Titration of Bromide and Iodide Ions with Mercuric Nitrate Solution Using Diphenyl Carbazide Indicator HAROLD R. R.lcCLE4RY1 Columbia Cniversity, New York, N. Y.
Experimental
HE determination of iodide by titration with standard 0.1 N mercuric nitrate solution using diphenyl carbazide indicator was reported in 1934 by Dubsky and Trt.ilek (3). Itoberts ( 7 ) showed in 1936 that this method could be used successfully in the determination of chloride and made a systematic investigation of the effect of acidity on the endpoint. The niethod of Dubsky and Trtilek using 0.025 K niei,curic nitrate was found to give errstt,ic resuks in this 1al)oratory and a modification of Roberts' procedure which is reliable for iodide determinations is offered here. The chloride niet'hod is found t o be equally reliable in the determination of bromide. The method depends on the formation, from mercuric ion and the alkaline form of the indicator, of a deep blue-violet' complex after all the halide ions have been removed in the form of slightly ionized or insoluble mercuric halide. The equilibrium existing between halide ion, mercuric ion, and the indicator has been discussed previously (7). The mercurimetric method for iodide ( 3 ) , using 0.1 .V nwcuric nitrate and diphenyl carbazide indicator, recomnientls the observa,tion of the blue-violet eiid point in the presence of the crimson-red precipitate of mercuric iodide. I t \\.as found in this laboratory, however, that' in titrations requiring 18 t o 20 cc. of 0.028 N mercuric nitrate the blue-violet color of the indicator complex formed by local excesses of mercuric ion was adsorbed irreversibly by the precipitating mercuric iodide and the end point mas completely obscured. dome tmitrstioiiswere carried out by adding the standard mercuric nitrate solution to within 2 to 3 cc. of the end point before atltling the indicator; even here, however, the end points were somewhat indefinite because of the brilliant crimson color of the precipitated mercuric iodide. In the course of a kinetic investigation ( 6 ) using diosanewater solutions it \vas observed that if the titrating mixt'ure for the iodide determination contains 10 to 15 per cent dioxane, the mercuric iodide precipitates in the metastable yellow modification. If in such a titration the diphenyl carixizitle indicator is not added until within 2 to 3 cc. of the end point, the color change in this solution a t the end point is from canary-yellow to blue-gray and is extremely sharp. The yellow mercuric iodide precipitate does not change appreciably t o the inure stable crimson form for 5 to 10 minutes, allowing ample time to complete a given titration. There are some ohjections t o the use of dioxane in this determination. On standing it undergoes autoxidation (6), forming peroxides which readily oxidize neutral or acidic iodide solutions to iodine. Such impure dioxane has in fact been used by Saifer and Hughes (8) in the colorimetric determination of very small concentrat'ions of iodide. Peroxides must therefore be removed from the dioxane. Distillation from sodium ( 1 ) yields dioxane which does not oxidize a n acidified potassium iodide solution for a t least 36 hours. For use in mercurimetric determinations of iodide the freshly distilled dioxane may be preserved hy the addition of 0.5 gram of hydroquinone per liter; such a solution remains free from detectable quantities of peroxides for at least 2 weeks and the hydroquinone does not int.erfere with the titration. 1
SOLUTIOSS. Primary standards mere (1) A. C. S. grade sodium chloride which was reprecipitated, fused in a platinum crucible, pulverized in an agate mortar, and stored over phosphorus pentoxide, and (2) the best grade of mercuric oxide which was reprecipitated and dried for 2 weeks over phosphorus pentoxide. These compounds were checked to 0.2 per cent against each other by analyzing the sodium chloride with mercuric nitrate solution prepared from the mercuric oxide. Standard mercuric nitrate solution (0.025 N) was prepared in a I-liter volumetric flask from identical weighed samples of the mercuric oxide. Sufficient nitric acid to dissolve all the oxide made the resulting solution 0.008 M in acid. .+Diphenyl carbazide (m. p. 172-173') from Eastman Kodak Co. was used directly to make a saturated 95 per cent ethanol solution; this solution was the indicator. 