564
ANALYTICAL CHEMISTRY
Table 11. Polarographic Determination of Sulfite in Various Solutions (P.p.m. a s sulfur) Calcd. Detd. 908 Concn. SO8 Concn. 15.2 16.1 3.8 3.9 7.6 6.9 11.4 11.7 15.2 15.3 31.0 30.0 225 222 31.0 31.7 29.0 29.4 29.0 26.7 22.5 21.7 45.0 47.8
Solution Dist. water
Sewage Sludge liquor
Average
Error, Error +0.9 +O.l -0.7 f0.3 +O.l -1.0 -3.0 +0.7 +0.4
-2.3 -0.8 +2.8 11.2
%
5.9 2.6 9.2 2.6 0.7 3.2 1.3 2.3 1.4 7.9 3.6 6.2 3.8
noted at the same applied potential. The difference between the two galvanometer readings is directly proportional to the sulfite concentration in the sample. This proportionality has been determined previously above. DISCUSSION
The accuracy of the polarographic method is shown (Table 11) by the recovery of sulfite added to distilled water, sewage, and sludge liquor from which the sulfite, thiosulfate, and sulfide were removed (3). The method is sensitive to at least 1 p.p.m. of sulfite sulfur. The diffusion current produced by this concentration corresponds to 18 divisions (0.335 pa.) on the scale of the galvanometer used. The method is not recommended for
use with samples containing more than about 200 p.p.m. of sulfite sulfur because of the longer time required for the desorption of the sulfur dioxide a t higher concentrations. Of all the substances present in sewage and sludge liquor, only sulfide and thiosulfate were found to interfere. When these were removed, the average error of the method was reduced to about 4%. The removal of sulfide and thiosulfate from the sample by the method of Mangan (3) required about 2 hours. Centrifugation consumed the major portion of this time. Several samples may be treated simultaneously, thereby reducing the time per sample. In most wastes, thiosulfate and sulfide are seldom found in the presence of sulfite, The conditions under which these compounds occurred together were artificially created in order to study the transformations of these sulfur compounds during sewage treatment. After the preparation of the sample, to remove these interfering compounds, the polarographic determination required only 15 minutes. LITERATURE CITED
S.,J. Am. Chem. Soc., 62, 2171 (1940). ( 2 ) Ibid., 63,2818 (1941). ( 3 ) Mangan, J. L., New Zealand J. Sei. Technol., 30B, 323 ( M a y 1949). (4) Scott, W. W., “Standard Rlethods of Chemical ilnalysis,” 5th ed., p. 925, Van Nostrand, New York, 1948. (5) Ibid., p. 926. (1) Kolthoff, I. M., and Miller, C.
RECEIVEDfor review June 1, 1954. Accepted November 13, 1954. Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgera University, t h e State University of New Jersey Department of Sanitation, New Brunswick.
Spectrophotometric Determination of Aliphatic Sulfides S. H. HASTINGS and B. H. JOHNSON Humble
Oil and Refining Co., Baytown, Tex.
A procedure for spectrophotometric determination of aliphatic sulfides has been modified to improve its accuracy and reproducibility.
I
S A previous paper ( 1 ) a procedure was given for the determination of aliphatic sulfides, utilizing the intense ultraviolet absorption spectrum of the complex formed between these sulfides and molecular iodine. Certain modifications have been made to improve the accuracy and reproducibility of the method and an error in the original paper has been noted. The decrease in absorbance of the iodine-sulfide complex with time while in the cell compartment of the Beckman DU quartz spectrophotometer was thought to be due to the fact that the sample was in the dark; however, it was caused simply by a shift in the equilibrium brought about by the higher temperature of the cell compartment. The thermal effect noted on the Beckman spectrophotometer also occurs with the Cary ultraviolet spectrophotometer (Model 11). The equilibrium involved is
R’SR
+
I1
C---r-
R’SR.12
(1)
where R’SR is an aliphatic sulfide, Ip is molecular iodine, and R’SR.12 is the complex. This reaction has been found to be temperature-sensitive, lower temperatures favoring the formation of the complex. As a result, it is necessary to perform the analysis under controlled temperature conditions or apply a temperature correction. The temperature coefficient of the “apparent” absorptivity of the complex is approximately 13 absorptivity units per degree Fahrenheit a t 79’ F., and absorptivity is 372 liters per gram cm. (at thermal equilibrium in the cell compartment). The term
-
“apparent” is employed because the absorption due to the complex has been correlated with the initial sulfide sulfur concentration and this relationship is significantly affected by the temperature. The iodine concentration specified in the original work was later found to be far from optimum. Study of the iodine-sulfide complex has shown that the complex is a 1 to 1 combination of iodine with the sulfide, as indicated above. The equilibrium constant for this reaction is
where i indicates the initial concentrations. Calculations based on the iodine and sulfide concentrations specified in the analytical procedure (1) show that the two species must be present in very close to a 1 to 1 mole ratio, and as a consequence, the complex concentration is very sensitive to slight changes in the concentration of either of the partners making up the complex. This is undesirable, as it is known that aromatic and olefinic hydrocarbons tie up some iodine and consequently the iodine concentration is not constant, as was previously assumed. However, if the iodine concentration is made large with respect to the sulfide concentration, the factor ( [I214 - [R’SR.Iz]) in Equation 2 is essentially constant and the absorbance due to the complex is significantly affected only by changes in [R’SR],. Another important advantage results when [I21,>>[R’SR];. The equilibrium constant can then be written, to a good approximation, as [R’SR.I,] K = [I214[R’SRIi - [R’SR.Iz])
(3)
V O L U M E 27, NO. 4, A P R I L 1 9 5 5
565
and Table I.
