could become, a solution 0.10M in lead ion and 5.00 X in cadmium ion was run to determine the height of the cadmium peak. The resolution gave a separate cadmium peak which permitted the calculation of the cadmium ion concentration n-ith as great a n accuracy as if the lead had not been present. This is the determination of the more difficultly reducible species when the two ions are in the ratio of 1 to 20,000. Figure 8 s h o w the reduction of a mixmole per ture of cadmium (1.00 x liter) and indium (1.0 X loe4 mole per liter) from 1.OM potassium chloride, with 0.1 mole per liter of hydrochloric acid added. Under these conditions the half-wave potentials differ by about 40 mv. and the conventional polarograph would not permit accurate calculations of the amounts of the two ions. The two peaks shown n-ere sufficiently well resolved to make possible calculation of the amounts of each ion present. Reproducibility. In t h e investigations outlined a t concentrations mole per liter the near 1.0 X square-wave polarograph gave measurements of about the same reliability as a conventional polarograph for the reduction of a reversibly reduced species. Because the capacitance current did not become a factor in the measurements as the concentration was reduced, the results became less reliable only when the noise in the circuit began to become a n important factor. As the circuit was constructed, concentrations as low mole per liter could be deas 1.0 x termined and further care in shielding should permit the determination of somewhat lower concentrations. CONCLUSIONS
When the performance of this instrument is compared with the report given by Ferrett and others (6) on three recently developed polarographs, it is
in the presence of a completely irreversibly reducible species, even if they are normally reduced a t the same potential; and analysis by normal polarograph techniques where the square-wave tech-. nique is not necessary. ACKNOWLEDGMENT
Figure 8. Square-wave polarogram of mixture of indium and cadmium ions
The author wishes to acknowledge the assistance of the Chemical Research Operation of the Hanford Atomic Products operation, ryhere this research was first started, and particularly indebtedness to Robert Connally of this laboratory for the preliminary design work on the circuit. He is also greatly indebted to the Research Corp. for a research grant which has permitted t h e continuation of this research a t tha University of Utah.
In 1.OM KCI, 0.1M HCI, each 1 .OO X mole p e r liter
seen that the sensitivity of this instrument is not so great as the Barker square-wave polarograph. and that its resolution is approximately the same, as shown on resolution of the indiumcadmium peaks (Figure S). This instrument is, hon-erer, considerably simpler electronically and therefore much cheaper to build. It can be simplified further by replacing the expensive square-wave generator with a single tube astable multivibrator without appreciably altering the results obtained. The instrument was constructed for use either as a square-wave polarograph or as a conventional polarograph and has proved remarkably versatile. This versatility arises because the instrument permits determination of lower concent,rations than the conventional polarograph; determination of small quantities of more difficultly reducible species in the presence of large quantities of a more easily reducible species; determination of a reversibly reducible species
LITERATURE CITED
Barker, G. C., Jenkins, I. L., Analysi. ~
77, 685 (1952).
Ferrett, D. J., Milner, G. IT. C.,
Zbid., 80, 132 (1955). Ibid.. 81. 192 la^' Ferrett, ’D. J., Milner, G. W. C.. J . Chem. Soc., 1956, 1186. Ferrett, D. J., Milner, G. IT. C., Shalgosky, H. I., Slee, L. J., Analvst 81, 506. (1956). Gutmann, F., Universlty of Sydney, I”
\-Y”Y,.
Sydney, Australia, private communi-Kamba ra, T., Bull. Chem. SOC.Japan t:nm
\rrn”I”II.
27,523, 527, 529 (1954).
Kelley, M. T., F isher, D. J., A x . 4 ~ . CHEM.28, 1130 (1956). Kolthoff, I. M., Lingane, J. J., “Polarography,” 2nd ed., Interscience, New York, 1952. Natl. Bur. Standards, “Handbook of Preferred Circuits,” Kavy Aeronautical Electronic Equipment,” Savaer 16-1-519 (1955). RECEIVEDfor revien. July --22, 1957. Accepted Sovember, 23, 1931. Northwest Regional Meetlng, ACS, Spokane, Wash., June 13-14, 1957. A considerable amount of work performed at Hanford Laboratories, Hanford Atomic Products Operation, Richland, Wash.
