each absorbance was measured in the spectrophotometer in quadruplicate. The mean values of each concentration %-ere used in plotting the standard curve. The standard deviation depends on the concentration, and the simplest relationship was found to give the standard deviation proportional to the square root of the concentration. s t d . dev. = 0.015
4
where c = concentration of vanadium (+nil.) in the solvent phase. Coefficient of variation
=
-.
= C
1.j
4;cc
The use of this formula gives the standard deviation within the various ranges of concentration shown in Table
I. The recovery of vanadium in pure solutions was quantitative in the electrolytic and carbamate separations, while the over-all recovery of vanadium added t o plant material n-as on the order of 95%. DISCUSSION
Although this procedure is less sensitive than t h a t involving the polarographic determination of vanadium, it is quicker, especially when a large number of samples must be handled. Being less sensitive, the proposed method has the disadvantages of longer digestion time, because larger samples are needed, and of the possibility of
Table 1. Coefficient of Variation within Various Ranges of Concentration of Vanadium in Solvent Phase
V, -,,hIl. _ _ 0 2 t o 1 1 to 2 2 to 3 3 t o 10
Coefficient of Variation, yG of Meal: ~ 3 1.5 1 0 5
having to measure the absorbance in very small volumes of solvent in a microcuvette. However, the procedure permits the determination of as little as 0.2 y of vanadium in plant materials in laboratories where a polaropraph is not available. Slight contamination of the plant material b y soil can give erroneous results because the ratio of soil vanadium to plant vanadium is very high. Titanium, likewise, occurs in much higher concentration in soil than in plants; the presence of this metal therefore affords a check for soil contamination. The titanium content of the sample can readily be gaged in this method from its peroxy color remaining in the aqueous phase after e-itracting vanadium with dithiocarbnmate into chloroform. The method for plants can also be applied to the acid extracts of soils. but requires modification to the estent of removing the silica by treatment with hydrofluoric acid, partially renioving iron by a preliminary elec-
trolysis, extracting the vanadium and any residual iron, and, finally, removing the last traces of iron by a second electrolysis in a solution of reduced acidity and salinity. ACKNOWLEDGMENT
Grateful acknowledgment is made to H. R. Marston of the Division of Biochemistry and General Sutrition, C.S.I.R.O., and E. R. Davies of the S e w Zealand Department of Agriculture for their stimulating interest and encouragement, to A. T. James of the Division of Mathematical Statistics, C.S.I.R.O., for the statistical analysis, and Murray Childs for preparing the figures. LITERATURE CITED
(1) Bode, H., 2. anal. Chem. 142, 414 (1954). (2) Compaan, H., Nature 180, 4593 (1957). 1 3 ) Cozzi. D.. Rasai. G.. Anal. Chim. . ~ 17,590 ~ t (i957j. ~ (4) Das Gupta, A. K., Singh, 11. &I.,J . Sci. & Znd. Research (Zndza) 11B, 268 (1952). ( 5 62,320 ) Gleu, (1950). K., Schwab, R., Angew. Chem I
,
(6) Jones. G. B.. Anal. Chznz. Acta 17, ’
254 (1957).
( 7 ) Malissa, H., Schoffmann, E., 31zkrochim. Acta 1955, 187. ( 8 ) Rooney, R. C., Anal. Chim. Acta 19, 428 (1958i. (9) Wise, 15. M., Brandt, W,IT.. .;liva~. CHEN.27, 1392 (1955).
RECEIVEDfor reviex November 1058. Accepted May 11, 1959.
21,
Polarography of Uranium(1V) in Noncomplexing and Complexing Media Amperometric Determination of Fluoride DAVID J. McEWEN and THOMAS De VRlES Department o f Chemistry, Purdue Universify, lafayefte, Ind.
b The polarography of uranim(1V)has been studied. The effect of pH on the half-wave potential of the anodic wave has been determined in noncomplexing (perchlorate, chloride, and sulfanilate-buffered) and complexing (formate, acetate, and monochloroacetate) media. The diffusion current constants of uranium(IV) in formate, acetate, and monochloroacetate buffers were found to be 2.67, 2.17, and 1.93, respectively. With the anodic wave used to detect the end point, an amperometric method for
determining fluoride in formate buffer of pH 3.6 i s given, for which the fluoride to uranium ratio is 2. From 0.04 to 2.2 mg. of fluoride have been determined.
