- Email: [email protected]
A turbidimetric method for colloid titrations
Analytica Chimica Acta, 69 (1977) 383-389 QBlsevier Sciertific Publishing Company, Amsterdam
-
Printed in The Netherlands
A TURBIDZMETRIC METHOD FOR COLLOID TITRATIONS
KYOJI
T&I
and MIHO
Department or Chemistry. Okayama-shi 700 (Japan) (Received
3rd September
SAWADA Faculty
of Science, Okayama
Univen-ity.
3-I-1,
Tsushima-naku,
1976)
%sitive colloid solutions can be titrated with the polyanion potassium polyvinylsulfate ~6th toluidine blue as indicator, but negative colloid solutions must be treated with an excess of the polycation pdydiallyldimethylammonium chloride which is backtitrated with potassium polyvinylsulfate. By turbidimetry however. positive or negative colloid solutions can be directly titrated with, respectively, the polyanionic or polyc&ionic t&rant. Two methods, the construction and differential methods, czn he used. The latter method is particularly useful when a flocculent precipitate appears during the titration.
Colloid titration is widely used for the determination of polyelectrolytes. Recently, PVSR (potassium polyvinylsulfate) and CatrFloc (polydiallyldimethylammonium chloride) were used as polyanionic and polycationic titrants, respectively [ 11. The color change of toluidine blue could be used for the direct titration of positive colloid solutions by PVSK, but negative colloid solutions could not be titrated directly by CatrFloc, because no indicator was available. A negative colloid solution must be treated with an excess of CatrFloc, which is back-titrated with PVSK with toluidine blue as indicator. The conductimetric method is useful; negative and positive colloid solutions can be titrated directly with Cat-Floe and PVSK, respectively [ 21. In the work described here, the turbidimetric method has been used to indicate the end-point in the direct titration of positive and negative colloid solutions by PVSK and Cat-Floe, respectively. EXPERIMENTAL
Apparatus ‘IurbidiQ was measured by a Metrohm Spectiocolorimeter El009 at 420 nm. Turbidimetric titration curves were recorded by a Metrohm Potentiograph E336 with a Metrohm EX36E Titzator. A Hitachi-Horiba F5ss pH meter wzs used.
364
Reagents
PVSK solution ad Cat-33oc solution were used as the anionic and c&ionic t&ants, respectively. The PVSK solution (0.00125 M or 0.0025 M) was standardized b;7 0.00125 M cetylpyridinium chloride monohydrate solution wi’th tiluidine blue as indicator, and the CatiFloc solution (0.00125 M or 0.0025 M) was evaluated with the PVSK solution. The turbidimetric standardization of PVSK by cetylpyridinium chloride monohydxate was not successful; the end-point appeared before the equivzlence point during automatic titration. Sample solutions
Glycolchitosan, methylglycolchitosan, polyethyleneimine, sodium chondroitin sulfate, sodium al&a@ ammonium alginate, caxrageenan, and sodium lignin sulfonate were dried in vacua below 5O”C, weighed accurately, and the solutions diluted to a constant volume. The concentration was adjusted to about 0.00125 M. Titration procedures Indicator method Toluidine blue was used as indicator as described previously 121. As the titration proceeded, the solution became turbid;
close to t,heend-point the clcudy solution coagulated suddenly, and the coIor changed from blue to red-violet. Turbidimetric method Positive and negative colloid solutions were titrated directly with PVSK or Cat-F&, :espectively. The transmittance at 420 nm was measured with the Spectrocolorimeter, and the titration curve was recorded automatically. The sampie solution (10 ml) was diluted to 40 ml with distilled water, and titrated in a lOOmI cylinder with mechanical stirring. FZS-IJLa'iS T’urbidimetric titration curves Cat-Floe solution (10 ml, 0.00125 M) was diluted to 40 ml with distilled. Tvaterand titrated with 0.00125 M PVSK turbidimetxically. The titration
curve is shown in Fig. 1. Conversely, when 40 ml of PVSK was titrated with CatcFloc solution, almost the same curye was obtained. In both cases, as the titration proceeded, the turbidity increased. Near the end-point., t.he transmittance decreased abruptly. The inflection point of the titration curve was determined either by the constnxtion method or by the different&l method by setting to “Diff” on the E336, as shown in Fig. 1.
