ANALYTICAL CHEMISTRY
602 Table 11. Comparison of 3Zethods for Removing Sulfur Interference i n Oxygen Analysis Using 50% Platinized Carbon a t 900” C. Sample Thiourea Mixtureof mesitylene benzyl disulfide, and benzoic acid
Theory
Sulfiir. Wt %
0.00 0 . 1 6 . 0 . 0 6 0 . 6 3 0.42, 0.51 0.99 1 . 1 0 , O . Q l 2.342.26,2.30
0.06 0.26, 0.25 0 . 4 F . O .66 0.53,0.77
42.0 1 .G 1 .O 2.2
1.67,1.65
0.53,0.73
1.3
4.96,5.00 2 6 . 6 6 &O.OS; 27.69i0.07
4.27,4.03 26.4 25.6.24 3
I 3 26.7 28.:
Mixture of mesitylene, CHHi?Ndhaand benzoic acid I , 60 Mixture of mesitylene, CnHnSzSP, and maleic an5,04 hydride Cystine 26.68 Sulfanilic acid 27.72 a b
Oxygen, Wt. 7% Found Cu at900’ C . Liquid Nr
Contains thiol and thioether groups. Average of 4 analyses. Average of 7 analyses.
Table I1 shows that the use of copper at 900” C. permit? accurate oxygen analyses of pure compounds and synthetic mixtures containing varying sulfur contents, types of sulfur compounds, and sulfur-oxygen ratios. The accuracy and repeatability are the same as in Table I. I t is thus possible to obtain correct oxygen analyses of such natural products as petroleum, shale oil, coal tar, and asphalt without interference by sulfui. On the other hand, the oxygen analyses obtained with the liquid nitrogen trap were 0.5 to 3% low. KO cracks, leaks, or obstructions developed in the tube of platinized carbon after a year’s service a t 900” C. This is in sharp contrast with experience with the conventional Schutze prore-
dure, in which tubes kept at 1120” C. usually develop leaks or crarkq or are plugged by sintered carbon after 2 to G months. ACKNOWLEDGMENT
The authors wish to express their appreciation to Lydia 11. Deluga, who carried out the exploratory work on metal-carbon mixtures. LITERATURE CITED
.\luise, V. A , . et al., ~ ~ N A CL m. h r . , 23,530 (1951). Campanile, V. A., Badley, J. H., Peters, E. D., Agarai, E. J., and Brooks, F. R.. I b i d . , 23, 1421 (1951). Dinnerstein, R. A., and Klipp. R. W., I b i d . , 21, 545 (1949). Dundy, AI., and Stehr, E., I b i d . , 23, 1408 ,(1951), Harris, C. C., Smith, D. AI., and Mitchell, J., J r . , Ibitl., 22, 1297 (1950). Hinkel, R. D., and Raymond, R . , Ibid.,25, 470 (1953). Holoiwhak, H.. and Wear, G. E. C., Ibid., 23, 1405 (1951). .Jones, IT. H., et al., Ibid., 25, 1449 (1953). Kiisten, W., Ibid., 25, 74 (1953). AIaylott, A. O., and Lewis, J. B., Ibid.,22, 1051 (1950). lIellor, J. W., “Comprehensive Treatise on Inorganic. and Theoretical Chemistry.” Val, 111, p. 216, London, Longmans, Green and Co., 1923. I h i d , , Vol. V , p. 976. 16id.,Vol. VI, 12. 114. Rchiitae, AI., Z . aaal. P h e m . , 118, 241 (1939). Shepherd, lI.,.%N.~L. CHEX.,19, 77 (1947). L-ntersaucher, J., Aiiallist, 7 7 , 584 (1952). L*ntersaucher., .J., Ber., 73B, 391 (1940). Walton, W.IT,, AIcCulloch, F. W.,and Smith, K. H., J . Rcsearch .Yatl. Bur. Standards, 40, 443-7 (1948). RECEIVED for review June 20. 1 9 . Z Acceptel December 4, 1953.
