excellent technique for determining the relative amounts of methyl ester, fatty acid, and triglyceride or other lipid in the reaction product. This thin layer chromatograph technique was demonstrated by converting a commercial cottonseed oil to the methyl esters by the described saponification-esterification procedure. A thin layer chromatograph was run on the methyl esters. The original triglyceride, methyl oleate and a fatty acid were also run by thin layer chromatography to show the comparative R, values. Figure 1 shows the results of these thin layer chromatograms using silica gel G plates. The solvent system was petroleum ether, diethyl ether, and acetic acid 9O:lO:l on a volume basis. The conversion of the triglyceride fatty acids to the methyl esters appear l o be quantitative by TLC. The amount of conversion was far more complete than with any short period interesterification procedures we have tried. The gas chromatography of these esters gave excellent results. One of the objections raised against esterification procedures that required the addition of water was the possible loss of lower molecular weight fatty acid esters. This loss occurs because of the much greater water solubility of these
lower esters and their low volatility. With acids below Cs this loss precludes the quantitative recovery of the esters. However, i t was found that if a saturated salt solution is added to the esterification mix, a quantitative recovery of acids down to the C4range can be effected. Butter is a n example of a fat with a very wide range of acids. Table I shows the quantitative results obtained with methyl esters of fatty acids obtained from butter. These results are compared to literature values generally accepted for butter (2, 5 ) . The results compare very favorably in the lower acid range. The higher acids vary, but are still in the expected range. This variation is dependent on the diet of the animal. This was not an attempt to make an exhaustive analysis of butter, The BF3-methanol esterification procedure for obtaining methyl esters has been extended to include fatty acids, soaps, triglycerides, polyesters, lipoproteins, phospholipids, and other esters of fatty acids. Fatty acid amides have also been converted to methyl esters with the procedure, though not quantitatively. The procedure as written is not applicable to phenols, rosin acids, and dimer acids.
I n conclusion, a rapid procedure for preparing methyl esters from lipids based on a rapid saponification followed by esterification with BF3-methanol in the same vessel was developed. The technique has been applied to a number of lipid systems. We have on occasion scaled it down to handle micro amounts of fats. The greatest use for the procedure will probably be in industry for the control analysis of fats and oils.
LITERATURE CTED
(1) Ast, H. J., ANAL. CHEM.35, 1539
(1963).
(2) Hilditch, T. P., “The Chemical Constitution of Xatural Fats,’’ Wiley, p.
591, New York, 1956.
(3) Metcalfe, L. D., Schmitz, A. A.,
ANAL.CHEM.33,363 (1961). (4) Morrison, W. R., Smith, L. M,, J. Lzpid Res. 5 , 600 (1964). ( 5 ) U. S. Dept. of Agriculture, “Fatty Acids in Animal and Plant Products,” 1959. L. D. M E T C ~ L F E A. A. SCHMITZ J. R. PELHA
Research Laboratory Armour Industrial Chemical Co. McCook, Ill. 60529
Thermometric Titration of Cetylpyridinium Chloride SIR: d number of analytical methods have been developed for the determination of quaternary ammonium surfactants. These include: (a) spectrophotometric determination of a colored complex; ( b ) formation and separation of a derivative by the addition of a reagent and subsequent determination of the unreacted reagent; and (cj titration with an anionic surfactant, usually in the presence of an indicator dye, in a two phase system. .ill of these methods are subject to some criticism. Method (a) requires standardization by the particular surfactant involved; method (b) requires time-consuming extractive procedures and standardization of both the reagent and titrant solutions; and method (c) is a relatively slow and tedious technique requiring dropwise addition of the titrant as the end point is approached. After the addition of each drop of titrant, the phases must be mixed and examined for dye transfer or color change. Quaternary ammonium surfactants are known to interact with a variety of high molecular weight species. Because alnioqt all reactions exhibit detectable enthalpy changes, it was expected that thermometric titrations could be utilized for the determination of these sur-
factants. Jordan, Pei, and Javick (1) demonstrated the applicability of this technique to the determination of alkylbenzenesulfonates. These workers reported that a titration employing a quaternary ammonium surfactant solution as titrant could be completed in approximately 5 minutes with a resultant average relative error of about 1% for titrate solutions in the concentration range of 10-3X. However, the typical enthalpogram reported exhibited considerable curvature, which makes accurate extrapolation to the end point difficult. The purpose of this study was to adapt thermometric titrations to the determination of quaternary ammonium surfactants. The use of alkylbenzenesulfonates as the titrant gave enthalpograms similar to those reported by Jordan, Pei, and Javick ( I ) , and the extrapolations necessary to obtain end points were subject to error. Furthermore, the problem of obtaining pure alkylbenzenesulfonates limited the usefulness of this procedure. I n an attempt to improve the linearity of the enthalpogram and to eliminate the difficulty of obtaining pure reagents, other titrants were considered. Orange 11, an anionic dye which has been shown to react with quaternary am-