The molari found for the Cat-Fhx solution by the iLndicatorand turbidimetric methods is shown in Table 1, in which & b, and c correspond to a, b and c in Fig. 1, respectively; point b indicates the end-point and the value is coincident with that of the indicstxx method within esper+.mental (XrOr.
385
differential
100
curve
>
’
0
Volume
of PVSK
or
Cat-Floc(ml)
Fig. 1. Turbidimetric titration curve. TABLE 1 Molarity of Cat-Floe deterhncd solution was 2.30 - IO” M Method
Indicator
Turbidimetric
by the indicator and turbidimetric methods. The PVSK
Cat-Fit-c k&xl
PVSK taken
PVSK titrated
Cat-FIoc titrated
WI
WI
WI
(ml)
10.00 10.00 -
-
9.62 a9.49
-
10.00
b9.55
c9.60 -
a10.38 b10.43 clO.47
Cat-Fhc concn. (-1O’M) 2.21 2.18 2.20 2.21 2.22 221 220
‘I%? end-point obtained by the construction method was compared with that given by the differential method by changing the titration speed. Good agreement between the me’thods was obtained at 0.33 ml min-’ when lU..OO ml of Cat-Floe or PVSK solution was used (Table 2). Standard solutiors of the same molarity of PVSK and Cat-Floe ranging from 0.0025 M-lO-c M were prepared; 10 ml of each solution was diluted to 40 ml with dktiUed water and titrated turbidimetricay with the titrant of the same strength. As a standard, 2.30 - lo-’ &I PVSK was diluted 2,3, 5 and 25 times, and the standard CaWloc solution (0.00125 M) was diluted in the same way. The molzrity of the standard CatLFloc solution, cdculated
386 TABLE
2
Effect of titration sped Titration
of Cat-Es
on the
conshction
ntration
with PVSK
%=ed (Id Ink-l)
PVSK constr.
Mff.
0.70 0.58 0.58, 0.335 0.33
10.63 [email protected] 10.65 10.64
10.81 10.75 10.66 10.66
“D-8
required
ml: 0.58 ml min-‘,
6-10
and differeniizd
(ml)
-
of Z’VSK with Cat-Fkc Cat-Floe
Sx=d
(ml r&l_‘) 0.70 0.58 0.58. 0.33a 0.33
ml: 0.33 ml r&x-l,
methods
PYSK:
required
CGZlStL
Diff.
S-48 9.39 9.46 9.44
9.52 9.57 9.49 9.44
(ml)
1.17 - low3 hf.
from the various concentrations of CatrFloc and PVSK obtained by turbidimetric titration, was constant at 2.20 + 0.01. 10m3 M. The titration cmxe for 0.0025 M PVSK or Cat-Floe is distorted initially, but the correct end-point can be obtained. In the titration of lo+ ill solution, the turbidity can hardly be seen and the decrease in transmittance at the end-point is very small, although the end-point is detectable. _4ccordingiy, the standard 0.00125 &I solution of PVSK or Cat-Floe can be used conveniently. Examples of colloid titration Glycolchitosax Dried glycolchitosan (0.1269 g) \~as dissolved in a 503mI measuring flask. The solution (10 ml) was diluted to 40 ml with distilled water and titrated with 1.13 * 10m3&I PVSK by the indicator and turbidimetric methods. The results are shown in Fig. 2. Below pH 5, the values of meq g-’ from the turbidimetric method are constant (3.47 meq g-l) and values given by the indicator method are 1.7% higher. In this pH range, the amino groups in glycolchitosan are in the ammonium form. As the color change of toluidine blue is not instantaneous above PH 6.5, the end-point is indistinct; in the turbidimetric method, the decrease in transmittance is not sharp and the end-point is indistinguiihable. MethyTgZyco1chitosa.x Dried methylglycolchitosan (0.2363 g) was dissolved in a 503m3 measurin g flask. The solution (10 ml) was titrated with 1.13 - 10m3 &I PVSK. The results are shown in Fig. 3. Below pH 6 a constant value was ob+&ed by the indicator and turbidimetric me’thods. At about .pH 10, the value is 6% lower than that of an acidic solution. Polyethyleneimine. Commercial polyethyleneimine solution is pale yellow and contains 30% polyethyleneirnine. The solution (0.1 ml) was dissolved and diluted to 11 and 10 ml of tb& solution was titzxted with 1.22 - 10e3M PVSK. The results zre shown in Fig. 4. The titration values by the construction method agree with those of the differential method. Above pH 7, the values given by the indicator method are scattered, because the color-change
0’
’
’
0,2
’
’
’
’
’
’
’
3
5
5
6
7
8
9
0’
’
0
’
’
’
17.3-G
t 5
A
P”
Fig. 2 Colloid tit&ion.
