Ninth Annaal Sammer Symposium-Analysis of Industrial Wastes
S pect ro photomet ric Dete rmination of AI ky I BenzenesuIfonat e Detergents in Surface Water and Sewage JOHN D. FAIRING and FRANK R. SHORT Central Research Depbrtment, Monsanto Chemical Co., Dayton 7, Ohio
A method for the determination of alkyl benzenesulfonates in surface water and sewage is based upon the isolation of the alkyl benzenesulfonate from interfering materials by solvent extractions of its l-methylheptylamine salt, and measurement of the isolated benzenesulfonate bs an improved methylene blue method. The procedure will measure less than 1 p.p.b. in water and 50 p.p.b. or less in sewage, It is not subject to any known interference from materials likely to be present in surface water or sewage.
A
KEED arose for a method for the determination of alkyl benzenesulfonate detergents (ABS) in surface water and
sewage which would be accurate, sensitive, reasonably rapid, and capable of general application (11). Therefore, this work was Imdertakeri as a part of the collaborative project of the -issociation of Xmerican Soap and Glycerine Producers, Inc. -11though the method (SO) presented on behalf of the association does not favor use of colorimetric methods based on methylene blue, the authors have found that their procedure will measure less than 1 p.p.b. of alkl-l benzenesulfonate in water and 50 p.p.b. or less in sewage and is not subject t o any known interference from materials likelj- to be present in surface Tmter or sewage. I t is offered for this reason and because it can be used in laboraatories n.hich do not have the equipment needed for the infrared procedures. The generic term alkyl benzenesulfonate, as used in t’his paper, rcfers to dodecyl benzenesulfonate and its closely related homologs, unless otherwise noted. Kumerous analytical methods have been proposed for the determination of alkj-l benzenesulfonate, the more import’ant of which may be groiiped into four classes: (I) colorimetric; (11) volumetric., based upon the titration of alkyl benzenesulfonate with a cationic surface active agent (f, 7 , 8, 1 8 ) ; (111)ultraviolet (T?): and (IT3 infrared (17, 28-30). The colorimetric methods itre based upon the formation of the alkyl benzenesulfonate salt of a cationic dye, the extraction of this salt from the sample with an immiscible organic solvent, and the colorimetric determination of the extracted material ( 2 4 ) . Several cationic dyes have been proposed 116, 23, 24, 331, but only methylene blur has found rside acceptance (6, 9, 13, 16, 19). These dye methods have the decided advantage of speed and simplicity, and are the only methods possessing sufficient sensitivity to enable the Iovi concentrations of alkyl benzenesulfonate usually encountered in surface m-aters to be determined accurately in a sample of reasonable size. They are, or can be made, highly accurate when their use is limited to t,he determination of alkyl benzenesulfonate in distilled water. Holyever, when they are used with surface n-ater or sewage samples, several sources of error are encountered. I n general, all dye methods are subject to the same errore, although their relative magnitudes vary somewhat with the dye and the technique used. The most serious error is caused by positive interferencesthat is, materials other than alkyl benzenesulfonate which form extractable salts with the dye and give rise to high values. Table I s h o w some of the apparent alkyl benzenesulfonate values
obtained by a direct methylene blue analysis of samples known to contain no alkyl benzenesulfonate. While many other positive interferences are known, both organic and inorganic, those shown were chosen as being representative of what might be found in practice. Unless otherwise noted, all methylene blue determinations reported in this paper were made by the improved method described at the end of t,he procedure. Significant errors are also introduced by negative interferences, such as proteins and some organic and inorganic cations, which tie up the benzenesulfonate by the formation of complexes or salts (4,$0, 21, 34) in such a way that it will not react with methylene blue. As a result,, low values are obtained. I n Table I1 are shown some of the recoveries obtained by a direct methylene blue analysis when knon-n amounts of alkyl benzenesulfonate viere added to various materials. Other sources of error also exist, such as the formation of stable emulsions during the extraction, which make the quantitative recovery of the alkyl benzenesulfonate-dj-e complex difficult or impossible; or the formation of precipitates that adsorb the alkyl benzenesulfonate or its salt. If the alkyl benzenesulfonate is isolated quantitatively from such interfering materials, then a dye method can be applied without error. Several approaches to the problem m-ere made. Chromatography, using acid alumina as an adsorbent and ammoniacal methanol as an eluent, offered one solution, but, although some promising results were obtained, the rather critical and timeconsuming elution technique made it necessary to abandon this approach. Carbon has been reported as an adsorbent for alkyl benzenesulfonate (12, 28, SO), but under conditions giving quantitative desorption, the benzenesulfonate is not separated from all interfering materials. ,41ky1 benzenesulfonate can be extracted from hydrochloric acid solutions with chloroform (6) or ether ( I $ ) , and the present
Table I.
