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 agree- ment 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 be- cause 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 pres- ent in the sample i t is removed as SOa by pyrohydrolysis (6). The result- ing 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 pyro- hydrolysis as arsenic(II1). This was shown by pyrohydrolyzing arsenic- containing 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. Anti- mony is not removed from the sample by pyrohydrolysis and does not interfere.

LITERATURE CITED

(1) Adams, P. B., Williams, J. P., J. Am.

(2) Clark, F. E., ANAL. CHEM. 22, 553 Ceram. SOC. 41, 377 (1958).

(iw,n). (3:

(4: GHEM. 29, ZYti

(5) Glaze. F. W

\ - - - - I -

) Cluly, H. J., Glass Technol. 2, 74 (1961 ). LGahler, A. R., Porter, G., ANAL.

’.- Bull. Am. Ceram. SOC. ~ - - - I (1957).

‘ 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

Pittsburgh Plate Glass Go. Box 11472 Pittsburgh, Pa. 15238

Determination of Long-chain Alkyl Sulfates as Chloroform- Soluble 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 dficul- ties-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 ar- rived a t the following azure A-chloro- form procedure.

EXPERIMENTAL

Azure A was obtained as a prepara- tion 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

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 0.01- 0.15 @moles of the alkyl surfactant (CI2-Cl7 alkyl chains), is brought to- gether 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. Cen- trifugation 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 @moles of 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-sur- factant 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 c17 ClZ Chloroform 100 100 1 : 2-Dichloroethane 100 100 o-Dichlorobenzene 83.6 62.5 Monochlorobenzene 70.6 28.8 1 : 2-Dichloropropane 77.8 43.7 Benzene <2 <2 Carbon tetrachloride <2 <2 2 : 2 : 4Trimethyl

pentane <2 <2

DISCUSSION

By means of the basic procedure de- scribed the influence of the following experimental variables was investigated.

Shaking Time. Two minutes of shaking resulted in an almost optimal absorbance of the chloroform layer; the speed of shaking was not critical. The volume of the water layer, varied between 10 and 85 ml., did not affect the results.

~

Anion Interference. Experiments were undertaken in which the water phase contained varying concentra- tions of nitrate or thiocyanate to assess their transfer to the organic phase by cationic dyes. No surfactant was present. Some results obtained with nitrate solutions are summarized in Figure 1. Relatively small nitrate concentrations suffice to cause a considerable staining of the organic

1250 ANALYTICAL CHEMISTRY

(b) cp. -0- e*--

e*- */-

- (a) T , I , I I I I

240 480 720 960 1200 NITRATE CONCN. (p.p.m.)

Figure 1 . Extraction of dye from water phase (56 ml.) containing increasing concentrations of nitrate, measured as the absorbance of the solvent phase ( 1 0 ml.) at 630 mp (azure A) and 655 mp (methylene blue)

(a) ozure A-chloroform (b) 0 azure A-1 :2 dichloroethane (cl A methylene blue-chloroform ( d ) A methylene blue-1 :2 dichloroethanc

phase (chloroform or 1:2 - dichloro- ethane) if methylene blue is used as the cationic dye (lines c and d) . With azure A, less dye transfer is effected by nitrate, especially if chloroform is used as the extractant (compare lines a and b). With a series of thiocyanate concentra- tions similar results were obtained. Here also the combination azure A- chloroform proved to be strongly pref- erable.

Up to 1000 p.p.m. nitrate and up to 200 p.p.m. thiocyanate hardly affected the results of alkyl sulfate surfactant determinations, if the azure A-chloro- form procedure was adopted (Table 11). Chloride (<O.lJI), phosphate, and sulfate anions did not interfere. Up to 1 mg. of yeast ribonucleic acid in 50 ml. of water phase did not affect the results. Proteins interfered by preventing a clear

separation of the liquid phases. De- proteinizing the samples, by the Nelson (IO) procedure, abolishes this interfer- ence.

