Physicochemical Basis of Quantitative Determination of Anionic

Downloaded by UNIV OF MASSACHUSETTS AMHERST on September 28, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch013

Chapter 13

Physicochemical Basis of Quantitative Determination of Anionic Surfactant Concentrations by Using an Autotitrator Robert W. S. Foulser, Stephen G. Goodyear, and Russell J. Sims Winfrith AEE, Dorchester, Dorset DT2 8DH, England The application of an autotitrator for the determination of surfactant concentrations has been investigated based upon turbidimetric and photometric techniques. The measured t i t r a t i o n curves for the two techniques were found to be very similar indicating a common underlying mechanism. Experiments to investigate this mechanism have shown that the l i g h t signal measured by the instrument depends on the texture of an emulsion formed by s t i r r i n g the aqueous and chloroform phases i n the t i t r a t o r cup. Considering the physio-chemical basis of the measurement a rapid, automatic method has been developed and successfully applied to SDBS. The quantitative determination of surfactant concentration i n solution i s an essential part of any experimental work on surfactant adsorption or phase behaviour. In the f i e l d of experimental enhanced o i l recovery the technique employed should be capable of determining surfactant concentrations i n sea water, and i n the presence of o i l and alcohols, the l a t t e r being frequently added as a co-surfactant. As part of the studies undertaken i n our laboratory i t was necessary to be able to determine quantitatively the surfactant present i n large numbers of samples (> 100 per week) a r i s i n g , f o r example, from core flooding experiments. The chosen method needed to be rapid to reduce analysis time, and to require l i t t l e manipulation of the sample to reduce errors. In this paper we report the development of a method for the determination of anionic surfactants based upon autotitration and comment on the physico-chemical basis of the technique. Numerous methods have been developed for the determination of anionic surfactants and these have been reviewed by Longman The measurement of absorbance of light by a dyestuff-anionic surfactant complex, which has been extracted into an organic solvent i s a key feature of many methods, and Sodergren has successfully used segmented flow colorimetry for an automated version of this procedure (2). An alternative i s the two phase t i t r a t i o n technique, pioneered by Herring (3) which uses dimidium 0097H5156/89/0396-0257$06.00/0 c 1989 American Chemical Society In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

OIL-FIELD CHEMISTRY

258


bromide (1) and disulphine blue (2) as the indicators. This technique, o r i g i n a l l y introduced by Holness and Stone (£) f o r q u a l i t a t i v e purposes, has been thoroughly investigated by Reid and co-workers (_5, 6) and adopted as a standard method {!). More recently potentiometric methods have been employed but these were considered unsuitable because the membrane electrode may f a i l on prolonged contact with organics as required i n t h i s application (8).

EXPERIMENTAL APPARATUS AND MATERIALS. A Mettler DL40 memotitrator, DK19 F i l t e r T i t r a t o r with f i l t e r s and a DK181 Phototrode were purchased from M.S.E. S c i e n t i f i c Instruments, Crawley. V i s i b l e spectra were recorded on a Perkin Elmer Lambda 3 spectrophotometer. Hyamine 1622 (4.0 mmol dm" solution), disulphine blue, dimidium bromide, sodium chloride (AnalaR grade), sodium hydroxide (AnalaR grade), chloroform (reagent grade) and decane (GPR grade) were purchased from B.D.H. Ltd., Poole. Dodecylbenzenesulphonic acid (98%, remainder sulphuric acid and unsulphonated o i l ) was purchased from Alpha Chemicals, Coventry. Water (conductivity 18 MOT*) was obtained from a reverse osmosis plant equipped with a MILLI-Q polishing unit. The MILLI-Q polishing unit contained ion exchange and charcoal cartridges, the l a t t e r to remove trace organics. Aqueous solutions of sodium dodecylbenzenesulphonate (SDBS) were prepared by neutralizing dodecylbenzenesulphonic acid solution with sodium hydroxide solution. 3

PRINCIPLE OF OPERATION OF THE AUTOTITRATOR. The a u t o t i t r a t o r operates by detecting the change i n l i g h t transmission through a s t i r r e d solution to which t i t r a n t i s added, the l i g h t intensity i s subsequently recorded as a voltage generated by a photocell. The l i g h t source (Figure 1) generates high frequency modulated l i g h t which passes through a f i l t e r , to select the required wavelength, then down the fibre optic cable. The l i g h t i s s p l i t at the probe; one route passing through the solution i n the t i t r a t i o n vessel, the other through a reference c e l l . I t should be noted that the l i g h t c o l l e c t e d at the detector c e l l i s the sum of the l i g h t transmitted through the solution (reflected back by the concave mirror) and any component which arises by back scattering of l i g h t d i r e c t l y from the solution. In the detector the returned l i g h t i s converted to a s i g n a l which represents the change i n transmittance of the sample i n the t i t r a t i o n vessel as the t i t r a n t i s added.

