 97 90 93 93 92 96 92 98 98 93 97 98 91 95 97 Av. 92 95 96
completely bypassing the heated graphite bed above. When the lower portion of the pipe was replaced by a section of boron nitride (like that of the final model, Figure I ) , oxygen that was introduced as C 0 2into the carrier stream was quantitatively recovered as 2 molecules of COS in the manometer per molecule of injected COS, according to the reactions :
Without making further changes in the apparatus, sucrose was reanalyzed. The results that were obtained, as well as values on osalic. acid, salirylic acid, and urea, arr listed in T a t h I I I . It was observed during the earlicr runs of this groul) that although most of the CO, produced from each sample was already collect,ed in the manometer (--tube only 3 minutes after the beginning of the heating cycle, a 15-minute rycle was usually not quite long enough to collect all of the extractable oxygen. Suspecting, as before, that sample vapors were VOL. 37, NO. 6, M A Y 1965
753
Table 111.
than with nonphosphorus organic compounds. The 100’ chamber walls were apparently cool enough to retain oxygenbearing decomposition vapors. With the idea of avoiding water cooling and of minimizing dead space in the reaction chamber (in which decomposition products might have been retained), some intermediate models were tested, one of which is shown in Figure 4. I n this envelope type of chamber the annular and end clearances between the graphite pipe and the quartz tube were reduced to a minimum to minimize the residence time of the carrier gas. Quite unexpectedly, the recoveries dropped to about 86%. Furthermore, the blank increased to 10 times its normal value of 0.025 mg. of oxygen, whenever the envelope was removed for the addition of a sample to the cup. This high sampling blank was caused by the adsorption of moisture and oxygen on the graphite-Bh’ pipe during its exposure to laboratory air. Air contamination was later prevented in the model shown in Figure 1 by the protective chimney. The greatly lowered recovery of 86% was doubtless due to sample loss by premature pyrolysis. I n the absence of water cooling, the upward-flowing helium probably had gained enough heat from the outer surface of the rapidly heating graphite pipe to raise the temperature of the sample to the point of thermal decomposition before the chip bed in the reduction zone was hot enough to react quantitatively with the first-appearing sample vapors. In the design and use of the final model (Figure 1))three measures were taken to avoid sample loss. Temporary cooling in the vicinity of the sample was provided by the liquid nitrogen reservoir; the heatup time was reduced by applying extra power to the work coil during the first 15 seconds of heating; and the rate of helium flow was reduced to about of its normal rate during the heatup period.
Oxygen Resultson Sucrose and Other Orgonic Compounds after Adding Boron Nitride Base to Graphite Pipe
Recovery, c/c
Compound Sucrose
Compound
Salicylic acid 98 9 100 1 (34.8% 0) 100 3 99.4 100.1 99.8 Av. 9 9 . 8 zk 0 . 5 7 0 , S.D.
(F11.4~,’60 )
Oxalic acid
99.2 99.5 99.3 99.3
(76.170 0)
Av.
Recovery, % 99.5 99.3 99.5 Av. 99.4
99.6 99.6 99.5 Av. 99.6
Table IV. Oxygen Results on Dibutyl Phosphate and Tributyl Phosphate after Adding Boron Nitride Base to Graphite Pipe
Recovery, yo
Compound Dibutyl phosphate (30 5YG0)
98 9 97 0 98.1 96.9 97 7
+o
97c, S.D.
Tributyl phosphate 96.4 (24.0% 0) 97.0 97.2 98.5 97.5 98.2 9 7 . 5 =k 0.8y0, S.D.
being retained on the water-cooled walls of the reaction chamber, the flow rate of the water was decreased to the point of permitting the temperature of the water to rise to its boiling point. Although this minor revision in procedure made reruns unnecessary for good recoveries, both salicylic acid and urea produced clearly visible, white deposits on the walls of the reaction chamber in a zone surrounding the porous cup 1 minute after startup. The deposits were apparently of thermal decomposition prod-
s 34 5 14
Figure 4. Intermediate model of reaction chamber
ucts that diffused rapidly from the site of the sample, through the graphite walls of both the cup and the pipe, and condensed on the relatively cooler wall surface (ca. 100’ (3.). These deposits disappeared during the heating cycle. Radiant heat from the pipe caused reevaporation into the carrier stream. More analyses were made at this point on tributyl and dibutyl phosphates. The recoveries (Table IV) averaged about 97.5’%. Sluggishness was still more of a problem with these compounds
J
tt
8
BOROSILICATE
GRAPHITE-
0 0 0 0
0
n
0A0 0 itlEA’T NO COIL
::I‘L
B-
C’
f_f
20
600
I 1000 800
1200 1400 1600 TEMPERATURE (OUTER SURFACEI.°C.
