cates that arsenic(II1) is more volatile than silver(1) a t all temperatures. “Loosely bound” arsenic in blood is reported (1) to volatilize as an unknown compound a t 56” C.
greatly appreciated. The alfalfa grown in Se75was obtained through the courtesy of C. Johnson, University of California, Davis, Calif. LITERATURE CITED
ACKNOWLEDGMENT
We acknowledge the valuable advice of Robert M. Main. The technical assistance of William Mills, Robert Wrigley, and Mrs. Ollwyn Brothers is
(1) AhAens, L. H., “Spectrochemical Analyam, p. 72, Addison-Wesley, Cam-
bridge, Mass., 1950. (2) Dunlop, E. C., in Kolthoff, I. M., Elving, P. J., Sandell,.E. B., “Treatise on Analytical Chemistry,” Part I, Chap. 25, Interscience, New York, 1961.
(3) Hempel, W., Z. Angew. Chem. 13, 393 (1892). (4) Pijck, J., Gillis, J., Hoste, J.. Intern. J . Appl. Radiation Isotopes 10, 149 (1961). (5) Satterlee, H. S., Blodgett, G., IND. ENG.CHEM.,ANAL.ED. 16, 400 (1944). (6) Schoniger, W., Mikrochim. Acta, 123 (1955); 869 (1956). ( 7 ) Thiens, R. E., in Glick,. D., “Methods of Biochemical Analysis," chap. 6, Interscience, New York, 1952. RECEIVED for review July 5, 1962. Accepted August 6, 1962.
Polarographic Investigations in the Ammoniate of Sodium Iodide D. E. SELLERS’ and G. W. LEONARD, Jr.2 Department of Chemistry, Kansas State University, Manhattan, Kan.
b The preparation and use of the ammoniate of sodium iodide for a polarographic solvent has been described. Measurements on both inorganic and organic compounds have been accomplished. In most instances, the results indicate normal polarographic behavior.
T
HE INVESTIGATION of the use of various inorganic ammoniates as suitable polarographic solvents has become more and more frequent ( I , 5, 7‘). These systems have certain advantages over other nonaqueous media in that there is no interference from oxygen, these systems are highly ionized resulting in low internal cell resistance, and large numbers of both inorganic and organic compounds which are polarographically reducible may be investigated. The purpose of this investigation was to study the KaI.(iTH3)1 solvent with respect to reproducibility in solution preparation, finding a suitable reference electrode, to characterize the usable polarographic range, and to note the effect of concentration on both the diffusion current and half-wave potentials and other pertinent factors which were considered necessary for the characterization of this solvent for polarographic use.
EXPERIMENTAL
Apparatus. The electrolysis vessel consisted of the upper 3 inches of a large 25 X 100-mm. test tube fitted
Present address, Department of Chemistry, Southern Illinois University, Car1
bondale, Ill.
a Present address, Code 452, Naval Ordnance Test Station, China Lake,
Calif.
with a three-holed rubber stopper which held the dropping mercury electrode, a glass-encased silver reference electrode, and an ammonia exit tube which was connected to a metallic sodium drying tube. A Sargent Polarograph Model X I I , coupled with a wave spreader (2), was used to record the current-voltage curves. Calibration points were marked on the polarographic record by adjusting the galvanometer a t 20 and opening the shutter a t the beginning and end of each polarogram. A span of 0.2 volt was used for the determination of the half-wave potentials except when it was impossible to record the entire electrode process when a span of 0.5 volt was used. A Rubicon portable potentiometer was used to measure the voltage a t the beginning and end of each polarogram a t the calibration points. The resistance of the cell circuit, measured with an Industrial Conductivity Bridge Model RC, was 100 ohms. The temperature of the sample being polarographed was maintained a t 24” =t 0.2” C. with a Sargent constant temperature bath. The dropping mercury electrode possessed a drop time of 4.98 seconds a t -0.484 volt us. the silver-silver iodide electrode and its capillary constant was 1.47 mg.2/3t-1/2. The silver-silver iodide reference electrode was made by taking a 6-inch piece of pure silver wire, 1 mm. in diameter, and making a six-turn coil with an outside diameter of approximately 3 mm. This coil was then encased in small-bore glass tubing in which a small hole was placed just below the rubber stopper. After being cleaned with dilute nitric acid, it was electrolyzed a t -3.0 volts for approximately 1.5 hours, rinsed, and stored in distilled mTater for future use. The area of the electrode which was in contact with the solution was approximately 1.5 sq. cm. A second reference electrode prepared in the same manner agreed with the first within 5 mv.
