dicted from the potential limits in Figure 9. The electrode reaction which would take place in the absence of halide may outcompete the electrode reaction involving a small concentration of halide ions, and useful end points are obtained. Removal of halides b y precipitation n i t h silver ion cannot be applied because silver ions are reduced b y metallic mercury. Interference of Oxygen. Ovygen present in t h e solution imposes a negative potential limit on the mercury electrode. T h e level of interference can be characterized with the half-n-aw potential of osygen, which depends somenhat on pH and on the 1)uffer type and strength. I n the pEI region from 3 to 10, itf value varied between -30 and -100 mv. us. S.C.E. Therefore, oxygen does not interfere nith titrations in acid solutions n-here the potentials are mor? positive than the oxygen potentials. However, titrations in low potential ranges are strongly affected b y oxygen. In the EDTA titration of barium or strontium in ammonia buffer, a distorted, late. or orcasionally even no end point break iq ohtained in the presence of oxygen In this case the indirect complex effect of ammonia contributes strongly to the shifting of the potmtial into the oxygensensitive range. T h e n the osygen iq removed 1)) bubhling nitrogrn through the solution before and during the titration. good end points are obtained for the titration of barium and strontium. Effect of Concentration of Mercury-
Only the absolute potentials shift u p or down n i t h increased or decreased mercury-chelonate concentration. I n practice, the addition of 1 drop of a to 10-*31 solution of mercurychelonate is sufficient to establish a reasonably constant value for the mercury content so that trace additions of this metal ion do not seriously alter the shape of the titration curve. A higher concentration of mercury-chelonate will furnish a better poked electrode, n-hich is desirable in cases nhere small amounts of halides or oxygen tend to interfere; also the shape of the titration curve hecomeq more symmetrical. LITERATURE CITED
RI., “Oxidation Potentials,” Prentice-Hall, Yew York, 1952. ( 2 ) Reilley, C. N., unpublished method. 13) Reillev, C. N.. Porterfield. W. W., ASAL. CHEM.’28, 443 (1956). (4) Reiller, C. X., Scribner, W. G., Temple, C., I b i d . , 28, 450 (1956). (5) Ringbom, A , , Vanninen, E., -4nal. China. d c t a 11, 153 (1954). ( 6 ) Schmid, R. W,, Reillep, C. ?;., J . Am. Chem. SOC.78, 5513 (1956). ( 7 ) Schwarzenbach, G., Heller, J., Helv. Chinz. d c t a 34, 5i6 (1951). (8) Schwarzenbach, G., Sanders, J., Ibid., 36, 1089 (1953). (9) Siggia, S., Eichlin, D. Rheinhart’, R. C., AKAL. CHEX 27, 1745 (1958). REVEITED for review July 10, 195i. Accepted Xovember 20, 1957. This research supported by the U. S. Air Force through the Air Force Office of Scientific Research, Air Research and Development Command, under contract Yo. AF lS(600)1160. (1) Latimer, IT7.
PX
Figure 9. Interference and sulfate ions
of
halogen
Chelonate. T h e potential of t h e mercury electrode depends on t h e total mercury concentration in solution. A tenfold decrease in total mercury concentration lowers the potential 29 mv. However, all t h e lines on a potential-pH diagram are shifted in the same way upon a change in total mercury concentration, with exception of curve 11, which remains unchanged. The extent of the end point break, therefore, does not in grneral depend on the amount of mercury-chelonate present in the wlution to he titrated.
Chelometric Titrations of Metal Ions with Potentiometric End Point Detection
(Ethy Ie ne d initriIo)tetra a cet ic Acid CHARLES N. REILLEY, R. W. SCHMID, and D. W. LAMSON Department o f Chemistry, University o f North Carolina, Chapel Hill, N. C.
b Application of the mercury electrode as a p M electrode permits the chelometric titration of metal ions with a potentiometric end point. The alkaline earth, the rare earth, and a large number of transition and heavy metals were titrated with (ethylenedinitril0)tetraacetic acid in this manner. Direct and back-titration procedures were employed for the titration of 29 individual metal ions. The results indicate an average titration accuracy to 0.1 to 0.4%. Through judicious applica-
tion of the p H effect, many multicomponent mixtures can be analyzed. The titration of a mixture containing bismuth, cadmium, and calcium is given as an example.