In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


13. FOULSERETAL.

FIGURE 1

Anionic Surfactant Concentrations

Schematic Diagram of Light Source and Probe 1 Light Source 6 Reference 2 Fixed Wavelength F i l t e r 7 T i t r a t i o n vessel 3 Fibre Optic Converter 8 Detectors 4 Light conducting cable 9 Demodulator 5 Probe 10 Concave mirror


259

OIL-FIELD CHEMISTRY


260

In a t y p i c a l t i t r a t i o n with the autotitrator a s i g n i f i c a n t f r a c t i o n of the equivalence volume i s added i n a single aliquot and allowed to e q u i l i b r a t e before further t i t r a n t i s added. The end point i s detected by comparing changes i n the m i l l i v o l t output of the l i g h t source (Figure 1) (9). After the addition of the i n i t i a l single aliquot the i n j e c t i o n of t i t r a n t can proceed i n two different modes: ( i ) a drop of t i t r a n t (of fixed size) i s added i f the EMF changes by less than DE (mV) i n a specified time i n t e r v a l DT ( s ) . Unless otherwise stated this mode was used for the t i t r a t i o n s reported with DE=1 and DT=1. ( i i ) a drop of t i t r a n t i s added after a preset time has elapsed from the last drop. This mode of operation has been used i n some carefully controlled comparative studies described l a t e r . BASIS OF MANUAL PHOTOMETRIC TITRATION. The determination of anionic surfactants by a photometric t i t r a t i o n employs a cationic indicator to form a coloured complex with the surfactant which i s insoluble i n water but readily soluble i n chlorinated solvents The end point of the t i t r a t i o n occurs when there i s a loss of colour from the organic phase. A considerable improvement i n this technique i s achieved by the use of a mixture of anionic and cationic dyes (4), for example disulphine blue and dimidium bromide (Herring's indicator (_3)). The sequence of colour changes which occurs during the two phase t i t r a t i o n of an anionic surfactant (AS) with a cationic t i t r a n t (CT) using a mixed indicator consisting of an anionic indicator (AD) and cationic indicator (CD) i s summarised i n Scheme 1• Scheme 1 CD/AS

+

Soluble i n CHC1 pink colour 3

AD + CT Soluble i n H0 green"colour 2

CD

CT/AS

AD/CT Soluble i n CHC1 blue colour

Soluble i n CHC1 colourless

Soluble i n H0 colourless 2

At the end the cationic indicator (CD) passes into the aqueous phase and a small quantity of the anionic indicator/cationic t i t r a n t complex (AD/CT) passes into the organic phase to give a grey/blue tint. BASIS OF MANUAL TURBIDIMETRIC TITRATION. When a cationic t i t r a n t i s added to an aqueous anionic surfactant solution a sparingly soluble complex i s produced, Scheme 2. Scheme 2 RS0 ~ + R^N* 3

RS0 NR 3

k

The quantity of precipitate formed can be controlled by the addition of an organic solvent such as chloroform to the system. The chloroform forms a separate phase i n which the complex i s soluble and a s i g n i f i c a n t quantity of the complex can be produced


13. FOULSERETAL.


261


before the s o l u b i l i t y l i m i t i n the aqueous phase i s exceeded. A plot of turbidity versus volume of t i t r a n t added would be expected to have a steep f a l l to the end point followed by a shallow r i s e as the turbidity of the solution i s diluted by excess t i t r a n t , i e a " t i c k " shape. CHOICE OF FILTER FOR AUTOMATED PHOTOMETRIC TITRATION. At the end of a photometric t i t r a t i o n using the above two indicators the colour of the chloroform phase changes from pink to blue. To choose a f i l t e r to detect this end point the v i s i b l e spectra of the separated chloroform layers of surfactant t i t r a t i o n s were recorded before, at and beyond the end point, see Figure 2. At 580 nm there was a greater change i n absorbance than at 440 nm, thus the 580 nm f i l t e r was preferred. The plot of l i g h t transmission versus volume of t i t r a n t added would be expected to be a step change, where the equivalence point might reasonably be taken as the position of greatest slope i n the t i t r a t i o n curve. EXPERIMENTAL PROCEDURES; AUTOMATED PHOTOMETRIC TITRATION. Indicator solution (5 cm*) (5) and chloroform (10 cm*) were placed in the t i t r a t i o n beaker together with the aqueous surfactant sample and water (30 cm less the volume of the surfactant sample). The t i t r a t i o n was then carried out with hyamine solution (4.0 mmol dm" ) added i n 0.05 cm increments after the addition of an i n i t i a l single aliquot. 3