I
the polarography of uranium has been studied quite extensively, and some important works have been reviewed (10, 1 7 ) . One of the least studied is the wave for the oxidation of uranium(1V) to uraniuni(V) which has a half-wave potential of about 0 volt us. the S.C.E. in weakly N RECENT YEARS
acidic solutions (11, 1 2 ) . Xarshall (14) studied the wave in conjunction with the reaction between uranium(V1) and (IV) to form uranium(V) in carbonate media. However, the m a e has been investigated in some detail only by Tishkoff (19, 21. 33), rvho determined the factors that influence the half-tyave potential in chloride and in acetate- and carbonate-buffered supporting electrolytes. S o n e of these researchers studied the relationship betveen the diffusion current and uranium(1V) concentration. VOL. 31,
NO. 8,
AUGUST 1959
1347
This paper reports the study of the uranium(1V) anodic wave and its use in the amperometric determination of fluoride with uranium(1T) ,
/E
EXPERIMENTAL
I
Apparatus. All polarograms n ere obtained with a Sargent Model XXI recording polarograph. Except where otherwise indicated, currents were measured a t 25’ C. with no condenser damping in t h e cell circuit, and maximum values of id were used in calculating diffusion current constants,
I
=
id/Cm213tl/6 =
Uranium reagent was uranous perchlorate containing some uranyl perchlorate
708nDll2,
A study was made of the effect of condenser damping a t setting No. 1 on the polarograph upon the ratio of the average current to the maximum current vhich is theoretically 0.857. Because the pen of the recording potentiometer had a relatively slow full-scale deflection time (about 10 seconds), a slow drop time (5.60 seconds) TTas used in determining this ratio experimentally. The solutions used were uranjl chloride, or perchlorate, in 0.1M potassium chloride, or sodium perchlorate, and lead nitrate in 0.1X potassium nitrate as supporting electrolyte. Ratios of 0.80 to 0.82 were obtained. Taylor. Smith, and Cooter ( I S ) also obtained such ratios using a cathode-ray oscillograph, galvanometer oscillograph, and Polaroanalyzer. The voltage scan was positive to negative in most cases, but in a few experiments the voltage was scanned in the opposite direction. The same capillary vias used for all experiments. The m and t values of 1.350 mg. per second and 5.6 seconds per drop ( r n 2 W / 6 = 1.63) a t -0.5 volt us. S.C.E. in the formate buffer, p H 3.70 (Table 11),are typical for the capillary. All polarographic solutions were deoxygenated with nitrogen gas purified by scrubbing with vanadium(I1) sulfate solutions (16). A maximum suppressor
Figure 1. Polarographic spectrum of uranium in 0.1M sulfanilate buffer0.1M sodium perchlorate, pH 3.1
-1.5
E
vc.