monium surfactants in the ratio of 1: 1 was selected. The reaction products of Orange I1 and quaternary ammonium surfactants were isolated and sho\m to be insoluble salts having K,, values in the order of to a t 25’ C. (3). Orange I1 is available in relatively pure form; aqueous solutions are stable for long periods of time; and standardized solutions are easily prepared. EXPERIMENTAL
The purification of the sodium salt of - (2 - hydroxy - 1 - naphthy1azo)benzenesulfonic acid (Orange 11) and cetylpyridinium chloride (CPC) are reported elsewhere ( 3 ) . The silver nitrate used was reagent grade. Solutions of CPC, Orange 11, and AgT\TO3 in deionized water were prepared. The concentration of the Orange I1 solution was determined spectrophotometrically with a Beckman Model D B spectrophotometer. A value for the molar absorptivity at 488 mp of 2.097 X lo4 (3) was used. The thermometric titration apparatus used is described by Raffa and Stern ( 2 ) . Titrant was delivered at a rate of 0.83 ml./minute. The end points were determined by extrapolation of the straight line portions of the curves as illustrated in Figure 1. p
VOL. 38, NO. 3, MARCH 1966
515
Table 1. Typical Results in Determination of CPC by Thermometric Titration with Orange II
Concn. of CPC (mrnole/liter) Taken Found 0.500 0.505 1.00 1.01 1 .oo 1.00 1.oo 1.01 1.00 0.99 1 .oo 1.04 2.00 1.99 2.00 2.01
t
c
2*o
,JOLUUE
I ,5Error,
%
OF TITRANT USED
r!I
END POINT
I I
\
1.o
1.0 0 1.0 1 .o
4.0 0.5 0.5
RESULTS AND DISCUSSION
Table I shows data concerning the accuracy attainable in the determination of CPC by thermometric titration with Orange 11. Since the CPC used in this study was free of halide impurities, a silver nitrate thermometric titration was used to verify the concentration of the sample solutions. The results of three titrations of a 5 x 10-4X CPC solution with 0 . W silver nitrate gave an average value of 4.99 x 10-4 i 0.04 x 10-4-11, It appears that in the absence of interfering halide ions, silver nitrate might be the titrant of choice for quaternary ammonium surfactants. However, in most practical situations, halide ion contamination would be expected to be present and thus preclude the use of silver nitrate. The analysis of a sample
I
0
J I
.3
.6
I
1.2 I.5 M I L L I L I T E R S OF TITRANT
Figure 1 .
.9
1.8
2.1
Typical enthalpogram
100 ml. of 1 X 1 O - W CPC titrated with 0.108M Orange II
by the use of both Orange I1 and silver nitrate could serve as-a measure of halide ion contamination. Preliminary work with other quaternary ammonium surfactants of varying chain length and polar groups indicates that thermometric titration with Orange I1 may be used for rapid and accurate analysis. Additional work is planned to determine the effects on this procedure of nonionic surfactants, amine salts, and inert materials usually present in preparations containing quaternary ammonium surfactants.
LITERATURE CITED
(1) Jordan, J., Pei, P. T., Javick, R. A., ANAL.CHEhf.35,1534 (1963). (2) Raffa, R., Stern, 1cI. J., College of Pharmacy, Columbia University, New York, N. Y., unpublished data, 1965. (3) Zografii, G., Patel, P., Weiner,' N. D., J . Pfiarm. Sci. 53.544 (1964). NORhlAN D. WEINER ALVIN FELMEISTER Of
College of Pharmacy ~ Columbia ~ New York, X. Y. 10023
~
i
Simultaneous Polarographic Estimation of M a ior Constituents in Lead-Tin and Lead-Tin-Indium Alloys SIR: Kolthoff and Johnson (8) observed that the diffusion current for the stannic-stannous polarographic reduction wave, in 4N HC1 and in the presence of a small amount of tetraphenylarsonium chloride (TPXC), is equal to one-half of the total diffusion current for tin. I n addition, they observed that the stannic-stannous halfwave potential is shifted to more negative values and its diffusion current is unaffected by the presence of moderate quantities of lead. While investigating procedures for the analysis of lead-tin and lead-tin-indium alloys as a part of a quality assurance program, it was felt that the observations made by Kolthoff and Johnson could be applied to the simultaneous estimation of each of the major constituents in a lead-tin or a lead-tin-indium solder. A well defined polarogram showing three reduction waves is obtained corresponding to the Sn+4-Sn+2, the Sn+" 516
ANALYTICAL CHEMISTRY
SnO, Pb+LPb0, and the In+"InO reductions. This offers a direct estimation of tin and indium and an indirect determination of lead. EXPERIMENTAL
Apparatus. A Sargent Model XXI Polarograph was used in conjunction with a water-jacketed (25.0' =t0.1' C.), mercury pool-DME polarographic cell in the recording of all current-voltage curves. T h e capillary characteristic for the D l I E was 2.03 mg.2'3 sec.-*/2 as measured in distilled water and open circuit. During initial investigations, a conventional SCE-DJIE cell was used in the recording of polarograms from which halfwave potentials were calculated; this cell possessed a cell resistance of 70 ohms as measured with an industrial Model RC conductivity bridge. When desirable, the potentials were measured a t the beginning and end of each polarogram with a Rubicon potentiometer.
Sample Preparation. Most of the samples investigated were of t h e nonflux variety; however, when samples also contained flus, they were melted in a small test tube under an argon atmosphere and manually moved away from the molten flux. This procedure was performed a t least three times before the samples were washed with xylene. dll samples were then machined and the turnings washed with xylene before weighing. Unknown Solution Preparation. The requisite amount (see subsequent discussion), weighed t o t h e nearest 0.1 mg., of unknown or standard solder sample Tvas placed in a 250-ml. Erlenmeyer flask. Concentrated HC1, 80 ml., and concentrated H S O s , 2 ml., were added and the flask a n d contents were heated until the resulting solution was colorless (or until the solution volume was approximately 50 ml.). The solution was cooled, quantitatively transferred to a 100 ml. volumetric flask, and diluted to the mark.
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