3

3

EXPERIMENTAL PROCEDURES: AUTOMATED TURBIDIMETRIC TITRATION. A method for the automated aqueous turbidimetric t i t r a t i o n of surfactants has been published (10) i n which anionic surfactants are t i t r a t e d against N-cetylpyridinium chloride to form a c o l l o i d a l precipitate near the equivalence point. N-cetylpyridinium halides have a disadvantage i n that they have the tendency to c r y s t a l l i s e out of solution (_5), consequently the strength of the solution may a l t e r s l i g h t l y without the knowledge of the operator, also the crystals suspended i n solution may cause damage to the a u t o t i t r a t o r . In view of these drawbacks hyamine was preferred as the t i t r a n t . An aqueous surfactant sample was placed i n the t i t r a t i o n beaker together with chloroform (10 cm ) and water (30 cm less the volume of the surfactant sample). The t i t r a t i o n was then carried out using hyamine solution as i n the photometric case. 3

3

TITRATIONS FOR COMPARISON OF METHODS. The automated photometric and turbidimetric methods were compared using 30 cm samples of surfactant solution containing a nominal 20 yjaol SDBS to give an equivalence volume of 5 cm . The effect of s a l i n i t y on the t i t r a t i o n s was studied using samples prepared containing sodium chloride concentrations of 0.0, 0.14, 0.70 and 1.46 wt%. The influence of the choice of f i l t e r (580 or 620 nm) was also investigated. 3

3


OIL-FIELD CHEMISTRY


262

O O

O ^

O «-

O 00

~»

«j

to

m

>flO r- f\»

*° ^>

WAVELENGTH /nm

FIGURE 2

V i s i b l e spectra of chloroform layers, before, at and beyond the end point of photometric t i t r a t i o n


13. FOULSERETAL.


RESULTS AND


263

DISCUSSION

COMPARISON OF METHODS. Both methods were f a i r l y rapid with a t y p i c a l analysis time of 5 minutes per sample as compared with 30 minutes per sample for the manual method. A t y p i c a l photometric t i t r a t i o n of SDBS against hyamine at low s a l i n i t y i s shown i n Figure 3. It was noted, however, that the t i t r a t i o n curve was "V" shaped and not the anticipated step curve. The turbidimetric t i t r a t i o n of SDBS against hyamine afforded a curve, Figure 4, very similar to that for the photometric titration. Photometric and turbidimetric t i t r a t i o n s at the same s a l t l e v e l were always similar suggesting that only a turbidimetric signal i s seen. Also, there i s l i t t l e difference between the results obtained at 580 and 620 nm wavelength, which further demonstrates the absence of a photometric signal because there i s a s i g n i f i c a n t difference i n the absorption of the indicator dyes between these wavelengths. Salt concentration, however, has a marked effect on the shape of the t i t r a t i o n curve. At low s a l t concentrations a l l the curves have a sharp minimum, as shown i n Figure 5. As the salt concentration increases this sharp minimum begins to broaden out, u n t i l the highest s a l t l e v e l studied (1.46 wt%), causes the curve beyond the t i t r a t i o n point to show very l i t t l e increase, as shown i n Figure 6. EMULSION MECHANISM. The above results show that the indicator was unnecessary because the method i s e s s e n t i a l l y a turbidimetric one. However, the occurence of a sharp minimum i n the t i t r a t i o n curve at low salt concentrations, suggests that the formation of a c o l l o i d a l precipitate i s not the underlying mechanism for the t u r b i d i t y . Consequently, e f f o r t s were made to c l a r i f y the underlying physico-chemical mechanism of the t i t r a t i o n . During surfactant t i t r a t i o n s two observations were made: (i) The contents of the reaction vessel were turbid being milky white i n appearance, although this was less intense near the endpoint of the t i t r a t i o n , ( i i ) If the addition of hyamine and the s t i r r i n g were stopped two clear phases separated. This occurred s i g n i f i c a n t l y faster when the t i t r a t i o n was i n the region of the endpoint. It was apparent that when the two immiscible f l u i d s were s t i r r e d droplets of chloroform formed i n the aqueous phase. It was hypothesised that the response of the phototrode was dominated by l i g h t scattered back from the droplets without reaching the mirror and that, as the droplet size decreases, the intensity of the back scattered l i g h t increases. This was confirmed i n tests by increasing the rate of s t i r r i n g and so decreasing the droplet size. This concept allows the shape of the t i t r a t i o n curves to be explained by postulating that the chloroform droplet size decreases as the i n t e r f a c i a l tension ( i f t ) between the aqueous and chloroform phases i s decreased by the presence of active surfactant. As the endpoint i n a t i t r a t i o n i s approached the amount of active SDBS decreases as i t complexes with the injected hyamine. The reduction i n the amount of active surfactant material results i n an increase


