Polarography of Zirconium Salts in Methanol - Analytical Chemistry

---

V O L U M E 2 5 , NO. 1 2 , D E C E M B E R 1 9 5 3 be made. Sow, however, as oil separation and other preparation difficulties are not encountered, the pressings are often prepared in advance and held until instrument time is available. Some tj-pica1 results are given in Figures 3 and 4 to show t h e marked superiority of the pressed salt technique over conventional macro mineral oil mulls which invariably show bands a t 3.5, 6.8, 7.2, and 13.8 microns. The potassium bromide curves are useful over their entire length, as potassium bromide itself shows no absorption bands. This is clearly evident when the potassium bromide and mineral oil records of the chemicals shown in Figures 3 and 4 are compared. Curves A , B , and C are of hydroquinone. The available data in the 5- to 6-micron region are increased in curve C 1%-here10% of hydroquinone was present in the disk. In this laboratory it has never been possible to secure records of this quality a t this concentration using mulling techniques. Curves D and E are of benzoic acid a t concentrations of about 1yoin potassium bromide and mineral oil. The marked increase in record quality around 7 microns is an important gain. Curves F and G in Figure 4 are of sodium sulfite. The minor band that can be seen a t about 7 microns was previously hidden by the mineral oil bands. Curves H and J are of ammonium chloride, and again the record in potassium bromide is an improvement over that in mineral oil. In one instance, 5 p.p,m. of ammonia in a water sample were detected and pictured by means of the micro infrared recordings. The ability to retain standards and samples of importance is particularly facilitated by the potassium bromide technique. The disks can readily be filed for future use as evidence; they are also valuable in case of controversy or for use as reference standards. For example, a standard hydroquinone disk has been run as 3n instrument performance check many times over a period of several months with no change in the curves indicative of decomposition or alteration of the material. This technique appears to be almost universal in its application

1909 to dry samples. As a matter of fact, only one compound so far has been found to give a poorer record in potassium bromide than in mineral oil. This effect in itself is interesting and will be investigated further as time permits, to allow correlating changes in structure or crystallinity that take place under pressure. The majority of this work has been confined to potassium bromide as the carrier salt, but work currently going on indicates that a n ide selection of carrier salts will soon be available. The work reported has also been confined to solids and nonvolatile liquids and only semiquantitative results have been attempted so far. The quantitative results are, however, most encouraging and all indications are that the microtechniques reported here v ill be readily adaptable to quantitative analysis. COhTLUSIONS

A combination of the pressed salt technique using potassium bromide and a silver chloride lens beam-condensing system produces records of excellent quality from microgram quantities of organic and inorganic chemicals. It has extended the use of the Baird double-beam spectrophotometer to the examination of microgram quantities of material, and i t accomplishes these results without basically altering the instrument. All the advantages of double-beam operation are retained and i t requires only seconds to convert from macro to micro infrared work. I n the authors' laboratory, the use of mineral oil mulls, even for macro work, has almost entirely disappeared because of the ease u i t h which potassium bromide records can be prepared using this system. LITERATURE CITED

(1) Anderson, D. H., and LIiller, 0. E., J . Opt. Soc. Amer., 43, 777 (1953). 12) Kremers, H. C., Ibid., 37, 337 (1947). (3) Schiedt, C., and Reinwein, H., .Vaturfororschung, 76, 270 (1952). (4) Stimson, 11.AI., J . Am. Chem. SOC.,74, 1805 (1952). RFCEIVED for review July 15, 1953. Accepted October 1, 19.53.

Polarography of Zirconium Salts in Methanol EUGENE L. COLICHMAN AND WALTER H. LUDEWIG Research Division, Livermore Research Laboratory, California Research and Development Co., Livermore, Calif. fundamental work on the thermodynamic and electroL potential properties of zirconium salts has been reported to ITTLE

date (4). The exact nature of quadrivalent zirconium in perchloric acid aqueous solutions, ordinarily considered noncomplexing, is still under active consideration ( I , 2 ) . Quadrivalent zirconium complexes readily with many anions ( I ) and undergoes hydrolysis except in strong acid solution or when highly complesed. This pronounced tendency toward complexing and hydrolysis makes it difficult to characterize zirconium species in any investigation. Laubengayer and Eaton (6) have reported the polarographic reducibility of quadrivalent zirconium in aqueous solutions. Solubility considerations in the useful range of acidity limit the analytical applications of the polarographic method in this case. Furthermore, the reported reduction of quadrivalent zirconium is obtained as a relatively small polarographic wave on top of a large hydrogen decomposition wave. The polarographic results i n methanol reported have eliminated some of the difficulties encountered in aqueous solutions. Well defined reproducible polarographic waves are obtained in methanol and are not complicated by the eimultaneous appearance of hydrogen decomposition naves. MATERIALS

