temperature reaction with zinc dust and Claisen alkali in methanol, was followed. Ten milliliters of test solution was required. Polarographic Method. Methods for determining disulfides polarographically by reduction a t the dropping mercury electrode have been suggested by Gerber (W) and Hall ( 3 ) . The techniques suggested by Hall were used to obtain polarograms of 16 disulfides. The test solutions were diluted 1 to 5 with the solvent electrolyte, andpolarograms were obtained a t 25” =t 1°C. Satisfactory curves were obtained for all compounds except the three secondary disulfides. No plateau was detectable for the secondary disulfides before breakdown of the electrolyte; interpretable inflections were observed when a greater dilution (2 t o 25) was used. RESULTS
Acid-Reflux Method. D a t a for the disulfide determination by the acidreflux method on the 15 compounds are given in Table I. This method is satisfactory for determining the normal and secondary disulfides and aromatic disulfides of high molecular weight. With the tertiary disulfides, recoveries of 62 to 83y0were obtained. Results were low with disulfides t h a t ieduce to volatile thiols of low molecular weight. These thiols may remain as gases in the apparatus or 10 to 307, may be lost in the wash water. Acid-Stirring Method. Good recoveries were obtained by this method
with all the normal and secondary disulfides (Table I). Except for 1,2-diphenyl-1,2-dithiaethane,recoveries greater than 95% were obtained with aromatic compounds. Low results (13 to 17%) were obtained with tertiary disulfides. The use of zinc amalgam (6) did not improve recoveries. Alkali Method. Except for the first two compounds, recoveries above 95yo ryere obtained for the normal disulfides (Table I). Low results were obtained for the secondary, tertiary, and aromatic disulfides. Results on duplicate determinations were often erratic. The use of air pressure to facilitate filtering probably contributes to the low piecision of this method, causing loss of thiols by ovidation and increased evaporation. Polarographic Method. Polaro. graphic data on the 16 disulfides are shown in Figure 1. (One additional disulfide, 2,7-dimethyl-4.5-dithia-o~tane, was added t o shon- the effect of branching.) The diffusion current constant, K, measured a t 25’* 1’ C., is expressed as I d / C where I d is the observed diffusion current in microamperes and C is the concentration of the disulfide in millimoles per liter. Half-wave potentials are reported in reference to the saturated calomel electrode. Internal resistance corrections, which would be high because of the high resistance of the electrode, have not been applied to the half-wave potentials. However, the data are internally consistent because measurements were made a t approxi-
mately equal current. The precision for the secondary and tertiary conipounds was less than for the other conipounds because of interference of the electrolvte. LITERATURE CITED
(1) Ball, J. S., Bur. Mines Rept. In-
vest 3591 (1941). (2) Gerber, M. I., Shusharina, 4. D., Zhur. Anal. Khim. 5 , 262-71 (1950). (3) Hall, M. E., ANAL.CHEM.25,556-61 (1953). (4) Harnish, D. P., Tarbell, D. S., Ibid., 21,968-9 (1949). (5) Kolthoff, I. M., May, D. R., Morgan, Perry, Laitinen, H. A., O’Brien, A. S., IND.ENG.CHEM.,ANAL.ED. 18.442 (1946). (6) Lykken, Louis,’ Tuemmler, F. D., Ibid.. 14, 67-9 (1942). ( 7 ) McAllan, .D. T.; Cullum, T. V., Dean, R. A., Fidler. F. A., J. A m . Chem. SOC.73,3627-32 (1951). (8) McCoy, R. N., Weiss, F. T., ~ X A L . CHEM.26, 1928 (1954). (9) ~, Rosenwald, R. H., Petroleum Processing 6,’973 (1951). (10) Tamele, M. W , Ryland, L. B., IND.ENG.CHELI.,ANAL. ED. 8, 16-19 (1936). RECEIVEDfor review June 11, 1956. Accepted August 26, 1957. Group session, Refining Division, American Petroleum Institute, Montreal, Quebec, May 14, 1956. Part of the work, of American Petroleum Research Project 48A on “Production, Isolation, and Purification of Sulfur Compounds and Measurement of Their Properties,” which Bureau of Mines conducts a t Bartlesville, Okla., and Laramie, Wyo.
