greater than 140 mg. of uranium. I n this work constancy is attained for 70 mg. of uranium. Figure 2 shows that proportionality is obtained from 10 mg. of uranium (the smallest amount tested) to higher values in the area where the visual titration showed anomalies. It must be emphasized that if the visual titration is carried out with a n indicator and under the same concentration conditions used in the potentiometric titration, the disproportionalities are observed equally and are not related to differences in concentration. Constant
Current Potentiometry.
This study was made t o apply potentiometric dichromate titrations t o dilute solutions of uranium (2, 7 ) . Preliminary tests showed a great sensitivity in dilute solutions equal or similar to that for the visual titrations. At such dilutions classic potentiometry cannot be applied as shown before. The values mentioned earlier for intensity of current and electrode surface (see Instrumentation) were adopted after varying the intensity (1 to 45 pa.) and the surface (1 to 96 sq. mm.) within
wide ranges. Those values were adopted
as the best because they yielded appreciable potentiometric increases (300 to 350 mv.) and well defined characteristic peaks for this type of potentiometry (Figure 3). The reproducibility and proportionality of the method for conditions equal to those for the visual titrations of uranium using a lead column as reducing agent ( 1 ) were studied. The standard deviation was 10.017 for eight deProterminations with : 16.79 ml. portionality was attained from about 20 mg. of uranium (Figure 4); with lower amounts the values were erratic. ACKNOWLEDGMENT
The author is deeply indebted to Reinaldo Vanossi for his counsel and advice during the present work.
(3) De Sesa, R l , First Conf. Anal. Chem.
Nuclear Reactor Technology, Gatlinburg, Tenn. (1957); U. S. Atomic Energy Comm. Rept. TID-7555, p. 58 (4) Kolthoff, I., Lingane, J., J. Am. Chem. SOC.55, 1871 (1933). (5) Kolthoff, I., Sarver, L., Zbrd., 5 2 , 4179 (1930). (6) Lingane, J., “Electroanalytical Chemistry,” p. 70, Interscience, New York, 1953. (7) Reilley, C., Cooke, W., Furman, S . ANAL. CHEM.23, 1223 (1951). (8) Rodden, C. J., “Analytical Chemistry of the Manhattan Project,” p. 582, McGraw-Hill, New York, 1950. (9) Rodden, C. J., ‘(FirBt Conf. Anal.
Nuclear Reactor Technology, Gatlinburg, Tenn. (1957); U. S. Atomic Energy Comm. Rept. TID-7555, p. 25 (10) Sarver. L., Kolthoff, I., J . Am. Chem. SOC.53,2902, 2906 (1931). (11) Swinehart, B. A., Second Conf.
Anal. Chem. Nuclear Reactor Technology, Gatlinburg, Tenn. (1958); E. S. Atomic Energy Comm. Rept.
LITERATURE CITED
TID-7568, p. 117. (12) U. S. Atomic Energy Comm, New Brunswick Laboratory, Manual of Analytical Methods for the Determination
(1) Cooke, W.,Hazel, F., McNabb, \V , ANAL.CHEM.22, 654 (1950). (2) Delahay, P., “New Instrumental Methods in Electrochemistry,” p. 256, Interscience, New York, 1954.
RECEIVEDfor review March 1, 1961. Accepted September 26, 1961. Sesiones Qufmicas Argentinas, Tucumh, Argentina, September 21, 1960.
of Uranium and Thorium in their Ores.
Cation Exchange Separation of Metal Ions with Hydrobromic Acid JAMES S. FRITZ and BARBARA 8. GARRALDA Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa
b Mercury(ll), bismuth(lll), and cadmium(l1) can be separated from most other metal cations by elution from a 16-cm. cation exchange column with 0.3 to 0.5M hydrobromic acid. Using different concentrations of hydrobromic acid, eluents ranging from 0.1 to 0.6M, mercury(ll), bismuth(lll), cadmium(ll), and lead(ll) can b e separated from each other and from other metal ions.