1,4-Dioxane was purified as described by Beste and Hammett (1) and preserved by the addition of 0.5 gram of hydroquinone per liter. Silver nitrate, potassium thiocyanate, and saturated ferric alum solutions for the Volhard determinations of halide were prepared from c. p. grade chemicals. METHOD. In the determination of bromide the method of Roberts (7) for chloride, using 0.025 N mercuric nitrate, was followed in all respects. Mercuric bromide is sufficiently soluble to cause no interference at the concent.rations used here. The indicator blank was determined by the method of least squares applied to a number of titrations requiring different volumes of mercuric nitrate; it Rmounts t,o 0.08 cc. of 0.025 N mercuric nitrate. The final volume of the solution being titrated should be 65 =t 10 cc. If the iodide solution to be titrated is acid, it is neutralized with sodium hydroxide solution using phenolphthalein indicator. A calculated amount of 0.2 S nitric acid is added, such that the final solution after titration contains the equivalent of 5 cc. of 0.2 K acid ( 7 ) . Eight cubic cent'imeters of peroxide-free dioxane are now added and 0.025 N mercuric nitrate is added rapidly to xithin 2 to 3 cc. of the end point. (The end-point titer is known very approximately as twice t'he volume of mercuric nitrate necessary to start precipitation of the yellow mercuric iodide. The first half of the mercuric nitrate added produces no precipitate, since the excess iodide forms the soluble complex ion. In some cases it was more reliable to make a preliminary rough determination of the end point.) About 15 drops of the diphenyl carbazide indicator solution are then added and the titration is continued t o the end point, which is very sharp. The indicator blank amounts to 0.07 cc. of 0.025 N mercuric nitrate as determined by the least' squares method. The standard procedure was followed in Volhard determinations of halide (4). In the determination of chloride the modification of Caldwell and 1Lloyer (2) was used. A few cubic centimeters of c. P. nitrobenzene were added to each titration mixture; vigorous shaking concentrates the solid silver chloride at the liquid interface and avoids the necessity of filtering. The silver nitrate solution was standardized with solid sodium chloride. >lArrmI.ILs
.ISD
Results The accuracy of the mercurimetric method in determining halide concentrations is shown by analyses of potassium bromide and potassium iodide solutions by both Volhard and mercuric nitrate methods:
Present address, 29 West High St., Bound Brook. S . J.
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Concentration of KRr solution: H g ( N 0 a ) ~method AgNOa method (volhard)
0.03255 0.03249
Concentration of K I solution: Hg(N0s)z method AgNOs method (Volhard)
0 02619 0 02620
*
* *
*
0.00006 N 0.00007 ,V 0.00003 S
0,OOOOG .\
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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All concentrations and blank corrections were determined by the least squares method applied to a number of samples of the potassium iodide solution requiring different volumes of mercuric nitrate or silver nitrate. A typical set of such data is that for the mercurimetric determination of the concentration of potassium iodide solution, given in Table I. TABLE I. MERCURIMETRIC ANALYSISOF POTASSIUM IODIDE SOLUTION Volume of KI S o h .
cc.
kinetic investigations this method has been found accurate, rapid, and more convenient than the Volhard method.
Acknowledgment The author acknowledges his indebtedness to L. P. Hammett for helpful guidance in the course of this investigation, and to H. T. Beans for various suggestions.
Literature Cited
Hg(N0;)r Titer%b
cc.
(1) Beste, G. W., and
The agreement of these results indicates that the mercurimetric method is reliable under the conditions employed here. The use of peroxide-free dioxane may be a cumbersome and undesirable essential in occasional iodide determinations; however, for frequent routine analyses of iodide solutions in
Vol. 14, No. 1
Hammett, L. P., J. Am. Chem. Soc., 62, 2481
(1940). ENG.CHEM.,ANAL.ED., (2) Caldwell, J. R., and Moyer, H. V., IND. 7, 38 (1935). (3) Dubsky, J. V., and Trtilek, J., Mikrochemie, 15, 95 (1934). (4) Kolthoff. I. M., and Sandell. E. B.. “Textbook of Quantitative Inorganic Analysis”, 1st ed., pp. 454, 544, New %ark, Macmillan Co., 1936.
