Analysis of Soap-Synthetic Detergent Mixtures in Bar Form DONALD BERKOWITZ AND RUBIN BERNSTEIN, Detergent Section, Test Laboratory, United States Navy Yard, Philadelphia, Pa. A procedure for the analysis of commercial soap-rynthetic detergent mixtures i s proposed which has given sufficiently accurate and reproducible results. The sample is extracted with 95% ethyl alcohol to remove the major portion of the active ingredients, followed by solution of the alcobol-insoluble salts in water and reprecipitation of them b y the addition of excess ethyl alcohol. Soap, fatty matter, and alcohol-soluble chlorides are determined directly, aynthetic detergent being determined as the difference between total alcohol-soluble matter and the sum of soap, fatty matter, and alcohol-soluble chlorides.
A
BAR form of soap-synthetic detergent mixture has recently come into wide use by the Navy for general cleaning in sea water. Several publicatiohs have described the use of soapsynthetic detergent mixtures as replacements for coconut oil soaps which are no longer available in large quantities (9,11, 18). Methods for analyzing these mixtures are being used by manufacturers for their own products, but as yet, except for a method contained in a government specification for bar form of sal& water detergent (f?), no general procedure for the analysis of such mixtures has appeared in the literature. Inasmuch as the Navy Department is ti large consumer of soap-synthetic detergent mixtures in bar form which must conform to specification requirements, it is important that an accurate method of analysis be available. This paper presents a sufficiently accurate and reproducible procedure for the analysis of soap-synthetic detergent mixtures in bar form, which was developed after an investigation of the literature and various procedures submitted by several soap and synthetic detergent manufacturers. Methods for the direct determination of synthetic detergents have been reported (1, 4-7, IO),but none has been applied t o the analysis of soap-synthetic detergent mixtures. Moreover, these methods are applicable only to those detergents whose exact structure is known, and cannot be used for commercial soapsynthetic detergent mixtures in which the synthetic portion is not identified and may consist of a mixture of indefinite composition. Soap-synthetic detergent mixtures of the type useful for saltwater cleaning consist of an active portion (soap and synthetic detergent) and an inactive portion (inorganic salts, moisture, and fatty matter). The term "fatty matter", as used in this paper, refers to all constituents preferentially soluble in petroleum ether; this will normally include hydrocarbons, fats, and free fatty acids. The term "active ingredient", as used in this paper, is applied to the alcohol-soluble portion corrected for determined impurities. The present method is based on the separation of active ingredients from inorganic salts by means of ethyl alcohol, and the subsequent determination of soap, fatty matter, and sodium chloride in the alcohol-soluble portion. Synthetic detergent is calculated as the difference between total alcohol-soluble matter and the sum of soap, fatty matter, and alchohol-soluble sodium chloride. PROCEDURE
ANHYDROUS,SALT-FREESODASOAP. Weigh to the nearest milligram a 2-gram sample of the soap- nthetic detergent bar in a tared 300-ml. Erlenmeyer flask. A& 50 ml. of water and 50 ml. of 95% ethyl alcohol. (Formula 2B or 30 alcohol may be used if 95% ethyl alcohol is not available.) Warm on the steam bath until no further solution takes place. Cool, add 5 drops of methyl orange indicator, and titrate with 0.5 N sulfuric acid to a pink color. Add 5 to 6 ml. in excess. Transfer the contents of the flask to a 500-ml. separatory funnel, washing out the flask with 50 ml. of water, then with 50 ml. of ethyl alc6hol. Add the washings to the separatory funnel.. Extract the fatty acids and fatty matter 4 times with petroleum ether, using 40-ml. portions.