S.C.E.,volts
3.2, ranb--ig in total fluoride coilcentration from 0.0001 t o 0 . 3 M , and were stored in polyethylene bottlrs. The potassium fluoride and hydrofluoric acid solutions used to prepare these buffers !$-ere standardized by a lead chlorofluoride gravimetric method (3). Uranium(1V) chloride and perchlorate solutions were prepared by electrolytic reduction of the uranyl salts, which xere made up by tivice evaporating a solution of uranyl acetate dihydrate with an excess of the corresponding acids. The uranium(1Vj solutions, about 0.012M, were standardized with potassium dichromate (16) and stored in sealed burets ( I S ) . Preliminary studies on the polarography of uranium Tvere made in buffer solutions of the acids listed in Table I. These buffers were prepared by mixing the proper amount of acid and potassium hydroxide solution. A modified Henderson equation (J), log [salt]/ [acid] = p H - pK 0.505 p 1 f 2 , n a s used to calculate the concentration of acid and base required. For dibasic acids the factor is 1.515 for the last term of the equation. The p K values of the acids and the moles of acid and potassium hydroxide per liter of solution are listed in Table I. The glycine buffer was prepared by using 0.045M Table I. Results of Polarography of Uranium in Variolus Buffers glycine, 0.05OM sodium perchlorate, and 0.005M perchloric acid per liter. E, 2 The phenylacetic acid was purified Concn., X Oxid. 1-T by vacuum distillation and 2-furoic .kCld pH .kcid KOH State pK S C.1;. Sotesa acid, by vacuum sublimation; succinic p-Toluene 2 1 0 100 0 086 VI -0 13 IT-(1 Composite and sulfanilic acids were recrystallized sulfonic \\ ave separates into t n o M-CI from hot water and dried a t room temperature under vacuum, and mandelic acid was recrystallized from benzene Glj cine 2 8 See text VI 2 33 -0 19 1 ciry w-d reversible and dried a t room temperature under IV $0 11’ n-d T rrv n-d Mandelic 3 0 0 181 0 100 trI -0 22 mcuum. The remaining acids were IV $0 14 i-(I, maximum on used as obtained from stock and nere wave reagent or purified grades. 3 . 7 0.255 0.200 VI 3.37 -0.26 Very w-d Fumaric 3 . 3 0.098 0.88 VI 3 03 -0 3 i-d RESULTS 4.47 IV s.R. Noncomplexing Media. T h e study 2-Furoic 3 . 3 0.150 0.100 VI 3.16 -0.3 i-ti IV S.R. of t h e polarography of uranium(1V) Salicylic 3 . 3 0.068 0.050 VI 2.97 -0.3 i-d shou-ed t h a t perchlorate, chloride, IV X.R. and sulfanilate-buffered solutions beSuccinic 3 . 5 0.610 0.098 VI 4.19 -0.34 Fairly w-d, slight have essentially as noncomplexing 557 maximum IV $0.1 i-d media. Although it has been reported 2-Chloro3 . 7 0.66 0.300 IV 4.06 N.R. t h a t chloride ions complex with urapropionic nium(1V) ( I ) , Kritchevsky and Hinda w-d, well-defined wave; i-d, ill-defined wave; N.R., no wave obtained. man (12) found that the half-wave potential of uranium(1V) cathodic wave 1348
ANALYTICAL CHEMISTRY
was not required in the study of uranium(1V) waves. Cell and Reference Anode. A saturated calomel reference anode similar t o t h a t described b y Hume and Harris (8) vas used m-ith satisfactory results, except that a platinum screen sealed at the end of the glass tubing of the salt bridge to hold the saturated potassium chloride-agar gel in place was highly desirable. Constant residual currents, even for 2 to 3 hours, rTere obtained only when the salt bridge dipped into a compartment separated from the polarographic solution by a fritted-glass disk. The over-all resistance of the cell circuit was of the order of 500 to 700 ohms. All p H measurements were made with a glass electrode and Leeds &Northrup p H meter. Reagents. All stock and polarographic solutions were prepared using viater doubly distilled, once from potassium permanganate solution. Unless otherwise stated, all reagents were reagent grade. Fluoride stock solutions were prepared in t h e form of buffers of p H
+
compound. Such a n evplanation has 30r-----l also been given by Kritchevsky and
:+.It v)
W
1 K I
!
