!,tarer Research Vo[. I I. pp. 205 to 20". Pergamon Pres~ t977. Printed in Great Britain.

DETERMINATION OF ALKYL BENZENESULFONATE IN WATER BY U.V. METHOD

M. UCHIYAMA

Gunma Research Centre for Environmental Science. 3-21-19, Iwagami-cho, Maebashi. Gunma, Japan

(Receired 20 July 1976)

Abstraet--Alkyl benzenesulfonates in water were determined by u,v. method. Alkyl benzenesulfonates in water were extracted by 1,2-dichloroethane as methylene blue complexes,

and, after being isolated from methylene blue by washing with conc. hydrochloric acid, were extracted by water from 1,2-dichloroethane solution.

Alkyl benzenesulfonate solutions were measured by absorbance at 222 nm. This band is characteristic of benzene and alkyl benzenesulfonates separated from other anionic surfactants completely.

INTRODUCTION

Numerous analytical methods have been proposed for the determination of the alkyl benzenesulfonate (ABS), the more important of which may be grouped into three classes: (1) colorimetric (Abbot, 1962), (2) i.r. (Sallee et al., 1956; Oba et al., 1976) (3), gas chro- matographic (lmaida et al., 1975). The colorimetric method is not accurate because of many interference materials forming chloroform extractable complexes with methylene blue. Although i.r. and gas chromato- graphic methods are rather accurate, they are not easy and not useful enough for routine analysis.

The u.v. method presented here is accurate and easy. This method will find its greatest use in reseach- ing environmental pollution.

EXPERIMENTAL

Outline of u.v. analytical method

Anionic surfactants contained in sewage or river waters, etc. were extracted by 1,2-dichloroethane as methylene blue (MB) complexes.

After washing the 1,2-dichloroethane layer with concen- trated hydrochloric acid, ABS was extracted with water from 1,2-dichloroethane and then the water solution was used for u.v. analysis. The wavelength used was 222 nm, which is characteristic of benzene.

Analytical operation The flow sheet of the analytical procedure is shown in

Fig. 1. (l) Add 5 ml MB solution (0.025%), 5 ml ammonium

sulfate solution (I tool l-t) and 20 ml 1,2-dichloroethane to 100 ml sample water in the separable funnel.

(2) Shake the funnel for 5 rnin and separate out the 1,2-dichloroethane layer.

(3) Add 5 ml concentrated hydrochloric acid to the 1.2-diehloroethane layer and separate out the 1,2-diehloro- ethane layer after shaking for 5 min.

(4) Shake the 1.2-dichloroethane layer two times with 10 ml water for 5 rain and separate out the layer of water.

(5) After mixing the two water layers, use the mixture for u.v. analysis (222 nm).

205

Authentic samples

Sodium dodeeylbenzene sulfonate (DBS):

CH~(CH,.)tt-- O - - S O 3 N a .

Sodium dodecyl sulfonate (DSS):

C=2HzsOSO3Na. Di-2-ethyl hexyl sodium sulfo succinate (HSS):

CH2CO2CH :CH(CzH~)I'CHz)3CH j NaO3S--CH COzCH2CH(CzHsXCH2)3CH 3.

Sample

= E Methylene blue solution Ammonium ~__

sulfate solution I. 2- dichloroethane

(Shakinq]

, I Water I, 2- dichloroe1~none

~ concn. hydrochloric acid

IShakin 9)

, I Water 1, 2 - dichloroethane

1 4 Water

(Shakingl

, I I, 2-di~loroe1"nane Water

7---- U.V.

l Concentration

ot ABS I

Fig. 1. Flow sheet of u.v. analysis.

206 M. UC~]YAMA

220 260 300 340

Wovelengl"h. nm

Fig. 2. Ultra-violet spectra of L2-dichloroethane extract. (l) MB solution. (2) 1,2-dichloroethane extract. (3)

1.2-dichloroethane. (4) ABS solution.

R E S U L T S A N D D I S C U S S I O N

1,2-Dichloroethane extraction

Figure 2 shows u.v. spectra of the 1,2-dichloroeth- ane extract. The excellent agreement between the spectrum of MB solution and 1.2-dichloroethane extract confirms that the extracted material is an MB complex.

Ammonium sulfate solution is necessary for separ- ating the 1,2-dichloroethane layer and water layer clearly.

According to Abbot (1962), it is necessary to purify the methylene blue solution before use. But it is not necessary at all for this proposed method.