Fluorometric and Colorimetric Estimation of Cyanide and Sulfide by Demasking Reactions of Palladium Chelates JACOB S. HANKER, ALAN GELBERG, and BENJAMIN WITTEN Chemical Research Division, Chemical Warfare laboratories, Army Chemical Center, Md.
b Rapid, sensitive, fluorometric and colorimetric methods have been developed for the estimation of microgram amounts of sulfide and cyanide. The methods are based on demasking reactions of palladium chelates. By the fluorometric procedure 0.02 7 of cyanide per ml. of solution may be estimated; the sensitivity to sulfide is 0.2 7 per ml. of solution. The colorimetric method is sensitive to 1 of sulfide or cyanide ion per ml.
T
of cyanide by demasking reactions has been reported by Feigl and Feigl ( I ) and Feigl and Heisig ( 2 ) . The former reported a colorimetric detection procedure in which the demasking of dimethylglyoxime by the action of cyanide ion on palladium(I1) dimethylglyoximate permits nickel ion present to form the red nickel dimethylglyoximate. Feigl and Heisig reported the detection of 2.5 y of cyanide by the demasking of oxine HE DETECTIOS
(8-quinolinol) from copper(I1) oxinate, which permits aluminum ion present to form the fluorescent aluminum(II1) oxinate. This work describes demasking reactions for the detection and estimation of cyanide which are more sensitive and more readily adaptable to quantitative instrumental analysis than the methods mentioned above. The fluorometric method depends upon the demasking of 8-hydroxy-5VOL. 30,
NO. 1,
JANUARY 1958
93
quinolinesulfonic acid by cyanide or sulfide from the nonfluorescent potassium bis (5-sulfoxino)palladium( 11). The
INONFLUORESCENTI
liberated 8-hydroxy-5-quinolinesulfonic acid then coordinates with magnesium ion present to form a fluorescent chelate which is a measure of the amount of cyanide or sulfide present. The colorimetric method depends upon the demasking of 8-hydroxy-7iodo-5-quinolinesulfonic acid from the yellow potassium bis(7-iodo-5-sulfoxino) palladium(I1). The demasked 8-hydroxy-7-iodo-5-quinolinesulfonic acid then coordinates with ferric ion present to form a blue-green chelate (4) which is a measure of the amount of cyanide or sulfide present.
1 gram of cyanide ion was dissolved in 1 liter of distilled water; 1 ml. of this solution was equivalent to 1000 y of cyanide ion. The appropriate dilutions were made with distilled water. Standard Sulfide Solution. Reagent grade sodium sulfide was analyzed argentometrically (3) and the value obtained was used as the sulfide content. The stock solution and dilutions were made in the same manner as for the cyanide solutions.
I
7
Effect of p H on Fluorescence. The effect of p H on the fluorescence of the magnesium chelate was determined by the addition of varying amounts of alkali to solutions containing 1 ml. of O . O O l ~ o 8-hydroxy-5quinolinesulfonic acid and 1 ml. of 0.1% magnesium chloride hexahydrate (Figure 1, A ) . Maximum fluorescence intensity occurred a t approximately p H 11.3. Effect of Glycine Buffer on pH. When a glycine-sodium chloride solution \\-as added t o an alkaline solution of magnesium chloride and 8-hydroxy5-quinolinesulfonic acid in order t o buffer a t p H 11.3, fluorescence intensity was much lower in the buffered solution than in a solution adjusted t o the same p H with alkali alone. The effect of varying the alkali content of the buffer solution (to vary pH) on fluorescence intensity of the magnesium chelate was then investigated (Figure 1, B). Maximum fluorescence intensity in the buffered solutions occurred a t pH 9.2 rather than 11.3, as in the unbuffered solutions. Therefore, the solutions were buffered with glycine-alkali to pH 9.2. Reagents and Apparatus. Standard Cyanide Solution. Reagent grade potassium cyanide was analyzed argentometrically (3) and the valueobtained was used as the cyanide content. A quantity of the potassium cyanide equivalent to
94
ANALYTICAL CHEMISTRY
, 9
, IO
I
II
P” Figure 1. Effect of glycine on pH for maximum fluorescence A. 6.