T
HEORETICAL PRISCIPLES which govern the application of the mercury electrode as a p l l indicator electrode h a r e been outlined ( 7 ) . It is possible to carry out chelometric titrations with a mercury electrode in a way analogous
to acidimetric titrations n-ith a glass electrode. Hon ever, in contrast to the titration of acids or bases, the titration of metal ions requires the maintenance of more definite solution conditions. such as pH, kind and concentration of buffer, and complexing agents. Information concerning the selection of these conditions is readily obtained from potential-pH diagrams of t h e type given previously ( 7 ) . I n this article suitable esperimental conditions are VOL. 30, NO. 5 , M A Y 1958
953
described for the titration of metal ions with (ethylenedinitri1o)tetraacetic acid (EDTA or H4Y), using the mercury electrode for end point detection. A mercury-plated platinum electrode was used b y Siggia and coworkers (10) in the determination of chelons with several metal ions. With direct and back-titration procedures the alkaline earth, rare earth, and many transition and heavy metals are accessible t o potentiometric titration. The range of metal ions successfully titrated is shown in Figure 1. The metal ions which have been successfully titrated in this way are listed in Table I. These data show that most ions which form a complex with E D T A of sufficient strength can be titrated using a potentiometric end point. Chelons other than E D T A (such as the polyamines) can also be used as titrants; a study of this is in progress. Solutions of 29 metal ions were prepared and standardized according to known procedures ivith a metal indicator end point, and then titrated b y use of the mercury electrode under proper conditions. The conditions are described below; the results of these titrations are listed in Table I. Only fiye of the more readily obtainable lanthanides were titrated in this investigation : cerium, praseodymium, neodymium, samarium, and lanthanum. Because of the similar chemical behavior and values of the stability constants of the E D T A complexes of the rare earths (9), the ions of the whole group can probably be titrated according to the same procedure. No results are given for the titration of iron. I n the EDTA titration of this metal, the mercury electrode functions simply as a redox indicator electrode (Y),because the redox systems Fe(III)/ F e (11) and Fe (111)Y/Fe (11)Y determine mainly the potential of the electrode. The use of a platinum electrode is then preferable and the titration may be carried out according to PIibil (6).
with the electrode reaction, especially for titrations performed under acidic conditions. The level of interference has been discussed (7). The pH effect can be for the analysis of a multicom~onent mixture provided the stability constants of the metal ions differ sufficientlyLe., at least a factor of lo4. The titration of a three-component mixture containing bismuth, cadmium, and calcium is discussed below. Mercury Electrode. -4 mercury elec-
Table
Taken, Ion
RIg.
Cs++
10 00
20 00
Sr++
2.78 111.07
Baf+
17.40 174.0
Mg++
Zn++
Cd++
Cu++
8.55 8.55 8.55 85.32 85.42 85.48 14.00 14.01 14.02 139.78 139.84 139.78 456.4 456.0 455.4 8.00 8.00 8.01 79. 97 79.97 79.97
14.00
455.4 7.97
954
ANALYTICAL CHEMISTRY
79.74
Ph++
26.88 266.78
hln
++
Co++ Ni++
a
41.65 39.69 44.96
Triethanolaminevbuffer.
* Ammonia buffer.
9.940 10. o o a 10.04a 9.994 20. Ogb 20.04b 20.w 2.77 2.77 2.77 111.03 111.11 111.11 17.54 17.37 17.54 175,O
8.53
139.95
Hg++
Mg.
55.50 55.45
85.32
I.
Results of Potentiometric
Dev.