OIL-FIELD CHEMISTRY


264

420 T 400-' 380360340320300280260240220200180-J 3

_ > HT

5

1

.

4

,

,

,

,

5 TITRANT (cm)

6

,

1

7

3

FIGURE 3

Typical photometric t i t r a t i o n of SDBS against Hyamine at low s a l i n i t y

:

i

FIGURE 4

480 460 440 420 400 380 360 340 320 300 280 260 240 220 200

Typical turbidimetric t i t r a t i o n of SDBS against Hyamine at low s a l i n i t y




FOULSER ET AL.


265


266

OIL-FIELD CHEMISTRY

in droplet size and a corresponding lowering of the transmittance. This process continues to the endpoint where there i s no more active surfactant present. At this stage the average droplet size i s maximised and, consequently, the transmittance i s at a minimum. Further addition of hyamine, which i s a cationic surfactant, makes possible the increase i n transmittance observed i n the t i t r a t i o n s (up to 0.70 wt% s a l t ) . It i s assumed that the presence of salt reduces the a b i l i t y of the hyamine to lower the i f t of chloroform and water (much more so than any reduction for SDBS) and offers an explanation for the variation i n the shape of the t i t r a t i o n curves with s a l t l e v e l . TEST OF THE EMULSION MECHANISM. The above hypothesis suggests that at the equivalence point a l l the SDBS i s complexed with hyamine and, e f f e c t i v e l y , only a brine and chloroform system i s present. It also suggests that an excess of either anionic or cationic surfactant causes a change i n droplet size and an increase i n l i g h t scattering. Therefore, i t should be possible to mimic the two branches of the t i t r a t i o n curve emanating from the equivalence point by starting with pure brine (35 cm ) and chloroform (10 cm ) and using either hyamine or SDBS as t i t r a n t s . Experiments undertaken to examine this hypothesis are described below. In order to achieve an i n i t i a l droplet size d i s t r i b u t i o n i n the t i t r a t i o n cup the contents were s t i r r e d for 230 seconds before i n j e c t i n g any t i t r a n t . The mode of operation of the autotitrator was changed to inject 0.05 cm of hyamine every 10 seconds to make conditions for each t i t r a t i o n exactly the same. The results when hyamine was used as the t i t r a n t are shown i n Figure 7. This figure shows the expected increase i n signal with increasing hyamine concentration and that increasing the s a l t concentration decreases the slope of the t i t r a t i o n curves. The procedure was then repeated using SDBS as the t i t r a n t to produce the results plotted i n Figure 8. Again the curves show the expected increase i n s i g n a l with increasing surfactant concentration and the decrease i n slope of the t i t r a t i o n curve at higher salt levels i s consistent with the trend observed i n the o r i g i n a l tests, although i t i s less marked than when hyamine i s used as the t i t r a n t . These tests established that detection of the chloroform emulsification was the p r i n c i p l e underlying action of the a u t o t i t r a t o r . However, while there i s agreement i n the qualitative dependence on the s a l t l e v e l there are differences i n the apparent rates of change i n signal with aliquot addition. These can be attributed mainly to non-equilibrium e f f e c t s . The i n i t i a l t i t r a t i o n aliquots were added automatically on the basis of the rate of change of EMF, mode ( i ) , and the resulting time between aliquot additions was usually shorter than the 10 second e q u i l i b r a t i o n time allowed i n the mode ( i i ) t i t r a t i o n s described above. The time differences were especially s i g n i f i c a n t when the transmittance change per 0.05 cm aliquot was small, f o r example when the hyamine was present i n excess at high salt concentrations. This means that the mode ( i ) t i t r a t i o n s are more influenced by kinetic effects and so the measured curves are less d i s t i n c t i v e as may be seen by comparing the results at 1.46% s a l t i n Figures 6 and 7. 3