Apparent Alkyl Benzenesulfonate Content of ABS-Free Samples (Positive interferences) Apparent A B S Found, P.P.M. Direct Double methylene blue extraction Sample determinations method i1 None 21.1 None
Urine 1 Urine 2 Urine 3 6.3 Urine 4 lT.l Aqueous extract of straw 1 5.6 Aqueous extract of straw 2 0.9 Aqueous extract of manure 1.5 Aqueous extract of leaves 0 5 Aqueous extract of rotted wood Sulfite waste liquor 14. 0 4I 9.3 Sodium lauryl sulfate, 7.56 p.p.m. Igepon T-73,10 p.p.m. (sodium-A’V-methylA’-oleoj-l taurate) 6 4 Aerosol OT,10 p.p.m. i.4 Sulfonated castor oil, 30 p.p.m. 6.2 Sodium lauryl ether sulfate, 30 p.p.m. 9.8 Cholesteryl sulfate, 12 p.p.m. i.3 1827
..
...
None None ... ...
i?&e None None None None None None
1828
ANALYTICAL CHEMISTRY
authors found that it can be extracted fiom 3 . 6 5 sulfuric acid with chloroform. I n all these cases, horrever, the protein interference is increased, because reduction of the p H increases the anionic detergent binding power of proteins (4). Sulfonic acids form salts with amines (2, S, a5, 26, 3,7)) and Ilarron and Schifferli (22) have shonn that the p-toluidine salt of alkyl benzenesulfonate can be extracted from an aqueous
funnel
StODC
ock
solution with carbon tetrachloride. Homever, it was found that this extraction did not overcome the effect of negative interferences. While aromatic amines have been used in almost all of the published n-ork on sulfonic acids, Smith and Page (32) used long-chain tertiary aliphatic amines (such as methyldioctylamine) for the extraction of strong acids from aqueous solutions. The problem \vas to find an amine and a solvent that would permit the q u a n t h t i v e extraction of alkyl benzenesulfonate in the presence of negative interferences, and, a t the same time, isolat'e the alkyl benzenesulfonate from positive interferences. Several amine-solrent combinations were found n-hich would accomplish one of these tasks, but none that n-odd do both satisfactorily-. Therefore, tn'o amine-solvent combinations mere used in the procedure: the first to remove the alkyl benzenesulfonate from negative interferences, the second to isolate it from positive interferences. Consequently, this method has been termed the double extraction procedure. Of the amines tested, 1-methylheptylamine proved to be the best for both extractions. APPARATUS
stopper
Glass-stoppered separatory funnels, 125 nil. arid larger, n i t h Teflon stopcocks. A11 must be Desicoted. Separatory funnels used for the methylene blue determination must be kept separate from the others, and may have glass instead of Teflon stopcocks. Filter adapter (Figure l ) , fabricated from n standard-taper 19/38 male joint, 9-cni. over-all length. with a 3.5-cm. length of 7-mni. tubing sealed to it 2 cni. i'i'oni the top. All-glass wash bottles for solveiits.
. vacuum Filter
adapter
125ml
funnel
116
RE'AGENTS
Cotton
Amine-chloroform solution. 1Iix 0.10 to 0.15 nil. of l-methylheptylamine in 100 ml. of reagent grade chloroform. .\lalie fresh daily. Amine-hexane solutioii. 3Iix 0.10 to 0.15 nil. of l-methylheptylamine in 100 nil. of commercial grade n-hesane. Make fresh daily. Ammoniacal methanol. Concentrated ammonium hydroxide, 1% in redistilled methanol. Make fresh daily. Buffer, p,H 7 . 5 . Dissolve 27.2 grams of potassium dihydrogen phosphate in 800 mi. of water, adjust to pH 7.5 \rith 25% sodium hydroxide, and make up to 1 liter with n-ater. Add 10 ml. of chloroform as a preservative. Buffer, p H 4.8. Dissolve 105 g r a m of cit,ric acid monohydrate and 15 grams of sodium hydroside in 800 ml. of xater! adjust to p H 4.8 with 25% sodium hydroxide, and make up to 1 liter with water. -4dd a 2- to 5-mm. layer of hexane as a preservative. llethylene blue solution. Dissolve 0.25 gram of methylene blue in 100 nil. of water, heat on a steam bath for 30 minutes, make up to 250 ml. Trith water, and filter into a brown glass bottle. Desicote, green label, from Beckman Instruments, Inc., or Fisher Scientific Co.
plug
300mI. Flath
Figure 1. Apparatus used for extraction when emulsions form in sample
Table 11.