titration results of glycolchitosan.
Fig. 3. Colloid titration.
titration results cf methylglycolchitc.
o Indicator
PH
I
I
I
7
8
91011
1
I
titration. o Turbidirnefric
o Indicator titration.
o Turbidimetric
is not instantaneous at the end-point and coagulation of the complex at the end-point may not occur. A constant value (meq 1-l) could not be obtained. This implies that polyethyleneimine has hydrogen-bonded imino groups. Sodium chondroitirz sulfute. The solution (0.2586 g 1-l) was titrated with 1.02 * IO-’ M Cat-Floe turbidimetrically, and also indirectly by the indicator method. The results are shown in Fig. 5. The value by the turbidimetric method (3.53 meq g-l) is 89% of the calculated value. Sodit;m alginate. The solution (0.2252 g 1-l) was titrated with 1.22 - 10S3M Cat-Floe turbidimetricahy. The solution (10 ml) was also titrated by the indicator method &ith 1.22 - 10S3M Cat-Floe and 1.17 - 10e3M PVSK. L-
2
P
L
5
6
Pn
7
8
9
10
11
0
1
2
3
5
6
7
8
9
PH
Fig. 4. Colloid titration results of polyethyleneimine. o Indicator titration. o Turbidimetric titration (construction method)_ o Turbidimetric t&&ion (differential method). F&
5. C&loa
titration results of sodium chondroitin
0 Indicatortiition.
sulfate. o Turbidimetric
titration.
10
11
388
The results are shown in Fig. 6. In the turbidimetric
method,
the construction
method cannot be used below pH 3 because a sol is formed nea,r the end-
point. Above pH 5, a constant value (4.62 meq g-‘) was obtained; this corresponds to 92% of the calculated value. Ammonium alginate. The solution (0.1348 g 1-i) was titrated by the turbidimetric and indicator methods (Fig. 7). The value (5.08 meq 9’) at pH 11 and above is equivalent to 98% o f the calculated value. In the titration of the copolymer of sodium maleate and methylvinyl ether, the values (meq g-I) given by sodium hydroxide are lower than those given by tetrabutylammonium hydroxide solutions at the same pH [ 3 1, but there was no difference in the titration of the dginate. Carrugeenun. The solution (0.4166 g 1-l) was titrated with 1.21. 10e3 M Cat-Floe. The construction method could not be used, because a flocculent precipitate was formed, and the end-point was found from the peak of the differential curve. The results are shown in Fig. 8. Carrageenan is a mixture of different fcrms, depending on its origin. Sodium Zigrzinsulfonate. A brown commercial sample of sodium lignin sulfonate (0.3550 g) was dissolved in 11 of water. When the concentration is higher than this (ca 0.0036 M) the end-point cannot be detected by the irrdicator and turbidimetric methods because of the color of the solution. The resuits are shown in Fig. 9. Between pH 2 and 6.5, the values given by the indicator and turbidimetric methods are almost the same: above pH 6.5 the indicator method gives ‘higher values than the turbidimetric method Above pH 6.5, the color of the solution deepened; phenolic hydroxyl, enol or ammonium groups etc. would be dissociated or decomposed by air. Hydrolysis of the ester content of the sample may occur and would be acceierated by the presence of Cat-Floe in the indicator method 143 ; direct titration by turbidimetry would therefore be preferable to the indicator method.
0
a
’ !
’ 2
3
* i
’ 5
* 6
. 7
. 8
’ 3
1 10
* 1,
3
0
,
3
, 3
, 5
* 5
8 6
Fig. 6. Cdloid titration results of sodium alginate A.(Bu,N@H). o Indicator titzation.
