V O L U M E 28, N O , 9, S E P T E M B E R 1 9 5 6 iron. This does not present any problem, however, because nickel does not usually contain gallium. The interference due to nickel, cobalt, copper, silver, gold, and the platinum metals can be readily eliminated by masking with cyanide. On the other hand, the interference due to zinc and cadmium cannot be entirely suppressed by the limited amount of cyanide that can be tolerated in the osine extraction separation (Table I). Fortunately the amount of zinc and cadmium present in nickel is usually less than 0.01%.
1445 The results obtained by the new rapid method in the analysis of nickel samples (Table 111) compare favorably with those previously obt,ained (1). LITERATURE CITED
(1) Luke, C . L., Campbell, 11.E., d s a ~C.H E M . 26, 1778 (1954)
RECEIVED for review February 23, 1956. Accepted M a s 19, 1956.
Photometric Titration of Small Amounts of Barium with (Ethyleaedinitri1o)tetraacetic Acid ALLEN I. COHEN and LOUIS GORDON D e p a r t m e n t o f Chemistry, Syracuse University, Syracuse 10,
N. Y.
A method for the photometric titration of small quantities of barium with (ethylenedinitri1o)tetraacetic acid uses as indicator Phthalein Purpur, a phenolphthalein derivative having iminodiacetate functional groups. This forms a coniplex with barium which shows an absorbance maximum at 570 mg. From 0.05 to 12 mg. of barium can be determined by titration with 0.01 o r 0.002.V (ethylenedinitrilo)tetraacetic acid.
R
O K L E T , Stoenner, and Gordon ( 4 ) have proposed a phot,ometric titration for the determination of from 0.1 to 5 mg. of barium. This is a modification of the method of RIanns, 1 h c h o v s k y I and Certa (3) for macro quantities of barium, whirh \\-as determined by titration with 0.1~17E D T A solution [(ethylenedinitrilo)tetraacetic acid ] using the magnesiumEriochrome Black T comples as an indicator for the detection of the end point. Anderepg, Flaschka, Sallman, and Schwarzenbach ( 1 ) have recently proposed a compound which forms a complex with all the alkaline earths and which would appear to have some advantages as a direct indicator over the magnesium-Eriochrome Black T complex in the titration of barium.
WAVE LENGTH ( m p )
Figure 1. Absorption spectra of complex of barium with Phthalein Purpur during titration with EDTA a. S t a r t of titration ( no EDTA added) b . 4 portion of barium removed from complex b y titration x i t h EDTA c.
d.
HOOCCH,, H-N-CH, -0OCCH:
After end point Untitrated blank (no added barium)
+
The present investigation was undertaken to study the applicability of Phthalein Purpur in photometric titrations of smaller quantities of barium, using more dilute solutions of EDTA.
OL‘“ The compound forms a purple-red complex with barium ions. The color of the indicator itself is a light pink in alkaline solution -i e., the color of phenolphthalein. T h e indicator has been called “phtalein complexone” ( 1 ) and “metallphtalein” ( 5 ) . and is conimercially available as Phthalein Purpur. Anderegg and associates have suggested the use of this indicator in a visual titration in 50% ethyl alcohol, so that the pink color of the free indicator will be suppressed. They used 0.1S E D T A in thew titrations and claimed an accuracy \Tithin 0.2 to 0.3%.
MATERIALS 4 N D EQUIPMENT
All reagents were of reagent grade quality, with the exception of triethanolamine, which was technical grade.
EDTA Solutions. Four grams of disodium dihydrogen (ethylenedinitri1o)tetraacetate and 0.6 gram of sodium hydroxide were dissolved in water and diluted to 1liter. This solution was standardized against known amounts of barium and found to be 0.01340M. iipproximately 120 ml. of this solution was then diluted to 1 liter. This solution was found to be 0.001610M as determined by subsequent standardization. Buffer Solution. A solution was prepared by adding 10 gram? of ammonium chloride to 1 liter of concentrated ammonium hydroside and storing in a polyethylene bottle. A solution of pH 1 1 was prepared by diluting 10 ml. of this buffer to 60 ml.