Automatic Determination of Uranium in Process Streams H. W. BERTRAM, M. W. LERNER, G. J. PETRETIC, E. S. ROSZKOWSKI, and C. J. RODDEN U. S. Atomic Energy Commission, New Brunswick, N. J.
b An automatic instrument composed of a derivative polarograph and a sampling and proportioning system has been developed to analyze high concentrations (100 to 200 grams per liter) of uranium in process streams. The derivative polarograph, based upon the resistance-capacitance circuit, scans the applied voltage in a reverse direction to decrease peak oscillations. Concentrations of ura-
354
*
ANALYTICAL CHEMISTRY
nium are recorded a t 5-minute intervals. Factors affecting the precision and accuracy are briefly discussed.
T
numerous chemical analyses required in the process control of uranium purification involve high costs. Automatic instrumentation of many of these control tests would reduce both laboratory costs and material holdup time in the plant. HE
I n the current uranium refining processes there are many points at which an aqueous process stream must, be analyzed for control purposes, Rodden (IS) has summarized all these control points, giving the number and type of analyses necessary at each, for representative diethyl ether and tributyl phosphate extraction plants. The ore digestion section of either type of plant is especially suitable for auto-
’
matic instrumentation. Periodic monitoring of the batchwise digestion proct‘ss would rapidly indicate the uranium concentration and thus eliminate excessive batch holdup. The continuous analysis of the extraction plant feed solution would ensure feeding of a constant concentration of uranium to the extraction columns. Several investigators have developed instruments to determine the uranium content of process streams automatically. Their use, however, has been restricted to solutions of low uranium content. Bisby, Brown, and Chapman (1) have reported the development of an “automatic uranium analyzer” to analyze the efluents from ion exchange columns. The instrument measures t h e intensity of the colored complex produced when proportionate volumes of the uranium-bearing solution and a n ammonium thiocyanate solution are mixed. The unit is completely automatic and gives a permanent record of the uranium concentration. Koyama, hlichelson, and Alkire (8) have described a n automatic polarograph which determines the uranium in process waste streams directly, without addition of other reagents. They also briefly investigated application of derivative polarography to the problem. Lewis and Overton ( I O ) also used a polarographic method to determine uranium in dilute solutions automatically. A tartrate base solution is added to the solution to be analyzed. The resulting solution is then passed through two polarographic cells equipped with synchronized dropping mercury electrodes. The voltage of one electrode is set a t the value corresponding to the bottom of the polarographic wave for uranyl ion, while the yoltage of the other electrode is set a t the plateau value. With a good wave form produced, the current difference flowing in thp tvio cells is a direct peasure of uranium concentration. I n the present study, which involved ihe analysis of process feed solutions containing high concentrations of uranium (from 100 to 200 grams per liter), derivative polarography n-as used. A derivative polarogram of a substance is a curve with a maximum, or peak, occurring approximately a t the halfn-ave potential of the ion being reduced. Such a curve represents the changes in the diffusion current as a function of the spplied voltage. Generally, this technique leads to better resolution-that is, clearer definition of the reduction curves of tmo ions that have halfwave potentials of nearly the same value. The formation of a discrete wave for the particular ion under scrutiny is often an advantage. Fisher and Kelley (3) and Kolthoff
and Lingane ( 7 ) have summarized the methods used to obtain derivative polarograms. For application to the present problem, the resistance-capacitance (RC) method (9) was investigated because of the simplicity of the circuit and was found to give highly reproducible results. A procedure for obtaining the derivative polarogram was developed, whereby the voltage is scanned in a direction opposite to that of conventional polarography. This reverse-scanning procedure possesses an inherent advantage over the usual resistance-capacitance technique, The optimum concentration of uranium determined by polarography is generally below 2.5 grams per liter. This concentration limit necessitates accurate dilution of the concentrated feed solutions. The dilution not only brings the concentration of uranium to within a measurable value, but also introduces the required supporting electrolyte for the polarographic measurement. The complete apparatus automatically dilutes the feed solution, makes the polarographic measurement, and repeats the cycle every 6 minutes, EXPERIMENTAL