FLUOROMETRIC METHOD
I
8
1 ml. of 0.001% 8-hydroxy-Squinolinesulfonic acid, 1 ml. of 0.1% magnesium chloride; 1 N sodium hydroxide added 1 mi. of 0.001 % 8-hydroxy-5-quinolinesulfonic acid, 1 mi. of 0.1% magnesium chloride, 1 ml. of glycine solution; 1N sodium hydroxide added
Sodium Hydroxide, 1N. Glycine Solution. A solution containing 77.4 grams of glycine and 58.6 grams of sodium chloride per liter of distilled water was prepared. If a precipitate appeared upon standing (about 2 weeks), the solution was filtered before use. Potassium Bis (5-sulfoxino) palladium(11) Solution, 0.01% w./v. in water. The chelate was prepared as follows. 8-Hydroxy-5-quinolinesulfonic acid
TIME
Figure 2. time
(4.50 grams, 0.02 mole) was added to a solution of palladous chloride (2.14 grams, 0.01 mole) in 300 ml. of 5% sulfuric acid. The solution was heated to boiling and then cooled to room temperature. Saturated potassium carbonate solution rras added until .the evolution of carbon dioxide ceased. The chelate separated as a fine, yellow precipitate. It JTas collected on a filter, washed successively with 10% potassium carbonate solution, water, alcohol, and ether, then dried in air. Magnesium Chloride Hexahydrate Solution, 1% w./v. Fluorometer. The Klett No. 2070 fluorometer used has been described ( 5 ) . Corning filter No. 5970 was the primary filter; Corning filters 4308 and 3389 served as secondary filters. The fluorometer was standardized before each series of readings by adjusting the slit width so that a sealed Klett cylindrical cuvette containing ethyl formate read 30 fluorometer scale units. The fluorescence of the ethyl formate was unchanged when checked periodically for 6 months us. a standard fluorescent glass. The fluorescenceof the glass corresponded to the fluorescence of a solution containing 0.08 y of quinine sulfate per ml. Determination. Standard curves (Table I) were prepared using known concentrations of cyanide or sulfide in distilled rrater. To 1 ml. of 1K sodium hydroxide in a Klett cylindrical cuvette was added 1 ml. of the cyanide or sulfide solution. Then 1 ml. of the glycine solution, 1 ml. of the palladium chelate solution, and 1 ml. of the magnesium chloride solution were added. The fluorescence intensity was measured after 8 minutes with a fluorometer. Results and Discussion. The precision of the method is evident from a consideration of Table I. The fluorescence intensity of the blank and sample increased continuously with time (Figure 2). The curves indicate that readings a t any set time from 5 t o 10 minutes after the addition of
(MINUTES)
Increase in fluorescence intensity with
Duplicate points are for duplicate samples 0.1 y of cyanide A. Reagents 6. Reagent blank
+
the last reagent would probably be useful. A period of 8 minutes was chosen because oi convenience with respect to the number of unknowns being determined. -4possible explanation for the effect of glycine on the p H for maximum fluorescence (Figure 1) can be offered if the equilibria involved are considered. Let M P
= =
B = G =
Mg++ phenolate ion of 8-hydroxy-5quinolinesulfonic acid hydroxyl ion glycinate anion
In the absence of glycinate anion, a greater concentration of hydroxyl ion is necessary to tie up excess magnesium ion so that maximum fluorescence occurs a t a higher pH, 11.3. However, the p H effect on maximum fluorescence intensity may be due to other factors which were not studied experimentally -e.g., the variation of chloride ion concentration or the variation in ionization of the M P and species with ionic strength of the solution. COLORIMETRIC METHOD
I n alkaline medium the competition of the ligands (P, B, and G) for Yi may be expressed by the equations: ki
M+X$MX
(1)
ki
+ x e MX2
(2)
MXz+M=2MX
(3)
MX
where X = P, B, or G and kl and are equilibrium constants for Equations 1 and 2, respectively.
