444
ANALYTICAL CHEMISTRY matograms, as well as by applying the color tests proposed by Buch and coworkers (d). A circular paper chromatogram (36 om. in diameter) containing 50 y of test acid per spot was prepared in the manner described [Airan and coworkers ( f ) ] . After being air-dried, the chromatogram was treated with the spray reagent, and was photographed (Figure . ._ 1). Maleic and malonic acids. which have an identical R, value in a pentanol-formic acid system, were separated. CONCLUSION
Indophenol dye is a better spray reagent than the usual indicator sprays because of its ease of preparation and use and its usefulness in differentiating certain organic acids. ACKNOWLEDGMENT
The authors' thanks are due t o F. R. Bharucha, Institute of Science, far his keen interest in this work
c.
citric F. Fumaric GLu. Gluconic MLn. Malonic
MLe. Maleic M. Malic
s.
sucoinio
T. Tartaric
acid, which bleached the dye immedirttely. With time, lactic acid, maleic acid, and malonic acid showed a tendency to bleach,
ANAL.C n m ~ .25,659 . (1953). (2) Buch, M. L..Montgomery, R.. and Porter. W. L.,Ibid., 24,489
,.~~"~
11WOZ).
(3) Wiggins, L. F..and Williams. J. A,, Nature, 170, 279 (1952). RECEIVED for review May 13, 1954.
Accepted October 28, 1954.
.."
,InriAn Inn via Golorimetric uetermination 01 Ch,,,
Inn Frchanan .VI. ~..IIIu116v
JACK L. LAMBERT and STANLEY K. YASUDA Department of Chemistry, Kansas State College, Manhattan, Kan.
Chloride i o n is d e t e r m i n e d colorimetrically over the range 0 to 180 p.p.rn. after exchanging for i o d a t e ion with g r a n u l a r silver iodate in a column. The released i o d a t e i o n reacts with o a d m i u m i o d i d e l i n e a r staroh r e a g e n t to f o r m rhe blue linear staroh-triiodide ion complex, the absorbancy of which at 615 mw is proportional t o the conoentration of chloride ion. No serious interferences w-ere f o u n d a m o n g ions commonly f o u n d in n a t u r a l waters, within the limits of their u s u a l concentrations. Bromide and iodide ions maet in the same manner as chloride i o n but are n o t commonly present.
c...
OLORIMETRIC procedures for the determination of chlo. . ride ion involving ion exchange with a solid phase reagent, such as silver chromate or silver ferrocyanide, have been described (5). Chloride ion exchanges for chromate or ferrocyanide ions, and is determined indirectly by the colorimetric determination of the released ion or the reaction products of the released ion. I n the method described here, chloride ion exchanges for iodate ion with granular silver iodate, and the concentration of chloride ion is determined by the absorbancy of the blue linear starchtriiodide ion complex formed by the reaction of the released iodate ion with cadmium iodide-linear Starch reagent in acid solution. The relatively low melting point of silver iodate permits its preparation in massive form, from which particles of uniform size suitahle for column reactions are obtained by grinding and sieving. Its n6e in a column ensures the attainment of equilibrium with chloride ion in solution.
REAGENTS AND EQUIPMENT USED
Silver iodate, granular, 100- to ZOO-mesh. Cadmium iodidelinear starch reagent (f), 11.00 grams of cadmium iodide and 2.50 grams of tu,icP-recryrtallized linear potato starch fraction per liter of solution. Hydrochloric acid,, LOA'. Standard chloride ion solution, 200 p.p.m., 0.330 gram of sodium chloride ~ e liter r of solution.
