Table II.
to be of ultimate advantage in specialized analytical areas where the analysis of large numbers of relatively noncomplex samples of sulfate of varying concentration is required. The method also is n demonstration of how radiotracers can be easily applied t o standard analytical methods at a considerable saving of time and labor.
Summary of Least Squares Analysis
c.p.m. = a.
+ n, [804-?]
Sulfate conm., _ _ _ _ ~ Intercept a0 Std. error a1 mmoles 4 . 5 2 X lo2 1.07 X lo3 6 . 6 8 X A 0-2.5 R 0-8.75 X -1.35 X l o 3 2.67 X lo2 4 . 8 0 X C 0-3.5 x 10-3 1 . 6 1 x lo4 7 . 8 1 X lo2 2 . 8 1 X D 0-1.0 x lo-' 1 47 x lo4 8 . 8 0 x lo2 2.18 x s 2s x 103 5.47 x 1 0 2 2 . 0 8 x E 0-1.0 x 10-3
Slope Std. error lo4 7 . 5 3 X lo2 lo5 6.43X lo3 lo7 4.67 X lo5 lo7 1 . 9 6 X lo5 107
1.04
x
106
Standard error' of fit 2.04 X 6.61 X 1.85 X 2.17 X 1.02 x
lo3 lo2 lo3 loa 103
LITERATURE CITED
(1) Driscoll, W. M., Scott, B. F., Huff, Edmund, "Final Report. Exploration of Radiometric hlethods for Industrial Process Control," TID-11306,Nuclear-
Chicago Corp., Des Plaines, Ill., Feb.
28, 1961. ( 2 ) Kolthoff,
of standard sulfate solution are analyzed at the same time as the unknown. Standard concentrations should be chosen so as to bracket the unknown concentration, if a t all possible. A plot of the activity (counts per minute) vs. concentration is macle so that the unknown value can be calculated. Since a t least 104 counts are usually accumulated, the background of 250 to 300 c.p.m. is insignificant. However,
I. >I., Elving, P. J., "Treatise on Analytical Chemistry," Part 11, Vol. 7 , Sulfur, pp. 1-135, Interscience, New York, 1961.
it is recommended that background determination be made to ensure the absence of extraneous activity. The only interferences with the radiotracer method are those anions that form precipitates with barium that are of the same order of solubility as barium chromate, such as barium ammonium phosphate. The combination of radiotracer and computer calculation would appear
W. J. ARMENTO' C. E. LARSON
Oak Ridge Sational Laboratory Oak Ridge, Tenn. Present address, Department of Clirmistry, Georgia Institute of Technology, Atlanta, Ga. Oak Ridge National Laboratory is opcrated by Union Carbide Corp. for the U. S. Atomic Energy Commission.
Determination of Trialkylphosphines and Their Oxid a tion Products by Gas Liquid Chromatography ,
SIR: Several recent publications have given data on the GLC determination of organic phosphorus compounds (2-4) , including phosphines, phosphine oxides, and phosphites. However, none of these investigators studied all the possible oxidation products of an organic phosphine. This communication attempts to fill partly this gap by reporting the relative retention data of most of the oxidation products of tributylphosphine and tricyclohexylphosplline on a Silicone Grease column and a Reoplex 400 (polyoxj-alkylene adipate) column. EXPERIMENTAL
Two six-foot columns were used, one containing20% by weight Silicone Grease (now Corning High T'acuum), and the other 20y0 by weight Reoplex 400. The solid support used for both columns was 60- t o 80-mesh Chromosorb IT. For the butylphosphine compounds, rolumn teinperatures were 200" C. for Silicone Grease and 206' C. for Reoplel 400. The cyclohesyl compounds \\ere chromatographed on a Silicone column a t 240" C. AZt a heliuni pressure of 15 p.s.i.g., the flow rate thru the Sil~cone column mas 79 nil. prr minute, and for the I l e o p l e ~column 60 nil. prr nirnute. Flow rates were measured a t the colimin outlets nith a soap bubble meter at room temperature. The instrument uicd n a b an F & II model 500 gas chromatograph with a filament-t~pe 920
ANALYTICAL CHEMISTRY
thermal conductil ity detector. The drtector and inlet teinperatures w r e 200" C. and 2'75" C., respectively, for all experiments. Details concerning the source and preparation of compounds used in this study are given in a srparate paper ( I ) , which also discusses thr mechanism of the autoxidation process. RESULTS A N D DISCUSSION
Qualitative. Results on the Silicone Grease column left much t o be desired because of the nonspecificity of the column with respect t o the ouidation products of tributylphosphine. I n addition, the polarity of some of these compounds resulted in tailing peaks. Thcsc difficulties wcrc re-
Table I.