3

3

3


13. FOULSERETAL.

Anionic Surf octant Concentrations

500

0.14% SALT

400 -


> E

261

0.0% SALT

f

300 -

200

1f\fni

0.70% SALT

1

r

1.46% SALT

100

I

I l l

10 I I I 100

ADDITION OF 0.05 ML DROP 20 l

I l

| I I t

«M

30 • I I 300

I I I

200

I I I

I

I I

400

TIME (sees)

FIGURE 7

3

3

T i t r a t i o n of 35 cm brine and 10 cm chloroform against hyamine. 230 seconds i n i t i a l e q u i l i b r a t i o n time and 10 seconds between successive t i t r a n t additions.

Son

100 ADDITION OF 0.05 ML DROP 10 ' ' l I ' ' l 'I ' l 100

I

20

l 1

-r-

200

-t-

30

40

300

400

TIME (sees)

FIGURE 8

3

3

T i t r a t i o n of 35 cm brine and 10 cm chloroform against SDBS. 230 seconds i n i t i a l e q u i l i b r a t i o n time and 10 seconds between successive t i t r a n t additions.



268

OIL-FIELD CHEMISTRY

Although the hyamine t i t r a t i o n s i n Figure 7 are i n p r i n c i p l e d i r e c t l y comparable with those obtained for t i t r a t i o n s (Figures 5 and 6), this is not the case for the SDBS. F i r s t l y , because the volume of water i n the reaction vessel is increasing as the concentration of active SDBS increases i n Figure 8, while i n a r e a l t i t r a t i o n i t decreases. Secondly, and more importantly, the mechanism by which the equivalence point is reached i n a t i t r a t i o n i s by the aggregation of chloroform droplets as the concentration of active surfactant f a l l s , whereas i n Figure 8 the increase i n the EMF with increasing SDBS i s related to the increase i n transmittance as the chloroform droplets break up with s t i r r i n g . If the rates for these processes are not equal then different curves w i l l be produced unless the reaction vessel contents are allowed to f u l l y equilibrate between aliquots. An example of these effects i s shown i n Figure 9 where a mode ( i i ) surfactant t i t r a t i o n has been performed i n the absence of s a l t and allowing a 10 seconds e q u i l i b r a t i o n time between each aliquot. This gives a more c l e a r l y defined equivalence point when compared to the mode ( i ) t i t r a t i o n i n Figure 5. A further difference is that the value of the transmittance minima of the t i t r a t i o n curves i s higher than that found for the water and chloroform system. This i s believed to be due to the fact that i n a t i t r a t i o n the equivalence point w i l l not correspond to an integer number of hyamine aliquots and so, even i f the contents of the reaction vessel were allowed to equilibrate f u l l y , there would s t i l l be a small amount of uncomplexed surfactant present which w i l l be sufficient to decrease the droplet size and so increase the back-scattered l i g h t . ERROR ANALYSIS. Although the endpoint might be expected to correspond to the steepest point of the curve, the equivalence point has been found to correspond to the minimum of the curve. At low salt levels the use of the steepest point on the t i t r a t i o n curve w i l l underestimate the equivalence point by 1% but at higher s a l t levels the application of this c r i t e r i a may lead to misleading results with the equivalence point being considerably under estimated. The i n i t i a l t i t r a t i o n s which possess clear minima ( i . e . 0 and 0.14 wt% s a l t ) can be analysed using the minimum as the equivalence point with the results shown in Figure 10, where the error bars represent one standard deviation. The results were compared using t - t e s t s . The use of the superfluous indicator gives s i g n i f i c a n t l y lower results compared to the purely turbidimetric method, because the mixed indicator has a net cationic dye content which complexes with the SDBS thereby reducing i t s active concentration. For the turbidimetric method consistent results are obtained at both s a l i n i t i e s and with both f i l t e r s , though the results show less scatter with the 580 nm f i l t e r and so i t s use i s preferred. EFFECT OF OIL. T i t r a t i o n s were performed in which small amounts of decane were added with the surfactant sample. The results were found to be insensitive to the presence of up to 2 cm of the decane. This allows the application of the method to both simple aqueous solutions and microemulsions containing significant quantities of decane. 3


FOULSER ET AL.