The methanol and lithium chloride were Baker and Adamson's reagent grade. The zirconium sulfate tetrahvdrate (zirconium oside: theoretical, 34.67; found, 34 88 and 34.86) and zirconyl chloride octahydrate (per cent zirconium ouide: theoretical,

38.24; found, 38.24 and 38.36) were prepared in this laboratory. Purity of these saI!s was substantiated by gravimetric ignition procedures a t 850 The pure zirconium sulfate and zirconyl chloride used in the polarographic investigation were prepared by a method described by Falinski ( 3 ) . The purified zirconium oxide used in these preparations was obtained by igniting a t about 360" a purified zirconyl chloride sample obtained from 9.D. McKay, Inc.

.

POLAROGRAPHlC APPARATUS

Polarographic data were obtained a t 25.0" rt 0.1" using a Leeds and Northrup Electro-Chemograph Type E and an H-cell. Characteristic polaro aphic properties were: drop time, 4.02 seconds per drop; m Kr the capillary, 1.79 mg. per second; and 1.86 mg.2/3sec.-l/2 (open circuit) for m2/3t1/6a t h = 50 cm. The supporting electrolyte employed in all cases reported was 0 . M lithium chloride in methanol. Oxygen was removed satisfactorily by rapid degassing with tank nitrogen for 5 minutes. RESULTS

Slope analysis results [plot of E d e us. log Z / ( Z d - Z ) ] for zirconium sulfate are in the range 0.12 to 0.16, indicating an irreversible reduction. E values were corrected for the small iR drop across the cell. The two waves reported for zirconium sulfate are attributed to two different quadrivalent species of zirconium in solution, as the total I d / c values are constant over a tenfold concentration range. Apparently, these two species are present in substantially equal amounts in the most dilute solutions (compare I d / c values for waves I and I1 a t 1 X 10-3M and below).

ANALYTICAL CHEMISTRY

1910

Table I. Polarographic Results in Methanol Salt, hf

x

lop

Wave I

Zr(S04)~.4Hz0 5.0 2.5 1.0

0.5

5.6 5.2 3.7 3.6

I d / C . ra./mM Wave I1 Total 1.6 2.0 3.4 3.5

7.2 7.2 7.1 7.1

- El/a volt UE. SCE

Wave I

Wave I1

1.25 1.24 1.25 1.25

1.56 1.55 1.55 1.54

of the polarographic method to the analysis of hydrated quadrivalent zirconium salts such as zirconium sulfate tetrahydrate. The addition of a few tenths of 1% of water to the anhydrous methanol did not appreciably alter the polarographic data. Polarographic results obtained in a mercury pool cell were no better than those obtained in the H-cell, if the polarogram was recorded within about 5 minutes. I n this way, diffusion of water through the agar plug in the H-cell was maintained below interfering quantities. ACKNOWLEDG,MENT

I J C values for wave I are seen to decreave with concentration of zirconyl chloride similar to the behavior obqerved with zirconium sulfate. Unfortunately, wave I1 for zirconyl chloride merges with the solvent-supporting electrolyte decomposition wave. Thus Id/C values are not ascertainable for wave I1 in this case. Diffusion current data for zirconium sulfate reduction waves a t various drop times between 3.0 and 6.0 seconds were analyzed. I d values obtained were in accordance with the IlkoviE equation, showing that kinetic currents are not involved in the present investigation. The data presented in Table I indicate the posible application

The authors are indebted to E. L. Anderson of this laboratory for pi oviding these compounds. LITERATURE CITED

(1) Connick, R. E., and McVey. IT-. H., J . A m . Chem. Soc , 7 1 , 31S2 (1949).

Connick, R. E., and Reas, W. H., Ibid., 73, 1171 (1951). (3) Falinski, M., Ann. chim., 16, 237 (1941). (4) Latimer, W. M., “Oxidation States of the Elements and Their Potentials in Auqeous Solutions,” 2nd ed., pp. 270-2, Yew York, Prentice-Hall, 1952. (5) Laubengayer, A. IT.,and Eaton, 11. B.. J . A m . Chem. Soc., 62, (2)

2704 (1940). RECEIVED May 16, 1953. -4ccepted August 5 , 1953. Work performed under Contrart S o .kT(11-1)-74 with the V. S Atomic Energy Commission.