,
solved by thc use of the Reoplex 400 column. T h e relative retention distances of tributylphosphine and its oxidation products us. liexadecane on both Silicone Grease and Reoplex 400 columns at 200" C. and 206" C., respectively, are given in Table I. The compounds tailing the most on Silicone Grease were tributylphosphine, tributylphosphine oxide, and dibutylphosphine oxide. On Reoplex, theFe compounds gave symmetrical peaks. Reoplex n-as also more effective than Silicone in separating tributylphosphine from butyl dibutylphosphinite, tributyl phosphite from dibutylphosphine oxide, and tributyl phosphate from butyl dibutylphosphinate.
Relative Retention of Tributylphosphine and Oxidation Products v5. Hexadecane"
Compound Formula n-Hexadecane Tributylphosphine Butyl dibutylpliosphinite Trihutyl phosphite I )ihutylphospliine oxide Dibutyl butylpliosphonate Tributyl phosphate Butyl dibutylphosphinate Tributylphosphine oxide Relative retention distances were measured 0
Relative retention Silicone at 200" C. Reoplex at 206" C. 1.00 ( 5 . 7 min.) 1.00 ( 2 . 0 min . ) 0.45 0.45 0.56 0.57 0.96 1 .07 1.11
0.78 0.27 1.17 7.74 4.94 5.99 6.76 13.8
1.48 from point of injections.
All of the cyclohexylphosphines and their oxidation products that were available were resolved adequately by Silicone Grease a t 240" C., thus eliminating the need for the Reoplex column. The relative retention distances of these compounds us. dibutyl sebacate are given in Table 11. KO peak was obtained for tricylcoliexyl phosphate on Silicone Grease at 240" C. or a t column temperatures as high as 350" C. The only peaks observred mere due to various low-boiling decomposition products which could not be duplicated with repeated injection. A 4-foot Reoplex 400 column a t 220" C. was also tried but without success. Quantitative. Three known mixtures of tributylphosphine, dibutyl butylphosphonate, arid tributylphosphine oxide were prepared using benzene as the solvent. Dibenzyl was added to each as a n internal standard and each mixture was chromatographed three or four times on the Silicone eolumn a t 200" C. The dibutyl butylphosphonate and tributylphosphine oxide gave linear results upon plotting weight ratio us. area r d o of each with respect to dibenzyl. Relative standard deviations of 1.0 and 1.9% were obtained for the area ratios of phosphonate and oxide, respectively, us. dibeneyl. The tailing of tributylphosphine on Silicone resulted in nonlinear response and a relative standard deviation of 5.370 for the area ratio
Table II.
Relative Retention of Cyclohexylphosphines and Oxidation Products vs. Dibutyl Sebacate" Relative retention, Compound Formula Silicone a t 240' C. Dibutyl sebacate 1.00 ( 6 . 7 min.) Cyclohexyl dibutylphosphinate BunP(O)OC';H,, 0.52 Butvl dicvclohexvluhosDhinnte (C~HII)~P(O)OBU 1.14 (C;HI;jsP' 1.26 Tric-yclohixylph6sphine Dicyclohexyl cyclohexylphosphonate (C&1)P(O) (OC'H11)Z 1.84 Cyclohexyl dicyclohexylphosphinate ( CeHI1)2P(O)OC,Hll 2.19 ( CeHii )*PO 3.11 Tricyclohexylphosphie oxide (CeHii0)J'O did not elute Tricyclohexyl phosphate Relative retention distances were measured from point of injections. '
relative to dibenzyl. Three additional standards of tributylphosphine and dibenzyl were prepared and eluted on the Reoplex column a t 206" C. The phosphine peak was symmetrical, a linear response was obtained, and the relative standard deviation improved considerably to a value of 1.9%. Decomposition. Dibutylphosphine oxide, a relatively unstable compound, was condensed after elution thru the Silicone column and examined by infrared spectrometry. Little decomposition of the compound had occurred as indicated by identical spectra of the original and eluted material. It was therefore assumed t h a t the more stable compounds in this study also eluted without structural change. Peaks having small retention times, which could be attributed to low-boiling decomposition
fragments, comprised less than 4% of the parent peak in all cases except tricyclohexyl phosphate. LITERATURE CITED
( 1 ) Buckler, S. A., 84, 3093 (1962).
