V O L U M E 28, NO. 9, S E P T E M B E R 1 9 5 6
1441
E D T A solutions, processed in the same manner as the sample, and compute the average absorbance index. Use the absorbance index to calculate the concentration of E D T A in the sample from its absorbance. LITERATURE CITED
(1) Bersworth Chemical Co., Framingham, Mass., Tech. Bull. 2, sec. I, pp. 6-13, 1954. (2) Ibid., 8ec. 111, pp. 2-4. (3) Derby, 1., ANAL.CHEM.24, 373 (1952).
Furness, W., Crawshaw, P., Davies, W. C., Analyst 74, 629 (1949). (5) Kerkow, F. W., 2.anal. Chem. 133, 281 (1951). (6) Plumb, R. C., Martell, A. E., Bersworth, F. C., J . Phya. and Colloid Chem. 54, 1208 (1950).
(4)
RECEIVED for review November 29, 195% Accepted rMay 22, 1956. Southeastern Regional Divisional Meeting, ACS, Columbia, 9. C., November 5 , 1955. Work carried o u t under Contract No. W-7405-eng-26 a t Oak Ridge Xational Laboratory, operated b y Union Carbide Nuclear Co., a division of Union Carbide and Carbon Corp., for the Atomic Energy Commission.
Pyrohydrolytic Separation and Spectrophotometric Titration of Fluorides in Radioactive Samples J. E. LEE, JR., J. H. EDGERTON, and M. T. KELLEY Analytical Chemistry Division, O a k Ridge N a t i o n a l Laboratory, O a k Ridge, Tenn.
Apparatus is described which is suitable for the pyrohydrolytic determination of fluoride in radioactive liquids or solids. Fluoride in the radioactive distillate from the pyrohydrolysis is determined by a remotely controlled titration in an apparatus of special design. The apparatus was evaluated by determining the fluoride content of solid uranium tetrafluoride, a mixture of solid fluoride salts, and a solution of fluoride salts. The relative standard deviation of the data for 2.5 to 15 mg. of fluoride was 3'7,~ for uranium tetrafluoride samples.
T
HE procedure described by Warf, Cline, and Tevebaugh ( 5 )
for the pyrohydrolytic determination of fluoride has been adapted to the analysis of semimicro quantities of highly radioactive liquids and solids. Modified apparatus was developed for the pyrohydrolysis of the sample and for spectrophotometric titration of fluoride by remote control. The fluoride contents of solid uranium tetrafluoride, of a mixture of fluoride salts, and of a radioactive liquid that contained fluorides were determined
satisfactorily by use of the apparatus. The radiation level of samples was sometimes as high as 100 roentgens at contact, and radioactive fission products were present in the distillates. I PYROHYDROLYSIS APPARATUS
The unique feature of the pyrohydrolysis apparatus employed (Figure 1) is that it can be used for the analysis of either liquid or solid radioactive samples. It consists of a steam generator and superheater, a pyrohpdrolpsis unit, and a collector for the fluoride distillate. The steam generator is constructed of standard borosilicate glassware. The superheater is a silica tube which passes through a furnace made from standard 8-inch-length heating elements. The furnace can be heated t o a temperature of llOOo C. Control of the steam supply is critical because of the small volume of the pyrohydrolysis unit. Control is maintained by leaving the steam generator open t o the atmosphere through a condenser. Steam passes through the system as a result of the reduced pressure that is maintained in the distillate receiver, The pyrohydrolysis unit is constructed of platinum [or nickel (S)] ; it incorporates a standard 20-ml. tubulated Gooch crucible.
b1R INTbKE SILICb SUPERHEbTER T U B E
-
S l L l C b COUPLING
B A L L bNO SOCKET JOiNT
UM REbCTlON CRUCiBLE
S T E b M GENERbTOR I500 ml. F L A S K 1
-
POLYETHYLENE RECEIVER U N i T
VACUUM RECEIVER U N l T
HEbTlNG MbNTLE
o m o , " ,
Figure 1.
.4pparatus for pyrohydrolysis
ANALYTICAL CHEMISTRY
1442
Figure 2.
Apparatus for spectrophotometric titration
t-se of this crucible was suggested t o the authors by Vogel ( 4 ) . T h e inlet tube of the crucible head is cemented t o the silica tube of the superheater by means of Sauereisen paste No. 1. A side arm of platinum estends from the esit tube of the tubulated crucible to form the inner tube of the distillate condenser. T h e pyrohydrolysis crucible is heated by a movable furnace 1 inch in inside diameter, which is constructed from standard 6-inch heating elements, supplied as replacement units that are mounted in an appropriate refractory. T h e elements are mounted in a stainless steel beaker and are insulated with asbestos fiber. T h e flange of the crucible is supported by the top of the furnace; the entire lower section of the cruci1)le extends into the hottest zone of the furnace. The tapered platinum-to-platinum seal of the crucible lid is held closed by the mild pressure of the supporting flange and is satisfactory without the use of a cemented seal, if rare is taken to keep the contact'ing platinum surfaces clean and free of deformations. A thin sleeve of silica tubing is inserted hetween the furnace and the crucible in order t o provide added protection t o the platinum crucible. The distillate is collected in a polyethylene container that is set inside a Fisher Filtrator, which is under moderate, regulated suction. T h e slightly reduced pressure (of the order of 1 to 2 inches of water) eliminates leakage at the crucible closure and surges that result from boiling phenomena. I condenser jacket is fitted t o the platinum side arm to form tlie distillate condenser. The jacket is attached a t the bottom to the platinum tube by means of a rubber stopper. The outlet port of the jacket is of larger diameter than the inlet' tube, in order to allox discharge of the (aooling water from the condrnser before the water reaches the
'Table I. Determination 1
2 3 4 5 6
7
8 9 10 11
Fluoride in Solid Irradiated Uranium Tetrafluoride Tejt Portion, 1Ig.