269

500


450 -

400

800

TIME (sees)

FIGURE 9

Turbidimetric t i t r a t i o n SDBS against hyamine. 10 seconds between successive t i t r a n t additions.

5.08 5.07 5-06

580 NI

5.05

f

1

I

620 Nl

5.04

Z 5.03 e

~

5.02

5 r-

5.01

580 I

5

4.99

FILTER I WAVELENGTH

620 I I = WITH INDICATOR Nl = NO INOICATOR

4.98 4.97 4.96 4.95 1

0.0% SALT

FIGURE 10

Analysis of equivalence minima.

1

0.14%

SALT

volumes from t i t r a t i o n curve


OIL-FIELD CHEMISTRY

270


CONCLUSIONS A detailed study of the determination of the anionic surfactant SDBS by automated t i t r a t i o n against hyamine using an autotitrator has been undertaken. The following conclusions and observations can be made. ( i ) An automated turbidimetric method using a chloroform phase and hyamine t i t r a n t without indicator dyes has been developed for the determination of SDBS concentrations. ( i i ) The mechanism producing the turbidity i n the t i t r a t i o n cup i s postulated to be the formation of chloroform droplets i n the aqueous phase under the action of vigorous s t i r r i n g . Chloroform droplets back-scatter l i g h t at an intensity which decreases with drop size and the drop size i s determined by the i f t between the aqueous and chloroform phases. The i f t , and hence the drop s i z e , i s decreased by the presence of active uncomplexed surfactant or hyamine. ( i i i ) The contents of the t i t r a t i o n cup should be s t i r r e d at the maximum rate available to enhance the rate of formation of the chloroform droplets. ( i v ) A l i g h t source of 580 nm wavelength gave a smaller error than a wavelength of 620 nm. (v) The equivalence point should be determined from the minimum i n the t i t r a t i o n curve which i s well defined for salt levels below 0.14% wt% for SDBS. Thus d i s t i l l e d water should be used to d i l u t e surfactant solutons. ( v i ) Sharper minima can be obtained by allowing a longer time i n t e r v a l between t i t r a n t additions, ( v i i ) This study has been s p e c i f i c to the t i t r a t i o n of SDBS against hyamine. However, i t w i l l probably apply to other anionic surfactants since the a n a l y t i c a l method works by i n d i r e c t l y measuring i n t e r f a c i a l tension, and i t i s a generic property of surfactants to a l t e r i f t . Whether or not the method i s suitable for a particular surfactant w i l l depend on the d e t a i l of the t i t r a t i o n curve s p e c i f i c to the surfactant system and the accuracy to which the determination i s required. Quantitative results w i l l only be possible when the method possesses a well defined equivalence point determined by the minima of the t i t r a t i o n curves. I f no such clear d e f i n i t i o n exists then the method cannot be r e l i e d on to give accurate results. ACKNOWLEDGMENT This work was carried out for the UK Department of Energy under contract number R5221 as part of i t s Enhanced O i l Recovery Research. LITERATURE CITED 1. 2. 3. 4.

Longman, G. F.; The Analysis of Detergents and Detergent Products; J . Wiley & Sons, 1978. Södergren, A.; Analyst 1966, 91, 113. Herring, D. E.; Lab Pract. 1962,91,113. Holness, H.; Stone, W. R.; Analyst 1957, 82, 166.


13. 5. 6. 7. 8.


9. 10.

FOULSERETAL.


Reid, V. W.; Longman, G. F.; Heinerth, E.; Tenside 1967, 4, 292. Reid, V· W.; Longman, G. F.; Heinerth, E.; Tenside 1968, 5, 90. Determination of Anionic - Active Matter - Direct Two-phase T i t r a t i o n Procedure, ISO 2771, 1972. Synthetic Anionic Active Matter i n Detergents by Potentiometric T i t r a t i o n . ASTM D4251-83. Operating Instructions f o r the DL40RC; Mettler Instruments AG, CH-8606 Griefensee, Switzerland. Turbidimetric T i t r a t i o n of Anionic Tensides, Mettler Application No 135; Mettler Instruments AG, CH-8606 Griefensee, Switzerland.

RECEIVED September 23,

1988


Physicochemical Basis of Quantitative Determination of Anionic

Recommend Documents