I
instances, the complexing effect of halogen acids has been used to elute metal ions selectively from a cation exchange column. A comprehensive paper on elution of metal ions with hydrofluoric acid has appeared (2). Kallmann, Oberthin, and Liu (3) have developed a very selective method for cadmium(I1) by elution with hydriodic acid. Yoshino and Kojima (5) and later Strelow (4) separated cadmium(I1) from zinc(I1) and other metal ions using a cation exchange column with 0.5M hydrochloric acid as the eluting agent. This separation depends largely N SEVERAL
102
ANALYTICAL CHEMISTRY
on the formationof cadmium(I1) chloride complexes, because a 0.5Af hydrogen ion concentration is not sufficient to elute a divalent metal ion in a reasonable time by the mass action effect. I n the present work, mercury(II), bismuth (111), cadmium( 11), tin(1V) , and lead(I1) are eluted from a cation exchange column with dilute solutions of hydrobromic acid. These elements can be separated from most other metal ions. Furthermore, by varying the concentration of hydrobromic acid eluent, i t is possible to separate mercury(11), bismuth (111), cadmium (11), and lead(I1) from each other. EXPERIMENTAL
I o n Exchange Resin. Dowex 5OVX8 cation exchange resin of 100- to
200-mesh is used. T h e commercial resin must be purified before using. This is done by placing t h e resin in a large column, backwashing with water t o remove any fine particles, and washing with 10% ammonium citrate (pH 3.0 to 3.3, 3 N HCl, and finally water until a negative chloride test is obtained with silver nitrate. The purified resin
is in the hydrogen form. It is removed from the column and air-dried. I o n Exchange Column. Conventional, 12-mm. i.d. glass columns are used. T o prepare the column, pour a slurry of resin and water into t h e column until the bed has a height of 16 em. Add t h e eluent dropwise with a flow rate of about 2 ml. per minute from a 125-ml. cylindrical separatory funnel inserted in the top of the column through a one-holed rubber stopper. The dropwise addition prevents disturbance of the resin bed. PROCEDURE
Make 0.05M solutions of the metal salts. The salts used are the nitrates, perchlorates, or chlorides, with the exception of vanadium(IV), which is the sulfate. Take aliquots of the salt solutions containing the desired amount of each metal ion. The column load should usually not exceed 0.5 mmole of metal ions. Adjust the sample volume to 25 ml. with water. Load the sample onto the column dropwise. Rinse the column with 20 ml. of water. Elute with the hydrobromic acid, collecting the eluent. Use slightly more than the minimum volume of
Table 1.
Elution of Individual Metal Ions from 1.2 X 16 Cm. Dowex 50W-X8 Cation Exchange Column Using 0.5M HBr 0 . 5 M HBr, 131. 0.5M HBr, M1.
Breakthrough
Metal Ion
>200 80 >200
~ 1 + 3
Au + l
Ba +2 Be +2 Bi + 3 Ca + 2
140
c o +2 Cr + 3 c u +2 DYc:" Fe Fe +3 Ga +a
22 K +1
Elution complete
0-10 >200
>200
>200
...
>200 >200 >200 >200 180 >200 >200 >200
... ...
100 0-10
Sc+3 Sn + 4 Sr +2 Th + 4 Ti + 4 UOZ+* VO +2 y13
60
0-10 >200 20 >200 >200 >200 >200 >200 >200 >200 0-10 >200 0-10
Breakthrough
Pb +2 Sb + 3
>200
60
Cd +2
Metal Ion Ka +1 S i +2
Elution complete
...
100 ...
...
...
... ... ...
40
Zn +z z r ~4
...
...
240
120
140
...
>200 ... ... ...
Figure 2. Profile curve of Bi+8-Cd+2 separation
40
>200
vu 30
...
...