McCleary, H. R., and Hammett, L. P., J . Am. C h m . SOC.,63, 2254 (1941).
Milas, N. A., Ibid.,53,221 (1931). Roberts, I., IND. ENQ.C H E M ANAL. ., ED.,8, 365 (1936). Saifer, A., and Hughes, J., J . Biol. Chem., 118, 241 (1937): 121 801 (1937).
Analysis of Divinyl Ether in Blood WILLIAM L. RUIGH’ University of Pennsylvania, and Merck & Co., Inc., Rahway, N. J.
T
HE prediction of Leake and Chen (10) that the unsat-
urated ethers might have valuable anesthetic properties led to the preparation of divinyl ether by Ruigh and Major (19). It has recently been estimated that the number of patients receiving Vinethene anesthesia now exceeds a quarter of a million (13). I n this paper is described the method used for the determination of divinyl ether in the blood of anesthetized dogs and man. Some of the results obtained have already been published in papers (8, 17, 18, 19) which include both experimental and clinical studies of divinyl ether. Root has also used the method described for ethyl ether determinations in dogs (12). A preliminary method employed in determining blood concentrations depended on the initial hydrolysis of the divinyl ether in the blood sample to acetaldehyde by strong mineral acids, followed by precipitation of the protein by the FolinWu tungstate reagents, distillation of the aldehyde, and its titration by the method of Neuberg and Gottschalk (16). I n this way it was found that in a dog the concentration of divinyl ether in the blood during light surgical anesthesia was 29 mg. per 100 cc., while at the point of respiratory failure it was 74 mg. per 100 cc. Because of rather a i d e variations in the check analyses, its time-consuming technique, and the fact that a t these anesthetic concentrations a correction factor of 25 per cent had to be added, the method was abandoned. The problem of satisfactorily determining the concentration of divinyl ether in the blood of anesthetized animals was finally solved by the development and modification of the iodine pentoxide method based on the reaction discovered by Ditte (2’) and first applied to the analysis of volatile organic compounds by Henderson and Haggard in the case of ethyl iodide (6-9). Haggard (4) later applied the method with I Present address, Squibb Institute for Medical Research, New Brunswick, N. J.
success to the analysis of ethyl ether in both water and blood. Since the completion of this work the method has been modified and adapted to the analysis of ethyl alcohol by Haggard and Greenberg (6) and to cyclopropane by Robbins (16). The original method as applied to ether consisted in aerating the sample of fluid, usually blood, and passing the stream of air carrying the volatile organic vapors over heated iodine pentoxide which oxidized the substance to carbon dioxide and water with the liberation of a stoichiometric amount of iodine. The iodine was absorbed in a solution of potassium iodide and titrated with thiosulfate in the usual manner. A simple calculation then gave the amount of volatile organic substance such as ethyl ether present in the blood or fluid being analyzed. Investigators in other laboratories have had great difficulty in handling the method (2] 6, 7, 11, 20). The main difficulties the author encountered and the means by which they were overcome were: Tubes filled with alternate layers of iodine pentoxide and glass wool prepared and “conditioned” according t o Haggard’s direc-
tions often failed to give reproducible results. Some tubes gave low and irregular results even after several days of conditioning. This was overcome by the use of a special pumice catalyst s u p port which offered a large surface and obvjated the “channeling” effect. Independently, Astapenya, Vapnik, and Zelkin (1) discovered the efficacy of a large surface in the use of iodine pentoxide for the analysis of carbon monoxide. With this type of filling, success was immediately obtained with each tube, whereas formerly tubes had to be abandoned even after a week of conditioning and numerous trial analyses. High and variable blanks were obtained. This was ascribed by Haggard mainly t o the quality of the iodine pentoxide. The author’s use of a tube of heated copper oxide removed any traces of organic impurities and carbon monoxide present in the air. This purifying train, together with the special contact mass, eliminated completely the necessity for a blank correction. Variations in the rate of air flow and very rapid rates of flow gave irregular results. The mechanical design of the apparatus