PROCEDURE
Recovery of Added Alkyl Benzenesulfonate by Direct Methylene Blue Determinations (Negative interferences)
Sample Surface water, 1 Surface water, 11 R a w sewage, 2 Aqueous extract of straw 1 Urine 1 -4queous extract of manure hqueous extract of rotted wood Albumin solution, 40 p.p.m. Albumin solution, 10 p.p.m. Gelatin solution. 23 p.p.m.
.4BS, P.P.AI. Apparent original Total content Added found 0 861 1.132 1.913 0 0 2.0 1.5 5.24 4 81 9.40 5 6 7 1
9 fi 21 8
12.1 25.8
.4dded ABS Recovered,
P.P.11.
Reco~ ery uf Added
ABS, % 9
1 052
1.5 4 16
I
J
86 5
G 3 18 7
811
68
1 5
5 0
5.5
4.0
60
0 4
5.0
4.9
4 5
90
0 00
1.00
0.70
0 70
70
0 00
1.00
0 88
0 88
88
0 00
1.20
1.00
1 00
83
Amine-Chloroform Extraction. Place in R separatory funnel of the smallest suitable size a v-ell-mixed sample of not over 150 ml. of selyage or 1.5 liters of rrater containing 5 to 200 -;of alkyl benzenesulfonate; the optimum is 50 to 100 y. (If desired, water samples up to 10 liters or more in volume mag be made alkaline, about pH 9, with sodium hydroxide, boiled d o m to between 50 and 200 ml., transferred to the separatory funnel, and neutralized with sulfuric acid,) Dilute x i t h water to TO ml. or more. Add 5 mi. of p H 7.5 buffer plus 1 nil. for every 100 ml. of solution. Extract for 2 minutes n-ith 25 nil. of amine-chloroform solution, plus 25 ml. of chloroform if the aqueous volume is greater than 250 ml. Swirl or stir to break the emulsion, and filter the chloroform extract through a chloroform-wetted cotton pledget into a 300-ml. Erlenmeyer flask with a 24/40 ground joint. If persistent emulsions form, filter through chloroform-wetted cotton into a 125-ml. separatory funnel, using the apparatus show1 in Figure 1. Lipply suction, if required, by nieans of a rubber bulb attached to the side arm of the filter adapter. Drain t,he chloroform from the lorn-er funnel into the flask. Return any aqueous phase to the original funnel, Rinse the solution in the funnel twice with 15to 20-ml. portions of chloroform without shaking, and filter into the flask. Repeat the extraction and rinsing. Add to the flask 35 ml. of water, 3 drops of pH 7.5 buffer, and glass boiling beads. Attach a short (110 X 18 nim.) air condenser, boil off most of the chloroform, and then remove from the heat. Repeat' the extraction and rinsing of the sample t n o additional times and collect the
V O L U M E 28, NO. 1 2 , D E C E M B E R 1 9 5 6 extract,s in the flask. Replace the condenser and boil o f f most of the chloroform. Rinse the condenser and flask walls n-it,h 5 to 10 nil. of chloroform, then heat until all the chloroform has evaporated and the aqueous solution has boiled 1 minute or more. Remove the air condenser, rinse it into the flask m-ith 10 to 15 ml. of water, add 5 drops of 25% sodium hydroside, cover the flask with a Short and Good special cover glass ( 3 1 ) , and boil until the volume has been reduced t o 15 to 20 nil. .Idd water if necessarjto enable boiling for at least 5 minutes. Acid Hydrolysis. Rinse the cover glass into the flask with 5 nil. of water: add 5 nil. of hydrochloric acid, and attach a long (500 x 8 nini.) air condenser. Reflux for 1 hour, keeping the condensate below the middle of the condenser. Cool and rinse the condenser with 15 ml. of ly, sodium hydroxide, draining it into the flask. Remove the air condenser and rinse it into a GOOml. beaker wit,h 15 