Reagents. Sodium iodide, C.P. (J. T. Baker Chemical Co.) was satisfactory for use without further purification: It yielded a clear solution upon condensation with anhydrous ammonia (-4rmour and Co.) and gave no reducible species within the usable polarographic range. Sodium iodide from other sources left a small white residue after complete condensation. To remove the last trace of moisture, the ammonia was passed through a 6- to 8-inch tube containing metallic sodium. The substances being analyzed polarographically were either reagent grade or prepared and purified by methods described in the literature. Procedure. Using a microbalance, weigh into the polarographic cell the required amount of solute. If necessary, add approximately 20 mg. of gelatin as a maximum suppressor. Add approximately, accurately weighed, 10 grams of sodium iodide (previously dried a t 110” C. for a t least 1 hour) to the cell and stopper the cell with a rubber stopper until the polarographic solution is prepared. Place the cell in the water bath maintained a t the proper temperature, and insert the rubber stopper containing the bubbler and exit tubes. Pass dry ammonia gas through the cell until complete condensation has occurred, approximately 15 to 30 minutes. Remove the bubbler system and immediately insert the D.il1.E.-reference electrode unit. Record the current-voltage curve over the desired range, making sure that the reference points and potentials are recorded. RESULTS A N D DISCUSSION
Stability and Composition Studies
of Various Ammonia Systems. T o describe these solutions more completely, i t was advantageous t o characterize them with respect t o their stabilities and compositions. Because VOL. 34, NO. 1 1, OCTOBER 1962
0
1457
there were many compounds which formed these solutions, the investigation was l i i t e d to those which were considered to be the most satisfactory for use as polarographic solvents. Thus the investigation was limited to systems involving the ammonium and alkali metal salts. The apparatus used in the preparation of the ammoniates was similar to that used in the polarographic studies with the exception that a small-mouthed, 150-ml. bottle was used as the condensation flask. I n all instances, the glass bubbler extended to the bottom of the container to aid in the mixing and condensation of the material. No special precautions were taken to exclude atmospheric moisture during the condensation period. Two different methods were used to obtain the mole ratios (moles ammonia per mole salt) of these liquid systems. The first method was to prepare some of the liquid a t a definite temperature and record its weight. The resulting liquid was then carefully heated until only a solid residue remained which was dried a t 110" C. for about 1 hour. From the weight of the residue, and the weight of ammonia required to form the condensation product, the mole ratio was calculated. The second method was to pass ammonia over a previously weighed quantity of the dry salt. After complete condensation, the resulting solution was then weighed and thn mole ratios were calculated. The results of this investigation may be seen in Table I.
Table I.
