(7) Cundiff, R. H., Markunas, P. C., Anal. Chirn. ilcta 20,506 (1959). (81 Fritz. J. S..“Acid-Base Titrations in r\Tonaqueous Solvents,” p. 28, G. Frederick Smith Chemical Co., Columbus, Ohio, 1952. (9) Fritz, J. S.,ANAL. CHEx 22, 1028 (1950). (10) Fritz, J. S., Yamamura, S. S., Zbid., 29, 1079 (1957). (11) Gormley, W. T., Spencer, R. D., Tech. Rept. No. 5 , Section VI, Office
of Naval Research, Contract Sonr2693(00), Task No. SR356-407. (12) . , Harlow. G. A.. Brues. D. B.. A N A L . CHEM. 30,‘1833 (i958:. ’ (13) Harlow, G. A., Noble, C. li., Wyld, G. E. A., Zbid., 28,787 (1956). (14) kfarple, L. W., Fritz, J. S.,Ibid., 34, 796 (1962). (15) Peak, D. A., J . Chem. SO?., 1952, 215. (16) Pinner, A., “Die Imidoather und ihre Derivate,” p. 154, Robert Oppen-
heim (Gustav Schmidt), Berlin, Ger many, 1S92. 117) Seaman. IT., Allen, E., ANAL.CHEM. 23, 592, (1951). (18) S.J “Quantitative Organic Analysis via Functional Groups,” p. 104, M-ilel-, Yew York, 1954. RECEIVEDfor review May 14, 1962. rlccepted September 11, 1962. Presented at the Pit,tvburgh Conference on Analytical Chemistry and -4pplied Spectroscopy, March 5-9, 1962.
Instrumentation for the Automatic Simultaneous Measurement of m, t, w, and Drop Count of a Dropping Electrode HELEN
P.
RAAEN and H. C. JONES
Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b Instrumentation i s described that will measure automatically and simultaneously the m, t, w, and drop count (c) of a dropping electrode at any h within the geometric limitations of the standtube-dropping electrode assembly rather than measuring only m at a single fixed h or recording only electrocapillary curves. The significant features are a precision-bore uniform-diameter standtube, a photoelectric mercury-level detecting unit t,iat can be positioned anywhere along the standtube, and the complete separation of the circuitry of the measuring system from the circuitry of the polarographic system. The accuracy and precision of the measurements are shown to be entirely satisfactory for polarographic work.
(Figure 1) are discussed. It consists of a precision-bore constant-diameter standtube, a device for measuring the time of f l o of ~ mercury, ti, from a known segment of the standtube a t any level of mercury, and a drop-counting device. The circuitry of the measuring system has no part in common with the polarographic system and no shock hazard exists. Measurement of t r is the one critical measurement made in the calibration and use of the apparatus. The accuracy and precision of this nieasurement are entirely satisfactory for polaroymphic work. DESIGN
Principle. T h e design of the instrunientation is based on t h e relationships m = k/tt
T
o evaluate dropping-electrode capillaries or to apply the IlkoviE rquation, it is necessary to measure the characteristics of the dropping electrode. The automatic recording of electrocapillary curves was accomplished by k i h a (9). The measurement of t was made automatically and accurately by Corbusier and Gierst ( 1 ) and by Gierst, Bermane, and Corbusier ( 3 ) . Both Lingane ( 5 ) and T s q i (10) have described apparatus for the automatic deteriinnation of only the flon- of mercury, m, a t a single filed height of mercury, I t . The instrunientation described herein has the advantage of meaAuring autoinntically and simultaneously in addition to ~ n the , drop time, f, the drop mass, to, and the drop count, c, a t any level of mercury in the standtube rather than a t a single fixed level. The design, calibration, evaluation, and use of this instrumentation 1594
ANALYTICAL CHEMISTRY
t = t,/c
w
=
k/c
where
m
flow of mercury from the dropping electrode, mg. per second k = standtube constant = niass of niercury contained in the known segment of standtube. mg. t t = time of f l o ~ of mercury from the known segment of standtube, seconds t = drop time, seconds c = drop count = number of drops that form and fall during tt w = drop mass, mg. Lingane’s (5) device for the automatic measurement of m is based on the first relationship. Standtube. The standtube is shown as a part of Figure 1. I t is constructed from precision-bore uniform-diameter =