Simultaneous Titration of Iron and Copper with Ethylenediaminetetraacetic Acid Spectrophotometric End Points A. L. UNDERWOOD Department of Chemistry, Emory University, Emory University, Ga. recent papers have pointed out the advantages of photometric end points in certain titrations (1, 2, 7 , 8) Sweetser and Bricker (8)have shown that the principal disadvantage of ethylenediaminetetraacetic acid (Versene, Sequestrene) as a volumetric reagent for various cations-viz., lack of suitable indicators-may be overcome in certain cases by this technique. Studies in this laboratory have indicated that the photometric approach permits the simultaneous titration of two or more cations provided: (a) the stability constants of their complexes with ethylenediaminetetraacetic acid are sufficiently large, ( b ) the constants differ sufficiently, and (c) the spectra of the complexes permit selection of suitable wave lengths. Many of the stability constants have been measured, and a convenient compilation has been given (4). Although these constants may be expected to vary considerably with the medium, they may be used as rough guides in predicting the feasibility of titrating certain metals simultaneously. Proviso c may easily be checked experimentally. Sweetser and Bricker have reported good photometric titrations of ferric and cupric ions, separately, with ethylenediaminetetraacetic acid (8). The stability constants reported for the complexes of these ions are large, and differ sufficiently to indicate the possibility of obtaining two consecutive end points when a mixture of the two is titrated with an ethylenediaminetetraacetic acid solution [ferric complex, log K = 25.1 (6); cupric complex, log K = 18.3 ( 5 ) ] . Furthermore, the cupric complex absorbs strongly a t a wave length (745 mp) where the ferric complex exhibits no absorption. Since the ferric complex is the most stable, the formation of the cupric complex with the attendant increase in absorbancy serves as indicator for the titration of the iron. The copper end point is indicated] of course, by a plateau representing maximal formation of the cupric complex. This paper reports results obtained in this fashion. and includes application to an aluminum alloy containing I o n percentages of iron and copper. EVERAL

3

REAGENTS AND APPARATUS

Ethylenediaminetetraacetic acid under the trade name Sequestrene A.4 was obtained from the Alrose Chemical Co., Providence, R. I. About 14.6 grams of this material was suspended in distilled water and treated with sodium hydroxide to dissolve the acid. The solution was diluted to 500 ml. with distilled water to give a 0.1.V reagent, and standardize against the standard cupric solution, using the spectrophotometric end point. As emphasized by Sweetser and Bricker (8), careful control of pH is essential for successful titrations with ethylenediaminetetraacetic acid. The buffer used in this work, 94.5 grams ( 1 mole) of monochloroacetic acid (Eastman Kodak Co. practical grade, distilled to remove dark-colored impurities), was dissolved in distilled water, adjusted to pH 2.0 with sodium hydroxide, and diluted to 1 liter. The standard cupric solution was about O.OIMl prepared by dissolving accurately weighed electrolytic copper foil in nitric acid, boiling the solution to remove oxides of nitrogen, and diluting with distilled water. The standard ferric solution of about the same molarity was prepared from Baker’s analyzed ferric ammonium sulfate. I t wits analyzed by passage through a Jones reductor, followed by titration with standard dichromate solution, and was kept sufficiently acidic to prevent hydrolysis of the iron. The Beckman Model DU spectrophotometer was adapted a s follows: The titration cell, which x i s a rectangular cuvette with a capacity of about 90 ml. designed for a Lumetron colorimeter, was mounted inside a Beckman test tube attachment with the test tube bracket removed. The cell, whose base projected beyond its sides, could be positioned and held securely by means of the setscrews designed to hold the test tube bracket. The cover for the test tube attachment was replaced by a flat wooden cover; molding around its edges gave a light-tight fit. Two holes in the cover, equipped with felt gaskets, admitted the glass stirrer and the 2-ml. microburet. The cover was painted TTith a flat black enamel. The exterior of the cell was likewise painted, leaving only small windows for the light beam. The stirrer and the buret were painted for a distance several centimeters above the cover down nearly to the tips, which were immersed in the solution. This arrangement mas essentially lighttight; moving a strong light source about the esterior of the cell