Registration Dossier

Physical & Chemical properties

Nanomaterial Zeta potential

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Administrative data

Endpoint:
nanomaterial Zeta potential
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2019-05-17 to 2019-08-01
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Cross-referenceopen allclose all
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
nanomaterial Zeta potential
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2019-05-17 to 2019-08-01
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sample TiO2 dispersion at 0.01% w/w was prepared by adding 20 mg of sample TiO2 powder to a stirring solution of 200 ml 10-3 M KCl in deionised water. To ensure dispersion, the solution was then stirred under shear for 1 minute at 2500 rpm.
The pH was then adjusted to pH 11 by addition of 0.01 M NaOH in deionised water. The conductivity was recorded, and a sample was taken for zeta potential measurement. The pH was lowered by 1 pH value by addition of 0.01 M HCl in deionised water, and the conductivity and zeta potential were recorded. This process was repeated to obtain final conductivity and zeta potential measurements across the pH range from pH 11 to pH 1.
GLP compliance:
no
Type of method:
other: Dynamic light scattering (DLS), and pH meter and conductivity meter
Sampling:
please refer to `Principle of method of other than guideline´
Specific details on test material used for the study:
Product name: Sample G2-5
Appearance: white odourless powder
Substance stability: Stable under normal conditions
Substance humidity: 8.4
Instruments:
- Magnetic stirrer plate
- Silverson L5 mixer
- Conductivity and pH were measured using a Mettler Toledo Five Easy pH Meter F20-Std-Kit.
- Zeta potential was measured using a Horiba SZ-100 particle sizer.
Calibration:
Both the pH meter and the conductivity meter were calibrated with standard buffers or conductivity standards, respectively, prior to use.
Zeta potential:
-39.1 mV
St. dev.:
3.5 mV
pH:
11
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-42.5 mV
St. dev.:
3 mV
pH:
10
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-19.4 mV
St. dev.:
4.4 mV
pH:
9
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-19.4 mV
St. dev.:
2.9 mV
pH:
8
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-10.4 mV
St. dev.:
3.2 mV
pH:
7
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
21.6 mV
St. dev.:
16.2 mV
pH:
6
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
36.3 mV
St. dev.:
7.1 mV
pH:
5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
44.7 mV
St. dev.:
1.8 mV
pH:
4
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
15.8 mV
St. dev.:
0.1 mV
pH:
3
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
11.6 mV
St. dev.:
1.8 mV
pH:
2
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-25.6 mV
St. dev.:
11.2 mV
pH:
1
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Key result
Isoelectric Point:
7
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Remarks on result:
other: no St.dev. was stated

The point at which the curve crosses a zeta potential value of 0 mV is known as the isoelectric point, where the particles effectively carry no net electrical charge.

Conductivity measurements obtained for each sample remained fairly consistent from pH 4 to pH 11, which is an important property for zeta potential measurement. Below pH 4, conductivity was found to increase markedly, likely due to the substantial amounts of HCl needed in order to reach the low pH values. As a result, the concentration of TiO2 also decreased substantially in this pH range. In addition, the composition of each of the samples is not known. It is often found that TiO2 is coated with e.g. Al2O3 or ZrO2 which, especially in the case of Al2O3 exhibit increased solubility at pH values > pH 10. It is therefore strongly noted that data points below pH 4 and above pH 10 are unreliable in comparison to the rest of the data set.