to 20 ml. of ammoniacal methanol. Add 1 ml. of lyGsodium hJ-droxide t o the beaker and reserve for later use. Amine-Hexane Extraction. Add 1 drop of 17, phenolphthalein solution to the flask, make alkaline tip dropxvise addition of 25% sodium hydroxide, cool, acidify with 10% sulfuric acid, then make just alkaline x i t h 1% sodium hydroside. Transfer the solution to :I 125-nil. separatory funnel containing 3 t o 4 drops of 1o/b sulfuric acid. nnd rinse in Kith water to a total volume of GO to i 5 nil. .4djust to pH 4 to G (indicatm paper) with 1% sulfuric acid or sodium hydroxide, add 2 nil. of pII 4.8 buffer, and estract for 2 minutes with 25 ml. of amine-hrxrtne solution. Drain the aqueous ph:iee into a second 125-ml. separetory funnel :tnd the hesane into a Desicoted 150-ml. bctiker. Rinse the funnel into the beakcr with 15 to 20 ml. of 1iex:aric. Est,ract the aqueous phase x i t h 25 nil. of h - m e , draw off the aqueous phase into the first funiiel : t i i d the lie aiie into t,hc bwlier, rinsing in as before. Decant the hexane 'om the 150-ml. 1)caker into the 600-nil. beaker into u-hich the condenser \vas rinsed, taking care not to transfer an>- : q i i e o u s droplet?. Rinse tjhe 150-ml. beaker tn-ice with 10- to 13-1111. portions of tiexme and decant the hexane into t.he large imilier. lti~isetlie 150-nil. bealicr into the first sepamtory funnel n-ith 5 nil. of water. llepeat the extractiori and rinsing of the sohition in the separatory funnel t v o :idditional times; using 25 ml. of amine-hexane solution foi the first and 25 nil. of hexane for the second extraction, and collect the extracts in the 150-nil. beaker previously used. -1fte:. tlie last rxtraction discard the aqueous phase instead of collecting it in a separntory funnel. Decant t,he hexane from the 150- to the 600-ml. beaker and rinse with hexane as before. Shake out and discard any itqueoiis droplets in the snisll beaker. liinse tlie 130-ml. beaker into one of the separatory funnels Ti-ith 15 nil. of ammoniacal methanol: swirl for a few des, then di,nin into the large beaker. Rinse with 10 nil. of ammoniacal methanol, then Repeat the above rinsing procedure using fiinnel. Add all rinsings to the 600-ml. e the 130-nil. henker into the large beaker
1829
Table 111.
Recovery of Added Alkyl Benzenesulfonate by Double Extraction Method ABS, P.P.M.
Sa1npIo Surface i w t e r 1 2 3 4
5 6
Raw sevnge 1 2 3 4
Sewa.ge PtIIilrnt
Original content
Added
0.76 0.00472
0.064
1.132 0.197 1.972 0.050 0 9815 0'00962
1 781 0 272 3.026 0.114 1.742 0 01428
3.83 4.22 2.94 6.77 3.21
t3.61 4 81 9 46 2.85 2.86
0.00 0 00 0.00
21.8 10 88 9.72
0.654 0.077 1.06
Recovery of Added ABS,
70
1.127 0.195 1 964 0.0.50 0.982 0 00956 Av. Std. dev.
99.6 99.0 99.6 100.0 99.6 99.4 99 5 - 0 2 3t0.3
10 47 9.00 12.30 9.60 6 11
6 64 4 78 9 31; 3.83 2 87 Ar.
100.5 99.4 98.9 99.3 100 3 99 7 3 t O . G 3tO 7
21.7 10 82 9.64
21.7 10 82 9.64
Std. dev.
Urine 1 Mixture I " Mixture 2 a All samples, av. Std. dev.
99.5 99 .5 99 2 99 6 i; 0 . 3 1 0 3
Tahlt: IV lists composition.
Table SV. Composition of 3Iixtures Tested for Interference with Double Extraction 3Iethod Concentration, P.P.M. Mixture Mixture Substance 1 2 500 300 200 50 ;00 10 NO3 000 200 NO2 200 50 C1856 1150 Br50 10 F5 2 I20 5 HCOa500 300 PO4--.9500 9500 100 Ca++ 50 Fe+++
100
hlg + +
100
25
2100
1432 3900 10 10 10
100
"A+
Stir the solution i n the largc I,c:d