tubing of 0.07Stj =k 0.0002-inch i.d. and 10-mni. 0x1. The tubing is available on special order from Fischer & Porter Co., Warminster, Pa. The use of precision-bore uniform-diameter tubing makes unnecmsary the determination of the k value at more than one position of the mercury-level detecting unit. To eliniiiiate the cushioning effects and air pockets that are sometimes associated ivit’li flexible tubing connections, the standtube is connected to the mercury reservoir via a Teflon-plugged stopcock and to the dropping electrode via both a Teflon-plugged stopcock and a standard-taper joint. A platinum wire contact is sealed into the standtube to permit grounding of the dropping electrode. The condition of the surface of the inner x i 1 1 of the glass standtube is a significant factor in the precision of the measurement of tt. If the wall of the standtube is wet to any extent by mercury, the mercury tends to cling to the wall and to form an irregular surface rather than a smooth meniscus. hft,er the standtube rvas fabricated, it was rinsed thoroughly with concentrated HSOs, clistilled water, and ethyl alcohol in that order and was dried in air. It Iyas cleaned subsequently in the same way. This treatment leaves t’he glass surface in such condition that it is not wet significantly by mercury. The treatment of the standtube a t any tinie with any cleaning agent that might attack glass, especially a caustic solution, m s avoided. Timing Device. The timing device f Figure 2 ) consists of a mercury-level detecting unit (Figure 3), a timer, and associated circuhy. The mercur?--level detecting unit contains tn-o light source-photocell sets, ~nounted in an aluminum block, that {Till detect the passage of the mercury surface past two points, fixed with respect to each other, on the standtube.
T 115;
-
5RJ -
Model A 3 A +40v
46000s I I -
&,
Clairex
j1;
METAL P-kTE,
Sigma
ac
‘soia No, 30785
Lamp
N.0:
5RJ 46000s
I -
1 1
Figure 2.
Circuit diagram of timing device
I
I ’
,
s c h T?OGEN
I
I
J V I B R A T I O R - T A B L E FREE
I
i Figure 1 . a ssembI y
Sketch of the standtube-dropping electrode
These points define the length of the so-called known segment of the standtube. The photocells are Clairex type CL-3 side-window cells. For the apparatus used, the distance between the two points is about 8.5 em., 3. distance calculated roughly to give a suitable value of t i for the particular diameter of precision-bore tubing used. The mercury-level detecting unit can be moved up and dorm the track provided about the standtube and can be fixed at any position along the standtube b y set screws. The upper photocell actuates a sensitive relay when the mercury falls past the photocell allowing the light to strike the surface of the photocell. The relay starts a timer and, if desired, starts the drop-counting circuit. When the level of mercury falls past the lower photocell, another relay is actuated which stops the timer and shuts off the drop counter. The time of f l o ~of mercury between the two points, t , , is thereby measured automatically. The mercury-level detecting unit is similar to a device described by Farquharson and Kermicle (2). The timer can be used independently
of the mercury-level detector unit. This arrangement is convenient when the standtube constant, k , is being determined, that is, when it is necessary to measure a long interval of time of mercury flow at a constant level of mercury. Drop-Counting Device. The dropcounting device (Figures 4 and 5) is constructed in such a way that a collimated beam of light is interrupted by the drop of mercury as i t grows on the bottom of the capillary. The interrupted light beam falls on a Clairex type CL-3 end-window photocell, which drives a transistor amplifier circuit. A relay in the transistor collector circuit switches power to a Sodeco impulse counter in such a way that one count is registered as each drop falls. The 10-K, 10-turn potentiometer, which shunts the transistor base signal t o ground, is adjusted under operating conditions to give the necessary currents (as indicated on the current meter) for the operation of the relay in the transistor collector circuit. The current must fall below 0.20 ma. as the mercury drop grows and must increase to at least 0.55 ma. when the drop falls.