Found,
55.50
EXPERIMENTAL
From the evidence obtained in the potential-pH diagrams and the titrations carried out in this study, some general rules were established for the potentiometric titration of metal ions with E D T r l (Table 11). The buffer has to be present in an amount sufficient to prevent p H changes during the titration. However, a large excess of buffer should be avoided, as this may decrease the extent of the potential break at the end point. The to 10-3M addition of 1 drop of solution of mercury-EDTA is usually sufficient to give well-poised electrode potentials. Halide ions must not be present in appreciable concentrations because they may interfere severely
trode of the type illustrated in Figure 2 W a s used @argent No. s-30413). Before use t h e mercury C U P was cleaned with dilute nitric acid and thoroughly rinsed with distilled water. The mercury must be clean. RIercury often contains a surface coating of metal oxides l&ich not only rvill interfere with the electrode response but also may dissolve and react with the chelon titrant, leading to erroneous results. I n case of doubt the mercury was washed with dilute nitric acid and then thoroughly rinsed with distilled water. Kashing in ammoniacal EDTA is also
26.78 26.78 26,78 267.92 267.82 267.72 41.76 41.76 39.68 39.45 45.01 45.01
Llg. -0 06 0 +o 04 -0.01 +O 08 +O 04 $0.12 -0 01 -0 01 -0 01 -0 04 $0 04 +o 04
% -0 6 0 0
+o -0 +o
4 1
$0 +O -0 -0 -0 -0 $0
4 2 6 4 4
4
+lo 0 -0 05
04 04 +O 04 +O 8 -0 2 +O 8 $0 6 0 0 -0 1
$0 02 +o 02 $0 02 0 +o 10 + O 16
$0 2 +o 2 $0 2 0 0 $0 1 +o 2
$0 14 -0 03
+o
14
0
+o $0 -0 -0 -0
0 0
01 02 17 11 17
+lo $0 6 0 +O 03 +O 03 +0 04 $0 23 +O 23 +0.23 $0 10
+o
10
+o $0 -0 -0 -0
1
1 1 1 1
+o
2 $0 1 0 0 $0.2 +o 4 $0 5 +o 2 +o 2 $0 2 $0.1 $0.4
$0 10 +1 14 $ 1 04 +o 94
+0.4
L O 11 $0.11 -0 01 -0.24 +o 05 +0.05
+0.3 +0.3 0.0
+o
4
+0.4 +0.4
-0.6
+0.1
+o.
1
effective. The mercury was allowed to remain in the electrode after each titration (being rinsed with distilled water prior to the nevt titration). ;in amalgamated gold electrode may be employed for the titrations. Such an electrode can be made by dipping a Reckman KO. 392’75 gold electrode Iwiefly into pure mercury. After rinsing with water, it is ready for use. .\lternatiT-ely, a simple gold electrode may be constructed in the laboratory :is shon-n in Figure 2. .I short piece of cold wire (pure, 24 carat) is soldered to
a brass rod and fixed into a glass tube by means of de Khotinsky cement. The brass-gold solder connection must not extend along the gold wire appreciably and the solder joint must be well covered with cement. If the solution is in contact with the solder, the electrode will not respond properly. Potentiometric E n d Point. The electrode system consisted of t h e mercury indicator electrode and a calomel reference electrode. T h e potential was followed b y means of a Leeds & Korthrup pH meter, T y p e 7664. T h e
Titration with EDTA
Taken, Mg.
6.332 40 03
7.035 10.6”
11.62 5.279
2.212 4.375
6.126
Follnd, Mg
6 313 6 313
40 39 40 39 7 035 7 035 10 61r 10 61r 10 6Ld 10 60d 11 54 11 63
5 5 2 2 2 4
287 292 228 214 214
384 4 379 4 384 6 154 6 133 6 119
A 051
7,531 7 ,394 1;.854
7 7 7 7 7 7 7 7 7 6
062 007 035 588 574 588 408
495 437 831
6 883 6 854
37.20
5s 89 I S . 17 00 83
6.32 25.29
37 37 59 59
28
38 12
03 18 3 7 18 56, 01 l i e 91 29f 6 33 6 35 6 33 25 39 25 42 25 46
e f
Back-titration m-ith zinc, pH 4 6. Direct titration,.pH 4.0; acetate buffer. Direct titration in acid solution. Back-titration with copper in acetate buffer.