Derivative Polarography. Fisher, Kelley, and coworkers a t the Oak Ridge Sational Laboratory studied the derivative polarography of uranium by several methods (3-6). I n working with the resistance-capacitance method, a quadruple parallel-?’ filter was used to eliminate the current oscillations, the presence of which has been a disadvantage in the application of derivative polarography. The resistance - capacitance circuit used, with the optimum values for the resistance and capacitance, is shown in Figure 1. With this circuit the oscillations a t the peak of the uranium curve can be eliminated, or reduced greatly, by scanning the applied voltage in the reverse direction-that is, from -1.0 to 0 volt. The peak height can then be measured more accurately. I n all the work reported here, only this reverse direction was used. The circuit diagram (Figure I) includes a compensator circuit to adjust the recorder pen to a desired position. This compensator was used during the initial phase of the study to observe maxima and the effect of impurities, but not under automatic operation. The potentiometer, RS, graduated in per cent of total resistance, is coupled to a reversible, synchronous motor geared to scan the total resistance in either direction in 3 minutes. I n automatic operation the potentiometer reverses after 60% of its resistance has been scanned. With a span voltage of 1.0 volt, the voltage scanned in this case is -1.0 to -0.4 volt. The variable resistors, Rz and R4, can be
used, however, to give any desired combination of initial and span voltage from the two 1.5-volt batteries. The sensitivity adjustment, R1, was held a t 100 ohms throughout the work. The selection of 100 to 2000 ohms for Rl is available for the analysis of a wider range of concentrations. The optimum values of R1and C1were selected on the basis of sensitivity and resolution-that is, peak height and speed of response to the current changes, respectively. I n the preliminary work with the polarograph, a 10-mv. Brown stripchart recorder was used. A 2.5-mv. recorder was later substituted for greater sensitivity and was used in the final assembly. Effects of Oxygen and Maxima. The presence of oxygen in the diluted uranium solution causes a significant increase (about 2 to 3%) in the uranium peak height. The solution must therefore be purged with tank nitrogen. The presence of a wave maximum, as expected, is shown by a n erroneously high peak plus a n inverted peak below the base line. With the concentrations of uranium normally determined, severe maxima are encountered. These maxima are suppressed efficiently by 4 X lod4% thymol. Supporting Electrolyte. The effect on the uranium peak height of the impurities normally present in feed solutions was studied initially with a 0.25M sulfuric acid medium conthymol. The taining 4 X interference of all elements except vanadium and molybdenum was insignificant. S o supporting electrolyte could be found in xhich the interference of vanadium or molybdenum was eliminated nhile a clearly defined curve was still maintained for uranium. The supporting electrolyte finally selected was a 0 . M sulfuric acid-0.1M sodium sulfate solution containing 4 X thymol. Although, as with most of the media tested, interference varies with pH, this causes no difficulty, because with the high dilutions used the p H of the final solution remains essentially constant. This supporting electrolyte was tested by analyzing several samples of representative feeds (Table I). These feeds ii-ere first carefully analyzed chemically and then diluted with the medium in ratios of 1 to 200 and 1 to 400 and analyzed by the derivative polarograph. These polarographic measurements together with the calibrations with standard uranium solutions were made in a conventional cell a t 25” C., with a mercury pool anode. The higher dilution, 1 to 400, effectively “dilutes out” the interferences in all samples except the Colorado feed, which is exceptionally heavy in vaVOL. 30.
NO. 3,
MARCH 1958
355
FEED S O L U T I O N S
M R
>RDER
ROTARY V A L V E PROPORTIONER
MIXING CHAMBER
--/\ 1
POLAROGRAPHIC
FRITTED D I S K ELECTRODE
DRAl N
Figure 1.
’LTO
Polarographic circuit
V I . Voltmeter, 0-1 volt d.c., initial voltage V I . Voltmeter, 0-1 volt d.c., span voltage Resistors, 2,000, 1,500, 1,000, 500, 100, and 100 ohms, sensitivity R1. Rz.
RB. R4. R5.
Re. R7.
RE. Rg.
C1.
C2. SI. Sz. Sa. Sd.
Sj.