i 2
I
1 3
! 4
CH
Figure 2. Dependence of of U(IV) anodic wave on pH in noncornplexing media 0 A
--_
0.1M sulfanilate buffer, 0.1M sodium perchlorate 0 . 2 M perchloric acid 0.2M perchloric acid, 0.1M sodium perchlorate Tishkoff's d a t a in chloride media
is unaffected when the chloride iron concentration in the supporting electrolyte is increased from 0.05 to 3.0-IF. Sulfanilic acid is about the only buffer medium of pH range 3 to 4 which does not noticeably complex a n y of the oxidation states of uranium ( 8 ) . Figure 1 shons a polarogram of uranium as obtained in sulfanilatebuffered supporting electrolyte, and indicates all of the polarographic waves of uranium except the uranium(II1) to (IV) anodic wave and the uranium(II1) to (0) reduction wave reported b y Heal ( 6 ) . Waves A and G represent the oxidation of mercury and reduction of hydrogen ions, respectively, while curve H represents the residual current of the supporting electrolyte. Waves B to F indicate the oxidation and reduction waves of uranium, which are: B , uranium(1V) anodic wave; C, uranium(Y)to (VI); D,uranium(V1) to (Y); and F,uranium(Il*) to (111). Wave B gave a log plot with a slope of 40 mv., in poor agreement with the theoretical value of 59 or 30 for a 1or 2-electron reversible transfer reaction, respectively. However, the proximity of wave C made examination of wave B difficult. Waves C and D gave a slope value of 60 mv., in good agreement with the theoretical value of 59 for a I-electron reversible transfer reaction (9). Kaves E and F gave slope values of 70 and 90 mv., respectively, indicating some irreversible character of these two reduction steps. K a v e E has been shown to be irreversible (6, 6, 1 2 ) ; however, the irreversibility of wave F is probably due to the hydrolysis of the uranium(1V) ( l a ) , in the weakly acidic supporting electrolyte,
Hindman (12) for some effects which they observed for uranium(1V) solutions. The dependence of the half-v,-ave potential of the uranium(1V) anodic wave ( B ) on the pH of the supporting electrolyte is slionn in Figure 2. The equation for the dependence of the halfwave potential on pH is El = e 0.059 (p,'n)pH, in n hich E approximates E", and p and n are the number of hydrogen ions and electrons, respectively, that are in1 olved in the electrode process. The slope of the solid line is i 120 mv., in good agreement with the theoretical value of 118 n hen p equal> I I I 1 I ] 2 and n equals 1. These data agree t0.2 -0.2 -0.6 -1.0 n ell with those obtained b y Tishkoff E va.S.C,E., volts (dashed line) (19) 17-110 used a chloride supporting electrolyte. Figure 3. Polarographic waves of Complexing Media. A preliminary U(IV) and (VI) chlorides in 0.2M acetate study of a number of n e a k organic buffer, pH 5.1 acids as buffers shoned t h a t t h e uranium n a v e s are best defined in supporting electrolytes of formate, acetate, and monochloroacetate buffers, a n d studies of t h e uranium(IV) waves were confined to 0.2 t o 0.5;l.i solutions of these buffers (Table I). There vas little difference in t h e shape of the uranium waves in the three buffers selected and so the uranium(1V) and (VI) waves obtained in the acetate buffer (Figure 3) are representatire of the others. Wave n is the uranium(V1) cathodic wave, b is the uranium(T-) cathodic wave, and c is the uranium(IV) anodic wave. Because waves u :ind b merge n-ith increasing uranium concentration, no diffusion current stud+0.08 ies were made using these waves. A 3 4 5 PH similar merging effect n a s obtained in formate buffer a t p H 3.7. Figure 4. Dependence of El,, of The dependence of the half-wave U(IV) anodic wave on pH in cornpotential of the uranium(1V) anodic plexing media wave on the p H of each of the three 0 Formate buffers is shown in Figure 4. The two A Acetate solid lines represent opposite directions V Chloroacetate - - - Tishkoff's data using 0.05M acetate of scanning the KaT-e, and the true Eliz buffer would probably be represented by a O p e n figures indicate voltage scan was line midway bet\\-een these tlyo, if the negative to positive; solid figures, voltage difference is due to a lag in the recorder. scan positive to negative The slope of the line is 100 mv., in fair agreement with the theoretical value of 118 when p / n equals 2. The as the uranium(1V) to (111) couple results obtained by Tishkoff (19, 21) in has been shown to be reversible (6, 9, acetate media are in good agreement 12). with the results indicated by the solid Studies of the relationship between figures in Figure 4,for which the direcuranium concentration and diffusion tion of polarization rras the same. current could not be made in sulfanilate Studies were not made in this ryork of buffer because the total height of the structure of the uranium complexes waves B, C, and D slowly decreased formed in these buffers. Tishkoff (21) with time. Even if the uranium(V1) and Tishkoff and Sunier (23) have and (IV) concentrations were changing listed structures of the various combecause of the formation or disproporplexes of uranium(VI), (V), and (IV) tionation of uranium(V), the total height formed in acetate media. As similar or waves B, C, and D should remain half-wave potentials for the uraniumconstant (11). This decrease in wave height was thought to be due to a slow (IV) anodic wave are obtained in forhydrolysis of the uranium to a n insoluble mate, acetate, or monochloroacetate VOL. 31,
NO. 8,
AUGUST 1959
1349
a4
-
Figure 6.
