99.7%. The standard deviation was 11.5. National Bureau of Standards 89 lead-barium glass, a plate glass, and an optical glass were used to investigate the precision of the method. These glasses represent a range of from 0.02 to 0.4y0 chloride. The results of these determinations, along with the standard deviations are shown in Table I. A good estimate of the accuracy of the method is not possible because of a lack of suitable standards. The agreement between the measured value and the certificate value of the NBS 89 glass in Table I is excellent. However, analysis of NBS 93 borosilicate glass (certificate value 0.036% C1) produced a mean value of 0.046%. The possible interference of boron was checked because some boron will be removed from the glass by pyrohydrolysis (IO). No interference was found. This method is believed to be accurate because the
chloride recovery data obtained with potassium chloride are acceptable, and the results obtained in testing various glasses are reproducible. Interferences. When sulfur is present in the sample it is removed as SOaby pyrohydrolysis (6). The resulting sulfite ions in the distillate bleach the color of the mercury-diphenylcarbazone complex causing high results. This interference is easily avoided by the addition of hydrogen peroxide to the distillate to oxidize the sulfite ions to sulfate. Arsenic is partially removed by pyrohydrolysis as arsenic(II1). This was shown by pyrohydrolyzing arseniccontaining glasses or sodium arsenate (NhHAsO,. 7H20) and titrating the distillate with iodine. The amount of arsenic normally found in glasses does not cause any interference. Antimony is not removed from the sample by pyrohydrolysis and does not interfere.
LITERATURE CITED
(1) Adams, P. B., Williams, J. P., J. Am. Ceram. SOC.41, 377 (1958). (2) Clark, F. E., ANAL. CHEM.22, 553
(iw,n). \ - - - - I -
(3:) Cluly, H. J., Glass Technol. 2, 74 (1961). (4:LGahler, A. R., Porter, G., ANAL. GHEM. 29, ZYti (1957). (5) Glaze. F. W’.- Bull. Am. Ceram. SOC. ‘ 33. 45 (1954). ’ (6) fiardozzi, M. J., Lewis, L. L., ANAL. CHEM.33, 1261 (1961). (7) Warf, J. C., Cline, W. D., Tevebaugh, R. D., Ibid., 26, 342 (1954). (8) Welcher, F. J., ed., “Standard Methods of Chemical Analysis,” 6th ed., Vol. 2, Part B, p. 2235, Van Nostrand, Princeton, 1963. (9) Ibid., p. 2239. (10) Williams, J. P., Campbell, E. E., Magliocca, T. S., ANAL. CHEM. 31, 1560 (1959). V. E. CALDWELL ~
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Pittsburgh Plate Glass Go. Box 11472 Pittsburgh, Pa. 15238
Determination of Long-chain Alkyl Sulfates as ChloroformSoluble Azure A Salts SIR: For the determination of anionic surfactants, cationic dyes have been in use for several years. Generally, the dye-surfactant complexes formed are extracted into chloroform or a similar solvent and the absorbance of the resulb ing solution is measured. The dye most widely used is methylene blue (8-6, 8, 9 ) , introduced by Jones (6). Some publications propose the use of other dyes, such as pinacyanol (6) and basic fuchsin (11). A serious drawback of these procedures is the sensitivity to various interfering anions-e.g., nitrate and thiocyanate. These anions form chloroform-soluble salts with the dye, thus giving too high results in surfactant determinations. Procedures to counter such dficulties-e.g., Degens’ (3)-are costly, as regards the time and solvent quantities required. Therefore, experiments were undertaken to develop a simpler method. The dye azure A was found to have remarkable advantages over methylene blue [See Reference ( I ) for the properties and formulas of these dyes]. We arrived a t the following azure A-chloroform procedure. EXPERIMENTAL
Azure A was obtained as a preparation of adequate purity (certified dye content 91%) from Allied Chemical Corp., National Aniline Division. Paper chromatography (7) showed this dye to be virtually free from colored contaminants. The azure A reagent 1250
ANALYTICAL CHEMISTRY
solution used in the following procedure contained 40 mg. of dye and 5 ml. of 0.1M sulfuric acid in 100 ml. Procedure. I n a 250-ml. volumetric flask, 50 ml. of the sample solution, which should be neutral or weakly acidic and which should contain 0.010.15 @moles of the alkyl surfactant (CI2-Cl7 alkyl chains), is brought together with 5 ml. of 0.1M sulfuric acid and 1 ml. of the azure A reagent solution described. Then 10 ml. of chloroform is added, and the mixture is shaken for 5 minutes by a Griffin flask shaker. The mixture is transferred to a measuring cylinder (100 ml.) and the phases are allowed to separate. A large part of the lower phase is removed and brought into a centrifuge tube. Centrifugation in stoppered tubes removes water droplets (3000 r.p.m., 5 minutes). The absorbance of the dye complex in the clarified chloroform solution is measured a t 630 mr. The surfactant concentration in the initial solution is obtained from a reference graph. Beer’s law was found to hold for up to 0.15 @molesof surfactant.
Nature of Extracting Solvent. As can be seen from Table I, relatively few of the solvents examined gave a complete extraction of the dye-surfactant complex. Chloroform and 1:2dichloroethane were both suitable in this respect. Table 1. Extraction of Heptadecyl Sulfate and Dodecyl Sulfate from Water by Various Solvents
(Procedure described in the text) Extd. from water phase in one extn., % Solvent c 1 7 ClZ Chloroform 100 100 1:2-Dichloroethane 100 100 o-Dichlorobenzene 83.6 62.5 Monochlorobenzene 70.6 28.8 43.7 1 :2-Dichloropropane 77.8 Benzene
