polarographic cell, the color at the solution-solid interface varies from yellow to red, depending on the amount of tin present, while the homogeneous solution is colorless. ACKNOWLEDGMENT
The author thanks Evan Morgan for his dkcussions and John c. M‘ebber for tracing the polarograms.
LITERATURE CITED
(1) Caley, E. R., J . Am. Chem. SOC.54, 3240 (1932). (2ilttJ\T ’ ANAL. 15, (3) Kern, D. M. H., J . Am. Chem. SOC. 76, 1011 (1954). i J: J.,~ (4) Kolthoff, 1. sf., ~ ~~Polarography, ,, p. 526, I ~ ~ New York, 1952. (6) (5) Lektorskaya, p*586. N. A,, Kovalenko, P. N., Nauch. Dokludy VyssheZ Shkoly, Khim. i Khim. Tekhnol. 1, 102 (1959).
(7) Lingane, J . J., J . Am. Chem. SOC 67 919 (1945). ( 8 ) Mjura, y., Japan Analyst 7(12), 779 (1998). ( 9 ) Schaap, W. V., Davis, J. A , , Neber(1954). gall, W. H., J. Am. Chem. SOC.76, 5226 (10)~ Steyermark, ~
1 % ~ “Quantitative ~ ,Or~ganic Microanalysis,” ~ ~ ~ p. 161, , Blakiston, ~ ~ Xew York, 1951. (11) Ibid., p. 231.
RECEIVEDfor review October 26, 1959. Accepted March 25, 1960.
Cathodic Polarographic Wave of Trivalent Arsenic in Alkaline Media W. B. SWANN, J. F. HAZEL, and WALLACE M. McNABB Department of Chemistry, University of Pennsylvania, Philadelphia, Pa. ,It has been reported that a polarographic wave i s not obtained when trivalent arsenic i s reduced at the dropping mercury electrode in an alkaline media containing sodium hydroxide. This paper describes the reduction of trivalent arsenic in a lithium chloride-lithium hydroxide electrolyte at the dropping mercury electrode to give a polarographic wave. The wave i s irreversible, but i s well defined and proportional to the arsenite concentration. It i s believed that this method of determining arsenite may be used advantageously in the determination of arsenic in many materials.
estimate the arsenite concentration. For satisfactory results, the conditions affecting the analysis had to be controlled carefully. I n this paper a well-defined wave due to the reduction of arsenitc ions a t the D M E in a 0.1V LiC1-0.01JI LiOH electrolyte is reported. The diffusion current was proportional to the concentration of arsenic in the range investigated, 1 X 10-4Alfto 6 X 10-4AlI. The diffusion current !vas not excessively affected by the p H of the solution. This method for determining the arsenite concentration is believed t o be applicable to many analytical procedures which are used to determine arsenic in a variety of materials.
id/Cm2
T
of arsenite at the dropping mercury electrode (DhIE) in acidic media has been extensively studied. Kacirkova (3) studied the reduetion in l d l hydrochloric acid and Lingane (5) used the same electrolyte but added O . O l ~ o gelatin as a maximum suppressor. Lingane (5) also studied the reduction in 0.5111 sulfuric acid and in 1N nitric acid. The reduction of arsenite in sodium hydroxide was studied by Bayerle ( 2 ) and by Kolthoff and Lingane (4). The latter reported that arsenite ions do not give a polarographic wave from 1,)‘ sodium hydroxide solutions and neutral or alkaline tartrate solutions. Bayerle ( 2 ) ,on the other hand, reported no polarographic wave but he did observe some polarographic activity due to the arsenite ions. Bambach (1) applied the technique to the determination of arsenic in biological materials. He measured the arsenite polarographically in a 1. O M hydrochloric acid solution and used one of several fairly well defined m-aves to HE REDUCTION
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The D M E was a conventional electrode (Fisher Scientific Co.) and was connected t o a mercury reservoir in the usual manner. The reference electrode was a silver-silver chloride electrode used with a 1 M lithium chloride salt bridge. Polarograms. The polarogram of arsenite in 0.1M lithium chloride0.01M lithium hydrovide ( p H 12) revealed t h a t reduction started at approximately - 1.75 volts and t h a t the limiting current (plateau) appeared between -2.0 and 2.1 volts. The characteristics of a typical polarogram were: Cell temperature = 30” i 0.1” C. Mercury-height = 35 cm. m2/3t1’6 = 1.98 (mg. of Hg)213 (sec.)1/6 Concn. of arsenic = 0.188 mmole/liter
ANALYTICAL CHEMISTRY
EXPERIMENTAL
The drop time used in calculating
Reagents. National Bureau of Standards and Baker Analyzed reagent grade arsenic trioxide (dsz03) were used t o prepare t h e standard solutions. T h e electrolyte solutions were prepared from Baker analyzed reagent grade lithium hydroxide and lithium chloride. Apparatus. A Leeds & Xorthrup Electrochemograph Type E was used t o record the polarographic waves.
Table 1.