In studying decomposition temperatures, the condensation was first allowed to proceed a t room temperature. The ammonia was allowed to pass over the salt from 0.5 to 1 hour, or until condensation took place. If nothing noteworthy resulted, the reaction container and contents were placed in an ice bath and the same procedure was followed. If the ammoniate did not form a t 0" C., the apparatus was placed in a dry iceacetone bath and gaseous ammonia was allowed to condense in the presence of the salt. Care was taken to dissolve as much of the salt as possible in the least amount of liquid ammonia. In all cases, as the temperature of these solutions was raised, a t some definite value it became constant and the solution boiled with the expulsion of ammonia until only a solid residue remained. The temperature a t which this occurred was called the decomposition temperature of that particular solution. For several of the compounds studied, there were no stable liquid systems which existed above the boiling point of ammonia. Several compounds were not investigated because their solubilities in liquid ammonia indicated that they would not form a stable liquid system. Results of this investigation are also listed in Table I. All of the compounds absorbed ammonia with the evolution of heat. The largest heat of reaction occurred in the reaction of ammonium thiocyanate with ammonia. If this particular solution were prepared a t room temperature and then allowed to cool, crystals
Stability and Composition of Various Inorganic Ammoniates
(Composition ratios determined at zero degrees unless otherwise noted) Solubility, Decomposition Moles NHJ g./100 g. liquid temperature, O C., mole salt Salt ~ N H ,= 1 atm. 8" (3) ... NHdF ... ... NHiCl 103 4 2.56 238 NH4Brb 3.01 25 36gd NHJ 2.60 (18" C.) NHiSCN 321 2.00 64 1.36 (29' C.) 1.54 NHdNOa 390 26 (I (I
LiNOs NaF NaCl NaBr NaI
244d 0.4 3 138 162
NaSCN
206
36
NaY'03 KF KC1 KBr
98
- 18 ...
KI
...
0.04 14 182
80
a
... 0
42
a
- 15
KSCN -8 KNO: io ' a No stable solution existing above -34' C. * Approximately 1%water added to aid in the condensation. c See reference (6). d See reference ( 4 ) . (I
1458
ANALYTICAL CHEMISTRY
1.56 (18' C.) 3 . 8gC ,..
3.85 3.63 (24' C.) 3.08 2.69 (29' C.)
... ...
...
were formed. If ammonia were passed continuously as the solution cooled, no crystals were observed. The formation of the ammoniate of ammonium bromide was slow a t 0" C. When ammonia was first passed over the crystals, a hard mass resulted which hindered the further absorption of ammonia. If steps were not taken to overcome this, the time for complete deliquescence was very long. If approximately 1% water was added to the reaction flask, condensation took place with greater ease. In certain cases (Table I), the amount of ammonia associated with a particular salt depends on the temperatureLe., ammonium thiocyanate. In other cases-ammonium nitrate and sodium iodide-there was less composition dependence on temperature of condensation. Preliminary Polarographic Investigation. I n general, the usable polarographic range for these various solvents was 1 to 1.5 volts. Many inorganic and organic compounds not previously reported were soluble in the sodium iodide solvent and most particularly were organic compounds containing nitrogen-Le., azobenzene, dithizon, nitrophenols, and nitroanilines. Honever, not all of these compounds yielded polarographic waves within the usable range of this solvent which was +0.2 to - 1.I volts us. the silver-silver iodide reference electrode. The silver-silver iodide reference electrode gave reproducible half-wave potentials. Effect of Concentration on Diffusion Current. When different concentrations were to be investigated. three methods were used for solution preparation. The most commonly used procedure was t o repeat the polarographic procedure using a different concentration of solute. The second method consisted of preparing in advance some ammonia-sodium iodide a t 24" C. and adding desired amounts of solute to selected volumes of this solvent. During investigations of this type, all studies and transformations were made in a dry box under an atmosphere of ammonia. Because the concentrations were to be expressed in terms of milligrams of solute per gram of sodium iodide, the volume used mas converted to corresponding weight of sodium iodide by adding a k n o m weight of sodium iodide to a m t e r jacketed, previously calibrated buret, passing ammonia through the buret tip until condensation was complete, nnd then measuring the resulting volume One gram of sodium iodide corresponded to 1.09 ml. of solution a t 24" C. After equilibrium had been established, there seemed to be no effect on the measured volume upon the continual passage of ammonia.