Figure 2.
control Variable resistance, 500 ohms, initial voltage control Potentiometer, from Leeds & Northrup Electra-Chemograph Variable resistance, 500 ohms, span voltage control Resistor, 1000 ohms Resistor, 10,000 ohms Resistor, 200,000 ohms Variable resistonce, 10 megohms, compensator control Resistor, 200,000 ohms Electrolytic condenser, 4000 microfarads Electrolytic condenser, 10,000 microfarads Switch, single-pole single-throw, main on-off for polarographic circuit Switch, single-pole double-throw, span voltage selector Switch, single-pole single-throw, conventional or derivative polarograph selector Switch, single-pole double-throw, Compensation range selector Switch, double-pole double-throw, compensation direction selector
nadium and molybdenum. K i t h the dilution of 1 to 200, eren the smaller quantities of these elements in the other feeds interfere badly. A dilution of a t least 1 to 400 is necessary to reduce the uranium concentration of the feeds to the best range for measurement. Although higher dilutions, which would give still less interference from impurities in the feeds, would be satisfactory if the uranium peak heights remained large enough to measure accurately, a dilution of about 1 to 400 was considered sufficient. Proportioning System. A means was required for automatically diluting the process streams containing from 100 t o 200 grams of uranium per liter t o a concentration preferably below 1 gram per liter. Several types of proportioning devices were tried: a displacement-type proportioning pump. a constant-flow measuring device, and a rotary-valve type proportioning unit. The latter was suggested by llichelson ( 1 1 ) . 356
e
ANALYTICAL CHEMISTRY
Only the rotary valve proportioner gave the desired accuracy. Basically the unit consists of a rotating plug valve controlling the flow of two lines perpendicular to each other, as shown in ~i~~~~ 2, The valve body is constructed of No. 316 stainless steel and the tapered plug is made of Teflon. The horizontal line is tied into the main Table I.
XBL Sample
DRAIN
Flow diagram for proportioning system
circulating line of the feed solution. When the valve-plug opening, rotating at a constant speed of 1 r.p.m., passes this line, the solution flows momentarily. The plug hole, nom retaining a definite small volume of the feed solution, then passes the vertical line. The trapped portion of feed solution together with a definite volume of medium, flowing through the valve from a constant head reservoir, is led to the mixing chamber. As the valve makes one complete revolution for each cycle, two volumes each of feed solution and medium are proportioned. Dilutions as high as 1 to 423 were made with this type of unit Kith a n error of less than =tO.5’% . - in the dilution factor. Under automatic operation the rotary valve can stop in any position except that with the plug hole in the vertical position. Although the through” position is someivhat better for stopping, in actual use the microswitch activating the valve was positioned to stop the plug hole a t a 45’
Comparison of Chemical and Polarographic Analysis of O r e Feed Solutions Chemical Polarographic iinalysis ~ ~ ~ 1 :l200 ~Dilution ~ i 1~:400, Dilution
Grams/ Grams/ Error, Grams/ liter Sample Description Liter liter 70 B-5939 Digest feed 165a 179 8.5 174 B-5930 Digest feed 18P 192 4.4 186 1340 141 5 . 2 134 B-5934 Digest feed 220 3 . 8 210 Aqueous feed 212’ C-9040 195* 201 3 1 195 C-9041 Aqueous feed 136 5.4 124 129b Scrap U metal C-94.55 C-9456 Scrap liquors and muds 1536 162 + 5.9 1.56 C-945i Colorado feed 181b 212 tl7.l 204 a Analyzed by tributyl phosphate-oxine colorimetric method (2’. * Analyzed by standard volumetric procedure Kith dichromate ( 1 2 ) . SO.
++ ++ + +
Error, %
+ 5.5 + 01 . 1 - 0.9 0 - 3.9 2 0 +12.T
+
OPENING FOR ELECTRICAL LEADS
l'im
SOLENOID
L ~ G L A s s
I -
250 BEAKER nl
-
BRASS N E O P R E N E -DIAPHRAGM
'\L"ClTE
Figure 3.
Solenoid valve
angle from the horizontal. The valve bypass line has a holdup volume much lcss than that swept through the plug hole by the circulating pump when the plug hole is momentarily in the "samplethrough" position. This position Fyas used to debermine if the holdup volume was efficiently removed and a fresh sample collected. As this holdup volume was found to be eliminated, the volume of diluent in the plug hole during the ''second take" presented no problem. The constant head reservoir is simply a lIariott,e bottle. Not shown in Figure 2 is a line with stopcock leading to the reserroir and used to draw a pnrtinl vacuum before the reservoir is used. Solenoid Valves.
Figure 4.