Combine the petroleum ether extracts and wash with small portions of distilled water until the water washings are no longer acid to meth 1 orange. Transfer t l e petroleum ether extracts to the original 300.d. tared flask, fltering if necessary, and wash the separato funnel with 2 s m d r t i o n s of etroleum ether, adding the wa.%ngs to the flask. vaporate t f e petroleum ether on the steam bath, then dry in an oven a t 100" to 105' C. to constant weight. Cool and wei h as fatty acids plus fatty matter. Dissoke the fatty acids and fatty matter in 50 ml. of neutral ethyl alcohol with warming; add henolphthalein indicator and titrate with standard alcoholic 0.1 sodium hydroxide. Calculate the per cent of soap plus fatty matter a? follows:
5
+
Per cent of soap (ml. of NaOH X normality factor x 0.022) (weight of fatty acids fatty matter) fatty matter weight of sample
+
+ x
100
Calculate per cent of soap by subtracting from this value the per cent of fatty matter determined later. ALCOHOLINSOLUBLE MATTER. Weigh to the nearest milligram a 2- ram sample in a 250-ml. beaker, add 100 ml. of 95% ethyl alcoaol, cover the beaker, and heat on the steam bath with frequent stirring and maceration of the sample until it is completely disintegrated. Let settle and filter through a tared Gooch crucible with suction into a tared 300-ml. Erlenmeyer flask, retaining as much of the residue as possible in the beaker. Repeat this extraction 3 times with 25-ml. portions of hot 95% ethyl alcohol, each time retaining as much of the residue as in the beaker. Finally, evaporate any remaining alco!~?%$ dissolve the residue in the smallest possible quantity of hot distilled water (5 ml. should be sufficient). Reprecipitate the alcohol-insoluble matter by slowly adding with vigorous stirring 50 ml. of 95% ethyl alcohol. Heat the solution to boiling on the steam bath, filter, and transfer the precipitate to the Gooch crucible, washing several times with 95% ethyl alcohol. Dry the crucible a t 100" to 105' C. to constant weight and calculate the per cent of alcohol-insoluble matter. Reserve the combined filtrate and washings. ALCOHOLSOLUBLE MATTER. Eva orate the filtrate and washings obtained in the determination ofalcohol-insoluble matter to dryness on the steam bath. Heat the residue to constant wei ht a t 100' to 105" C. and calculate the per cent of alcohol-solu%le matter. FATTY MATTER. Dissolve the alcohol-soluble matter in a mixturd of 50 ml. of water and 50 ml. of 95% ethyl alcohol, warming if necessary. Transfer the solution to a 500-ml. separatory funnel, washing out the flask with 50 ml. of water, then with 50 ml. of 95% ethyl alcohol. Cool and extract fatty matter 4 times with petroleum ether, using 25-ml. portions. Combine the petroleum ether extracts and wash 4 times with 10-ml. portions of 0.2 N sodium hydroxide adding the washings to the alcoho!ic solution which is reserved for the determination of chlorides. Finally, wash the petroleum ether extract with small portions of water until the water washings are no longer alkaline to phenolphthalein. Transfer the washed petroleum ether extract to a tared 300-ml. Erlenmeyer flask, washing out the separatory funnel with 2 small ortions of petroluem ether, and add the washings to the flask. Eva orate the petroleum ether on the steam bath and dry the resiiue a t 100' to 105' C. to constant weight. Calculate the per cent of fatty matter. CHLORIDES IN ALCOHOLSOLUBLE MATTER. Add 15 ml. of 20% magnesium nitrate solution to the alcoholic solution remaining after the determination of fatty matter. Heat on the steam bath until the preci itate is coagulated, filter and wash thoroughly with water. &ke the filtrate acid with dilute nitric acid and determine chlorides by the Volhard method. SYNTHETIC DETERGENT, BY DIFFERENCE.Calculate the per cent of anhydrous, salt-free, synthetic detergent as follows: yosynthetic detergent = (yoalcohol-soluble matter) - ( % soda soap % fatty matter % NaCl in alcohol-soluble matter)
+
+
DISCUSSION
The usual method for analyzing commercial synthetic detergents consists in the separation of alcohol-soluble and insoluble portions by extraction with ethyl alcohol. The alcohol-soluble portion is then generally considered to be "active synthetic deter-
239
INDUSTRIAL AND ENGINEERING CHEMISTRY
240 Table 1.
Vol. 16, No. 4
of eight samples by the nonprecipitation and precipitation methods are also given in Table I.