The third technique used was to remove the electrode unit and transfer another weighed quantity of solute to the cell. When this procedure was used, the transfer had to be made as quickly as possible so there would be the least contamination from the atmosphere. Although this procedure differed basically from the previous ones, the results were comparable. The diffusion current of the reducible species, both inorganic and organic, was linear with respect to the concentration. However, there was more scattering of i d values when the diffusion current was obtained from individual solutions than when one master solution was used. This scattering was attributed to the slight inconsistency which might be expected in sample preparation. The results obtained with lead iodide and m-nitroaniline are summarized in Table 11, A and B. The diffusion current for each of the reduction steps and the total diffusion current for the entire reduction of m-nitroaniline in the absence of gelatin are linear with respect to concentration. The log [ i / ( i d - i)] us. voltage plots R ere straight lines with very little scattering of points. Copper gave more than one wave, of which only one was in the usable polarographic range. This wave gave a plot whose slope was 0.059, indicating a one-electron change, probably corresponding to the cuprous to copper reduction. The plot for the lead wave possessed a slope of 0.041 which indicated something other than a direct one- or two-electron reduction occurred. Similar irreversible slopes were observed for the organic-nitrogen compounds. Half-Wave Potentials of Various Compounds. The half-wave potentials were dependent on the species being reduced (Table 111). For the derivatives of nitrobenzene, the halfwave potential was dependent on the type of other groups present and their position on the benzene nucleus. The half-wave potentials also shifted slightly to larger negative values as the concentration was increased. In the case of p-nitroacetanilide, the first reduction wave occurred a t -0.082 volt a t a concentration of 0.331 mg. per gram of h’aI and a t 1.53 mg. per gram of S a 1 the half-wave potential was -0.114 volt. Similar results were observed for lead iodide and m- and p-nitroaniline. This shift \vas somewhat expected because these compounds appeared to give irreversible electrode reductions (6,8). Other compounds which were investigated and gave measureable half-wave potentials were o - nitroaniline, CU(XH,)~(SCX)~, o - nitrophenol, and benzil. Their half-wave potentials were, in the presence of gelatin, -0.21 and -0.45, -0.05, -0.23, and -0.20
Table II.
Correlation Between Diffusion Current and Concentration
A. LEADIODIDE WITH GELATIN
Concn., mg./g. NaI
Diffusion current, pa.
id/C
0.263 0.494 0.676 0.945 1.24
1.36 2.39 3.27 4.46 5.87
5.17 4.85 4.84 4.73 4.74
B. m-NITROANILINE WITHOUT GELATIN
First wave 0.083
0.329 0.594 0.928 1.3s1.72
1.14 4.21 6.59 11.2 17.1 17.7
Diffusion current, pa. Second wave id2/C
id,/c
13.7 12.8 11.1 12.1 12.4 10.4
Total i d
33.8 31.1 27.6 32.2 34.8 31.6
2.81 10.2 16.3 29.9 48.1 54.4
idtotP1/C
47.6 43.8 38.7 44.4 47.1 41.9
3.95 14.4 22.9 41.1 65.2 72.1
c. m-NITROANILINE WITH GELATIN ___
Diffusion current, pa. First wave Second wave Third wave Total i d
0..OR?
0.165 0,329 0.928 1.38 1.72 2.15
1 2 2.6 4.7 12 19 20.3 30.4
2.3
3 3 4 0 0 0
idtotallc
51.5 48.0 46.9 46.8 48.2 44.0 45.7
4.35
0.9 1.7 7.7 27 47.4 53.3 67.8
7.94 15.4 43.4 66.5 75.6 98.2
Table 111. Half-Wave Potentials and Diffusion Current Constants for Lead Iodide and Various Organic Compounds vs. the Silver-Silver Iodide Reference Electrode
Compound Lead iodidea m-Nitroaniline p-Nitroaniline p-Nitroacetanilide 4,4’-Bis(acetamho)-
-Ell2
V.