effluent necessary for separation, as indicated by Tables I and 11. When removal of the element(s) eluted by hydrobromic acid is complete, rinse the column with 20 ml. of water and strip the remaining element($ from the column with nitric, hydrofluoric, or hydrochloric acid (see Table 111). Evaporate the hydrobromic acid effluents to approximately 50 ml., add 5 ml. of concentrated nitric acid, and evaporate to approximately 1.5 ml. If Hi is Present, evaporate almost t o
400-7-
'
1 1 1 2
~
1
8- 250-LL
l
W
u
-
,200-
0
dryness. Dilute with water to about 150 ml. and determine the amount of metal ion present by titration with E D T A as outlined in Table 111. The Hg elutions are neutralized rather than evaporated to prevent volatilization. DISTRIBUTION COEFFICIENTS AND COLUMN ELUTIONS
Hydrobromic acid, rather than hydrochloric acid, n-as selected for eluting metal ions from a cation e.;change column because in general metal-bromide complexes are more stable than the corresponding chloride complexes. Values listed b y Bjerrum, fichmarzenbach, and Sillen (1) bear this out for the halide complexes of bismuth, cadmium, and lead. Zinc, copper(II), and many other metal ions either do not form complexes under the conditions employed, or the complexes are so weak t h a t there is little difference in their elution with hydrochloric or hydrobromic acid. Iodide complexes of mercury(II), bismuth(III), cadmium(II), and Iead(1I) are stronger than either
the chloride or bromide complexes. However, the use of iodide introduces the possibility of oxidation-reduction side reactions and disturbing precipitations in some cases. I n Figure 1, the distribution coefficients of several metal ions are plotted as a function of hydrobromic or hydrochloric acid concentration. The fact that the distribution coefficients for cadmium(I1) and lead(I1) are lower in hydrobromic than in hydrochloric acid confirms the fact that the bromide complexes are more stable than the chloride complexes. The distribution coefficients for manganese(I1) and zinc(II), although not plotted for both acids, are about the same in hydrochloric as in hydrobromic acid. Conditions for elution can be predicted approximately from a distribution coefficient plot such as shown in Figure 1. The distribution coefficient curves for mercury(I1) and bisniuth(II1) both fall below the cadmium curve. Cadmium(1I) should be eluted quantitatively but some\?-hatslowly n i t h 0.3M hydrobromic acid, but elution with 0.4 or 0.5JI hydrobromic acid should be more rapid. From the distribution coefficients, elution of lead(I1) with about 0.6JI hydrobromic acid should provide a separation from zinc, manganese, and other metal ions.
3
m
E 150-
i
m D
Table II. Elution of Individual Ions from 1.2 X I6 cm. Dowex 50W-X8 Cation Exchange Columns with HBr
100 -
Hg +2 50
0.
I
0
0.2
03
'.._ Cd-204 M of H B r
-0
- - - \-
05
HBr BreakConcn., through, 31 ml. HBr I 0.6
Figure 1. Distribution coefficients with Dowex 50W-X8 resin
0.1 0.2 0.3
0.4 0.5 0.6 a
0-10 0-10
0-10 ... 0-10
0-10
Bi +3 Elution
Breakcorn- through, plete ml. HBr 60 a0 60 40
20 0-10
40
0-10 0-10 0-10
... 20
Cd +2
Elution complete 220 120
60 60
60 40
Breakthrough, ml. HBr
>zoo
160
80 20 20 0-10
Pb +2 Elu-
tion complete .,.
Breakthrough, ml. HBr ...
380 200 120 100 80
>id0 180 100 60
Elution complete ... ... ,200
240 240 140a
40"
Excess lead precipitated with HBr prior to column loading.
VOL. 34, NO. 1, JANUARY 1962
e
103
Table 111.
Metal Ions Bi + 3 c o +2
Ion Amounts, Mmoles 0.25 2.50 0.25 5.00
Quantitative Separations on 1.2 X 16 Cm. Dowex 50W-X8 Cation Exchange Columns
Eluent M1.