I’
475
5w
550
6W
700
ow
1
1
Preliminary experiments indicated that good sensitivity could be obtained with this method if the cyanide were allowed to react with the potassium bis(7 - iodo - 5 - sulfoxino)palladium(II) in alkaline solution and the color developed by the addition of the ferric salt in acid solution. The visible absorption spectrum of the potassium tris(7-iodo-5sulfoxino)iron(III) in the presence of excess potassium bis( 7-iodo-5-su1foxino)palladium(I1) was determined with a Beckman Model DK recording spectrophotometer (Figure 3). The absorption maximum occurred a t 650 mp. Reagents. The standard cyanide and sulfide solutions prepared for the fluorometric procedure were used; because of the difference in sensitivity of the two methods, different dilutions were used. Sodium Hydroxide, 0.1N. Potassium Bis(7-iodo-5-sulfoxino)palladium(I1) solution, 0.2% w./v. The chelate was prepared by essentially the same procedure described above for potassium bis(5-sulfoxino)palladium-
(11) 0
900
WAVE LENGTH IMILLIMIcRONS)
Figure 3. Absorption spectrum of poTable I. Fluorescence vs. Concentratassium tris(7-iodo-5-sulfoxino)iron(lll) tion of Cyanide or Sulfide ion in presence of potassium bis(7-iodo-
5-sulfoxino)palladium(ll)
It is assumed that MP2 is the fluorescent species and NIP is nonfluorescent. From a consideration of Equations I, 2, and 3, it is to be expected that the mass action effect of the great excess of magnesium ion to 8-hydroxy-5-quinolinesulfonic acid used should tend to decrease the concentration of MP2 and increase the concentration of MP. I n the system containing glycinate anion there is less magnesium ion present a t pH 9.2 than in the system a t the same p H from which glycine has been omitted. The mass action effect of this decrease in magnesium ion concentration is in favor of the formation of MP2, the fluorescent species, a t the expense of MP, the nonfluorescent species.
Concn. of Sample, y/Ml.
0.1 0.2 0.3 0.4 0.5 0.6
0.7
0.8 1
Net Fluorometer Scale Reading“ Cyanide 30 29 60 59 84 86 116 118 146 146 174 171 195 194 235 235 12
3
25 41
5
71
4
Table II. Absorbance vs. Concentration of Cyanide or Sulfide ion
Concn. of
Sample, y/Ml.
S e t Colorimeter Scale Reading. Cyanide
10 20
~.
30 40 50
82
156 219 280 340
78 151 215 276 338
Sulfide in
42
39
Each reading represents a separate determination. 0
As expected, the colorimetric method is not so sensitive as the fluorometric method. Thiocyanate, thiols, and certain disulfides also give this reaction. LITERATURE CITED
27 57 79 111
143 173 199
...
Sulfide 2
Ferric Chloride Solution. A 10% w./v. ferric chloride (calculated as FeC18) solution was diluted with an equal volume of 1N hydrochloric acid. Determination. Standard curves (Table 11) were prepared using known concentrations of cyanide or sulfide in distilled water. T o 1 ml. of 0.10N sodium hydroxide in a Klett cylindrical cuvette mas added 1 ml. of the cyanide or sulfide solution. Then 1 ml. of the palladium chelate solution and 1 ml. of ferric chloride solution were added. The blue-green color that formed was stable after 1 minute and was measured with a Nett-Summerson colorimeter using a No. 64 filter.
55
14
27
44 58 73
13 26 42 56 72
a Each reading represents a separate determination.
(1) Fiegl, F., Feigl, H. E., Anal. Chim. Acta 3,300 (1949). (2) Feigl, F., Heisig, G. B., Ibid., 3, 561 (1949). (3) Kolthoff, I. M., Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” p. 574, Macmillan, New York, 1947. (4)Welcher, F. J., “Organic Analytical Reagents,” Vol. 1, pp. 336-7, Van Nostrand, Kew York, 1947. (5) Willard, H. H., Merritt, L. L., Dean, J. A., “Instrumental Methods of Analysis,” 2nd ed., pp. 30-1, Van Nostrand, New York, 1951. RECEIVED for review February 12, 1957. Accepted August 21, 1957. Syfnposlum on Chemical Corps Methods, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., February 27, 1956. VOL. 30, NO. 1, JANUARY 1958
0
95