0.027 0.102 0.404 0.25 0.50 0.082 0.448
Concentration, mg./g. NaI 1.24 0,329 0.336 0.331
id,
cm.218tli6 3.11 7.55 18.85 9 23 31.6‘ 4.34 10.80
azoxybenzeneG 0.342 0.298 8.88 c p-Nitrosoacetanilidea 0.37 ... Gelatin used as a maximum suppressor. * Total diffusion current. c A reaction occurs with the solvent with the eventual liberation of free I I . Q
volt us. the silver-silver iodide reference electrode, respectively. Use of Gelatin as a M a x i m u m Suppressor. Gelatin, although not extremely soluble in this system, served satisfactorily as a maximum suppressor. The use of gelatin also had a direct influence on the n u m b e of reduction waves which were observed for the nitro compounds as well as shifting their half-wave potentials. This effect was observed in all cases for 0-, m-, and p-nitroaniline and also for p nitroacetanilide. A similar effect caused by gelatin has been reported in aqueous media (9). Well defined polarograms were obtained for the nitroanilines in this system. As can be seen from Table 11, the reduction of the nitro group is represented by two waves: The i d of the second is approximately twice the
first. ,4t lower concentrations of the nitro compound, gelatin causes a new wave t o appear between the first and second waves (Table 11, C). As the concentration of the reducible species is increased, the new wave is overshadowed until there no longer remains an indication of this middle wave. However, contrary to the usual effect of gelatin, the total diffusion current is greater in the presence of gelatin than for an equal concentration in the absence of gelatin. This increase in diffusion current, in the case of m-nitroaniline, was also true for high concentrations where the middle wave caused by gelatin was no longer noticeable. The ratio of the total diffusion current constants for the reduction in the presence of gelatin to the reduction free of gelatin was alwaye greater than unity. Not only did the addition of gelatin VOL. 34, NO. 1 1 , OCTOBER 1962
9
1459
result in the formation of a new wave, but it also shifted the half-wave potentials. The first reduction wave of pnitroacetanilide a t 1.53mg. per gram of NaI occurred a t -0.114 volt and upon the addition Of the potential shifted to -0.124 volt. Similar results were observed for m- and p nitroaniline. The second reduction wave showed less dependence on the effect of gelatin. A discussion of the possible effect
of gelatin on the reduction of nitro compounds in this system will be published a t a later date. LITERATURE CITED
(1) Hubicki, W., Dabkowska, M., ANAL. 33, go (1961). (2) Hume, D. N., Gillbert, T. W., Ibid., 24, 431 (1952). (3) Hunt, H., J . Am. Che7n. S O C . 54, 3509 (1932). (4) Hunt, H., Boncyk, L., Ibid., 55, 3523 (1933).
(5) Ichniowski, T. C., Clifford, A. F., J . "9 133 (lg61)* Inorg* (6) Kolthoff, I. ,,M., Lingane, J . L., "Polarography, Vol. I, 2nd ed., p. 202, Interscience, New York, 1952. ( 7 ) Leonard, G. W., Jr., Sellers, D. E., J. Electrochem. Soc. 102, 95 (1955). (8) Page, J. E., Smith, J. W., Waller, J. C., J . Phys. & Colloid Chem. 53,545 (1949). (9) Straasner, J. E., Delahay, P., J . Am. Chem. Soc. 74, 6232 (1952).
RECEIVEDfor review RIay 14, 1962.
Accepted August 6, 1062.