Wiring diagram for
mechanical operations
A,B,C,D.
Microswitches, activated by lugs on potentiometer drive gear, upper left contacts normally open, upper right normally closed E. Synchronous motor, reversible, 2 r.p.m., drive for potentiometer F. Timer, motor-driven clutch type G,H. latching relays, one half of G contacts not used 1. Synchronous motor, 1 r.p.m., drive for proportioner J. Synchronous motor, 1 r.p.m., drive for cams K,l. Solenoid valves, activated b y cams Ail motors and lotching relays, 60 cycle, 1 15 volts
Solenoid valves
wcre needed t o drain, flush, and refill
the polarographic cell automatically. As the commercially available valves did not meet all requirements, a n appropriate device was designed and cmonstructed following the basic features of the Baird and Tatlock (London) valve and similar t o the valve used by Beckman Instruments, Inc., in the dquameter. The main features of its design, shown in Figure 3, are a small volume holdup and corrosion resistance to dilute sulfuric acid. The body of the valve is constructed of Lucit'e. A circular neoprene diaphrag~n seals the central valve port. The spring action of the solenoid arm maintains a positive seal. When the wlenoid is energized, the diaphragm, \vhich is bonded to the swiveled plunger of the arm, is raised t o allow the solut'ion to flow. The action of the two valves is controlled by cams shown in Figure 4. The cams are adjusted to allow the cell to drain conipletely after the polarographic. measurements, to be flushed nith nhout half of the contents of the mixing c,hamber, and finally to be filled iyit'li the remaining solution in the mixing chamber. Automatic Operation. The halfwave pott.ntial for t,he reduction of uranyl ion in the selected medium is
W
>
3'
1
I 'OOt
4%
20 02
0.4
0.6
0.8
URANIUM
1.0
1.2
1.4
1.8
1.6
CONCENTRATION ( q / l . )
Figure 5. Calibration curves for uranium feed solutions and a pure standard solution Standard uranium solution
0 Feed sample (B-5939) X Feed sample ( 8 - 5 9 3 0 ) A Feed sample ( 8 - 5 9 3 4 )
VOL. 30 NO. 3, MARCH 1958
0
357
approximately -0.5 T olt, os. the mercury pool. The potential a t the peak of the derivative polarogram closely corresponds to this value. To reduce the time for each cyclet h a t is, each uranium determinationthe voltage is scanned from -1.0 to -0.4 volt. At the end of each measurement, the potentiometer returns to its starting position of -1.0 volt. The operation of each mechanical unit in the apparatus is synchronized with the scanning of voltage. The time for each complete cycle is about 5 minutes. The wiring diagram for the mechanical portion of the instrument is given in Figure 4. The sequence of operations can be given as follows, with zero time taken at the start of the voltage scanning: Time, Applied Min- Voltage, Utes Volt 0 -1 0 1.5
-0 5
18
-0 4
3 0
-0 8
3 3
-0 9
3 G
-1 0
5 1
-1 0
Operations Performed Potentiometer drive on, recorder on (Peak of uranium polarogram) Potentiometer reverses, proportioner starts, diluted sample delivered t o mixing chamber Proportioner stops, recorder off, sample drained from polarographic cell Cell flushed and filled with new solution from mixing chamber Potentiometer off for 1 5 minutes Cycle repeats
The stainless steel circulating pump shown in Figure 2 is on continuously during operation. Its purpose is to circulate the solution to be analyzed from the sampling site through the instrument and back. The rate of flow produced by the pump is approximately 4 liters per minute; thus a relatively fresh sample is presented a t all times. The apparatus is set up to analyze either of the tn-o feed solutions shown. RESULTS
Calibration curves for the sulfuric acid-sodium sulfate supporting electrolyte were made with the derivative polarograph in a static cell a t 25' C. with both a standard uranium solution and three plant feed solutions. These curves, shown in Figure 5, indicate that with concentrations of less than 1 gram per liter after dilution a maximum error of =t3.5% due to interferences can be expected for these typical feeds. Above a final concentration of 1 gram per liter, the standard curve and particularly the feed curves fall
358
ANALYTICAL CHEMISTRY
u f -zz
*
V
v)
II
m
N