E
I .o
0.5
0
Titration curves
-
of 2.5 X 10-jM fluoride
-
0 Formate, p H 3.6
-
@
in buffers Acetate, pH 5.0 Monochloraacetate, p H 3.5
I .5
U/ F
1.0 1.5 2,O U(iv)Concn., m M Figure 5. Diffusion current of U(IV) anodic wave in buffers
0.5
1.
2. 3. 4.
Formate Acetate Monochloroacetate, fluoride present Monachloroacetate, fluoride absent
buffers, it is reasonable to assume that complexes with comparable stability constants are formed in these buffers. Good linear relationships between diffusion current and concentration of uranium(1V) chloride \-cere obtained in formate and acetate buffers, as shown by lines 1 and 2 in Figure 5 . A linear relationship was not obtained in 0.5.M monochloroacetate buffer alone (curve 4), but mas obtained when sodium fluoride was present (line 3). The data for this curve were obtained by adding increasing amounts of uranium(1V) solution to 21 ml. of the buffer containing 0.030 mmole of fluoride ion (1 ml. of 0.030M sodium fluoride was used) until a total of 0.070 mmole had been added. The fluoride to uranium ratio was found to be 2.0 (Table IV) and was required in calculating the net concenTable 11.
Diffusion Current Constants of Uranium(IV)
Buffer pH Formate 3 7 Acetate 5 1 Chloroacetate 3 5 a Fluoride preeent.
U( IV) Concn., mJl
I
1 5 1 0
2 6i 2 17
0 9
1 93a
Table 111.
Buffer Chloroacetate Formate
Formate Acetate 1350 *
Analysis of Uranium(1V) Anodic W a v e
PH
Concn., X -4cid KOH
3 3 4 5
0 0 0 0
5 7 3 1
tration of uranium(1V) which is shown in Figure 5 . KOprecipitation occurred. The reason for the nonlinearity is not readily apparent but i t could be due to changes in the uranium(1T’)-monochloroacetate complex as the uranium concentration increases. Table I1 lists the values of the diffusion current constants obtained for uranium(1V) chloride in these buffers. The constants were greatest in formate, less in acetate, and least in monochloroacetate buffer. A qualitative explanation is that the molecular weights of the uranium coniplexes increase in that order and the viscosities of the solutions also increase as one goes from formate to acetate to monochloroacetate buffer of the same concentration. I n general, the diffusion current constant for uranium(1V) perchlorate was slightly greater than for the chloride but the difference is not significant. An analysis of the uranium(1T’) anodic wave in these three buffers by plotting log i/(ia- i) against E gave, in each case, a plot of two straight lines intersecting approximately a t the halfwave potential. Table I11 lists the values of the slopes. The fact that this wave changes slope approximately a t the half-wave potential suggests that the wave is made up of tvio waves very close together, much the same as the situation observed with the uranium(V) to (111) composite cathodic wave. Thus, the uranium(1V) anodic n a v e in these buffers is probably made up of two wives, uranium(1V) to (V) and uranium(V) to (VI). These observations, plus the values obtained for the diffusion current constants, suggest that the value of n is greater than 1, and may approach the value of 2. I n acetate
58 367 344 268
ANALYTICAL CHEMISTRY
0 0 0 0
500 200 300 200
’Iof i
c(Iv),
Acid
mM
2 86 3 75 3 75 4 76
0 0 0 0
80 91 77 87
Slope, ~ v . iid/2 11 19 21 31
22 24 27 40
media, Tishkoff (10) obtained a value for the slope of the anodic wave of about 90 mv. (in poor agreement with the authors’ values) and concluded that the electron change was 1. Amperometric Determination of Fluoride. Quadrivalent uranium has been proposed several times as a reagent for determining fluoride. Hess (7) and Flatt (W), and more recently Vogel (sd), titrimetrically determined fluoride as potassium uranium fluoride, detecting the end point potentiometrically. However, the end point is difficult t o establish because of the sluggishness of the U(VI)/U(IV) couple to establish a n equilibrium potential a t a platinum electrode. Tishkoff (20, 221 proposed an amperometric method using a uranyl salt and detecting the end point with the nitrate catalytic wave. Although the method is quite sensitive to small concentrations of fluoride, the end point is not sharp because of the current contributions of the uranyl cathodic wave, with the result that the current increments change from linear to exponential at the end point. I n preliminary work toward amperometric determination of fluoride with uranium(IV), the uranium(1V) cathodic wave was first investigated as a means of establishing the end point. However, unlike the uranium(1V) anodic wave, the cathodic wave n-as found to become ill-defined when fluoride mas present and merged with the terminal wave. The use of the cathodic wave is therefore not recommended. Study of the uranium(1V) anodic wave in formate, acetate, and monochloroacetate buffers indicated that fluoride did not appreciably affect the well-defined characteristics of the Tvave. Therefore, a number of titrations were performed in each buffer, titrating the fluoride with uranium(1V) chloride or perchlorate, For 0.012V uranium chloride as titrant, the solution was prepared with 0.15-11 hydrochloric acid and 0.8M potassium chloride; for the 0.01251 uranium perchlorate. 0.1M perchloric acid ]-cas also present in the solution. From 0.04 to 2.2 mg. of fluoride were added to 20 ml. of the appropriate buffer, For titrations made in for-
mate a i d monochloroacetate buffers of p H 3.5 to 3.7, the current readings became constant in a fen- minutes, and increased linearly with increasing uranium(1V) concentration after one mole of uranium(1T’) had been added for every t m moles of fluoride present (Figure 6 and Table IV). For eight determinations, fluoride to uranium ratios of 1.8 to 2.1 were obtained, with an average of 1.93. Hence, the error may be as large as &lo%. I n formate buffers of pH 4.2, however, 10s- results uere obtained for the fluoride to uranium ratio, and it appears that on the addition of fluoride the uranium-formate complex changes appreciably. I n the acetate buffer, the results were qomewhat disturbing. At a pH of 4.1, fluoride to uranium ratios of 1.6 m-ere obtained. K h e n t h e pH was increased to 5.0, the ratio increased to 4 or even 5 and occasionally to 6. The current readings became constant after longer intervals and led to the rejection of the acetate buffer as a suitable supporting clectrolyte. The recommended procedure for determining fluoride is as follows.
from the solution because of the ease of uranium(1V) oxidation. Small amounts of chloride or sulfate will not interfere seriously by shifting the niercuric anodic wave to more negative potential values, but large amounts should be avoided. The main advantage of this method is that very few n-aves interfere with the uranium(1V) anodic TTave and a fluoride to uranium ratio of 2 is obtained. Otherwise. the method is not superior to existing amperometric methods for fluoride.
Twenty milliliters of formate buffer. 0.211.1 and p H 3.5 to 3.7, are pipetted into a polarographic cell. After deoxygenation of the solution b)- bubbling of nitrogen, the fluoride in the solution is titrated with uranium(1V) chloride or perchlorate. After each addition of reagent, the solution is stirred and :illowed to stand a few minutes until the current readings become constant. The diffusion current is measured a t about +0.10 to SO.15 volt (US. S.C.E.) and is corrected for residual current and for dilution of the polarographic solution by the titrant,
naissance de l’Uranium,” Cniversity of Paris, Imprimerie Mulhousienne, 1936. (8) Hume, D. X., Harris, IT. E., IND. ESG. CHEV., .%SAL. ED. 15,465 (1943). (9) Kern, D. 11. H., Orlemann, E. F., J . d r n Chem. SOC.71, 2102 (1949). (10) Kolthoff, I. RI., Lingane, J. J., “Polarography,” 2nd ed., pp. 462-7, Interscience, SeTv York, 1952. (11) Kraus, IC. .I.,Selson, F., J . Am.