A N A L Y T I C A L CHEMISTRY
1446 Barium Solution. .S solution was prepared froin barium nit,rate m-hich had been twice recrystallized from water. The solution contained 124.0 mg. of barium per 50 ml., as was determined by evaporating an aliquot t o which sulfuric acid has been added and weighing the ignited residue (900" C.). Phthalein Purpur. This reagent was obtained from B. Siegfried, Zofingen, Switzerland. Sixt,y milligrams were added to 60 ml. of triethanolamine and the mixture was allowed to stand for several days until complete solution was effected. This solution appeared t o be very stable; even after 4 months there were no signs of decomposition. A solution made by dissolving the reagent in dilute ammonium hydroxide showed signs of deterioration within 1 week. Apparatus, The titration cell used was similar to that devised by Goddu and Hume (Z), but was modified in that t,he cell coiild be capped with a T 55/50 cover provided ivith a precision Trubore shaft to which the helical stirrer was attached. The stirrer could thus be run a t high speeds \vithout hitting t,he sides of the titration cell. The cell fitted into an Evelyn colorimeter. .in opening in the T cover permitted the insertion of a 10-nil. buret, the t8ip of which could he immersed in the solution so that small amounts of titrant could be easily added. Absorbances were read 1 to 2 minutes after the addition of an increment of titrant. Aibsorbaricereadings could he made ivit,hout turning off the stirrer. The light, path through the titration cell \vas 2.2 cm. A 565 Evelyn filter was used with the colorimeter. The spectra of this filter us. air as measured with a Heckman AIodelU spectronhotonieter showed a transmittancv band from 547 to 575 1iiw r Lvith a niasiniuni a t 557. ;vith -4bsor tion spectra were measured xT\ iith rlbsorption t h a Rec.kman Model H spectropiotonieter and pH measurements were made Jvith :t spectrophotometer Uecknian 1Iodel H pH meter. ~
~~~
PROCEDURE
Takc :t sample for analysis \\-hich contains from 0.03 to 12 mg. of barium in 1 to 50 nil. of a nelitral solution (acid solutions should be neutralized \\-ith sodium hydroxide and not ammonia), which should he carbonate-free. Add 10 ml. of pH buffer and dilute the solution to approximately 60 nil. Adjust the colorimeter so that
Table I. I-isual Titration" of Barium (I) with 0.01JZ EDTA Bariuir~I'ound (Difference) t , llg.
IIg.
Barium Taken, Mg. 9.92
Barium/lIl
EDTA
+ o , 02
1.872 1.851 1.85% .\v.
1.838
.iY.
1.893 i.890 1.89'
4.96
+O. 13 10.04
-0.0; -0.04
10.00 -0.12 -0 04 -0.04 a One d r o p of tric.tllanolamine solution of indicator. 13.8 ixig./'inl., used. b Rariuni found was calcrilared using standardization d a t a obtained i n visual titration of 12.40 mg. o f barium: titer ralue. 1 1 1 ~ .of barluin per 1111. of solution, )\-as 1.87;, average of three titrations.
Table 11.