, 7 PM
SH
e Turbidimetric
LTig.7. Colloid titration results of nrcmonium alginate. 3 hdicator metric titration (PiaOH). a (Bu,XOH).
titration titration.
I
B
*
I
9
10
(NaOH). 9 Turbidi-
I
I,
h-
s
,-
E”
2-
1 -
,, 0
.
,
1
2
3
I
I
I
4
s
6
,
t
I
7
B
9
.
10
*
‘1
*
II
0’
0
*
I
o
2
’
3
’
’
.t
s
DH
Fig. 8. Colloid titration results of carrageenan. o Indicator
titration_
l
a
6
)
D”
7
*
8
’
9
n
10
Turbidimetric
tit.EItiOfi
Fig. 9. Colloid titration results of lignin sulfonic acid, sodium salt. o Indicator e Turbidimetric titration (NaOH). A (Bu,NOH).
titration_
CONCLUSIOIG
The indicator method is useful for cationic polymers such as glycolchitosan, methylglycekhitosan and polyethyleneimine; the values obtained agree with those from t.he turbidimetric method within experimental error. Anionic polymers with sulfate groups combine strongly with Cat-F& and the turbidimetic titration values agree with those obtained by titrating the excess of CatcF’loc with PVSK by the indicator method. Anionic Flymew with carboxyl groups can be titrated directly with Cat-Floe turbidimetrically. The titration values agg fairly well with those from the indicator method. An intricate anionic polymer such as sodium lignin sulfonate should be titrated directly by the turbidimetric method; higher values wouid be given by the indicator method because of a secondary reaction in +Sle presence of CatrFloc at higher pH. REFERENCES 1 K. T&i am&K+ Kawada. Japan Ansiyst, 21 (1972) 1510. 2 K. T&i and T. Kohara. Anal. Chim. Acta. 83 (1976) 59. 3 E. Kokufuta, S. Kokubo, hi. Hinta and S. Iwai, Chemistry Associations Union Tohoku District Meeting, Preprint 2DOl (1975). 4 -4. Mizote, H. Odagiri, K TGei and K. Tanaka, Analyst (London), 100 (1975) 822.
1
I1
*
12
-
Printed in The Netherlands
A TURBIDZMETRIC METHOD FOR COLLOID TITRATIONS
KYOJI
T&I
and MIHO
Department or Chemistry. Okayama-shi 700 (Japan) (Received
3rd September
SAWADA Faculty
of Science, Okayama
Univen-ity.
3-I-1,
Tsushima-naku,
1976)
%sitive colloid solutions can be titrated with the polyanion potassium polyvinylsulfate ~6th toluidine blue as indicator, but negative colloid solutions must be treated with an excess of the polycation pdydiallyldimethylammonium chloride which is backtitrated with potassium polyvinylsulfate. By turbidimetry however. positive or negative colloid solutions can be directly titrated with, respectively, the polyanionic or polyc&ionic t&rant. Two methods, the construction and differential methods, czn he used. The latter method is particularly useful when a flocculent precipitate appears during the titration.
Colloid titration is widely used for the determination of polyelectrolytes. Recently, PVSR (potassium polyvinylsulfate) and CatrFloc (polydiallyldimethylammonium chloride) were used as polyanionic and polycationic titrants, respectively [ 11. The color change of toluidine blue could be used for the direct titration of positive colloid solutions by PVSK, but negative colloid solutions could not be titrated directly by CatrFloc, because no indicator was available. A negative colloid solution must be treated with an excess of CatrFloc, which is back-titrated with PVSK with toluidine blue as indicator. The conductimetric method is useful; negative and positive colloid solutions can be titrated directly with Cat-Floe and PVSK, respectively [ 21. In the work described here, the turbidimetric method has been used to indicate the end-point in the direct titration of positive and negative colloid solutions by PVSK and Cat-Floe, respectively. EXPERIMENTAL
Apparatus ‘IurbidiQ was measured by a Metrohm Spectiocolorimeter El009 at 420 nm. Turbidimetric titration curves were recorded by a Metrohm Potentiograph E336 with a Metrohm EX36E Titzator. A Hitachi-Horiba F5ss pH meter wzs used.