Figure 6. Recorder trace, automatic operation off badly. Because of this apparent concentration limit, the 10-mv. recorder used in the initial tests was replaced by a 2.5-mv. recorder. Calibration curves, made a t 25" C. and a t room temperature (26.5" C.) with standard uranium solutions having a final concentration of 0 to 0.56 gram per liter, were linear. The dilution factor of the proportioner was determined by means of the 25" C. calibration curve. A solution of uranyl nitrate hexahydrate analyzing 110 grams of uranium per liter by ignition to urano-uranic oxide was analyzed also by automatic operation of the instrument. The average height of 30 consecutive peaks was 122 mm. with a relative standard deviation of 0.5%. This height corresponds to 0.26 gram per liter. The dilution factor is then calculated to be 110/0.26 or 423. Two additional synthetic solutions were made from uranyl nitrate hexahydrate to contain approximately 100 to 200 grams of uranium per liter, and set up for analysis as shown in Figure 2. With proper manipulation of the threeway stopcocks, either solution could be circulated through the system. The drain line from the stopcock above the circulating pump flushes the line with the new solution to minimize any change in concentration in the reservoirs. The solutions were analyzed continuously with repeated changing from one solution to the other. A section of the recorder trace of this test is shown in Figure 6. The flushing of the cell with the new diluted solution appears to be adequate, as no lag in peak height results on changing from one to the other. The temperature of the room and the solutions during this test was 26.5' C.;
therefore, the 26.5" %. calibration curve was used to determine the uranium concentrations. From the average peak heights and the dilution factor of 423, the concentrations were calculated to be 98 and 205 grams per liter. A gravimetric analysis of the solutions gave 98 and 206 grams per liter, respectively, indicating a n accuracy to =k0.5yO for the automatic determination. The precision of the results (including the peaks obtained immediately after changing from one concentration to the other) was nearly identical to that found previously. DISCUSSION
The main source of error in determining the uranium in feed solutions can be related to the type and concentration of impurities in the solutions. Vanadate and molybdate, which interfere seriously, show compound reduction patterns when polarographed separately by conventional methods and the waves are frequently distorted by maxima. Molybdenum apparently interferes by wave coalescence. I n the case of vanadium, however, the reason for the interference is not clear, as no wave for vanadium is found near the half-wave potential of uranium in the medium used. The analyses of the typical feed solutions shown in Table I indicate the accuracy to be expected. With a 1 to 400 dilution, the error ranged between 0 and 12.7y0 for the eight typical feeds analyzed. If the Colorado feed is disregarded as being exceptionally high in vanadium and molybdenum, the maximum error is 5.5%. With separate calibration curves for the Colorado-type feeds as discussed below, the error for this type of feed probably can be kept within this
lower figure. This value does not appear to be excessive for plant use. The error produced by temperature changes in the polarographic cell, approximately 391, per degree, can be eliminated by maintaining adequate temperature control of the diluent and the cell contents. The diluent reservoir is easily kept in a large mater bath equipped with a thermostat. On the other hand, if the cell is immersed in another water bath, a siphon arrangement is required because of the drain line. For a plant instrument a better arrangement for maintaining the cell a t constant temperature would be to use a water-jacketed cell. Water from the reservoir water bath then could be circulated to the polarographic cell. The precision of the method has been s h o m above to be within 0.5y0 (relative standard deviation). The precision (and accuracy) is dependent upon the proper functioning of the proportioning unit. Some minor difficulties with this unit have been experienced. The Teflon plug of the rotary valve has a diameter of approximately 0.63 inch, a length of 1 inch, and a 1 to 10 taper. I n operation it was necessary to use stopcock grease on the plug to ensure a tight seal. If the diameter of the plug is made larger (from 1 to 1.5 inches) and the power of
the drive is increased, a tight seal can probably be made without the use of lubricant, which has to be applied regularly. A single selector valve could be used for changing from one feed solution to another in plant operation. The valve would open a given pair of feed and return lines to the circulating pump and proportioning system within the instrument. With proper design, such a valve might acconimodate four or five pairs of lines to permit sampling of several points in the plant. For plant operation, it would be desirable to include a standard uranium solution in the operational sequence by means of a standard uranium line as one of the multiple lines mentioned above. Solutions of different representative feed samples of known uranium content could be used to obtain specific calibration curves for each type of feed. ACKNOWLEDGMENT
The authors wish to thank A . R. Eberle and W. A. Peavy for the chemical analyses of the feed solutions. LITERATURE CITED
(1) Bisby, H., Brown, L. H., Chapman, D. R., J. Sci. Imtr. 33, 467 (1966).