Titration Method Direct Direct
IndicatoI X Or XA
Titrations of Ions, EDTA or EDTA Eq. Column Diff ., Theory elutions ml. 4.43 2 k O . 00 4.43 52.87 -0.02 52.89 +0.01 4.43 4.44 105.75 $0.63 105.78 13.27 -0.01 13.28 f0.03 15.81 15.84 +0.04 22.15 22.19 5.27 f0.00 5.27 4.43 f0.00 4.43 -0.01 5.59 5.58
X Or KAS
PH 1-3 5 1-3 5 1-3 5 1-3 5 1-3 5
Direct Direct
X Or NAS
1-3 5
8.08 44.72
8.05 44.73
+0.01
0.321l HBr 3.OM "03
Direct Direct
X Or P Vlt
1-3 5
8.08 38.66
8.10 38.63
$ 0 , 02
200
200
0.3M HBr 1.OM H F
Direct Direct
X Or P Vlt
1-3 3-3.5
44.36 51.33
44.38 51.36
+o. 02 f0.03
0.25 0.25
100 100
0.3M HBr 1.O M H F
Direct Direct
X Or Erio T
1-3 10
4.43 5.55
4.43 5.54
1 0 .00 -0.01
Bi + 3 Ni +2
0.45 4.50
140 200
0.3M HBr 1 ,OM HCl
Direct Direct
X Or P Vlt
1-3 8
8.08 44.94
8.08 44.99
10.00 $0.05
Bi + 3 Ni + 2
0.25 0.25
150
0 . 3 M HBr 2.OM HC1
Direct Direct
X Or P Vlt
1-3 8
4.43 5.62
4.46 5.61
+0.03
100
Bi + 3
2.50 2.50
200 200
0 . 3 M HBr 2.OM HC1
Direct Direct
X Or Erio T
1-3
Pb +2
10
44.36 57.23
44.33 57.21
-0.03 -0.02
Bi + 3 Th
2.50 2.50
200 0.3211 HBr No stripping done
Direct
X Or
1-3
44.36
44.34
-0.02
Bi + 3
uoz+2
0.25 0.25
100
0 . 5 M HBr 2M HC1
Direct Redox
X Or
1.5
150
5.00 8.67
5.00 8.71
+ O , 04
B
0.25 0.25
100 150
0 . 5 M HBr 2.0211 HC1
Direct B( Zn +2)
X Or NAS
1.5 6
5.00
4.99
-0.01
Bi + 3 Zn + 2
0.25 0.25
150
100
0 . 5 M HBr 2 . OM HC1
Direct Direct
X Or NAS
1.5 6
4.00 5.12
5.00 5.15
+0.03
Bi + 3 Zr + 4
2.50 2.50
200 250
0.124 H F
0.3M HBr
Direct B(Bi+3)B
X Or X Or
1-3 1-3
44.36 56.08
44.37 56.07
$0.01 -0.01
Cd +l c o +2
0.25 0.25
220 250
0.3111 HBr 1.011.1HC1
Direct Direct
KAS NA
7 5
5.50 5.27
5.50 5.26
f0.00 -0.01
Cd t 2
0.25 2.50
220 300
1.OM HC1
0.3M HBr
Direct Direct
NAS NA
7 5
5.50 52.89
5.53 52.90
$0.01
0.25
0 . 3 M HBr 1.O M HC1
0.75 0.75 1.25 0.25
80 300 80 300 180 200 200 200
0.25 0.25
100 150
0 . 3 M HBr 2.0M Hh'Os
Direct Direct Direct Direct Direct Direct Direct Direct
Bi + 3 c u +2
0.45 4.50
140 200
0.3M HBr 3.0M "03
Bi + 3 Fe t 3
0.45 4.50
140 200
Bi + 3 Ga + 3
2.50 2.50
Bi + 3 Mn +2
Bi + 3 c o +2 Bi + 3 c o +2 Bi + 3 c o +2 Bi + 3 c u +2
+3
vo
+2
co +2
0.3M HBr 1.O M HC1 0.3dI HBr 1 ,OM HC1 0.3M HBr
1. O M HC1
X Or XA
X Or WA X Or
KA
...
...
-0.03 -0.03
-0.01
f0.00
...
2ko.00
$0.03
co + z
160 300
0.3M HBr 1.OM HC1
Direct Direct
NAS NA
7 5
5.50
5.0
I105.28
5.53 105.39
$0.03 $0.11
Cd +2 c o +2
1.25 0.25
200 150
0 . 3 M HBr 1.OM HC1
Direct Direct
X AS NA
7 5
27.51 5.27
27.56 5.27
+0.05
Cd + 2 c u +2
0.25 0.25
220 150
0 . 3 M HBr 2,Oh!f "03
Direct Direct
KAS NAS
7 5
5.50 5.58
5.51 5.60
$0.02
Cd +2 c u +2
0.45 4.50
240 200
0.3M HBr 3 . OM HXOa
Direct Direct
NAS NAS
7 5
9.90 44.72
9.95 44.73
$0.05
Cd + 2 c u +2
0.25 0.25
140 150
0.5M HBr 2 , OM HC1
Direct Direct
NAS NAS
6 6
5.00 5.17
4.99 5.17
f0.00
Cd + 2 Fe + 3
0.25 0.25
220 200
0.3M HBr 1.OM HC1
Direct Direct
N AS P Vlt
7 5-6
5.50 4.83
5.51 4.84
+0.01 $0.01
Cd+2 Fe + 3
0.45 4.50
240 200
0.3211 HBr 3 ,0211 "0s
Direct Direct
SAS P Vlt
5-6
7
9.90 38.66
9.92 38.69
+0.02 +0.03
Cd+2
0.25 0.25
220 200
0 . 3 M HBr 1.OM HC1
Direct B( Mn+Z)o
NAS Erio T
7 10
5.50 5.80
5.81
5.50
f0.00 +0.01
Cd + 2
vo
+2
f0.00
$0.01 +O.Ol
-0.01
Erio T. Eriochrome Black T. NA. Naphthyl Azoxine. NAS. 7-( 6-Sulfo-2-naphthylazo)-8-hydroxyquinoline5-sulfonic (Continued) acid. P Vlt. Pyrocatechol Violet. X Or. Xylenol Orange. TMK. Thio-Michler's ketone.