Determination of Fatty Oils in Citronella Oil A. 1. BlGGS Department o f Chemistry, University
HE
o f Malaya,
and Government Department o f Chemistry, Singapore, M a l a y a
estimation of fatty oils (such as coconut or palm oil) in
Tessential oils either by Schimmel’s test or by the method of Zimmerman (5), is valid if the amount of fat is appreciable, (1)
say more than 5%, but in recent years the analyst in Malaya has been confronted with the problem of determining amounts of fat as low as 0.1% as an impurity in oil of citronella. The methods of Schimmel and Zimmerman were not designed for this type of analysis. Moreover, Finnemore (2) records that Schimmel’s test is not always reliable when applied to citronella oil. I n these laboratories positive tests have been obtained in some cases from oils known to be fat-free, while a t other times fat present in considerable amount has failed to react to the test. Other methods based on steam distillation, determination of the fatty acids or the soap produced by saponification, or of the amount of glycerol produced in this way have been studied in these laboratories. The last method was the only one found to give accurate reproducible results and the problem therefore reduced itself to finding a method for the estimation of glycerol in small amounts. The best method found is based on the oxidative degradation method of Malaprade (3, 4)in which glycerol is oxidized quantitatively to formaldehyde and formic acid by acidified potassium periodate, which is itself reduced to iodic acid. The problem now resolves itself into finding a method for the estimation of formaldehyde. Some preliminary experiments were made to find if Schiff’s reagent could be used, but although the reagent gave pronounced colors even R-ith very dilute solutions, the excess periodic acid interfered with the quantitative nature of the analysis and attempts to remove the acid by treatment with sodium thiosulfate or sulfurous acid met with only limited success.
Schryver’s method, however, proved much more promising; it consists of the addition of phenylhydrazine followed by treatment of the phenylhpdrazone with potassium ferricyanide in concentrated hydrochloric acid solution to produce a red coloration detectable even with very small amounts of formaldehyde. This method, however, required some modification because the residual portions of the periodic acid introduced earlier in the analysis inhibited the formation of the color complex. Attempts were made to remove this excess of periodic acid by reducing agents such as sulfurous acid or sodium thiosulfate, but the slightest excess of any of these agents resulted in erratic color formation in the final stage of the reaction. I n the earlier experiments sufficient phenylhydrazine was used to combine with the formaldehyde, leaving only a very slight excess. It was found, however, that phenylhydrazine itself can be used as a reducing agent to destroy excess periodic and iodic acids and this excess of phenylhydrazine does not interfere with the color formation. This use of excess phenylhydrazine is essen-
Table I. E s t i m a t i o n of Coconut a n d P a l m Oil by Saponification a n d D e t e r m i n a t i o n of Glycerol Formed .-lint. of Oil Calcd. from Glycerol, G.
Amt. of Oil Teighed Out, G. Coconut Oil 0.110 0.210 0.103 0.117
Palm Oil
0.112 0.213 0.107 0.120
V O L U M E 2 6 , NO. 3, M A R C H 1 9 5 4
603 of 0.5N methanolic potassium hydroxide for 1hour. Methanol is preferable to ethanol as a solvent hecause the evaporation in the next stage can be done a t a lower temperature, thus avoiding loss of glycerol. The residual solution is diluted with saturated sodium chloride solution, made slightly acid with dilute sulfuric acid, and warmed on a water bath until the methanol has evaporated. The aqueous solution is extracted with ether, made alkaline andextractedwith ether, and neutralized and extracted twice with ether. The aqueous solution is warmed to remove residual ether, cooled, and diluted with water to give a concentration of glycerol between 0.001 and 0.006%, and the concentration is determined as describkd above.
T a b l e 11. D e t e r m i n a t i o n of C o c o n u t and P a l m Oils in Citronella Oil Sample
1
2
Coconutoil, % a s m a d e u p Coconutoil, % byanalysis
1.06 1.06
1.06 1.07
1 . 0 6 0 . 1 0 0.10 1.07 0.11 0.11
Sample Coconutoil, % a s m a d e u p Coconutoil, Y’byanalysis
10 5.0 5.0
11 5.0 5.1
12
13
0.44 0.44
0.44 0.44
3 0.73 0.73
4 1.4 1.5
Sample Palin oil, To a s made up by analysis Palin oil,
1
2
0.20 0.20
0.38 0.37
3
4
5
6 0.21 0.22
15 14 1.16 0.34 1.15 0 . 3 5
7
8
9
0.21 3 . 1 3.1 0.23 3 . 1 3.2 16 0.52 0.50
tial in the method now proposed. I n addition, i t was found better to use ferric ammonium sulfate in place of potassium ferricyanide. The color so obtained has maximum absorption a t a wave length of 5200 A. The optimum conditions for color development have been studied; it has been found that the time of reaction a t each stage is critical and the concentrations of each reagent have to fall nithin defined limits, but the method proposed can be used n-ith confidence if the conditions to be described are observed. EXPERIMENTAL
The experimental part of this work is divided into two sections: degradation of the fatty oils in citronella oil to glycerol and determination of the glycerol. Methods for Determining Small Amounts of Glycerol in AqueA series of aqueous solutions of glycerol is prepared to cover the concentration range of 0.001 to 0.00670 by weight. Two milliliters of each solution are pipetted into a test tube containing 0.2 ml. of 1.25% solution of potassium periodate in 1N sulfuric acid. This is sufficient to reduce the glycerol without leaving an unduly large excess of periodate. The mixture is shaken for 10 minutes. Next, 0.5 ml. of a freshly prepared 1% aqueous solution of phenylhydrazine hydrochloride is added and the mixture is shaken well and allowed to stand for 10 minutes. After the addition of 0.5 ml. of a 1% aqueous solution of ferric ammonium sulfate to the mixture, the mixture is shaken for betaeen 5 and 10 seconds and then 25 ml. of 6N sulfuric acid are added quickly. The resultant mixture is well shaken. A reddish color develops after 1 minute and is stable for a t least 15 minutes; the percentage transmittance or the optical density is determined a t a wave length of 5200 A. The time elapsing between the addition of sulfuric acid and the addition of the ferric salt seems to be critical.