-
Mg.
-0 019 -0 019
TO 36 T O 36 0 0
-0 01 -0.01 0 -0.02 -0 08 +0.01
+o.oos
$0.013 i0.016 $0.002 $0.002 $0. 009 $0.004 $0.009 $0 028 $0.007 -0.007 $ 0 . 111
$0.056 $0.084 $0.057
$0.043
+0. 05’7 $0.014 + O . 101
f0.043 -0 023 +0.029
0.000 $0.08 $0. 18
$0.23 $0.14 $0.20 +0.39 + 0 . 34 + O . 46 $0.01
+0.03
$0.01 +o. 10 + O . 13
$0.17
Ilev.
__ r-
-0 -0 $0 $0 0 0 -0
3 3
9 9 0 0
1 -0.1 0.0
-0.2
-0.7 $0.1 $0.2 -70.2 $0.7 $0.1
i o .1 $0.2
+o. 1 f0.2
+0.4
i o .1 -0.1
$1.6 $0.8
$1.2 $0.8
$0.6 $0.8
f0.2 +1.4 $0.6
-0.3 +0.4 0.0
+0.2 +0,5
$0.4 $0.2
$1.1 t2.1 $0.4 $0.5 $0.2
+o.
1
$0.2
i0.4 $0.5 i0.7
sensitivity of this meter is readily increased b y placing a resistor across the “Auto. Temp. Comp.” and sritching the “Temp. Comp.” switch t o “Auto.” The resistor should have a value in ohms equal to the desired millivolts for full scale less 20. Thus, for a full-scale sensitivity of 140 mv., a resistance of 120 ohms (140 - 20) is used. This rcsistor may be conveniently mounted in a n Amphenol l I C 2 F 1 plug; in this m y different plugs can be used for various sensitivity values. Alternatively, a Helipot (1000 ohms) can be used as the resistance; this permits the full-scale sensitivity to be dialed directly, the dial being attached a t a position to account automatically for the 20-ohm factor. The end point was determined either from the inflection point on a graphical plot or by interpolation betneen readings as the point of steepest potential break. I n the case of asymmetrical titration curves the point of steepest potential break was always taken for the end point. Chemicals. All chemicals were reagent grade. E D T A was obtained from J. T. Raker Chemical Co., Phillipsburg, S. J. Mercury-EDTA was prepared by mixing equivalent amounts of mercuric nitrate and E D T d solutions. The liberated acid was then neutralized. I n acid solutions of mercury-EDTA a n insoluble precipitate, probably HgH2Y, forms after a fen days. The ammonia buffer was made from ammonia and ammonium nitrate. Similarly, triethanolamine buffer was made u p from triethanolamine and nitric acid. Chlorides must not be used for the preparation of buffers. Standard Solutions. E D T A . Standard 0.5 and 0.05M solutions of t h e disodium salt were prepared according t o Blaedel and Knight (1). Metal Ion Solutions. The metal ion solutions were made from primary standard chemicals or were standardized by titration n ith EDTA, using indicator methods. Calcium. Standard calcium carbonate (Jlallinckrodt) dissolved in nitric acid. Chromium. Reduction of primary standard potassium bichromate with sodium sulfite in sulfuric acid solution. Magnesium, zinc, cadmium, lead, manganese. Direct titration using Eriochrome Black T (8). Aluminum. Rack-titration with manganese using Eriochrome Black T(8). Strontium, barium. Direct titration using metal phthalein (8). Nercury, indium. gallium, thalliuni(111), vanadyl(1V). Direct titration using copper-PAN indicator ( 2 ) . Copper. Direct titration using murexide (8). Cobalt, nickel, bismuth. Direct titration using pyrocatechol violet (5, 8). Scandium, yttrium, rare earth. Backtitration with zinc using zincon indicator (4). Zirconium, hafnium. Back-titration 11ith iron using salicylic acid (8). Thorium. Reverse titration using Alizarin S (3). VOL. 30, NO. 5 , M A Y 1958
955
H 121
He B
l3f.