RESLTLrS ATI) DISCUSSION
Iterults obtained with -1nderegg's method ( 1 ) with 0.0131 EDTA-i.e., titration in 50% ethyl alcohol with visual detection of the end point-are shown in Table I. The ratio, milligruns of barium per milliliter of titrant, varies to some extent with the amount of sample being titrated and t'hus introduces a slight crror, unless the iveight of barium used to standardize the E D T A solution is close to that in the unknown. Khen the more dilute, 0.001610M E D T A solution was employed as titrant, the end point could not visuallj- be detected. All photometric titrations were performed in the abveiice of :ilcoliol. Figure 1 shoivs the spectral characteristics of the solutions a t various stages of the titration. The maximum of thc :il)sorption peak of the barium complex is a t 570 mM. -4s is hliown in Table 11, the variation in the titer values with amouiit ol' barium taken is not as large as with the visual titrtttion. The data of Table I1 were used to determine the molarity of tlie 1;DTA solution. This solution was then used in the titration of 2 to 12 nig. of barium, with the results shown in Table 111. .1 niore dilute solution of EDT.l w:ts then prepared, standardized 1)). titration against kI1on.n aniounts of barium, and used in the titration of 0.05 to 2.00 mg. of barium. These results ;tre also shown in Table 111. Volume corrections for absorbance wcre not made in any of the photometric titrations. Figures 2 and 3 show that relatively sharper end points can be obtained by the present method than by the method of Rowley, Stoenncr, and Gordon (4). I t was found that the I)Iniik correction n-as due to the prcsencc of foreign materials in the 10 nil. of buffer solution used in each titration. A precise value of the blank correction was obtained by utilizing a tenfold quantity of the buffer solution in the hliink titration. First, 90 ml. of the buffer was evaporated to less than 50 nil., 10 ml. of the buffer vias added, and the resulting solution was titrated. The blank for a 10-ml. quantity of buffer amounted to 0.022 ml. for the 0.0134051 E D T A solution and 0.183 nil. for the more dilute titrant. If the buffer was subjected to L: Ihttch treatment with D o w x 50 repin, in the ammonium ion form, to rcmove traces of alkaline earths, the values of the blank \Yere reduced to 0.008 and 0.063 nil., respectively.
Standardization of 0.01.M EDTA Solution by Photometric Titration Barium Taken, Mg.
Rla.
Barium/Ml.
EDTA5 1.838
12.40 Av.
1.858 1.848
Av.
1,848 1.850 1.841 1.846
Air.
1.828 1,839 1.835 1.834
9.92
4.96
a JIolarity
the absorbance of the solution is zero. Finally, add 10 drops of the Phthalein Purpur soliition and stir the solution thoroughly before t,itrating. Titrate with 0.0131 EDTA solution if more t,haii 2.0 mg. of barium is present and with 0.002X EDTA if less is present. S e a r t'he end point take 0.050-ml. and 0.100-ml. increments for 0.01M and 0.002X EDTA solutions, respectively. Allow the solution to mix for 1 to 2 minutes before measuring the absorbance. Obtain the enti piint from a graph of milliliters 2's. absorbance. Determine thc I ~ l ~ i ncorrection k (see Resiilts :itid Discussion) by a similar titration in the absence of bariinn. Standardize the EDT-1 solutions by t'itration agaiwt kiio\vn cluant it ies of hariuni.
L
I
0.0
10
3.0
MILLILITERS
of E D T A solution found to be 0.01340, using over-all average
of eight titrations.
2.0
Figure
2.
of barium 0.01340.M EDTA
Titration
with
V O L U M E 28,
NO. 9, S E P T E M B E R 1 9 5 6
1447
-Table 111.
a
0.101
Figure 3.
4.2
4.4
4.6 MILLILITERS
4.8
5.0
Molarity of EDTA
Barium
0.01340
2.48 6.20 9.92 12.40
I 0.OOlC10
Titration of barium with 0.001610M EDTA
Preliminary work in the application of the colored comples to :I spectrophotometric determination of barium indicated that color fading caused serious errors. The fading was apparently due to the conversion of the phenolphthalein part of the indicatoi, molecule to a colorless form in alkaline solution. However, fading was no problem in the titration itself, which could be carried oiit in a reasonable length of time. The titration can he easily cwmpleted within 30 minutes. The photometric method is recommended for t,he determination 01 0.05 to 12 mg. of barium. Larger quantities can tie determined iwtlily 11)- the visual method (1). ACKNOW~LEDGJIENT
The authors wish to thank the Atomic Energy Commission siiiiport of this investigation under Contract AT (30-1)-1213.
1'01.
Photometric Titration of Bariurn Taken, Mg.
0,050 0,099 0.149 0,248 0.496 0.99 1.24 1.98
Barium Found (Difference), Mg.
+ O 0:3 -0.02 +0.02, +0.01. +o 01 +0.01, 1 0 00, - 0 . 0 4
+ 0 . 0 3 , fO.06,
++0.002, 0.007, f O
+o
-0,001, - 0 +0.002. +o 10.000,+ O -0.01. -0 i.0 00, +o -0 01, - 0
000, 001, 004, 002, 003, 01.