Spectrophotometric Determination of Formaldehyde and Formaldehyde-Releasing Compounds with Chromotropic Acid, 6-Ar I in0-1- na pht hol-3-suIf o nic Acid (J Acid), and 6-Ani in0-1- na pht h01 - 3-suIf o nic Acid (Phenyl J Acid) EUGENE SAWICKI, THOMAS R. HAUSER, and SYLVESTER McPHERSON Robert A. Taff Sanifary Engineering Cenfer, U. S. Department of HeaNh, Education, and Welfare, Cincinnati 26, Ohio
b Three highly selective procedures for the determination of formaldehyde releasing comand formaldehyde pounds are introduced. In all cases xanthylium cationic or dicationic dyes are formed. The procedures have sensitivities approximately two and one-half times that of the chromotropic acid method. A sensitive thermochromic blue spot test for formaldehyde with 6 amino 1 naphthol 3 sulfonic acid is described, and nine different methods for the determination of formaldehyde are compared. The interference of formaldehyde-releasing compounds is discussed.
-
-
- -
- -
T
he spectrophotometric determination of formaldehyde with chromotropic acid has been described in many papers since the original observations of Eegriwe (6). By the same procedure or through the use of higher temperatures or longer heating times, many formaldehyde-releasing compounds give a positive purple color and thus can be determined (1, 4). A formaldehyde-releasing compound is defined BS any organic compound which is hydrolyzed or oxidized in warm sulfuric acid under test conditions to give formaldehyde as one of the products. Other organic compounds, such as formic acid, can be reduced t o formaldehyde (6) or, like methanol, can be oxidized to formaldehyde (8) 1460
*
ANALYTICAL CHEMISTRY
and then determined by the chromotropic acid procedure. Recently the 2-hydrazinobenzothiazole (9), the 2-hydrazinobenzothiazole - p - nitrobenzenediazonium (II), and the tetrafluoroborate 3 - methyl - 2 - benzothiazolone hydrazone (10) procedures for aldehydes were studied. All of these methods can be used to determine formaldehyde. The advantages and disadvantages of these various methods in the determination of formaldehyde are discussed and are compared Ivith ne\? methods. EXPERIMENTAL
Reagents and Apparatus. Chromotropic acid was purified by recrystallization from water, as some commercial samples contained only 50oJ, of the acid. The reagent solution used was 1.0% chromotropic acid in concentrated sulfuric acid. The solution was stable for a t least 1 day b u t darkened slightly on further standing. 6-Amino-1-naphthol-3-sulfonic acid (J acid; K & K Laboratories, Inc., Jamaica, N. Y.)was purified by washing with boiling dimethylformamide, filtering, washing the cake with acetone, dissolving the cake in boiling aqueous potassium hydroxide, treating with charcoal, filtering hot, reprecipitating with hydrochloric acid, filtering, and again washing the cake with acetone. The reagent solution used was 0.2% in concentrated sulfuric acid and was stable for at least 2 days.
6-Anilino-1-naphthol-3-sulfonic acid (Phenyl J acid; K & K Laboratories, Inc., Jamaica, N. Y.) was purified in the same manner as the 6-amino derivative. The reagent solution used was 0.1% in Concentrated sulfuric acid and was stable for at least 2 days. Sodium metabisulfite was a 20% aqueous solution containing 1 ml. of concentrated sulfuric acid oer 100 ml. of solution. Formaldehyde was a 39.7% ACS reagent solution from Matheson, Colemag, and Bell. The solution was analyzed by the gravimetric method of Yoe and Reid (14). In the preliminary spectrophotometric experimentation, a Beckman Model B spectrophotometer was used, and in all quantitative analyses, a Cary Model 11 recording spectrophotometer with 1-cm. cells was used. Chromotropic Acid Procedures. The spectrophotometric procedures of West and Sen (IS) (Procedure A) and Bricker and Johnson (8) (Procedure B) were applied t o compounds containing combined formaldehyde. The spectral data obtained from these procedures are recorded in Table I. J Acid Procedures. PROCEDURE A. Two milliliters of aqueous test solution and 5 ml. of 0.2Q/, reagent solution are mixed in a 10-ml. volumetric flask without control of the hea,t of mixing. After the mixture has cooled t o room temperature, it is diluted to 10 ml. with concentrated sulfuric acid. A positive test gives a yellow color, whereas a blank produces no color. The absorbance is de-