364
Reagents
PVSK solution ad Cat-33oc solution were used as the anionic and c&ionic t&ants, respectively. The PVSK solution (0.00125 M or 0.0025 M) was standardized b;7 0.00125 M cetylpyridinium chloride monohydrate solution wi’th tiluidine blue as indicator, and the CatiFloc solution (0.00125 M or 0.0025 M) was evaluated with the PVSK solution. The turbidimetric standardization of PVSK by cetylpyridinium chloride monohydxate was not successful; the end-point appeared before the equivzlence point during automatic titration. Sample solutions
Glycolchitosan, methylglycolchitosan, polyethyleneimine, sodium chondroitin sulfate, sodium al&a@ ammonium alginate, caxrageenan, and sodium lignin sulfonate were dried in vacua below 5O”C, weighed accurately, and the solutions diluted to a constant volume. The concentration was adjusted to about 0.00125 M. Titration procedures Indicator method Toluidine blue was used as indicator as described previously 121. As the titration proceeded, the solution became turbid;
close to t,heend-point the clcudy solution coagulated suddenly, and the coIor changed from blue to red-violet. Turbidimetric method Positive and negative colloid solutions were titrated directly with PVSK or Cat-F&, :espectively. The transmittance at 420 nm was measured with the Spectrocolorimeter, and the titration curve was recorded automatically. The sampie solution (10 ml) was diluted to 40 ml with distilled water, and titrated in a lOOmI cylinder with mechanical stirring. FZS-IJLa'iS T’urbidimetric titration curves Cat-Floe solution (10 ml, 0.00125 M) was diluted to 40 ml with distilled. Tvaterand titrated with 0.00125 M PVSK turbidimetxically. The titration
curve is shown in Fig. 1. Conversely, when 40 ml of PVSK was titrated with CatcFloc solution, almost the same curye was obtained. In both cases, as the titration proceeded, the turbidity increased. Near the end-point., t.he transmittance decreased abruptly. The inflection point of the titration curve was determined either by the constnxtion method or by the different&l method by setting to “Diff” on the E336, as shown in Fig. 1.
The molari found for the Cat-Fhx solution by the iLndicatorand turbidimetric methods is shown in Table 1, in which & b, and c correspond to a, b and c in Fig. 1, respectively; point b indicates the end-point and the value is coincident with that of the indicstxx method within esper+.mental (XrOr.
385
differential
100
curve
>
’
0
Volume
of PVSK
or
Cat-Floc(ml)
Fig. 1. Turbidimetric titration curve. TABLE 1 Molarity of Cat-Floe deterhncd solution was 2.30 - IO” M Method
Indicator
Turbidimetric
by the indicator and turbidimetric methods. The PVSK
Cat-Fit-c k&xl
PVSK taken
PVSK titrated
Cat-FIoc titrated
WI
WI
WI
(ml)
10.00 10.00 -
-
9.62 a9.49
-
10.00
b9.55
c9.60 -
a10.38 b10.43 clO.47
Cat-Fhc concn. (-1O’M) 2.21 2.18 2.20 2.21 2.22 221 220
‘I%? end-point obtained by the construction method was compared with that given by the differential method by changing the titration speed. Good agreement between the me’thods was obtained at 0.33 ml min-’ when lU..OO ml of Cat-Floe or PVSK solution was used (Table 2). Standard solutiors of the same molarity of PVSK and Cat-Floe ranging from 0.0025 M-lO-c M were prepared; 10 ml of each solution was diluted to 40 ml with dktiUed water and titrated turbidimetricay with the titrant of the same strength. As a standard, 2.30 - lo-’ &I PVSK was diluted 2,3, 5 and 25 times, and the standard CaWloc solution (0.00125 M) was diluted in the same way. The molzrity of the standard CatLFloc solution, cdculated
386 TABLE
2
Effect of titration sped Titration
of Cat-Es
on the
conshction
ntration
with PVSK
%=ed (Id Ink-l)
PVSK constr.
Mff.