C
S
O
F
Ye
Fr R,L 4c
’ Cr
Pr
Nd Pm Sm Eu Gd Tb 1)y Ho f,:r Trn Y b I,u
‘ T h €’a U
S p Pu Am Crn Bk Cf
Figure 1.
Table II.
PH
Range of metals titrated
Conditions for Potentiometric Titration of Metal Ions
Metals That May Be Titrated a DIRECTTITRATIOK WITH EDTA Th, Hg, Bi (use NHaN03 in salt bridge of calomel cell to avoid introduction of chloride ion) 4 to 5 5 Acetic acid or hexamethyl- DIRECTTITRATION WITH EDTA enetetramine Sc, Y, La, rare earths in $3 oxidation state, VO++, Mn++, Cu, Zn, Cd, Hg, Pb, Bi WITH Cu, Zn, Cd, Hg, OR Pb BACK-TITRATION STANDARD SOLUTIONS: Cr+++ (heat near boiling with excess EDTA for 10 minutes before back-titration) Fe+++, Xi, AI, Ga, In, Zr, Hf, Th, Sc, Y, La, rare earths in + 3 oxidation state, V0++,&In++, Cu, Zn, Cd, Hg, Pb, Bi 8:to 10 Ammonia, triethanolamine, DIRECTTITRATIOS WITH EDTA ethanolamine hlg, Ca, Sr (pH lo), Ba (use pH 10 and remove dissolved oxygen by bubbling out solution with nitrogen) Co, Xi, Cu, Zn, Cd, In, Pb (add tartrate to keep lead and indium in solution during titration) WITH Zn, Ca, Rlg, Cu, OR Cd BACK-TITRATIOK STANDARD SOLUTIONS C r + + + (boil for 10 minutes in Dresence of excess EDTA before back titrationf Sc, Y, La, rare earths in + 3 oxidation state, Hg, Bi, Mg, Ca, Sr (pH lo), Ba (pH 10 and re2 first), Co, Ni, Cu, Zn, Cd, Pb, T1 (oximove 0 dize first to $3 by boiling with nitric acid) a hlost of the metal ions listed under pH 4 to 5.5 or pH 8 to 10 will not interfere with titrations at pH 2. Alkaline earth ions do not interfere with titrations a t pH 4 to 5.5. 2
Buffer Systems Sitric or chloroacetic acid
POTENTIOMETRIC TITRATION OF METAL IONS
Unless otherwise stated, the amount of mercurv-EDTA added was 1 drop of a 10-3~1Isolution. Direct Titration in Ammonia Buffer. Strontium(II), barium(II), calcium(11),cobalt(II), and nickel(I1). To 15- or 25-ml. aliquots of 0.05M (or more dilute) solution of metal ion w r e added 10 to 25 ml. of 0.5iM animonia buffer. The titration was carried out a t p H 9.5 to 10 with 0.05 or 0.005M EDTA after the addition of mercuryEDTA. Oxygen interferes with the titration of barium; it n-as excluded from the solutions by deaerating with nitrogen before and during the titration. The titration must be carried out slonly near the end point. For the titration of barium, 1 ml. of 10-3At4’ mercuryEDTA was added; high results were obtained with only 1 drop. Direct Titration in Triethanolamine Buffer. RIagnesium(I1) and calcium(11). T o 15 or 25 ml. of 0.05M (or more dilute) solution of metal ion, 10 ml. of 0.5V triethanolamine buffer of p H 8.5 ‘cr.ereadded. After addition of mercuryE D T A the solution was titrated with