V O L U M E 27, NO. 3, M A R C H 1 9 5 5 attached to a double-acting rubber bulb in such a manner that the bulb acts as a source of air pressure. A No. 00 one-hole rubber stopper, which fits the top of the buret, is attached to the other end of the rubber tube by means of a short length of glass tubing. If the column is accidentally allowed to run dry, it may be reverse-flushed by reversing the rubber bulb and using it to suck distilled water up through the column. PROCEDURE
The column in the buret is washed twice with the solution to be analyzed by filling the buret (with the stopcock closed) and inverting to empty, taking care to keep liquid around the silver iodate particles. The glass wool plug on top of the column effectively prevents liquid from draining out of the column, if the rinsing solution is poured off quickly. -4buretful of the solution is allowed to run through a t normal speed (about 80 drops per minute) or, alternatively, two buretfuls are forced through by the use of the pressure bulb.
445
Table I.
Effect of Possible Interferences Concentration, P.P.31.
Substance NaF KSOi KaHCOs NaCzHsOz ZnSOd NazHPOc KCzHsOz KaCrHaOr NHaCzHaOz
F-
50 500 500 500 500 50 500 500 300
Color Equals blank" Equals blank Equals blank Equals blank
Equals blank Equals blank Equals blank Appreciable b 200 Eouals blank Aipreciable 500 Ca++ Equals blank 400 300 Appreciable Mg7' Equals blank 200 Zn++ Equals blank 500 400 Appreciable AI + + + 300 Equals blank 300 Fe+++ AoDreciable 200 Ehbals blank Hf 10-aN Equals blank lO-8N OH *Equals blank U- Color approximately as intense as that obtained with distilled water by the regular procedure. b Significantly more color than is produced by distilled water.
Water Samples Table 11. Analysis of Typical .Sample Ib
S o . of Detns.' 5 4
C1- Added, P.P.M. 0 0
4
C1- Found, P.P.M. Xohr This method method 68
70
~.
IIId
4 4 4 4
0 25 50 100
28
55 79 130
a Good agreement between results of multiple determinations. b Kansas river water collected near Manhattan, Kan., with suspended solids removed by filtration and/or centrifugation. C Manhattan, Kan , city water supply, obtained from wells in Blue River valley. d Manhattan, Kan , city water supply, different date.
P P M.
GI-
Figure 1. Absorbancies of linear starch-triiodide ion complex produced by chloride ion solutions of known concentrations A t 615
mp
The buret is filled approximately to the zero mark, and the solution is allowed to run out until the meniscus is exactly on the 10-ml. mark. The next 10.0 ml. are very carefully measured into the 100-ml. volumetric flask and diluted up to the calibration mark with distilled water. .Ifter thorough mixing, 10.0 ml. of this solution are pipetted into the 250-ml. volumetric flask. and diluted up to the calibrated volume. From this, 20.0 ml. are taken as a sample, and 1.0 ml. each of the 1.ON hydrochloric acid and cadmium iodide-linear starch reagent are added. The absorbancy of the qolution at 615 mM is determined 5 minutes from the time the acid and the starch-iodide reagent are added. The absorbancies produced at all the concentrations studied were practically constant betwren 5 and 20 minutes after addition of the acid and starch-iodide reagent. DISCUSSION
From data given in the literature (Z),the solubility product constant of silver iodate a t 25" C. is calculated to be 3.57 X and that of silver chloride to be 1.85 X 10-lo at the same temperature. At equilibrium, the ratio oi iodate ions to chloride ions in solution Lvould be 193. Equilibrium is apparently reached quickly in the column, as the dark band of silver chloride is seen to form a t the very top of the column and progress downward slowly, as long use of the column exhausts the silver iodate. Less than 0.25 inch of the column was darkened as a result of all the determinations made in this study, indicating a long useful life for the column. Silver iodate is not very light-sensitive but should be protected from direct light by an opaque cylinder around the buret. The calibration curve, Figure 1, was determined using pure sodium chloride solutions of known concentrations. The vertical