Adsorption of Synthetic Detergents
(Values represent average of 4 individual determinations, expressed 8 8 per cent of total sample) Alcohol+ oluble Loss in Weight on Matter Recovered Ignition of Alco- from, Precipitate of hol-Insoluble Alcohol-Insoluble Residue Salts Synthetic Detergent Method Method Method Method Method Method Sample 14 IIb I I1 I I1 8.3 0.0 1 4.1 0.90 37.1 46.3 5.0 0.0 2 2.2 0.1 34.9 40.9 0.0 0.2 4.0 3 1.5 30.5 34.7 5.7 0.0 4 4.9 0.3 47.2 53.8 0.1 1.4 0.0 6 1.5 19.9 22.0 0.0 0.4 3.4 6 2.8 25.6 29.7 3.6 0.0 22.8 26.9 7 1.8 0.3 0.0 0.2 3.2 17.1 21.1 8 1.2 a Method I, no reprecipitation of alcohol-insoluble matter. b Method 11, reprecipitation of alcohol-msoluble matter. c High result prob,ably represents loss of water of hydration of borax which is present in thls sample.
Sam les 1, 2, 3, and 4 were four commercially available synthetic ietergents. Sample 1 was the sodium salt of a sulfonated straight-chain hydrocarbon; samples 2 and 4 were sodium salts of alkyl aryl sulfonates; sample 3 waa the sodium salt of a sulfonated glyceryl ester of a straight-chain fatty acid. Samples 5, 6, 7, and 8 were mixtures in bar form of soap and the above synthetic detergents.
I n addition EO giving incomplete separation of alcohol-soluble matter from alcohol-insoluble salts, most of the methods investigated gave incorrect values in the determination of soap, chlorides, and fatty matter. As the synthetic detergent is determined b j difference, the values reported for it may be correspondingly inaccurate. Experience with the submitted methods showed that soap values tended to be low and fatty matter values high, while the d f i Table II. Analyses of Known Soap-Synthetic Detergent Mixtures culty' in determining the end Mixture 1 Mixture 2 Mixture 3 Mixture 4 Mixture 5 PresPresPresPresPrespoint in the chloride determinaDetermination ent Found ent Found ent Found ent Found ent Found tion led to either high or low %
%
Alcohol-soluble matter 77.7 77.8 Alcohol-insoluble matter 22.3 22.4 Soap fatty matter 44.5 44.3 Fatty matter 1.3 1.1 43.2 43.2 Soap 1.2 1.3 Chlorides Synthetic deter ent 32.0 32.2 Sum of alcofol-insoluble matter, chlorides, soap, uynthetic detergent, and 100.0 100.2 fatty matter Type of soap used Synthetic detergent used A
+
%
%
%
%
%
%
%
%
67.8 32.2 43.2 4.4 38.8 4.7 19.9
67.9 32.0 43.1 4.4 38.7 4.7 20.1
74.0 26.0 41.3 2.0 39.3 2.6 30.1
74.0 26.0 41.2 2.0 39.2 2.6 30.2
81.1 18.9 48.6 1.2 47.4 1.1 31.4
81.1 18.8 48.9 1.2 47.7 1.1 31.1
74.8 25.2 46.2 0.8 45.4
74.5 25.2 46.2 0.8 45.4 0.8 27.5
100.0 99.9 Toilet Soap B
100.0 100.0 C
gent". Low results were always obtained by this procedure in this laboratory. I n the analysis of soap-synthetic detergent mixtures by the above alcohol-extraction method, low results for synthetic detergent were also obtained. These low results are caused by the fact that some synthecic detergent is adsorbed by the alcohol-insoluble salts: (1) When the residue of alcoholinsoluble matter was dried in an oven a t 105' C. and then ignited a t 500' C., the loss in weight in some instances amounted to almost 5% of the total sample. (2) The residue of alcoholinsoluble matter foamed in water, indicating the presence of some active material, which might be soap or synthetic detergent. (3) The residue of alcohol-insoluble matter formed a very turbid solution upon the addition of Pedersen's reagent, which does not react with soaps or the salts present (9). Investigation showed that the adsorption of synthetic detergent by the alcohol-insoluble residue can be very greatly reduced and the separation made more complete by a procedure which involves initial extraction of the sample with 95% ethyl alcohol to remove the major portion of the alcohol-soluble matter, followed by solution of the residue in the smallest possible quantity of water and precipitation of the inorganic salts by the addition of ethyl alcohol. T o determine directly the amount of adsorption, samples were extracted with ethyl alcohol, and the residue of alcohol-insoluble matter was filtered on a Gooch cruclble, dissolved in the minimum amount of hot water, and reprecipitated by the addition of excess ethyl alcohol. The precipitate was filtered off and the filtrate evaporated to dryness and weighed. This weight represented the amount of synthetic detergent which could be recovered from the thoroughly extracted residue by solution and reprecipitation.