EDTA. Direct Titration in Acetate Buffer. Zinc (11), cadmium(11), copper( 11). lcad(II), mercury(II), manganese(II), vnnadyl(1V) and indium(II1). T o 15 or 25 ml. of 0.05Jf (or more dilute) solution of metal ion, 10 to 25 nil. of 0.5M acetate buffer of p H 4.6 IT-ere added. After addition of mercuryEDTA the solution was titrated n ith EDTA. I n the case of vanadyl ion a p H of 3.9 was chosen and a platinum electrode was used instead of a mercury electrode. The mercury electrode gave abnormally shaped titration curves because of “mixed potential” effects. Indium was titrated a t p H 4.0. Copper must be titrated slowly near the end point. Back-Titration with Zinc in Acetate Buffer. Aluminum(III), gallium(111),indium(III), thallium(III), and chromium(II1). A 10-ml. portion of 0.1X aluminum solution was acidified (pH 1 to 2 ) and boiled for 1 minute. T o the hot solution were added 15 ml. of 0.1N EDTA. The solution was chilled, then acetate buffer of p H 4.6 and mercury-EDTA were added. Excess EDTA was back-titrated with zinc. Gallium was determined by heating 5 ml. of 0.02X gallium solution, 10 ml. of 0.02M EDTA, and 10 ml. of 0.2M acetate buffer (pH 4.6). The solution was then chilled, mercury-EDTA was added, and the excess EDTA was backtitrated nith zinc.
Figure 2. Electrodesfor potentiometric titration of metal ions S. C.E.
956
MERCURY ELECTRODE
ANALYTICAL CHEMISTRY
GOLD AMALGAM ELECT RODE
a.
b. c.
de Khotinsky cement Glass tubing Brass rod
d. e.
Solder Gold wire
adjusted to p H I .2 to 2 with nitric acid. After addition of mercury-EDTA the solution was titrated to the first end point break. which corresponds to the amount of bismuth present. The p H n-as changed to 4 by adding sodium acetate-acetic acid, and the titration \vas continued until a potential break was again obtained. The E D T A consumed between the first and second potential breaks corresponds to the amount of cadmium ions. Finally, the p H was adjusted to 8 with ammonia buffer and calcium was titrated.
p H = 1.2
-\i
J
“f
1-
Bi
Q I-
z W
ii typical titration curve for this three-component mixture is shown in Figure 3. Results for the titrations of various bismuth-cadmium-calcium mixtures are given in Table 111. N a n y other multicomponent mixtures can be analyzed b y judicious application of the p H effect.
1i
t0
a
5 0 MV.
I C ,
I
7
6
8
9
IO’
I/
/
12
M L . 0.1 M
13
14
!
I
I6
17
18
19
20
EDTA
Figure 3. Typical titration curve for three-component mixture of bismuth, cadmium, and calcium
ACKNOWLEDGMENT
G. P. Hildebrand and W. G. Scribner performed the analyses for several of the ions, and their help is appreciated. LITERATURE CITED
Table Ill.