Figure 3. Detail drawing of mercurylevel detecting unit The sensitivity of the drop-counting circuit can be adjusted by means of the 10-K, 10-turn potentiometer. This adjustable sensitivity makes possible the use of a water-jacketed cell if necessary. The counter can be turned on and off automatically b y the timing circuit or i t can be operated independently of the timing circuit. VOL 34, NO. 12, NOVEMBER 1962
1595
tamp
145v ac
lamp
Z4E
I I
Figure 4.
Circuit diagram of drop-counting device
CALIBRATION
Calibration of the apparatus consists in determining the value of t h e standtube constant, k . Either of two procedures can be used. The procedure recommended by Lingane ( 5 ) is to determine m in the usual way, that is, by collecting the mercury that falls from the capillary over any measured time interval, t, (longer than t,) during which interval the height of mercury, h, is kept constant. The weight of the mercury collected, w,, is determined. The time of flow of mercury from the known segment of standtube (t,) is then measured automatically with the timing device (the midpoint between the photocells ofthe detector unit is set a t the same h). The value of k is calculated from t h e relationship 12 = (w,t,)/t, = mtc The procedure described by llilner (7) is to collect and determine the weight
Figure 5.
1596
of mercury, w,, delivered from the capillary as the mercury flows from the known segment of standtube during the time, t t , the standtube being closed off from the mercury reservoir during this time; w m is then taken to be k . The procedure recommended by Lingane, although longer, is preferred and was used in this work because the collection of the mercury for a longer time results in more precise and accurate measurements of t , and w,,,, and thereby of k . Also, when the procedure described by Milner is used under conditions that cause the drop time, 1, to be large-e.g., when h is small or the capillary orifice is large-the precision and accuracy of the measurements of w, will be decreased. This decrease occurs because the instants of the automatic starting and stopping of the timer will not necessarily be synchronized with the instants of fall of the terminal drops, that is, the activation
Detail drawing of drop detector
ANALYTICAL CHEMISTRY
or deactivation of the timer may occur a t some instant during the growth oi the drop. The k value for the particular standtube used was determined by allowing the mercury to fall from a Sargent S-29419 "2-5 see" 7-micron-diameter glass capillarv into nitrogen-deaerated 0.1MKCl. The temperature of the O.1M KC1, T , ranged from 24.0' to 26.0' C.; the temperature of the air a t the level of mercury in the standtube. 8, ranged from 23.8' to 27.4" C. The mercury !vas collected with an apgaratus of the type described by Lingane and Kolthoff ( 6 ) except that the cup n-as cjlindrical rather than funnel - shaped. The collected mercury 1% as n ashed with distilled water and acetone, air-dried, and weighed. The value for k was established from the data given in Table I. The precision and accuracy of the measurement of k are related directly to the precision and accuracy of the measurement of t , , discussed below. The precision is ewellent; it is somewhat better than that reported by Lingane for the measurement of the k of his apparatus ( 6 ) . The accuracy appears to be excellent also. the calculated value for k at 24.5" C., based on the specified diameter of the precisionbore tubing and the measured distance between the two sets of light bulbphotocell units, was 3.590 grams. The data of Table I confirm tbe fact that k need be determined a t only one height of mercury if the standtube is constructed of precision-bore tubing. EVALUATION
Precision and Accuracy of Measurement of t,. The measurement of t t is the one critical measurement t h a t is made with the instrumentation, both when k is determined and when a dropping electrode is characterized b y establishing the values of m, t , and w. It was desirable to determine the precision of this measurement independently of the formation and fall of mercury drops, that is, to determine the precision of the operation of the timing device only. It thus becomes possible to distinguish imprecision in the behavior of a capillary from imprecision in the functioning of the timing device. 1 throttling capillary, suggested by D. J. Fisher, and a vacuum arrangement to prevent back pressure a t the exit orifice of the capillary were used in determining the precision of the measurement of t t (Figure 6). The capillary was identical with that used in determining k except for the modification a t the exit orifice. The mercury was thus allowed to flow freely and continuously from the standtube through a capillary rather than to drop from a capillary. With a prototype apparatus and under conditions equivalent t o t s 5 seconds, the results of six automatic measurements of t t , each a t 25" C., were: it = 514.4 seconds and 5' = 0.26 second or 0.05%. With the apparatus
Table I. h , mni
Data Taken in Establishing the Value of
4so
se: l99i 4
813
1165.5
1145
823.9
Table II.