Conclusions:
The test item G2-5 has an approximate isoelectric point of 7.0 in a dispersion (0.01% w/w) in 10-3 M KCl in deionised water.
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
nanomaterial Zeta potential
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2019-05-17 to 2019-08-01
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sample TiO2 dispersion at 0.01% w/w was prepared by adding 20 mg of sample TiO2 powder to a stirring solution of 200 ml 10-3 M KCl in deionised water. To ensure dispersion, the solution was then stirred under shear for 1 minute at 2500 rpm.
The pH was then adjusted to pH 11 by addition of 0.01 M NaOH in deionised water. The conductivity was recorded, and a sample was taken for zeta potential measurement. The pH was lowered by 1 pH value by addition of 0.01 M HCl in deionised water, and the conductivity and zeta potential were recorded. This process was repeated to obtain final conductivity and zeta potential measurements across the pH range from pH 11 to pH 1.
GLP compliance:
no
Type of method:
other: Dynamic light scattering (DLS), and pH meter and conductivity meter
Sampling:
please refer to `Principle of method of other than guideline´
Specific details on test material used for the study:
Product name: Sample G6-3
Appearance: white odourless powder
Substance stability: Stable under normal conditions
Substance humidity: 0.4
Instruments:
- Magnetic stirrer plate
- Silverson L5 mixer
- Conductivity and pH were measured using a Mettler Toledo Five Easy pH Meter F20-Std-Kit.
- Zeta potential was measured using a Horiba SZ-100 particle sizer.
Calibration:
Both the pH meter and the conductivity meter were calibrated with standard buffers or conductivity standards, respectively, prior to use.
Zeta potential:
-67.5 mV
St. dev.:
0.9 mV
pH:
11
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-50.3 mV
St. dev.:
1.7 mV
pH:
10
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-33 mV
St. dev.:
0.8 mV
pH:
9
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
5.4 mV
St. dev.:
2.4 mV
pH:
8
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
16.3 mV
St. dev.:
3.6 mV
pH:
7
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
16.3 mV
St. dev.:
3.1 mV
pH:
6
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
28.2 mV
St. dev.:
0.4 mV
pH:
5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
20.8 mV
St. dev.:
1.7 mV
pH:
4
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
27.6 mV
St. dev.:
1.7 mV
pH:
3
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
11.4 mV
St. dev.:
0.9 mV
pH:
2
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-6.5 mV
St. dev.:
0.9 mV
pH:
1
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Isoelectric Point:
7.5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Remarks on result:
other: no St.dev. was stated

The point at which the curve crosses a zeta potential value of 0 mV is known as the isoelectric point, where the particles effectively carry no net electrical charge.

Conductivity measurements obtained for each sample remained fairly consistent from pH 4 to pH 11, which is an important property for zeta potential measurement. Below pH 4, conductivity was found to increase markedly, likely due to the substantial amounts of HCl needed in order to reach the low pH values. As a result, the concentration of TiO2 also decreased substantially in this pH range. In addition, the composition of each of the samples is not known. It is often found that TiO2 is coated with e.g. Al2O3 or ZrO2 which, especially in the case of Al2O3 exhibit increased solubility at pH values > pH 10. It is therefore strongly noted that data points below pH 4 and above pH 10 are unreliable in comparison to the rest of the data set.

Conclusions:
The test item G6-3 has an approximate isoelectric point of 7.5 in a dispersion (0.01% w/w) in 10-3 M KCl in deionised water.
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
nanomaterial Zeta potential
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2019-05-17 to 2019-08-01
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sample TiO2 dispersion at 0.01% w/w was prepared by adding 20 mg of sample TiO2 powder to a stirring solution of 200 ml 10-3 M KCl in deionised water. To ensure dispersion, the solution was then stirred under shear for 1 minute at 2500 rpm.
The pH was then adjusted to pH 11 by addition of 0.01 M NaOH in deionised water. The conductivity was recorded, and a sample was taken for zeta potential measurement. The pH was lowered by 1 pH value by addition of 0.01 M HCl in deionised water, and the conductivity and zeta potential were recorded. This process was repeated to obtain final conductivity and zeta potential measurements across the pH range from pH 11 to pH 1.
GLP compliance:
no
Type of method:
other: Dynamic light scattering (DLS), and pH meter and conductivity meter
Sampling:
please refer to `Principle of method of other than guideline´
Specific details on test material used for the study:
Product name: Sample G8-2
Appearance: white odourless powder
Substance stability: Stable under normal conditions
Substance humidity: 0.6
Instruments:
- Magnetic stirrer plate
- Silverson L5 mixer
- Conductivity and pH were measured using a Mettler Toledo Five Easy pH Meter F20-Std-Kit.
- Zeta potential was measured using a Horiba SZ-100 particle sizer.
Calibration:
Both the pH meter and the conductivity meter were calibrated with standard buffers or conductivity standards, respectively, prior to use.
Zeta potential:
-61.4 mV
St. dev.:
0.5 mV
pH:
11
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-13.8 mV
St. dev.:
3 mV
pH:
10
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-55 mV
St. dev.:
1.6 mV
pH:
9
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-37.1 mV
St. dev.:
3.6 mV
pH:
8
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-52.8 mV
St. dev.:
1.2 mV
pH:
7
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-30.8 mV
St. dev.:
3 mV
pH:
6
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-46.5 mV
St. dev.:
0.9 mV
pH:
5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-18.6 mV
St. dev.:
1.9 mV
pH:
4
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-2.6 mV
St. dev.:
0.9 mV
pH:
3
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
1.2 mV
St. dev.:
1.9 mV
pH:
2
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-3.2 mV
St. dev.:
17.5 mV
pH:
1
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Isoelectric Point:
2.5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Remarks on result:
other: no St.dev. was stated