diameter of each circle indicates the range of four determinations made at that concentration. The relationship apparently would be linear over a greater range than is shown, but practical difficulties in reading the absorbancies a t high concentrations limit the concentrations that can be determined directly. The loss of precision a t higher concentrations may be due partly to errors in reading absorbancy values. The optimum concentration range for analysis without resort to dilution is apparently 0 to 150 p.p.m. of chloride ion. A faintly colored blank is obtained when distilled water is run through the column and determined in the regular manner. This could perhaps be reduced by greater dilution, but at a loss of sensitivity of the method. The absorbancy of the blank is very small (about 0.015) but constant, and is due to the very slight solubility of silver iodate, which is 1.89 X lo-= mole per liter a t 25' C. The solutions analyzed in Figure I nere compared with such blanks obtained at the time each series of samples was determined. Another calibration curve n as obtained by comparing the absorbancies against distilled vater as a reference. This line was displaced upward at all concentrations by the optical density of the zero chloride ion blank. The constant value of this blank would permit use of distilled vater as a reference in spectrophotometric determinations. KO attempt was made to control temperature for any of the determinations. Potential interferences were studied up to a niaxiinum of 500 p.p.m., with the results shown in Table I. The colors produced by the various substances s h o w which were approximately the same as the zero chloride ion blank are listed as "equals blank," and are considered not to interfere. From these data, it is evident that very few ions would interfere a t the concentrations usually found in natural vaters or drinking water supplies. The inorganic salts of several of the cations showed interference a t slightly lower concentrations than the acetate salts of the same cations, probably because of trace amounts of chloride ion present as an impurity in the inorganic salts. Bromide and iodide ions would give the same reactions as chloride ion, but they are not usually present in natural waters in concentrations that Tvould give high chloride ion values. Chloride ion concentration in tm o representative waters was analyzed with the results shown in Table 11. Determinations were made on the ran- samples and on samples to which known amounts of chloride ion n-ere added. The river water, after removal of suspended matter, was diluted with 200 p.p.m. of
ANALYTICAL CHEMISTRY
446 standard chloride ion solution to give the desired increase in chloride concentration. Solid sodium chloride was added to one batch of the city water to give the increased chloride ion concentrations. The values obtained bv this method agree well with those obtained by the Mohr mefhod. D
-
ACKNOWLEDGMENT
The research of which the development of this analytical procedure was a part was made possible through the aid of a grant from Research Corp.
LITERATURE CITED
J.
23p 1247 (Ig5l). (2) Seide& -Ltherton, “Solubilities of Inorganic and Metal Organic Compounds,” Vol. I, 3rd ed., pp. 32, 60, Van Kostrand, New York, 1940.
Ah-AL. CHEM.,
L.i
(3) Snell, E”. D., and Snell, C. T., “Colorimetric hlethods of Analysi%” 1-01. 11, 3rd ed., pp. i15-16, Van Sostrand, NewYork, 1949. RECEI~E forD review July 9, 1954. Accepted October 4, 1954.
Determination of lead in lead Drosses and lead-Base Alloys Application of Ethylenediaminetetraacetio Acid Method JACK L. PINKSTON and CHARLES T. KENNER’ Southern
Lead Co, Dallas, rex,
The rapid and accurate determination of lead in lead drosses and similar materials is often difficult owing to the high lead content and numerous impurities. The purpose of this investigation was to develop a simple, rapid, and accurate determination of lead in lead drosses by use of a Versenate titration. The average relative error of the method in the determination of pure lead was less than 0.5 part per thousand, and the standard deviation in the analysis of a series of typical drosses was 0.106%. The method should be applicable to the determination of lead as a major constituent in lead drosses and lead-base alloys.