sec 3071 6 3096,l 3327.5 2735.2 2774.6 1599.2 2362.4
'1,
Precision of the Measurement of t t
h, cm.0 115
S b 10
48
11
it, sec.
780 2000
S,
7;
0.22 0 16
b = h at the midpoint of the mercurp!eve1 detecting unit. 'I' = number of measurements. Table 111.
Run 1
2 3
4 5
Precision of Measurement of t a t -0.40 Volt
sec. 4.036 4.040 4 038 4 03s 4 038 1,
Run
I
t , sec 4.040 4 038
h
4 038
fi $1
10
4 035 4 038
t, 4 038
s,%, 0 029
in its final form, the precision was rechecked a t two values of i but with less control of temperature; the data are given in Table 11. The precision of the t t measurement is entirely satisfactory for polarographic work. The precision is decreased if the inner wall of the standtube is wet by mercury or if it is irregular because, in either case, the mercury may cling irregularly to the wall as it flou-s from the standtube. Both these difficulties were encountered with a staiidtube that contained sealedin tungsten wire contacts as a means of defining the known segment of tubing. The accuracy of the measurement of t t is a function of the accuracy of the timer and the response times of the light bulb-photocell detector units, which include the relays. The Precision Scientific Co. "Time-It" timer was used; i t registers tenths of a second, The accuracy of the timer was checked against a calibrated stopwatch and found t o be satisfactory. The responsr times of the relays were measured and were found to be much smaller than the smallest time unit measured by the timer. Precision of Measurement of t at Negative Applied Potential. It was of interest t o know with what precision t h e drop time t of a dropping electrode
W m , g.
5 5212
5.5670 5.9960 8 ,4437 8.5415 6.9680 10.3031
-0 STANDTUBE
k
t
k , g. 3 5903 3.5913 3.5993 3.5884 3.5880 3.5899 3.5933 Av. 3.5915 s,yo,0.11
a t negative applied potential could be measured when t h e drop counter and timer were used independently of t h e mercury-level detecting unit. T h e instrumentation is used in this way t o obtain electrocapillary-curve d a t a . The terms precision aiid accuracy are not applicable to the operation of the drop-counting device, because it must count each drop that forms and falls. The conditions under which the precision of the measurement of t was determined IT ere as follows : capillary, Sargent S-29419 *'2-5 sec." of 7i-microndiameter orifice ; medium, nitrogendeaerated 0.1.11 KCl; T , 25" + 0 5" C.; reference electrode, mercury pool; source of applied potential, O R S L model Q-l98&11 controlled-potential derivative polarograph; potentiometer, Rubicon 0 - to 1.61-volt range; applied potential, -0.40 volt; and 12, constant at 646 mm. The t value was determined by measuring the total time required for 100 drops to form and fall and dividing that total time by 100. Tlie drops were counted automatically, and the time was measured automatically. The data are given in Table 111. The precision is excellent. Measurement of t h e Influence of Potential of the Dropping Electrode on m, t , W , and r n 2 V ' 6 . T h e instrumentation wab evaluated more extensively by using it to measure t h e influence of the potential of the dropping electrode on nz, t , w, and m* 3 t l 6 over the range of applied potential from 0 t o -1.60 volts. K i t h the folloning exceptions, the conditions 11ere the
Table IV.