The results in Table I show that the adsorption of synthetic detergent by the alcohol-insoluble residue, as indicated by (1) loss in weight upon ignition of the alcohol-insoluble residue and (2) recovery of synthetic detergent from the alcohol-insoluble residue, can be markedly reduced when the reprecipitation procedure is employed. Values for the synthetic detergent portion
I t is believed that the low values obtained forsoap are due 0.8 to the decomposition 27.8 of the soap and consequent incomplete extraction of the fatty 100.0 99.9 100.0 99.7 acidswhenmineralacidisadded Oleic acid soap only to a methyl orange end D E Doint. Judzinz from the resulta obtained, the small excess of acid added in the proposed method is sufficient to decompose the soap completely, but insufficient to decompose the synthetic detergents used. The high values obtained for fatty matter are believed to be due to solution of acid soaps in the ether used for extraction. Such acid soaps cannot be removed by washing with water alone (8). Washing the petroleum ether solution of the fatty matter with dilute alkali seems to overcome this difficulty,
- -
APPLICATION OF M E T H O D T O KNOWN MIXTURES
Inasmuch as no referee method exists for the analysis of commercial soap-synthetic detergent mixtures in bar form, the present method was tested by analyzing mixtures of known composition, containing soap, synthetic detergent, sodium sulfate, fatty matter, and sodium chloride. The mixtures were prepared by dissolving the constituents in 50% alcohol, diluting to a definite volume, and taking aliquots for
the analyses. The fatty matter used in the mixtures was obtained by extraction of the synthetic detergent in the commercid available form with petroleum ether in a Soxhlet extractor. ?$he filtered petroleum ether solution was then washed thoroughly with 50% alcohol, evaporated, and dried to constant weight a t 105' C. and this extract was used to furnish the fatty matter. The material left in the Soxhlet after extraction with petroleum ether was extracted with absolute alcohol to remove alcohol-soluble synthetic detergent. The alcoholic solution was then evaporated and dried t o constant weight, and after being corrected for sodium chloride present was used in the preparation of known mixtures. The soap used in the mixtures was obtained by first extracting solutions of two commercial soa s with petroleum ether to remove unsaponified and unsapon&able matter. The residue obtained on drying was dissolved so far as possible in alcohol and the filtered alcoholic solution evaporated to dryness and to constant weight. This residue, corrected for glycerol and sodium chloride present, was used in the mixtures. Table I1 gives values obtained by the proposed method on 5 known mixtures. Synthetic detergent A is the sodium salt of a sulfonated glyceryl ester of a straight-chain fatty acid; B and C
Table 111.
Analysis of Known Soa Prepared in
S nthetic Detergent Mixture
& form
Type of soap, toilet soap. Synthetic detergent, sodium salt of a sulfonated amide of a straight-chain fatty acid) Determination Present Found Alcohol-soluble matter Alcohol-insoluble matter Synthetic detergent Soap Chlorides Fatty matter
%
%
72.1 27.9 23.4 46.6 2.1
72.0 27.7 23.3 46.5 2.2 0.0
0.0
are sodium salts of alkyl aryl sulfonates; D is the sodium salt of a sulfonated amide of a straight-chain fatty acid; E is the sodium salt of a sulfonated straight-chain hydrocarbon. I n order to guard against the possibility that results obtained by the proposed method on a mixture in bar form, rn opposed to mixtures reported in Table 11, might be incorrect,, an additional sample of known composition made up in bar form was analyzed. The results as given in Table 111 are of satisfactory accuracy. The figures given are on the anhydrous basis. ACKNOWLEDGMENT
The authors are indebted to R. C. Hughes and C. W. Schroeder (present address, Continental Foods Corp., Hoboken, N. J.) of this laboratory for their many helpful suggestions, and also to the following for suggested methods: Jay C. Harris, Monsanto
A
241
ANALYTICAL EDITION
April, 1944
Carr-Price Reagent Dispenser LYLE A. S W A I N
Pacific Fisheries Experimental Station, Vancouver, 6. C.