2 L 2000 I800
Figure 5. Recovery of oxygen in C O S vs. temperature of graphite pipe
754
ANALYTICAL CHEMISTRY
BORON NITRIDE-
Figure 6. BN pipe
Variation of blank with temperatures in graphite-
Reduction Zone Temperature. I n Unterzaucher's apparatus the temperature of the specially prepared carbon bed had to be held fairly close to 1120" C. ;\t higher temperatures t h e CO blank, resulting from the interaction of carbon in contact with t h e quartz container, became significant, whereas a t lower temperatures the conversion of oxygen-bearing vapors to CO tended to be incomplete. Special, platinumcat'alyzed carbon has since come into use with which the carbon bed can be operated a t lower temperatures. The induction heating unit used in this work provided graphite-pipe t'emperatures from about 600" to 2000" C. No special treatment went into the preparation of the chip bed except that of crushing up ACC-grade graphite, sifting it on a 20mesh sieve, and preheating it in the graphite pipe in an inert gas st.ream a t 1800" C. The minimum operating temperature of about 1 4 0 0 O C. (outer surface of the graphite pipe) was established by observing the recovery of oxygen from known quantities of O2 and of COOthat were injected into the helium, upstream from the reaction chamber. Figure 5 shows a plot of the data obtained on COOsamples. Boron Nitride Pipe Section. Hotpressed boron nitride (a white, polycrystalline solid which resembles graphite, in t h a t it is slippery, easily machined, and has a high resistance to temperature shock) was substituted as the base section of the graphite pipe because of its negligible permeability to gases. It, does not pick u p energy from an induction heating work coil (as would a metal base) and it is chemically inert to many substances. Two disadvantageous properties had to be taken into account in the ])resent application. Boron nitride
'"1 eo
ure 1 ) . For each reading t h a t was entered on the plot, the reaction-tube envelope was removed twice: once as for removing the sample cup and again as for returning it to the chip bed. In accordance with this plot, 5 liters per minute was adopted as the minimum flow rate for the maximum protection against air contamination. In the interest of economy and on the assumption that moisture might be the only component of air to affect the blank, t n o runs were made using dried, compressed air at 5 liters per minute. h s indicated in Figure 6, this substitute was not effective in holding down the blank; hence it was assumed that an appreciable amount of O2 may have been adsorbed on the graphite-BS pipe when exposed to dry air.
x7A1R
c
X
E
0
I
2
Figure 7. nitrogen
3 4 5 6 7 FLOW RATE 01 NZI LITERS/MIN.
6
9
1
10
Blank vs. flow rate of
slowly hydrolyzes in the presence of moisture; hence it had to be protected from the air when small amounts of oxygen were to be measured. Furthermore, the material used in this work contained oxygen impurities in the form of 2.4% methanol-soluble borate, 0.1% alkaline earth oxide, and 0.2% alumina and silica. Tests were made to see how high the temperature of the graphiteBN, threaded joint could be raised without seriously affecting the blank (because of interaction of the graphite with the oxygen impurities in the boron nitride). Figure 6 illustrates that if the temperature of the boron nitride is to have a negligible effect on the blank, the top edge of the boron nitride section (curve C) should not exceed about 1200" C. (These measurements were taken earlier in the investigation when the hottest zone of the graphite pipe was being operated at 2000' C.) Optimum NzFlow Rate. I n Figure 7 the procedure blank is plotted against the flow rate of the nitrogen through the protective chimney (Fig-
ACKNOWLEDGMENT
The author is indebted to Adolph Venters, who performed all of the analyses t h a t were made by the fluorination method, and to Edniund E. Klocek of ANL Central Shops, who gave helpful suggestions toward the application of boron nitride to the apparatus. LITERATURE CITED
( 1 ) Hinkel, R. D., Raymond, R., ASAL. CHEM.2 5 , 470 (1953). (2) Jones, W. H., Zbid., 2 5 , 1449 (1953). ( 3 ) Kristen, W., Zbid., 2 5 , 74 (1953). 14) Oita. I. J.. Conwav. " , H. S.. Ibid.. 26. 600 (1954). ( 5 ) Sheft, I., Katz, J. J., Zbzd., 2 9 , 1322 (1957). ( 6 ) Smiley, W. G., .l'ucl. Sci. Abstr. 3, 391 (1949). (7) Unterzaucher, J., Analyst 77, 684 (1952). ~
RECEIVED for review November 24, 1964. Accepted January 7 , 1965. Division of Analytical Chemitry, 149th Meeting, ACS, Detroit, hlich., -4pril 1965. Based on work performed under the auspices of the U. S.Atomic Energy Commission.
VOL. 37, NO. 6, M A Y 1965
0
755