Fluoride", Wt. "c 24.9 26.0 23,2 24.1 22.6 24.6 24.7 23.7 24.3 23.9 23.8
29.7
25 5 20.6 15 2 13.4 10 9
10 0 26.5 27.0 43.2 38.0
Av.
24. I
Theoretical fluoride content, 24.20 w t , c ; . .4n experimental value of 24.18 n t . yo was obtained on the sample before it was irradiated. A macroapparatus. similar t o t h a t described by Warf, Cline, and Terebaugh (6). and visual end point detection were used. T h e relative standard deviation was 1.07% for 1 5 consecutii-e analyses of test portions t h a t weighed 35 t o BO a
Pig.
top of the jacket; it is therefore not necessary to support the jacket against' the hot upper end of the platinum tube. SPECTROPHOTOhl ETRIC TITRATION APPARATUS
Fluoride in the radioactive distillate from the pyrohydrolJ.aic apparatus is determined by a remotely controlled titration apparatus of special design (Figure 2 ) . T h e titration procedure is similar to that described by Kichols and Iiindt ( 2 ) . The titrant is thorium nitrate solution, the buffer is monochloroacetic acid-sodium hydroxide solution, and the indicator is alizarin red S. K i t h the exception of the light-trap cover for the absorption-cell chamber of the Beckman spectrophotometer, t'he apparatus is constructed from stock items. The titration cell is made from an extraction cell or from the end of a large buret. The test solution is circulated from the titration cell through the absorption cell by means of an Eastern Model 8-1 RIonel centrifugal pump, available from Burrell Corp., Pittsburgh, Pa. I n this way the radiation hazard to the operator is decreased, and the apparatus therefore has an advantage over the assembly described by Goddu and Hume ( 1 ) . T h e radioactive solutions can be discarded with a maximum of safety through the drain provided in the line. T h e radioactive, fluoride-containing distillate collected from the pyrohydrolgsis in a solution of excess sodium hydroxide is titrated by transferring the distillate t o the titration cell and neutralizing it t o the phenolphthalein end point with hydrochloric acid, The centrifugal pump is used to stir the solution. T h e buffer solution and indicator are then added, followed by enough water to make a total volume of approximately 200 ml. The titrant is added in increments, and the solution is circulated for 10 t o 20 seconds, and then alloived to rest, for 30 t o 40 seconds before the per cent transmittancy of the solution a t 525 mp is read and recorded. The point of maximum change in the per cent transmittancg is taken as the empirical equivalence point (2). Air is trapped in the solution if the pump is not properly primed. .kiter the titration is completed, the solution is drained from the
Table 11.
Fluoride in Radioactive Mixture of Solid Fluoride Salts
Determination 1 2 3
Test Portion, 110. 40.8 40.4 42.7
Fluoride, Wt. 7c" 41.4 40.8 40.3 sv. 4 0 . 8
a h value of 41.6 wt. sl, was obtained on the sample before it was irradiated. A maoroapparatus, simllar t o t h a t described by Warf, Cline, and Tevebaugh (j), and visual end point detection were used.
1443
V O L U M E 2 8 , NO. 9, S E P T E M B E R 1 9 5 6 cystem, and the system is flushed clean by pumping distilled water through it.
Table 111.
Fluoride in Radioactive Solution of Fluoride Salts
EXPERIMENTAL EVALUATIOY OF APPARATUS
\.j-iiiI.