T
HE saturated chloroform solution of antimony trichloride, used in the chemical determination of vitamin A, must be kept under anhydrous conditions a t all times, and provision must be made for rapid dispensing of accurately measured volumes.
k -\
Chemical Company; Armour and Company; American Cyanamid and Chemical Corporation; General Dyestuff Corporation; L. F. Hoyt, National Aniline Division, Allied Chemical and Dye Corporation; and Colgate-Palmolive-Peet Company. They are indebted to Lever Brothers Company for suggesting the uee of 50% alcohol solution for dissolving the sample, and to J. H. Shipp and Harold Jones of E. I. du Pont de Nemours and Company for n suggested method of analysis and for supplying the sample of Pedersen’s reagent. LITERATURE CITED
(1) Biffen, F. M.,and Snek F. D., IND.ENQ.CHBY.,ANAL.ED., 7,234 (1935). (2) Bureau of Ships, Navy Department, Specification 51D7 (INT) (1 November 1942). (3) Flett, L., Chem. Eng. N e w , 20,844 (1942). (4) Harris, J. C., IND.ENG.CHEY.,ANAL.ED., 15, 254 (1943). (5) Hart, R., Ibid., 5, 413 (1933). (6) Ibid., 10,688 (1938). (7)Ibid., 11, 33 (1939). (8) Jamieson, G. S., “Vegetable Fats and Oils”, 2nd ed., p. 391, A.C.S. Monograph, New York, Reinhold Publishing Corp., 1943. (9) Pedersen, C. J., Am. D u e s t q Y Reptr., 24,137 (1935). (10) Percy, J. H., and Arrowamith, C. J., IND.ENG.CHEM.,ANAL. ED., 14, 151 (1942). (11) Ruckman, N. E.,Hughes, R. C., and Clarke, F. E., Soap, 19, NO. 1 , 21-3 (1943). (12) Sunde, C. J., Ibid., 19,No. 7,30 (1943). THE.views in this article are those of the authors and should not be construed as the o5cial views of the Navy Department.
An ordinary pipet is unpleasant to use with this solution and is slow in delivery. The apparatus described serves to solve the problem where a considerable number of determinations are to be made. A constant-level reservoir for the reagent (Figure 1, A ) consists of a 300-ml. flask (or other convenient size) with an angular bottom offset leading to a side-arm reservoir wide enough for insertion of a 10-ml. Luer hypodermic syringe. To fill the reservoirs the small one is stoppered and the solution is added to the large one, which is then securely stoppered. The liquid level in the small reservoir remains constant when liquid is withdrawn therefrom. The solution is removed in measured volume by a hypodermic syringe (Figure 1, B ) with needle removed, fitted with a brass collar which can be clamped on the syringe barrel. A wrapping of surgical tape on the barrel forms a firm cushion for the collar, Two vertical rods are soldered to the collar and the limiting distance to which the syringe plunger may be withdrawn is governed by a swiveling top bar which may be turned aside when the plunger is to be removed. A stopper around the barrel assures its suitable depth of immersion in the small reservoir and excludes contact between solution and atmospheric moisture. A pipet of similar principle but not suited t o the present purpose was described by Krogh (1). A paper which appeared after submission of this note includes another design of apparatus for the same purpose (2). For accurate measurement the plunger must be inserted in definite position of orientation with respect to the barrel. This is maintained by suitable markings on the syringe parts. Tests, using water, gave four successive delivery weights of 9.02, 9.05, 9.03, and 9.04 grams. KO tendency for the syringe orifice t o drip during transfer was encount,ered. The syringe should not be left overnight without washing, as there is danger of freezing due to deposition of antimony trichloride. Rubber stoppers should be changed periodically because of attack by the reagent. The solution should be kept in the reservoir only during its actual use to avoid possible contamination from the rubber stoppers. LITERATURE CITED
Krogh, A., IND.ENQ.CHEM.,ANAL.ED., 7, 130 (1935). (2) Oser, B. L.,Melnick, D., and Pader, M.. Ibid., 15,724-9 (1943). (1)