T
H E rapid and accurate determination of lead in lead drosses and similar materials is difficult owing to the high lead content and the varying amounts of other materials such as silica, rubber, and compounds of arsenic, antimony, tin, copper, iron, and zinc, Of the many methods suggested, the molybdate titration ( 7 ) is perhaps the most widely used, even though it requires an outside indicator. Schwarzenbach (6) first suggested the use of ethylenediaminetetraacetic acid (Versene) for titration of solutions containing lead. This method has been further developed by Flaschka and his coworkers (2-4). Kinnunen and ’A7ennerstrand ( 5 )have applied the method to the determination of small amounts of lead in nickel sulfate. The purpose of this investigation was to develop a rapid, simple, and accurate method for the determination of lead in lead drosses and alloys by titration with disodium dihydrogen ethylenediamine tetraacetate (Versenate) using Eriochrome Black T (F241) as the indicator. The proposed method is rapid and the results are accurate and precise. REAGENTS AND SOLUTIONS
Indicator Solution. Approximately 0.20 gram of Indicator F241 was dissolved in 50 ml. of ethyl alcohol. This solution was not stable and was discarded after 48 hours. Ammonium Acetate. Approximately 454 grams of animonium acetate were dissolved in water and diluted to 1 liter. EXPERIMENTAL
Owing to the fact that drosses and similar materials contain relatively large amounts of lead and varying amounts of materials which interfere in Versenate titrations, the recommended titration method was developed using lead sulfate. Accurately weighed samples were dissolved by boiling with 30 mi. of ammonium acetate solution to which 2.0 grams of tartaric acid were added to keep the lead in solution upon dilution and adjustment of pH. After dilution t o 100 ml., the p H was adjusted to 9.5 with concentrated ammonium hydroxide and the solutions were titrated warm using 7 drops of indicator. The color change of the indicator from pink to sky blue a t room temperature occurred over a range of 1.0 ml. of the titrant, but with experience could be reproduced satisfactorily. I t was noted, however that the color change v a s much sharper a t elevated tempera-
TabIe I.
Determination of Lead MetaI and Lead Sulfate Lead Metal
Taken, mg.
Found, Error, mg. mg.
450.1 454.1 449.6 453.8 449.6 450,6
450,2 454,O 449.0 453.6 449.6 460.5
0.1 0.1 0.6 0.2 0.0 0.1
-4verage 0.18
b
Present address, Department of Chemistry, Southern Methodist University, Dallas, Tex.
%
0.02 0.02 0.13 0.04 0.00 0.02
Taken, Found, Error, mg. mg. mg. 658.4 602.0 602.2 611.7 605.4 607.6 604.5
658.1 601.6 601.9 611.6 605.6 607,s 604.1
0.038
Relative error,
70
0.3 0.4 0.3 0.1 0.2 0.2 0.4
0.05 0.07 0.05 0.02 0.03 0.03 0.07
0.27
0.046
Table 11. Determination of Lead in National Bureau of Standards Alloys
N.B.S. 127a Reagents. All reagents used were C.P. or analytical grade chemicals which conformed to AMERICAN CHEMICAL SOCIETY N.B.S.Q Solder (65/33) specifications. Analytical reagent grade disodium dihydrogen value, Found, ethylenediamine tetraacetate (disodium dihydrogen Versenate) % 70 was used to prepare the titrant solutions. The indicator was I 69.01 69.16 68.97 the sodium salt of 1 (l-hydroxy-2-naphthylaxo)-5-nitro-2-naph69.14 thol-Csulfonic acid, which is also k n o m as Eriochrome Black T 69.08 and as Indicator F241. 69.14 Solutions. Standard Versenate. Approximately 18.6 grams of disodium dihydrogen Versenate were dissolved in water and diluted to 1 liter. This solution was standardized against pure lead by the recommended procedure used in sample analysis. One milliliter of this solution equals approximately 10.0 mg. of lead. a By difference. I
Lead Sulfate Relative error,.
Error,
70
0.15 0.04 0.13 0.07 0.13
N.B.S.53c Lead-Base Bearing Metal Pr-.B.S.G value, Found, Error,
%
84.28
Calculated from range and deviation factor. Calculated from range and confidence factor.
%
%
84.22 84.28 84.26 84.30
0.06 0.00 0.02 0.02
84.27
0.025
0.039 84.27
*
0.06