Figure 6. Sketch of the throttlingcapillary apparatus used to determine the precision of ths t t measurement
same as those defined for the data of Table 111: range of T , 23.8" to 26.0' C.; range of 0,24.8" to 27.9" C.; and position of mercury-level detector unit, E , 646 mm. The condensed data are given in Table IV; the values of t. m, and w are weighted averages over some 8.5 cni. The data are consistent with those obtained for a glass-capillary droppingmercury electrode in 0.1M KCl by more laborious methods (4) and are entirely satisfactory. The electrocapillary curve and the plot of negative applied potential us. m 2 W 6 have the proper shaues and maxima (4). USE
The instrumentation was designed primarily to facilitate the characterization aiid evaluation of Teflon dropping electrodes for which purpose i t is being used satisfactorily t o make a large number of measurements of m, 1, w
Influence of the Potential of the Dropping Electrode on f, rn, w, and 2 /3f1/6
Applied potential, v. 0
-0.20 -0 40 --O
50
-0.56 -0.60 -0.80 -1.00 -1.20 -1.40 -1.60
m?/3t116
1, sec.
3.52 3.92 4.10 4 11 4.10 4 on 4.01 3.89 3 .68 3,41
3.08
m, mg./sec. 2.464 2.453
2.455 2.455 2.449 2.455
2.456 2.457 2.462 2.462 2.466
w ,mg. 8.654 9.577 10.06 10.12 10.06 10.06 9,840 9.577 9.069 8.391 7,577
rng.%ec.-1/a
2.248 2.284 2.302 2.304 2.300 2.302 2.294 2.284 2.267 2.238 2.201
VCL. 34, NO. 12, NOVEMBER 1962
1597
and c. It is of general value in determining automatically, simultaneously, and rapidly certain of the data needed in fundamental polarographic studies and practical polarographic analyses. Siirnberg (8)has suggested : “This new device enables one to record quickly the electrocapillary curve simultaneously with a polarogram. This seems of major importance for the investigation of adsorption and inhibition problems, which are one of the main fields of electrochemical research in this decade.” ACKNOWLEDGMENT
This work was done under the supervision of P. F. Thomason and D . J. Fisher. John Farquharson provided the
sets of detectors and the track for the mercury-level detecting unit and advised regarding use of the unit. V.L. illaddox assisted in the fabrication of the apparatus. The illustrations mere prepared by B. S. Dunlap. The very valuable help of these persons is gratefully acknowledged. LITERATURE CITED
(1) Corbusier, P., Gierst, L., Anal. Chim. Acta 15, 254 (1956). (2) Farquharson, J., Kermicle, H. A,, Rev. Sci. Instr. 28, 324 (1957).
(3) Gierst, L., Bermane, D., Corbusier, P., Contributi teorici e Sperimentali d i Polaroarafia Vol. IT ~,
ography,”’2nd ed., V;l. I; p. 88, Interscience, New York, 1952.
(5) Lingane, J. J., IND.ESG.CHEM., ANAL.ED.16,329 (1944). (6) Lingane, J. J., Kolthoff, I. M., J . Am. Chem. SOC.61, 525 11939); esp. pp. 829-30 and Figure 4. (7) Milner, G. R. C.. “The Principles and Applications of Polarography.” p. 97, Longmans, Green and Co., Yew York, 1957. (8) Xurnberg, H. W.) Kernforschungsanlane Julich, German\.: communi- private . ca:tion, 1962. (9) Riha, J., “Advances in Polarography,” I. 8. Lonzmuir. ed.. n. 210. Vol. 1. Pergamon Tress,’ Xev,. i’ork, 1960. (10) Tsuji, IC,, Sci. Papers Znst. Phys. Chem. Res. ( T o k y o ) 54, No. 2, 223 (1960). RECEIVED for review July 18, 1962. ilccepted September 20, 1962. Oak Ridge National Laboratory is operated by Union Carbide Corp. for the .itomic Energy Commission.