Even though the oxygen wave does not interfere with the uranium(1V) anodic wave, oyygen must be removed
Table IV.
Concn. of Buffer,
Titration of Fluoride with Uranium(IV)
JI
riH
0 2
3 3 3 4 4
F--Idded, 1Ig.
F,V Ratio
Formate
0 3
5 6 7 2 2
0 0 0 0 0
46 27 46 34 51
2 1 2 1 1
0 8 1 3 4
LIonochloroacetate
LITERATURE CITED
(1) Day, R. a.,Wilhite, R . X., Hamilton, F. D., J . Am. Chem. SOC.77, 3180 (1955). (2) Flatt, R., Helu. Chim. Acta 20, 894 (1937); Angew. Chem. 50, 329 (1937). (3) Furman, N. H., ed., “Standard llethods of Chemical Analysis,” 5th ed., p. 405, Iran Sostrand, Sen- Tork, 1939. (4) Glasstone, S., “Electrochemistry of Solutions,” p. 210, hlethuen, London, 1930. (5) Harris, W.E., Kolthoff, I. 11 , J . d m . Chem. SOC.67, 1484 (1945). (6) Heal, H. G., Trans. Faradau SOC. 45, 1 (1949).(( (7) Hess, IT.> Contribution de la Con-
Chem. SOC.71, 2517 (1949). (12) Kritchevskr, E:. S.,Hindman, J. C., Ibid., 71, 2096 (1949). (13) McEn-en, D. J., De S-ries, Thomas, .%SAL. CHEW30, 1889 (1958). (14) Marshall. E. D., TJ.S.Atomic Energy Commission Document AECD 3289 fdeclassified Dec 21. 1951). f l 5 ) Meites, L., Meites, T.. ASAL CHEN. 20, 984 (1948). (16) Rodden, C. J., ed , “Lhalx-tical
Ahetate n 2
4.1 ~~
5.0 5.0 5.1
0.51 0.44 1.24 0.51
1.6 3.9 5.0 4.0
Chemistry of the Manhattan Project,” NSES, Div. VIII, p. 68, McGraw-Hill, New Tork, 1950. (17) Ibid., pp. 596-610. (18) Taylor, J. K., Smith, R . E., Cooter,
I. L., J . Research A-atl. Bur. Standards
42, 387 (1949). (19) Tishkoff, G. H., “Physico-chemical Mechanisms of Uranium Transport in the Body,” Ph.D. thesis, University of Rochester, 1951. (20) Tishkoff, G. H., E.S. A4tomicEnergy Commission Document M 1719. (21) Voegtlin, C., Hodge, H. C . , eds.,
“Pharmacology and Toxicology of Uranium Compounds,” NSES, Div. 1-1, Vol. 1, pp. 102-46. PIIcGraw-Hill, Nen-
York. 1948. (22) Ibid., pp. 184-90. (23) Ibid., pp. 1124-38. (24) Vogel, K,, Silikat Tech. 4,483 (1953).
RECEIVEDfor review October 27, 1958. .Iccepted April 20, 1959. Abstracted in part from the thesis submitted by D. J. McEn-en for the Ph.D. degree in chemistry, Purdue University, Lafayette, Ind.
Amperometric Titration of Barium H. E. ZITTEL, F. J. MILLER, and
P. F. THOMASON
Analytical Chemisfry Division, Oak Ridge Nafional Iaborafory, Oak Ridge, Tenn.
,An amperometric titration of barium in a medium of tetraethylammonium bromide in an ethyl alcohol-water solution is described. Lithium sulfate is the titrant and the dropping mercury electrode is the indicator electrode. The method is similar to that first described by Heyrovski and Berezicky but differs in the medium and supporting electrolyte. Because of these modifications, the sensitivity of the method is greatly increased. It was possible to titrate solutions that were 5 X 10-5M in bar-
ium with reasonable accuracy. The accuracy varies from less than 1% error in the concentrated samples-i.e., >2.5 X 10-3M-to less than 10% error in the more dilute samples-i.e.,
x