104
ANALYTICAL CHEMISTRY
Table 111.
Metal Ions Cd +2 1'0
Cd +2 Zn +2
Cd +2 Zn + 2 Cd +2 Zn +2
Hg+i" Bi c o +Z Hg + 2 Cd+2 Cu +z
Ion Amounts, Mmole 0.25 0.25 0.25 0.25
140 150 140 150
0 . 5 M HBr 2 . OM HC1 0 . 5 M HBr 2 , O M HCl
0.25 0.25 0.45 4.50 0.25 0.25 0.25 0.25 0.25 0.25
220 200 240 200 120 150 200 120 250 150
0.3M HBr 1 . O X HC1 0 . 3 M HBr 1 .OM HC1 0.12M HBr 0.3M HBr 1 .O M HC1 0.12M HBr 0.5M HBr 2 , O M "03
M1.
Eluent
Titration Method Direct B(Zn +%) Direct Direct Direct Direct Direct Direct Yanolb Direct Direct Vanolb Direct Direct
(Confinued)
Indicator NAS NAS KAS NAS
PH 6
NAS X Or
Titration of Ions, EDTA or EDTA Eq. Column Diff., Theory elutions ml. 5.00 5.01 $0.01
6
...
...
6
5.00 5.12
5.04 5.14
7 5 7 5 5-7 1-3 5 5-7 7 5 3 5
5.50 5.24 9.90 41.95 4.86 5.16 5.27 4.86 5.50 5.20 5.22 5.20
5.48 5.25 9.91 41.96 4 85 5.15 5.28
6
1;AS X Or TRIK X Or I i-4
TRIK sAS -1'AS X Or NAS
Sn + 4 0.25 200 0.5M HBr B(Th Cu +z 0.25 150 2 , O M HSOa Direct Sn + 4 0.25 200 0 . 5 X HBr B(Th+4)a X Or 3 5 22 Fe+3 0.25 200 1.O M HC1 Direct P Vlt 5-6 4.71 0 Back-titration of excess EDTA with ion in parentheses. * Titration with Thiovanol (1-mercaptoglycerol). +4)5
Table IV.
Ion Amounts, Ions Mmole M1. Hgf2 0.25 70
...
4-0.04
-+0.02
-0.02
+ O . 01
$0.01 $0.01 -0.01
-0.01 $0.01
+o. 02 $0.01 -t0.01
4.88 5.51 5.21 5.23 5.19
-t0.01 -0.01
5.23 4.73
-to. 02
$0.01
Separation of Five-Component Mixture on Cation Exchange Column
Eluent 0.1M HBr
Bi+3 Cdf2
Titration Method Vanolo
0.25 100 0 . 2 M HBr Direct 0.25 100 0.3M HBr Direct Pb+2 0.25 200 0 . 6 M HBr Direct Cu +2 0.25 100 2 , OM " 0 8 Direct 4 Titration with Thiovanol (1-mercaptoglycerol).