The Q ua nt it a tive Se pa ration of PI utonium from Various Ions by Anion Excha nge IVAN K. KRESSIN and GLENN R. WATERBURY 10s Alarnos Scientific laboratory, University of California, 10s Alamos, N. M. b The anion exchange resin separation of plutonium has been investigated as a possible technique for the rapid quantitative separation of plutonium from various metal ions. A slurrycolumn technique provides satisfactory separation of plutonium from quite a large number of metal ions. In this method, plutoniurn(1V) is adsorbed from 7.2M nitric acid onto Dowex 1 x2 resin, and the other metal ions are washed from the column with nitric acid of this same strength. Then the plutonium is eluted with a 0.36M hydrochloric-0.0 1 M hydrofluoric acid mixture. The separation is rapid and permits an average recovery of 1 OO.OO~o of the plutonium with a standard deviation of 0.048% for known solutions, Of the 46 diverse ions investigated, only silicon reduced the recovery of the plutonium below 99.9%. Applications of this separation to various methods of analysis of plutonium-containing materials are discussed.
S
IN~ESTIGATIOSS of anion exchange resin separations of plutonium from various ions have been reported (1-7>9-16, 18). I n general these methods involve the adsorption of plutonium(1V) onto basic anion exchangers such as Dowex 1, or less frequently, Dowex 2 (18) from solutions not less than 6114 in nitric acid ( 1 , 4, 7 , 12-16) or hydrochloric acid (2, 3, 5, 8, 9, 11,18). -21~0the adsorption and elution EVERAL
1598
0
ANALYTICAL CHEMISTRY
behaviors of many other metals ions on Dowex 1 from hydrochloric acid (8) and nitric acid (4) solutions of various strengths have been reported, thus making possible the selection of the most advantageous system for a particular separation. Of these systems, the adsorption of plutonium from 6 to 8 X nitric acid onto Dowex 1 anion exchange resin reportedly is applicable to a wider range of materials,-a consequence, no doubt, of plutonium(1V) forming a highly stable anion complex in nitric acid solutions of these concentrations whereas most other metal ions do not. Investigations of this separation have been reported ( 2 , 4, 7 ) in which the metals were determined spectrochemically. However, in spite of the apparent applicability of the separation, no comprehensive investigation of the quantitative nature of this method for separating plutonium has been reported. Data giving the recoveries of plutonium following separation from various ions, and the dispositions of these ions, would permit applications of the separation method in many fields of chemistry. Several applications to analytical chemistry problems immediately are obvious in the determination of plutonium and various elements in plutonium-containing materials. The goal of the present investigation Tvas to obtain data showing the reliability of the separation of plutonium from many other ions. T o accomplish this goal efficiently, the most favorable conditions, such as
type of resin, loading solutions, and eluents, \%-eredetermined experimentally or selected according to the recommendations of past investigators. Once these \%-ereestablished, a procedure was developed for handling known solutions, and quantitative data were obtained. It is recognized that the plutonium recoveries and other data apply specifically to separations performed under conditions similar to those described. Horn-ever, the separation is sufficiently insensitive to small changes in conditions and procedure that minor modifications may be tolerated. The investigation of the separation of plutonium from 46 other ions is described here. Data showing the average recoveries of plutonium. as determined by a precise titrimetric method ( l 7 ) , are presented for each separation. In several cases, data also are presented to show the disposition of some metal ions of specific interest. A continuation of this investigation is anticipated as the need develops for information concerning separations of plutonium from other metals. EXPERIMENTAL
Special Apparatus and Reagents.
ASION EXCHASGE RESIN, Dowex 1, 2% cross-linked, 100 to 200 mesh. An analytical reagent grade of this resin was obtained from BioRad Laboratories, Richmond, Calif. The resin, received in the chloride form, was mashed in a fritted-glass funnel