Therefore, the initial sulfide concentration is linearly related to the complex concentration and a Beer’s law equation can be used to calculate the sulfide concentration from the measured absorbance due to the complex. The deviation in the apparent absorptivity for the condition, [I2]% [R’SR] is 17% over an absorbance range of 0.5 to 2.0. mith the proposed changes in [I*],and [R’SR], the deviation is reduced to 4%. The procedure has been modified to provide a large excess of iodine over sulfides by taking 1 ml. of the appropriate dilute sample and making up to 10 ml. with the stock iodine solution. In this manner, the iodine concentration is increased 9-fold, while the sample concentration is reduced by a factor of 1/9. Under these conditions the absorptivity for sulfide sulfur is 372 liters per gram-em. (on the Cary instrument) for a cell compartment temperature of 79” F. The absorptivity is adjusted for actual cell compartment temperature using the temperature coefficient of - 13 absorptivity units per degree Fahrenheit increase. Thermal equilibrium is generally approached closely in about 10 minutes. The use of a lower sample concentration has the added advantage of permitting the examination of more highly absorbing samples than would othern-ise be possible. As a matter of fact, it has been possible to analyze stocks such as heavy gas oils, which generally have considerable absorption near 310 mp. The sulfide sulfur contents of a number of heavy virgin gas oils, as determined by this method, are shown in Table I, along with the total sulfur content determined by the Dietert method. A significant proportion of the sulfur in these gas oils is of the sulfide type. This sulfide sulfur may be in acyclic or cyclic saturated systems or in side chains attached to aromatic nuclei. It is definitely not directly connected to an aromatic ring (1). A further modification of the method is employed when it is desired to know the sulfide sulfur content of samples R hose actual sulfide content is extremely low. In cases of this sort, considerably improved accuracy may be obtained by treating a portion of
a
b C
Aliphatic Sulfide Sulfur Content of Virgin G a s Oils”
Sulfur, Weight % Source of Gas Oil Sulfide b Totalc 0.46 2.15 West Texas 0 . 2 5 0.43 Panhandle 0.07 0.17 Tomball 0.16 0.27 Heavy coastal Hawkins 0.56 2.41 0.61 2.05 R e s t Texas Nominal 700-1000° F. equivalent atmospheric boiling range. Determined by revised iodine-complex method. Determined b y Dietert method.
the sample with solid mercurous nitrate to remove sulfides. This is followed by a wash with 10% aqueous mercuric nitrate solution to assure complete removal, a water wash, and filterpaper drying. The treated sample may then be employed as B blank by adding iodine to the treated sample in the manner in which it is added to the untreated sample. Comparing the two solutions directly on the Cary spectrophotometer yields a delta spectrum which is due only to the sulfide sulfur complex (after a slight correction for differences in cell absorbance). This procedure is more or less restricted to the gasoline boiling range. Attempts to remove sulfides from stocks of gas oil boiling range showed that the mercurous nitrate-sulfide complex, although actually formed, was oil-soluble. Attempts to remove the complex by water washing resulted in destruction of the complex and regeneration of the original sulfides. ACKNOWLEDGMENT
The authors wish to express their appreciation to the management of the Humble Oil and Refining Co., in whose laboratories this work was conducted, for permission to publish this paper. LITERATURE CITED
(1) Hastings,
S. H., ANAL.CHEM..25, 420-2 (1953).
RECEIVED for review July 29, 1954. Accepted Sovember 26, 1954.
Determination of Acetovanillone in Oxidized Alkaline Cleaved Sulfite liquor by Paper Chromatography E. T. REAVILLE and G . W. SHREVE Monsanto Chemical Co., St. Louis,
Mo.
A rapid method of analysis for acetovanillone in oxidized alkaline cleaved waste sulfite liquor by paper chromatography has been developed. A n accuracy within =k5% is indicated.
T
HE oxidation of waste sulfite liquor in strong caustic solution at elevated temperatures produces vanillin, vanillic acid, acetovanillone, guaiacol, and many other substances qith a guaiacyl nucleus (2). To study the formation of cleavage products from waste sulfite liquor, rapid analytical methods are desirable. Stone and Blundell ( 3 ) have devised a paper chromatographic technique for determining vanillin directly in oxidized alkaline cleavage hardwood liquors. In this laboratory, experiments on oxidized waste sulfite liquor from gymnosperm lignin showed that it was not possible to separate vanillin from acetovanillone with any of the solvent systems used or modifications of them ( 3 ) . In an analysis for va-
nillin, the failure to separate vanillin from acetovanillone is of little importance. The vanillin content in a solution of vanillin and acetovanillone is calculated readily from ultraviolet absorbance using a suitable pair of wave lengths. However, where acetovanillone contributes little to the total absorbance, the ca‘culation of the acetovanillone content by this method results in differences of large numbers and gross inaccuracies. Newcombe and Reid ( 1 ) reported a method of separation of vanillin from acetovanillone by pretreatment of the paper with sodium bisulfite but gave nothing quantitative nor any applications. h paper chromatographic method for determining the acetovanillone content of oxidized alkaline cleaved waste sulfite liquor has been developed through which, by the action of the developing solvent, vanillin, acetovanillone, p-hydroxybenxaldehyde, and vanillil are separated from the other organics but not completely from one another. The action of the developing solvent is therefore supplemented by the application, just above the sample, of a bisulfite “block”