0.70 0.58 0.58, 0.335 0.33
10.63 [email protected] 10.65 10.64
10.81 10.75 10.66 10.66
“D-8
required
ml: 0.58 ml min-‘,
6-10
and differeniizd
(ml)
-
of Z’VSK with Cat-Fkc Cat-Floe
Sx=d
(ml r&l_‘) 0.70 0.58 0.58. 0.33a 0.33
ml: 0.33 ml r&x-l,
methods
PYSK:
required
CGZlStL
Diff.
S-48 9.39 9.46 9.44
9.52 9.57 9.49 9.44
(ml)
1.17 - low3 hf.
from the various concentrations of CatrFloc and PVSK obtained by turbidimetric titration, was constant at 2.20 + 0.01. 10m3 M. The titration cmxe for 0.0025 M PVSK or Cat-Floe is distorted initially, but the correct end-point can be obtained. In the titration of lo+ ill solution, the turbidity can hardly be seen and the decrease in transmittance at the end-point is very small, although the end-point is detectable. _4ccordingiy, the standard 0.00125 &I solution of PVSK or Cat-Floe can be used conveniently. Examples of colloid titration Glycolchitosax Dried glycolchitosan (0.1269 g) \~as dissolved in a 503mI measuring flask. The solution (10 ml) was diluted to 40 ml with distilled water and titrated with 1.13 * 10m3&I PVSK by the indicator and turbidimetric methods. The results are shown in Fig. 2. Below pH 5, the values of meq g-’ from the turbidimetric method are constant (3.47 meq g-l) and values given by the indicator method are 1.7% higher. In this pH range, the amino groups in glycolchitosan are in the ammonium form. As the color change of toluidine blue is not instantaneous above PH 6.5, the end-point is indistinct; in the turbidimetric method, the decrease in transmittance is not sharp and the end-point is indistinguiihable. MethyTgZyco1chitosa.x Dried methylglycolchitosan (0.2363 g) was dissolved in a 503m3 measurin g flask. The solution (10 ml) was titrated with 1.13 - 10m3 &I PVSK. The results are shown in Fig. 3. Below pH 6 a constant value was ob+&ed by the indicator and turbidimetric me’thods. At about .pH 10, the value is 6% lower than that of an acidic solution. Polyethyleneimine. Commercial polyethyleneimine solution is pale yellow and contains 30% polyethyleneirnine. The solution (0.1 ml) was dissolved and diluted to 11 and 10 ml of tb& solution was titzxted with 1.22 - 10e3M PVSK. The results zre shown in Fig. 4. The titration values by the construction method agree with those of the differential method. Above pH 7, the values given by the indicator method are scattered, because the color-change
0’
’
’
0,2
’
’
’
’
’
’
’
3
5
5
6
7
8
9
0’
’
0
’
’
’
17.3-G
t 5
A
P”
Fig. 2 Colloid tit&ion.
titration results of glycolchitosan.
Fig. 3. Colloid titration.
titration results cf methylglycolchitc.
o Indicator
PH
I
I
I
7
8
91011
1
I
titration. o Turbidirnefric
o Indicator titration.
o Turbidimetric
is not instantaneous at the end-point and coagulation of the complex at the end-point may not occur. A constant value (meq 1-l) could not be obtained. This implies that polyethyleneimine has hydrogen-bonded imino groups. Sodium chondroitirz sulfute. The solution (0.2586 g 1-l) was titrated with 1.02 * IO-’ M Cat-Floe turbidimetrically, and also indirectly by the indicator method. The results are shown in Fig. 5. The value by the turbidimetric method (3.53 meq g-l) is 89% of the calculated value. Sodit;m alginate. The solution (0.2252 g 1-l) was titrated with 1.22 - 10S3M Cat-Floe turbidimetricahy. The solution (10 ml) was also titrated by the indicator method &ith 1.22 - 10S3M Cat-Floe and 1.17 - 10e3M PVSK. L-
2
P
L
5
6
Pn
7
8
9
10
11
0
1
2
3
5
6
7
8
9
PH
Fig. 4. Colloid titration results of polyethyleneimine. o Indicator titration. o Turbidimetric titration (construction method)_ o Turbidimetric t&&ion (differential method). F&
5. C&loa
titration results of sodium chondroitin
0 Indicatortiition.
sulfate. o Turbidimetric
titration.