Batch distribution coefficients vary somewhat with the loading of the resin. Although small variations in loading will not greatly affect the distribution coefficient, the distribution coefficient for heavily loaded resin will be significantly lower than for the case where a t equilibrium the metal ion loading of the resin is low. The distribution coefficients in Figure 1 are for a ratio of initial metal ion to resin capacity of approximately 0.20 mmole per 1.0 gram. I n Table I, data are given for elution of individual metal ions from a 16 X 1.2 cation exchange column (H+form) with 0.5M hydrobromic acid. These data, which were obtained by testing fractions of column effluent for the presence of the metal ion, indicate that 140 ml. or less of 0.554 hydrobromic acid is sufficient to elute Bi(III), Cd(II), Hg(II), Mo(VI), Sb(III), and Sn(IV) completely. Except for Pb(I1) and a few others, metal ions studied failed to break through in the first 200 ml. of effluent. In an effort to increase the selectivity of elution, similar elutions on individual metal ions were carried out with more
Indicator ThioMichler's ketone X Or NAS Erio T NAS
PH 5-7
Buffer Pyridine
1-3 7 10 6
Acetate Pyridine
dilute hydrobromic acid. These data, summarized in Table 11, indicate the possibility of separating mercury(II), bismuth(lII), and hadmium(I1) from each other as Ivell as from other metal ions. For several elements, profile elution curves were obtained by collecting fractions and determining the metal content of each. An example is shown in Figure 2. These profile curves show that there is essentially no tailing of bands. Figure 2 also shows that the elution behavior of mixtures closely approximates the behavior predicted from elution of the individual elements. Elution of tin(1V) caused difficulty a t first. Tin(1V) was a t least partially eluted by 0.5M hydrobromic acid, but the profile curve was erratic and unsymmetrical. This difficulty was finally avoided by rinsing the column with 0.5M hydrobromic acid (instead of with water) before adding the tin(1V) sample, which was also in approximately 0.5X hydrobromic acid. If the acid medium becomes too dilute, apparently some hydrolysis to basic tin salts occurs. Using 0.4N hydro-
3"
Pyridine
Titration of Ions, EDTA or EDTA Eq. Column Diff., Theory elutions ml. 4.42 4.42 10.00 5.11 4.98 5.01 5.30
5.10 4.99 5.03 5.30
-0.01 $0.01 $0.02 +O.OO
bromic acid, a poor and erratic profile curve was obtained for tin(IV), even n-ith a preliminary acid rinse of the column. Lead(I1) can be eluted with 0.534 hydrobromic acid, b u t the elution is slow. Elution with 0.6N hydrobromic acid is much faster and is quantitative. h precipitate (presumably lead bromide) appears on the column during the elution, but is gradually dissolved. If the amount of lead present is small, no precipitation occurs and the elution of lead with 0.6M hydrobromic acid is more rapid. Precipitation of lead(I1) on the column can be avoided by precipitating part of the lead as lead bromide and filtering before adding the sample to the column. The separation of lead(I1) from other elements by hydrobromic acid elution 11-ill be the subject of a later study. Bismuth(II1) will precipitate on the column if added from a water solution. With the solution 0.531 in nitric acid as the loading solution, very little precipitation occurs. Any precipitate that does occur dissolves readily. lIercury(I1) will also precipitate on VOL. 34, NO. 1, JANUARY 1962
105
the column, but rapidly dissolves during elution. QUANTITATIVE COLUMN SEPARATIONS
The study of the elution behavior of individual metal ions (see Table I) indicates that mercury(II), bismuth (111), cadmium(II), and tin(1V) should be separated easily from most of the other metal ions studied. Quantitative data for actual separations using 0.3 or 0.5M hydrobromic acid are reported in Table 111. For samples containing tin(IV), pretreatment of the column by rinsing with 20 ml. of 0.5M hydrobromic acid was required for a satisfactory separation. Although most separations have been carried out on samples containing ap-
proximately equal amounts of each constituent, the separation is also successful for samples that contain a large excess of one particular element. Data are reported in Table 111. The elution of bismuth or cadmium is speeded up slightly in cases where a large excess of another element uses up a significant fraction of the column capacity. Quantitative separation of mercury (11), bismuth(III), and cadmium(I1) from each other as well as from other elements has been accomplished. Lead(11) can be separated from a t least some elements by elution with 0.6M hydrobromic acid. I n Table IV, the successful separation and analysis of a five-component mixture is reported. In this separation, the lead was not precipitated before adding the mixture to the column.
ACKNOWLEDGMENT
K e thank Richard Greene for checking some of the separations experimentally. LITERATURE CITED
(1) Bjerrum,
J., Schwarzenbach, G., Sillen, L. G., "Stability Constants," Part 11, Chemical Society, London, 1958. (2) Fritz, J. S., Garralda, B. B., Karraker, S.K., ANAL.&EM. 33, 882 (1961). (3) Kallmann, S., Oberthin, H., Liu, R., Ibid., 32, 58 (1960). (4) Strelow, F. W. E., Ibid., 32, 363 (1 960) , - - - - I .