: l)

2)

° j \

I \ , 220 260 ~ 340

Woveleetgl"h, n m

Fig. 3. Ultra-violet spectra of cone. hydrochloric acid extract. (1) 1,2-dichloroethane layer after extraction with cone. hydrochloric acid. (2) Cone. hydrochloric acid extract. (3) MB solution plus conc. hydrochloric acid. (4)

ABS solution.

(D u'3 ,..o

8 so-- g

-g p-

-I O O 2 4 6 8 tO )2

HCL(N), conch.

Fig. 4. Efficiency of the concentration of hydrochloric acid. Hydrochloric acid: 5 ml.

Concentrated hydrochloric acid extraction

Figure 3 shows u.v. spectra of concentrated hydro- chloric acid extract. The excellent agreement between the spectrum of MB solution and concentrated hydro- chloric acid mixture and concentrated hydrochloric acid extract confirms that the extracted material is MB.

The bands 245, 292 and 325 nm in Fig. 2 shifted to 259, 300 and 338 nm in Fig. 3, respectively. This shift is caused by hydrochloric acid.

Figure 4 shows the relationship between the con- centration of hydrochloric acid and the transmittance of 1,2-dichloroethane at 650 nm after extracted with hydrochloric acid. Not diluted but concentrated hy- drochloric acid ( ~ 12 N) is necessary for isolating MB complexes.

i <t

220 260 300

Wovele~'t;'1, nm

Fig. 5. Ultra-violet spectra of water extract. (I) 1,2-dichlor- oethane layer after extraction with water. (2) Water extract.

Determination of alkyl benzenesulfonate in water by U.V. method 207 k II 2) 3)

. o

220 260

Wovelengl'h, nm

Fig. 6. Ultra-violet spectra of ABS solution and solvents. (I) Water shaken with chloroform. (2) 1,2-dichloroethane. (3) Chloroform. (4) ABS solution. (5) Water shaken with

1,2-dichloroethane.

Water extraction

The spectra of water extract are shown in Fig. 5. The excellent agreement between the spectra at the characteristic wavelength of 222 nm confirms the identification of the isolated material as alkyl ben- zenesulfonate. This band of 222 nm is characteristic of benzene and corresponds to excitation of a n elec- tron of the conjugated system to a n* orbital [i.e.

n---, n* transition; Roberts and Caserio (1965)]. In the colorimetric method, chloroform has usually

been used as the extracting solvent. But in this pro- posed method, 1,2-dichloroethane is used as the extracting solvent.

It is illustrated in Fig. 6 that the spectrum of ABS solution is overlapped by the spectra of chloroform, 1,2-dichloroethane and the water shaken with chloro- form, but not by the spectra of water shaken with 1,2-dichloroethane.

Table 1. Separability of DBS from DSS and HSS

DBS added DSS added HSS added DBS found (~g) (~g) (~g) (~g)

100 50 - - 97.0 100 100 - - 96.5 100 200 - - 103.0 100 300 - - 105.0 100 - - 50 104.0 100 - - 100 105.4 100 - - 200 105.0 I00 -- 300 103.0 100 200 200 105.0

Standard curve

The standard curve was prepared by analyzing known amounts of alkyl benzenesulfonate from 0 to 300 /~g per 100 ml water by the proposed method described above. The net absorbance obtained at 222 nm was plotted against the weight of lakyl benzene- sulfonate. Beer's law is obeyed.

Separability of ABS from other surfactants

Table 1 shows the separability of ABS from other surfactants. In this experiment, DSS and HSS are used as diverse surfactants.

REFERENCES

Abbot D. C. (1962) The colorimetric determination of anionic surface-active materials in water. Analyst 87, 286-293.

Imaida M., Sumimoto T., Yata M., Yoshida M., Kayama K. and Kunita N. (1975) A new gas chromatographic analysis of alkyl benzenesulfonate. J. Fd Hyg. Soc. Japan 16, 218-224.

Oba K., Miura K., Sekiguchi H., Yagi R. and Movi A. (1976) Microanalysis of anionic surfactants in waste water by infrared spectroscopy. Water Res. I0, 149--155.

Roberts J. D. and Caserio M. C. (editors) (1965) Basic Prin- ciples of Organic Chemistry, W. A. Benjamin, New York.

Sallee E. M., Fairing J. D., Hess R. W., House R., Maxwell P. M., Melpolder F. W., Middleton F. M., Ross J., Woel- fel W. C. and Weaver P. J. (1965) Determination of trace amounts of alkyl benzenesulfonates in water. Analyt. Chem. 28, 1822-1826.