10
11
388
The results are shown in Fig. 6. In the turbidimetric
method,
the construction
method cannot be used below pH 3 because a sol is formed nea,r the end-
point. Above pH 5, a constant value (4.62 meq g-‘) was obtained; this corresponds to 92% of the calculated value. Ammonium alginate. The solution (0.1348 g 1-i) was titrated by the turbidimetric and indicator methods (Fig. 7). The value (5.08 meq 9’) at pH 11 and above is equivalent to 98% o f the calculated value. In the titration of the copolymer of sodium maleate and methylvinyl ether, the values (meq g-I) given by sodium hydroxide are lower than those given by tetrabutylammonium hydroxide solutions at the same pH [ 3 1, but there was no difference in the titration of the dginate. Carrugeenun. The solution (0.4166 g 1-l) was titrated with 1.21. 10e3 M Cat-Floe. The construction method could not be used, because a flocculent precipitate was formed, and the end-point was found from the peak of the differential curve. The results are shown in Fig. 8. Carrageenan is a mixture of different fcrms, depending on its origin. Sodium Zigrzinsulfonate. A brown commercial sample of sodium lignin sulfonate (0.3550 g) was dissolved in 11 of water. When the concentration is higher than this (ca 0.0036 M) the end-point cannot be detected by the irrdicator and turbidimetric methods because of the color of the solution. The resuits are shown in Fig. 9. Between pH 2 and 6.5, the values given by the indicator and turbidimetric methods are almost the same: above pH 6.5 the indicator method gives ‘higher values than the turbidimetric method Above pH 6.5, the color of the solution deepened; phenolic hydroxyl, enol or ammonium groups etc. would be dissociated or decomposed by air. Hydrolysis of the ester content of the sample may occur and would be acceierated by the presence of Cat-Floe in the indicator method 143 ; direct titration by turbidimetry would therefore be preferable to the indicator method.
0
a
’ !
’ 2
3
* i
’ 5
* 6
. 7
. 8
’ 3
1 10
* 1,
3
0
,
3
, 3
, 5
* 5
8 6
Fig. 6. Cdloid titration results of sodium alginate A.(Bu,N@H). o Indicator titzation.
, 7 PM
SH
e Turbidimetric
LTig.7. Colloid titration results of nrcmonium alginate. 3 hdicator metric titration (PiaOH). a (Bu,XOH).
titration titration.
I
B
*
I
9
10
(NaOH). 9 Turbidi-
I
I,
h-
s
,-
E”
2-
1 -
,, 0
.
,
1
2
3
I
I
I
4
s
6
,
t
I
7
B
9
.
10
*
‘1
*
II
0’
0
*
I
o
2
’
3
’
’
.t
s
DH
Fig. 8. Colloid titration results of carrageenan. o Indicator
titration_
l
a
6
)
D”
7
*
8
’
9
n
10
Turbidimetric
tit.EItiOfi
Fig. 9. Colloid titration results of lignin sulfonic acid, sodium salt. o Indicator e Turbidimetric titration (NaOH). A (Bu,NOH).
titration_
CONCLUSIOIG
The indicator method is useful for cationic polymers such as glycolchitosan, methylglycekhitosan and polyethyleneimine; the values obtained agree with those from t.he turbidimetric method within experimental error. Anionic polymers with sulfate groups combine strongly with Cat-F& and the turbidimetic titration values agree with those obtained by titrating the excess of CatcF’loc with PVSK by the indicator method. Anionic Flymew with carboxyl groups can be titrated directly with Cat-Floe turbidimetrically. The titration values agg fairly well with those from the indicator method. An intricate anionic polymer such as sodium lignin sulfonate should be titrated directly by the turbidimetric method; higher values wouid be given by the indicator method because of a secondary reaction in +Sle presence of CatrFloc at higher pH. REFERENCES 1 K. T&i am&K+ Kawada. Japan Ansiyst, 21 (1972) 1510. 2 K. T&i and T. Kohara. Anal. Chim. Acta. 83 (1976) 59. 3 E. Kokufuta, S. Kokubo, hi. Hinta and S. Iwai, Chemistry Associations Union Tohoku District Meeting, Preprint 2DOl (1975). 4 -4. Mizote, H. Odagiri, K TGei and K. Tanaka, Analyst (London), 100 (1975) 822.
1
I1
*
12