PH 11.0 11.6 12.0 12.1 12.3 12.6
Effect of pH on Polarographic Wave
-1.86 -1.87 -1.88 -1.88 -1.89 -1.89
15.4 14.8 14.4 14.3 13.3 11.6
Ell2 measured against (Ag-hgC1) reference electrode. 5
= 14.4
m2/3t1’6 was measured a t the half-wave
potential of the wave. Effect of Concentration. -1series of polarograms was made of solutions containing 0.2 t o 0.6 mmole per liter of arsenic in the 0.1X lithium chloride-0.01M lithium hydroxide electrolyte. -4plot of the limiting diffusion current against concentration gave a straight line passing through the origin. Effect of pH. As shown in Table I, t h e DolaroeraDhic wave height decreaied ivirh -increasing pH.- However, it was essentially constant at a p H of 12.0 i 0.1 as provided by a 0 . l M lithium chloride-0.01.M lithium hydrovide solution. DISCUSSION
The absence of a polarographic wave for arsenite in alkaline media as noted by Lingane (5) was verified by running a polarogram of arsenite in a 0 . l N sodium chloride-0.01M sodium hydroxide electrolyte. Curve A of Fig-
~
ure 1 is a polarogram of a solution containing 3.76 X 10-4M arsenic as arsenite ions, whereas curve B is a polarogram of the same solution but without arsenic. The increase in current of the solution containing the arsenite ions occurred earlier along the voltage axis than the solution containing no arsenite. This difference may indicate that the arsenite ions were reduced in this medium but that the polarographic wave was not formed because of the early reduction of the sodium ions present in the supporting electrolyte. This theory agrees with the work of Bayerle (2), who reported polarographic activity for arsenite ions in a sodium hydroxide solution. I n the case of the lithium chloridelithium hydroxide electrolyte the lithium ions were not reduced until a potential of -2.1 volts had been reached as shown by curve C. This additional range permits full development of the arsenite wave. Logarithmic analysis of the polarographic curve indicated that it mas irreversible. The same analysis indi-
The diffusion current constant, i d / Crn2W8 for the single wave of arsenic was 14.4 a t pH 12. The diffusion current constant reported by Meites (6) for the six-electron reduction of arsenic(II1) to arsenic( -111) in dilute acid mas 12.0. The agreement in magnitude of the two diffusion current constants indicates that the reduction in the lithium chloridelithium hydroxide media was probably a &electron reduction to produce arsine. L OLTS (-1
Figure 1 . Comparison of supporting electrolytes A. 0.1M sodium chloride-0.01M sodium hydroxide containing 3.76 X 1 0-4M trivalent arsenic
B. C.
0.1M sodium chloride-0.01M
sodium hydroxide 0.1 M lithium chloride-0.01 M lithium hydroxide
cated that a t pH 12, the half-wave potential was - 1.88 volts. The change in half-wave potential with pH is shown in Table I.
LITERATURE CITED
(1) Bambach, K., ISD. ENG. h”, ANAL.ED. 14, 265-7 (1942). (.2.) Baverle, V., Rec. trav.chim. 44,514-10 (1925). . . (3) Kacirkova, K., Collection Ceechoslov. Chem. Communs. 1 . 477 119291. ( 4 ) Kolthoff, I. JI:, Lingane; J. J., “Polarography,” Vol. I, pp. 206-7, Interscience, Kew York, 1932. ( 5 ) Lingane, J. J., IND. ENG. CHElf., ANAL.ED. 15, 583-90 (1943). (6) Meites, L., J . A m . Chem. SOC.76, 5927 (1954).
RECEIVED for review February 12, 1960. Accepted May 13, 1960.
Polarographic Determination of Metal Driers in a Nonaqueous Solution E. J. KUTAIlnsfifufe of Marine Resources, Hilgard Hall, Universify of California, Berkeley, Calif.
b A polarographic procedure is given for the rapid determination of metal driers. The solvent is benzene-methanol ( 1 to l ) , and sodium acetate is the supporting electrolyte. Cobalt, copper, iron, lead, manganese, nickel, and zinc driers give a linear relationship between diffusion current and concentration in the range of 1 X 1 O W 4 to 1.5 X 10-3M. Application of the procedure to the determination of iron in menhaden oil showed that the presence of free fatty acids and peroxides interferes with the determination.
find wide application as oil-oxidation catalysts in paints, fungicidal agents, lubricating greases, and waterproofing compounds. Although most methods for the determination of the metal are based on preliminary ashing or extraction from the organic matter, three methods are ETAL DRIERS
Present address, General Foods Research Center, Tarrytown, N. Y .
available without ashing of the sample. The chelometric method (9) determines cobalt, calcium, lead, zinc, and manganese driers, and the photometric method (8) determines all of the above driers with the exception of zinc. By the polarographic procedure presented in this paper, copper, iron, and nickel driers can be determined directly in addition to cobalt, manganese, lead, and zinc driers. Three groups of investigators have used polarography for direct determination of metal driers. Skoog and Focht ( I d ) suspended lead acetate, naphthenate, octoate, linoleate, linoresinate, and resinate in an aqueous dodecylamine acetate solution for the determination. Later, Georgans (6) estimated lead, cobalt, and copper driers in aqueous ethyl alcohol or monoethyl ether of ethylene glycol (Cellosolve) with various supporting electrolytes, depending on the driers being determined. Kaufmann and Bernard (6) polarographically determined lead, zinc, cobalt, iron, and manganese driers with a composite solvent of aqueous 1-propanol, heptane, and ethylene gly-
col, with potassium acetate as the supporting electrolyte. Preliminary experiments showed that all of the metal driers tried, except iron octoate a t concentrations greater than 1.5 mmoles per liter, were completely soluble in a solution of benzene and methanol (1 to I ) in 0.3M sodium acetate. The simplicity of this solvent system suggested that it might be more useful than those previously described. Details for the polarographic determination of the metal driers of cobalt, copper, iron, manganese, nickel, lead, and zinc in this solvent system are described. The n-ave height was directly related t o the concentration of the metal in the drier. Calcium, zirconium, and rare earths did not give a reduction wave under the conditions used. EXPERIMENTAL
Metal Driers. The metal driers and analyses of the metal content were supplied by Advance Solvent and Chemical Division, Carlisle Chemical Works, Inc., New Brunswick, N. J., and are as follows: VOL. 32, NO. 9, AUGUST 1960
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