Titration of Mixtures Containing Bismuth, Cadmium, and Calcium
Sample 1
2 3 4 5 6 7
Bi+++, Rlg. Taken Found 100.0 100.4 100.0 99.6 100.0 99.0 200.0 194.4 200.0 196.2 200.0 202.8 200.0 194.6
For indium, 10 nil. of 0.01121 solution were used. T o this !Yere added 25 ml. of 0.2111 acetate buffer (pH 4.6), 10 ml. of 0.02M EDTA, and mercury-EDTA, follom-ed by back-titration with zinc. Thallium was determined like indium, except that the p H was 4.0. The titration had to be carried out rapidly; otherwise. peculiar curves were obtained. For the titration of chromium, 5 ml. of 0.0251 chromium solution, I O ml. of 0.0231 EDTA, and 10 ml. of 0 . 2 V acetate buffer (pH 3.5) were heated to boiling for 10 minutes, whereupon a violet complex formed. The solution was cooled, the p H was adjusted to 4.8, and mercury-EDTA was added. The solution n a s then back-titrated with zinc. Back-Titration with Zinc in Ammonia Buffer. Cerium(III), scandiuni(III), yttrium(III), lanthanum (111), neodymium(III), praseodymiuni (111).and samarium(II1). To 10 ml. of O.OO5M rare earth solution nere added 15 ml. of 0.005Jf E D T A ; the p H was then adjusted t o 9.5 to I O with concentrated ammonia. Mercury-EDTB was added and the evcess EDTA was back-titrated v, it11 zinc solution. Back-Titration with Copper in Ace-
Cd++, Mg. Taken Found 56.0 54.8 56.0 55.2 56.0 56.4 112.0 110.2 112.0 109.9 112.0 110.1 112.0 110.4
Ca++, Mg. Taken Found 20.00 20.16 20.00 20.20 20.00 20.00 40.00 40.04 40.00 40.20 40.00 39.20 40.00 39.20
tate Buffer. Zirconiuni(IS’), hafnium(IV), and thorium(1T’). Zirconium or hafnium solution ( 5 ml., 0.05~11)\vas treated with an excess of 0.05M EDTA. The p H n-as then adjusted to 4 with acetate buffer and sodium acetate. 1Iercurg-EDTA was added and the excess EDTA \vas backtitrated with copper(I1). Direct Titration in Acid Solution. Bismuth (111) and thorium ( 1 1 7 ) . 1lercui-y-EDTA was added t o 25 ml. of O.OO5M bismuth nitrate and the p H was adjusted with ammonia or nitric acid to 1.5. The solution as then directly titrated with EDTA. T o avoid the introduction of chloride ions into the solution from a calomel reference electrode (chloride may cause precipitation of bismuth oxychloride), a n ammonium nitrate salt bridge was used. I n the case of thorium, an aliquot of solution was added to 90 ml. of 0.001JI nitric acid containing 1 drop of mercuryE D T A ; the p H was then adjusted to 3.2 with 3N ammonium hydroxide. Direct titration with E D T A follon-ed. Titration of Three-Component Mixture. A mixture of bismuth, cadmium, and calcium was prepaied b y miving aliquots of t h e standardized solutions of the components. The solution was
Blaedel, W. J., Knight, H. J., ASAL. CHEJI.26, 741 (1954). Flaschka. H.. Abdine. H.. Chemist Analyst 45, 58 (1956). Haar, K. ter, Bazen, J., ,4nal. Chim. Acta 9, 235 (1953). Kinnunen, J., Merikanto, B., Ibid., 44, 50 (1955). Malat. RI.. Suk. V.. Jenickova. A,. Collkctio; Czechoslbv. Chena. Corn: mum. 19, 1156 (1954). (6) PFibil, R., Koudela, Z . , Rfatyska, E., Zbid., 16, 80 (1951). (7) Reillev. C. N.. Schmid. R. W., ASAL. CHEX 30, 947 (1958). (8) Schwarzenbach, G. “Die Komplexometrische Titration,” Ferdinand Enke Verlag, Stuttgart, 1955. (9) Schaarzenbach, G., Gut, R., Anderegg, G., Helv. Chim. Acta 37, 937 11954). (10) Siggia, S., Eichlin, D. W.,Rheinhart, R. C., AXAL. CHEX. 27, 1745 (1955). ,
I
RECEIYEDfor review July 26, 1957. Accepted November 20, 1957. Research supported by the U. S. Air Force through the Air Force Office of Scientific Research, Air Research and Development Command, under contract No. AF 18(600)-1160.
Structural Analysis of Clinical Dextrans by Periodate Oxidation and Isotope Dilution Techniques-Correction
In the article “Structural Analysis of Clinical Dextrans by Periodate Oxidation and Isotope Dilution Techniques” [Noyer, J. D., Isbell, H. S.,ANAL. CHEJf. 29, 1862 (1957)], the value 0.9598 given on page 1865, Table 11, for sample S-155 should have been 0.8598. J. D. ~ I O Y E R
H. S. ISBELL VOL. 30, NO. 5, M A Y 1958
e
957