(5) Toshino, Y., Kojima, RI., Bunseki Kagaku 4, 311 (1955).
RECEIVEDfor review August 28, 1961. Accepted November 13, 1961. Cqntribution 1067. Work performed in the Ames Laboratory, U. S. Atomic Energy Commission.
Polarimetric Determination of Boric Acid with Tartaric Acid KAZUNOBU KODAMA and HAZIME SHllO Nagoya Municipal Indosfrial Research lnsfifufe, Afsvfa-Kv, Nagoya, lapan
b A polarimetric method for the semimicrodetermination of boron utilizes the mutation of optical rotation of tartaric acid solutions after addition of boric acid. The effect of pH was examined; the optimum value is 4.10 to 4.1 5. Various polyvalent cations and anions interfered, but silica did not. To test the practical applicability of the method, tile glaze was analyzed.
T
mutation of optical rotation of various organic compounds by the addition of boric acid m s discovered more than 100 years ago, but it has recrired little attention from inorganic analytical chemists. Rosenheim and Leyser (4) determined less than 30 mg. of boric acid in 10 ml. of 0.5X tartaric acid solution, using a 22-cm. tube with a sensitivity of 0.25 mg. per 0.01" optical rotation. Rochelle salt could not be substituted for tartaric acid. *4slight interference from sodium chloride and sulfate and a serious one from nitrate were noted. A borax solution was neutralized with 0.1N hydrochloric acid to the methyl red end point and a correction for the sodium chloride formed was made. The error was as much as 10% for 30 to 50 mg. of boric acid in the borax solution. Sciarra and Zapotocky (5) found that the effect of boric acid on the rotation of tartaric acid was most pronounced in RE
106 *
ANALYTICAL CHEMISTRY
various organic compounds. The results with tartaric acid were much the same as those obtained by Rosenheim and Leyser. The pH effects were not studied. I n our previous paper (3) a polarimetric determination of boron with mannitol mas proposed.
To a 10.00-ml. solution containing less than 25 mg. of boron as borax was added 1.0 gram of mannitol with stirring. After 3 hours, 2.0 grams of sodium hydroxide was added, and the solution was stirred and cooled. The number of milligrams of boron, X , is calculated by an equation, -VI = 4.81 9 . 4 4 ~ ~ 0 . 1 5 9 ~(10" ~ ~ C.), where CY is the optical rotation angle in a IO-em. cell. The standard deviation was mg. and the sensitivity 0.1 mg. per 0.01 .
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The difference in optical rotation of a mannitol solution and a solution containing both mannitol and borax increased with increasing alkalinity and became nearly constant over a concentration of lhr in sodium hydroxide. The value was 10% lower when optical rotation was measured immediately after the addition of sodium hydroxide. When mannitol was added after sodium hydroxide, the value immediately after the addition was about one third that of the final value, two thirds after one day, and it took as long as one week to reach the final value, which coincided with that of the solution prepared by the
standard method. A break in a calilration curve was seen near the point where the mole ratio of mannitol to boric acid n-as 2.4 to 1 under the above conditions or when the amount of mannitol was half the above value. Silicate, tungstate, and aluminum ions interfered seriously. Molybdate, vanadate, chromate, and zinc ions had little effect. S o interference was found from fluoride, chloride, sulfate, nitrate, and phosphate. h white precipitate appeared when fluoride or phosphate n-as present in the above solution, but the optical rotation of the supernatant fluid v a s measured successfully. While this paper n as in preparation, a similar method vias reported by DeFord, Blonder, and Braman ( 2 ) . They used a n ammoniacal mannitol solution or a solution of mannitol in 0.6-11 sodium hydroxide and measured optical rotation promptly after mixing Jvith a sample solution. Their method is about one sixth as sensitive as ours. The age of the solution and the order of addition of reagents are important in the mannitol method. I n the present study tartaric acid was used and the effect of p H was studied in detail because it forms a dextrorotatory compound, H3B032C4H608,with boric acid and a levorotatory complex in basic solution, as reported by Darmois (1). The method proved to be superior to that with mannitol as reagent be-