17 6.5 6.3
18
19
9 7 2.0 9 . 8 2.0
The determination should be carried out in duplicate and as a precaution a blank glycerol determination should be made on the unsaponified oil, although on numerous samples of citronella oil the blank has been found to be negligible (corresponding to less than 0.02% fat in the oil). A number of solutions of coconut oil or palm oil in fat-free citronella oil were made, covering a range of oil in the essential oil from 0.1 to 10.0%. Table I1 shows the results of analyzing these mixtures by the method described. The error of the analysis is less than 5% except in one case where a very small amount of coconut oil was present. Several samples of commercial citronella oil containing small amounts of fatty oil were analyzed in replicate with the results shown in Table 111.
ous Solution.
I n most of these experiments, measurements 1Tei-e made with a Spekker absorptiometer, zeroing the instrument by using a water cell a t a drum reading of 1.0, but a few experiments were made to show that the Beckman spectrophotometer (IO-mm. cells; water in the blank cell) could also be used. I n either case, a plot of absorption density against concentration of glycerol was a straight line. This was the calibration curve for the glycerolwater mixtures. Numerous results were obtained on solutions of known glycerol content to show that glycerol could be determined nithin 2% by this method if the technique described was adhered
to. Determination of Glycerol Liberated by Fatty Oils after Saponification. I n a preliminary experiment samples of coconut oil and palm oil were saponified with alcoholic potash, the alcohol was evaporated, and the residue was extracted with water. The extract was extracted three times with ether and diluted to a concentration corresponding to 0.001 to 0.006% of glycerol. The glycerol content of the aqueous solution was determined as described above, with results in good agreement with the original amount of oil as is shown in Table I. Method for Determining Fatty Oils in Citronella Oil. Ten milliliters of citronella oil are weighed, washed in succession with dilute acid, dilute alkali, and water, and saponified with 20 nil.
mscussIon-
From the work described in this paper it is claimed that glycerol can be estimated by degradation to formaldehyde followed by a reaction of the formaldehyde to give a colored complex. Furthermore, the absorption density of this complex is directly proportional to the original glycerol content if the analysis is made under specified conditions. The method can be adapted to the estimation of a fatty oil, like coconut oil or palm oil, in oil of citronella.
T a b l e 111. F a t t y Oil Calculated a s Coconut Oil i n Commercial Samples of Citronella Oil Sample 1 2 3
4
F a t t y Oil Found, 70 1.15, 1 . 1 6 . 1 . 1 1 0.16,0.20,0,l5,0.15 4 2.1.4.20 2 . 6 5 , 2 . 6 2 , 2.67, 2 . 6 i 4 . 2 0 , .4.30
It would be of interest to know more about the nature of thf, colored complex. This is a problem on which further work is being done. The preliminary results suggest that phenylhydrazine is oxidized to a diazonium salt, which then couples with the phenylhydrazone of formaldehyde to give the colored complex. ACKNOWLEDGMENT
The author is indebted to R. A. Robinson and Morris Jamieson, late Director of Chemistry, Malaya, for their interest and assistance in this work. LITERATURE CITED
(1) A n n . Rept. Essent. Oils,Synthetic Perfumes, etc., Schimmel & Co., 1923, No. 20. ( 2 ) Finnemore, “The Essential Oils,” London, Ernest Benn, Ltd.,
1926. (3) Malaprade, Bull. soc. chim. France, [4], 43, 683 (1928). (4) Malaprade, Compt. rend., 186, 382 (1928). (5) Zimmerman, Chem. Weekblad., 27, 276 (1930). RECEIVED for review M a y 20, 1953. Accepted December 15, 1953.