The apparatus was evaluated by determining the fluoride raontent, of uranium tetrafluoride; no accelerator was used in the jq.rohydrolysis. The results of 11 consecutive determinations 011 t w t portions t h a t ranged in size from 10 to 58 mg. are given in Table I. The relative standard deviation of these test result? i. :3%. A solid sample that \\-as principally a mixture of uranium fluorides and alkali-metal fluorides, and had been shown by macro;iiialysis t o contain 41.6 weight % fluoride, F a s also analyzed by iize of the apparatus. Aluminum oside was used as the accelt~ratorfor the pyrohydrolysis reaction; the test portions of the 5:iniple were bedded in 0.5 gram of alumina and hydrolyzed for 1i0 minutes. The results of the three determinations of fluoride :tre given in Table 11. The average of these results agrees satist'artorily with the value obtained by use of the macroapparatus. The apparatus was also evaluated by the analysis of a radio:irtive solution of fluoride salts that was prepared to contain 2 3 ~1.p.m. of fluoride. The solution was 1M in nitric acid and also contained thorium, 7.3.1l; aluminum, 3.0M; vanadium, 1.5M; iron, 0.0lX; nickel 0,OlM; and chromium, 0.01M. T h e test portion of the sample \vas absorhed in the bed of aluminum oside accelerator in the 1)yrohydrolysis crucible. -4pellet of sodium hydroxide was also included in the crucible charge. This provided a sufficiently wluble residue from the high-temperature pyrohydrolysis reacrion to permit subsequent cleaning of the crucible Tvith a miniilium of handling. T h e charged crucible was nest' positioned in t l i r b cold apparatus. After the superheater was heated to 1100" C. :inti the suc-tion turned on, the temperahre of the crucible furnace v.:ts elevated sloi\-ly. T h e volatile constituents of the test portion
t c a t portions)
Determination
Fluoride, P.l'.M.a 23
ti
\\-ere thereby removed M o r e the niasimum supply of si11)w1irl:ited steam came in contact with the test portion. The results of the annlysis of the sample are given in T:rl)le 111. The agreement I)et'ii-een the amount of fluoride :iddc~i:iiitl that recovered is sntisfactory, especially for the .small fluoiitlr concentration conccrnetl. \CliNOWLEDGRIENT
The authors wish to acknoxledge assistance receivtd I I T J I ~ I I). ,J Fisher, H. L. Hemphill, and P. F. Thomason. L I T E H T U R E CITED
Goddu, 11. F.. Hrmie, n.s., . ~ N A L . C H m f . 26, 1710 (l!L54). Sichols, 11. L.. Kindt., B. H., I b i d . , 22, 785 (1950). Susano, C . D., XVhite, J. C . , Lee, J. I?., Jr., Ibid., 27, 453 (195.5). Vogel, R. C . , .irgonne Sational Laboratory, private coniiiirinicstion t o AI. T. Kelley, June 1952. (5) R-arf, J. c y . , Cliiie, I\-. D . , Tevebaugh, It, D., . ~ N A I . . CHEJI.26, 342 (1954).
(I) (2) (3) (4)
RECEIT-ED for review l l a i 1.11 2 2 ,
l!l,jlj,
;\ccepted .June -1, 19.56
Rapid Photometric Determination of Magnesium in Electronic Nickel C. L. LUKE
Bell Telephone Laboratories, lnc., M u r r a y Hill, N.
J.
The photometric oxine method €or the determination of magnesium in nickel has been modified to permit rapid determinations. 1nterfe;ence is eliminated by removing certain interfering metals with an ammonium hydroxide separation and by masking others with c? anide.
T
HE photometric osine method for the determination o f mag-
nesium in nickel ( 1 ) gives reliable results, but is time-con-uming because of the number of separations involved. Bernuw most of the nickel samples submitted for analysis contain less than 0.01 % calcium, and because interference due to this nietzl is not serious, it seemed probable that the previously published method could be greatly simplified if no attempt was made to remove the calcium. This has proved to be true. By removing manganese with the hydroxide precipitate, rather than n-ith cartinmnte, and by masking with ryanide the interference d u to ~ nickel>cobalt, and the like, it has been possible to reduce the tinie oi :jiialyPis t o about 15 minutes. REAGENTS
Nickel Metal. The nickel metal used in the preparation of the cnlihration rurve should not contain more than 0.001 5 mag-
nesium or 0,005To cdriuni. zinc, clitiiiiium, or gallium. (Sivatc supplied by Vacuum Metals Corp., Syracuse, S . Y., has proved to be satisfactory.) Ferric Nitrate Solution. 1)issolvc 2 grams of pure iron ill 25 nil. of nitric acid (1 t o 1): heat to expel osides of nitrogen, cool, dilute to 200 ml. with x-ater, and mix. Ammonium Persulfate Solution. Dissolve 1 gram of :inimonium persulfate in 100 ml. of water. Prepare fresh each day as needed. Sodium Cyanide Solution. T1,uiisfei. 20 grams of sotliuin cyunide to a 500-ml. polyethyle~iebottle. Add 200 ml. of n-nter :irid swirl to dissolve. Keep stoppered when not in use. I'ROCEDURE
Preparation of Calibration Curve. Dissolve five 0.100-graiii portions of pure nickel by warming gently in 2-ml. portions of nitric acid (1 to 1 ) in covered 125-m1. conical flasks. hvoid unnecessary loss of acid bl- evaporation. When solution is coniplete, blow the bron-n fumes from the flasks and then cool. Traiiafer 0, 2.0, 4.0, 6.0, and 8.0 ml. of standard magnesium solution (10 y of magnesium per ml.) to the flasks and dilute each sample to 35 ml. Kith water. lldd 1 ml. of ferric nitrate solution plus 1 ml. of ammonium persulfate solution (to oxidize manganese). Add ammonium hydroxide (specific gravity, 0.90) dropwise with swirling until the iron just precipitates, then add I ml. in escess from a graduate. (The ammonium hydroxide used herc arid subsequently must not be allowed to lose its strength before use tiy standing in an open container.) Heat the solution to 6.5' C. a n d filter through R rapid 1)apor into