+0.034 10.00
00, 01,
- 0 01 - 0 01
-0.009 +0.003 -0.004 +0.002
LITERATURE CITED
Anderegg, G., Flaschka, H., Sallnian, R.. Schwaraenbnch. G., H e h . Chini. Acta 37, 113 (1954). (2) Goddu, It. F., Hume, D. s., ~ A L C .H m f . 22, 1314 (1950). (3) Manns, T. J., Keschov\ky, 11. Y.,Certa, A. J., Ibid,, 24, 909 (1)
(1952).
Roa-ley, K., Stoenner, R. W., Gordon, L., I b i d . , 28, 136 (1956). ( 5 ) Schwaraenbach, G., "Die Komplexometrische Titration," Ferdinand Enke Verlag, Stuttgart, 1955. (4)
R E C E I V E Dfor reriew January 28. 1956. .hct=pted May
1 1 . 193,;
Effect of Iron on Determination of Tin in Brass and Bronze Application of Radioisotope Techniques C. N. L A ROSA, ISADORE GELD, ARTHUR TICKER, S. F. DI LAURO, and J. L. KALINSKY M a t e r i a l Laboratory, N e w York N a v a l Shipyard, Brooklyn,
ltadioisotope tracer techniques ha\ e been utilized for quantitatite evaluation of the effect of iron on the nitric acid precipitation of tin in brass and bronze. T w o digestion temperatures were studied. with iron-59 and Lin-113 used as tracew. l h e degree of accurac: of the gravimetric procedure, the amount of iron coprecipiLated, and the effect of the presence of iron on the solubilit? of the metastannic acid precipitate were determined. Coprecipitation of iron is shown to follow l'rcundlich's adsorption equat ion.
T
I S in brass and bronze can be determined ( 7 , f l )by digesting with nitric acid, filtering. igniting the resultant metastmnic :icid, and weighing as stannic oside. TTO significant sources of ei~i'orare inherent in this method: Iron, copper, and zinc copreril)itate, and iron increases the solubilitJ- of the metastannic :ic.id ( ? ) . Detailed quantitative studies of these interferences hxve not been reported. The purpose of the present study is to provide more extensive data hj- utilizing the improved sensitivity or radioisotope tracer techniqiies. Earlier investigators recognized the existence of these errors i i i the determination of tin. I n 3022 IIeyer (8)experienced diffiriilty in the quantitative recovri'y of tin in alloys containing iron i n ercess of 0.5%. Lundell nnd Hoffman ( 7 ) state, "Tlic, preripitation of tin as metastannic acid
N. Y. is not complete if the alloy contains much iron, say above 0.25%." They further maintain that the metastannic acid that separates from solution is always contaminated bj- compounds of iron, copper, and zinc. If the alloy contains antimony, phoephorw, silicon, or arsenic, these are also found in the precipitate, often Willard and Furman (13) state that t h r quantitatively (I). volumetric determination of tin is capable of great,er accnrac). than the gravimetric determination because the coprecipitatiori error is eliminated. The present paper applie5 radioisotope tracer techniques to investigate the gravimetric procedure, to evaluate quantitatively the effect of iron on the precipitation of tin as metastannic acmid in brass and bronze, and to elucidate its mechanism. Various investigators differ regarding the digestion temperature of the metastannic acid precipitate. Hillehrand and Lundell ( 4 ) recommend digestion at boiling temperatures to help minimize the effects of the colloidal character and solubility of the precipitate. Kolthoff and Sandell (6) state that the digestion should be carried out a t '30" to 100" C. to ensure a more quantitative separation of tin. Norwitz, Boyd, and Bachtiger (5) suggest that the arid digestion of the alloy be maintained a t a hoil for low-tin samples and a t 95' C. for high-tin samples. Goldherg (3) advocates a nitric acid digestion :it :I hoiling temperature for manganese bronzes. It \vas desirable to resolve this problem of digestion temperature lvith respect to the two soiirces of error by investigating two digestion temperatures XT-ith samples of varied iron caontents. This approach is in line \T-iththe research of Kolthoff :ind lloltzan