Quantitative Analysis of Mixtures. Chloroform extracts the dye-surfactant complex completely from its watery solution. With monochlorobenzene, ex- traction is incomplete; here the extent to which the complex is extracted de- pends on surfactant chain length (Table 1).

The extraction of one surfactant-e.g., CI2-as azure h complex by monochloro- benzene is not changed by the presence of another surfactan&e.g., C l r a s is shown in Table 111. This fact opens the possibility of an analysis of mixtures of alkyl sulfates of different chain length. Two separate applications of the azure A extraction procedure are necessary: one

Table II. Extraction of Dodecyl Sulfate from Water by Chloroform, in the Presence of CNS- and/or NO,-

Water phase: 85 ml.; chloroform: 10 ml. Comparison of methylene blue and azure A methods.

Dodecylsulfate found, pmolese Dodecyl sulfate, Methylene Azure A

total pmoles CNS-, p.p.m. NOa-, p.p.m. blue method method

0.0800 . . . 0.0800 5 0.0800 25 0.0800 100 0.0800 . . . 0.0800 . . . 0.0800 5

. . . 5

a Mean values of three detns.

. . .

. . . 200 800 200 200

0,0800 0.0799 0.1411 0.0801 0.1962 0.0805 0.2346 0.0830 0,1220 0.0803 0.1396 0.0821 0.1840 0,0804 0.1020 0.0006

~~

Table 111. Extraction of C12, Cl7, and Mixtures of C12 and C17 Alkyl Sulfates as Azure A-Complex by Chloroform

and Monochlorobenzene

Water phase: 50 ml.; solvent: 10 ml.

Surfactant (pmoles) ClZ C17

0.040 . . . 0.080

0,080 0:040 0.040 0.040 0.080

. . . 0: 040

0.080 0.040 Mean value of 3

Absorbance (630 mp)“

Mono- Chloro- chloro- form benzene 0.245 0.071 0.491 0.144 0.247 0.176 0.490 0.345 0.492 0.247 0.736 0.416 0.738 0.322

determinations.

with chloroform and one with mono- chlorobenzene. With a mixture of 2 moles CI2 and y moles C1, surfactant:

x + y = a (1)

and

0.2882 + 0.706~ = b (2) where a = total quantity of surfactant extracted by chloroform, and b = total quantity of surfactant extracted by monochlorobenzene.

ACKNOWLEDGMENT

J. A. A. de Jong gave valuable tech- nical assistance.

LITERATURE CITED

(1) Conn, H. J., “Biological Stains,” 7th ed., Williams and Wilkins, Balti- more, Md., 1961.

(2). Critchfield, F. E., “Organic Func- tional Group Analysis,” p. 171, Per- gamon Press, Oxford, 1963.

(3) Degens, P. N.,. Jr., Evans, H. C., Kommer, J. D., Winsor, P. A., J. AppZ. Chem. (London) 3,54 (1953).

(4) Freier, R. K., “Wasseranalyse,” p. 113, De Gruyter, Berlin, 1964.

( 5 ) Jones, J. H., J. Assoc. O f i c . Agr. Chemists 28, 398 (1945).

(6) Mukerjee, P., ANAL. CHEM. 28, 870 ( 1956 ):.

(7) Persip, J. P., Stain Techn. 36, 27 (1961).

(8) Rosen, >I. J., Goldsmith, H. A., “Systematic Analysis of Surface-Active Compounds,” p. 53-60, Interscience, New York, 1960.

(9) Schwartz, A. hl., Perry, J. W., Berch, J., “Surface-Active Agents and De- tergents,” Vol. 11, Interscience, New York, 1958.

(10) Nelson, N., J . Biol . Chem. 153, 375 (1944).

(11) Wallin, G. R., ANAL. CHEM. 22, 616 (1950).

JOHNNY VAN STEVENINCH J. C. RIEMERSMA

Laboratory of Medical Chemistry University of Leiden Holland

ceived from Unilever, N.V. Financial support for investigation re-

VOL 38, NO. 9, AUGUST 1966 1251