J. Am. Chenz. SOC.
[ a ) DeRose, A., Gerrard, W., >looney, E. F., Chem. Ind. (London), 1961, 1449.
(3) Gudeinowicz, B. J., Campbell, R. H., ANAL.CHEM.33, 1510 (1961). (4)Shipotofsky, S. H., Ibid., p. 521.
RAYMOND FEXNLAND JEREMY SASS SHELDON A. BUCKLER' Central Research Division American C anamid Co. Stamford, d n n . Present address: Chemical Research Laboratories, American Machine & Foundry Co., Springdale, Conn.
Controlled-Pote nt ia I Coulometric Determination of Ura nium(V1) in Ura nium-Nio bium Alloys SIR: The precise and accurate determination of uranium in alloys that contain uranium and niob um is becoming increasingly important because of the usefulness of niobium as an alloying material in the fabrication of nuclear reactor fuel elements. Accordingly, the application of controlled-potential coulometric titrimetry to that type of sample has been studied. These studies have resulted in the development of two procedures, one in whicn uranium is determined in the presence of niobium and a second in which uran um is separated from niobium and then titrated. The first procedure can be used for fairly pure uranium-niobium solutions in which the Nb:U weigh, ratio is 3 : l or less. The second procedure is used for solutions containing Nb: 1 7 n-eight ratios greater than 3 1 or for solutions containing contaminants, such as Fe, that interfere in the subsequent uranium titration, Both methods are precise, accurate, and can be applied to the andysis of samples
in which the Nb : U li-eight ratio is much greater than presently encountered in dissolver solutions of this type. EXPERIMENTAL
Apparatus. An ORKL Model Q-2005 controlled-potential coulometric titrator was used exclusively for this work (2). Instructions as to the use, care, and calibration of this instrument have been prepared by Jones ( I ) . A diagram of the titration vessel is presented in Figure 1. The stirrer is a flat disk of about 1-cm. diameter placed horizontally a t the mercury-electrolyte interface; it is driven a t 1800 r.p.m. by a motor mounted above the cell top. Exact details of the construction are available as ORYL-LR-Dwg. 66274. Water-washed helium gas of high purity was used to provide the inert gas blanket. The extraction vessel is formed from glass tubing (i.d. = 1 inch; length = 4l/2 inches). The bottom is tapered, and a stopcock with two outlets is at-
tached. One outlet is provided for discharge of aqueous waste and the other for discharge of stripping solutions into the titration vessel. The glass stirrer is formed by flattening (vertically) the last inch of a glass rod, and it is driven by a variable speed motor. Complete and intimate mixing of both organic and aqueous phases can be obtained when the stirrer extends to near the bottom of the vessel. A drawing of this vessel is available as ORKL-LRD R G . 73571. Reagents. A stock solution of niobium was prepared from niobium powder (Fisher Scientific Co., Fairlawn, K. J., Xo. 721098) to contain 20.44 mg. per ml. of N b in 5-If HXO3-0 5 M HF. Tri-n-octylphosphine oxide, TOPO, (Eastman No. 702, Distillation Products Ine., Rochester, N. Y.) was dissolved in cyclohexane to the extent of 0.1M and used without further purification. Other reagents were prepared from analytical grade materials. The mercury had been washed thoroughly with l.5.U HX03, distilled once under VOL. 35, NO. 7, JUNE 1963
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