(2) Eberle, A. R., Lerner, M. \V., ANAL.CHEM.29, 1134 (1957). (3) . , Fisher. D. J.. Kellev. 11. T.. U. S.
Atomic Energy“ ‘ Commission, ORNL-1233, 1 (1951). (4)Ibid., ORNL-1361, 1 (1952). (5) Kelley, M. T., Fisher, D. J., U. S. Atomic Enernv Commission. ORNL-1276, 7 71952). ( 6 ) Kelley, > T., ‘I. Fisher, D. J., Meeks, L. A, Palmer, J. P., U. S. Atomic Energy Commission, ORNL-1423, 1 (1952). (7) Kolthoff, I. AI., Lingane, J. J., “Polarography,” 2nd ed., Vol. I, p. 331, Interscience, Xew York, 1952. (8) Koyama, IC., Michelson, C. E., Alkire, G. J., U. S. Atomic Energy Commission, HW-30148 (1953). (9) . , Leveaue, Lf. P , Roth, F , J . c h m . phis. 46, 480 (1949). ‘ (10) Overton. K. C.. U.K. ~, Lewis. J. 8.. Atomic Energy Authority,’ CRL,/ AE-79 (1951). (11) Michelson, C. E., General Electric communiHanford Works,. private cation. (12) Rodden, C. J., “Analytical Chemistrjof the Manhattan Proiect.” 1st ed , p. 68, McGraw-Hill,’ SenYork, 1950. (13) Rodden, C. J., U. S. Atomic Energy TID-5295, 215 Commission, (1956). RECEIVED for revieiv May 15, 1957. Accepted Kovember 26. 1957. Division of Analytical Chemistry. Beckman ilward Symposium, 131st Meeting, ACS, Miami, Fla., .kpril 1957
Photometric Determination of Chromium in Electronic Nickel C. L. LUKE Bell Telephone luborutories, Inc., Murruy
b A
method for the determination of
0.001 to 0.0270 of chromium in nickel has been developed in which the chromium i s oxidized to the sexivalent state, nickel i s removed b y precipitation as nickel ammonium perchlorate, and the chromate in the filtrate is determined b y the photometric diphenylcarbazide method.
T
of the present investigation has been to develop a suitable method for the determination of chromium in nickel used for the fabrication of electronic devices ( I ) . As the chromium content of such nickel is usually very low, a photometric method was indicated (I). Unsuccessful attempts were made to determine the chromium directly in acid solution without prior separation of the nickel or any of the impurities therein. except HE PURPOSE
Hill, N. J. silicon or tungsten. The photometric dichromate method proved to be too insensitive. The diphenylcarbazide method was found to be sufficiently sensitive, but copper caused low results and no suitable method was found for destroying the permanganate formed during the oxidation of the chromium. Some reduction of the dichromate invariably occurred. ilfethods for isolating the chromium were next considered. An attempt was made to separate it from the bulk of the nickel, cobalt, copper, manganese, and magnesium by precipitating it from ammoniacal solution as chromic hydroxide, using 10 mg. of ferric iron as a coprecipitant. Recovery of the chromium was incomplete. Eventually a successful method of separation was evolved in which copper is removed by dithizone-chloroform extraction, chromium is oxidized to the sexivalent state,
and nickel, cobalt, iron, titanium, and aluminum are removed by an ammonium hydroxide separation-the nickel and cobalt being separated in the form of their difficultly soluble ammonium perchlorate salts. The chromate in the filtrate from this separation is then determined by the diphenylcarbazide method. REAGENTS
Standard Chromium Solution (10 y of chromium per ml.). Dissolve 0.283 gram of Bureau of Standards sample No. 136a of potassium dichromate in water and dilute to 1 liter in a volumetric flask. Dilute 100.0 ml. of this solution t o 1 liter in a volumetric flask. Dithizone Solution. Dissolve 0.5 gram of dithizone-diphenylthiocarbazone-in 500 ml. of chloroform. Keep the solution in a refrigerator when not being used. VOL. 30, NO. 3, M A R C H 1958
a
359