The point at which the curve crosses a zeta potential value of 0 mV is known as the isoelectric point, where the particles effectively carry no net electrical charge.

Conductivity measurements obtained for each sample remained fairly consistent from pH 4 to pH 11, which is an important property for zeta potential measurement. Below pH 4, conductivity was found to increase markedly, likely due to the substantial amounts of HCl needed in order to reach the low pH values. As a result, the concentration of TiO2 also decreased substantially in this pH range. In addition, the composition of each of the samples is not known. It is often found that TiO2 is coated with e.g. Al2O3 or ZrO2 which, especially in the case of Al2O3 exhibit increased solubility at pH values > pH 10. It is therefore strongly noted that data points below pH 4 and above pH 10 are unreliable in comparison to the rest of the data set.

Conclusions:
The test item G8-2 has an approximate isoelectric point of 2.5 in a dispersion (0.01% w/w) in 10-3 M KCl in deionised water.
Reason / purpose for cross-reference:
reference to same study
Reference
Endpoint:
nanomaterial Zeta potential
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2019-05-17 to 2019-08-01
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sample TiO2 dispersion at 0.01% w/w was prepared by adding 20 mg of sample TiO2 powder to a stirring solution of 200 ml 10-3 M KCl in deionised water. To ensure dispersion, the solution was then stirred under shear for 1 minute at 2500 rpm.
The pH was then adjusted to pH 11 by addition of 0.01 M NaOH in deionised water. The conductivity was recorded, and a sample was taken for zeta potential measurement. The pH was lowered by 1 pH value by addition of 0.01 M HCl in deionised water, and the conductivity and zeta potential were recorded. This process was repeated to obtain final conductivity and zeta potential measurements across the pH range from pH 11 to pH 1.
GLP compliance:
no
Type of method:
other: Dynamic light scattering (DLS), and pH meter and conductivity meter
Sampling:
please refer to `Principle of method of other than guideline´
Specific details on test material used for the study:
Product name: Sample G10-4
Appearance: white odourless powder
Substance stability: Stable under normal conditions
Substance humidity: 0.4
Instruments:
- Magnetic stirrer plate
- Silverson L5 mixer
- Conductivity and pH were measured using a Mettler Toledo Five Easy pH Meter F20-Std-Kit.
- Zeta potential was measured using a Horiba SZ-100 particle sizer.
Calibration:
Both the pH meter and the conductivity meter were calibrated with standard buffers or conductivity standards, respectively, prior to use.
Zeta potential:
-37.3 mV
St. dev.:
11.1 mV
pH:
11
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-31.9 mV
St. dev.:
3.4 mV
pH:
10
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-21.3 mV
St. dev.:
1.1 mV
pH:
9
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-18.3 mV
St. dev.:
2 mV
pH:
8
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-16.2 mV
St. dev.:
0.4 mV
pH:
7
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
19.2 mV
St. dev.:
9.4 mV
pH:
6
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-6.7 mV
St. dev.:
1.8 mV
pH:
5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
12.2 mV
St. dev.:
2.6 mV
pH:
4
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
29 mV
St. dev.:
2.6 mV
pH:
3
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
11.2 mV
St. dev.:
0.9 mV
pH:
2
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-0.2 mV
St. dev.:
2.7 mV
pH:
1
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Isoelectric Point:
6
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Remarks on result:
other: no St.dev. was stated

The point at which the curve crosses a zeta potential value of 0 mV is known as the isoelectric point, where the particles effectively carry no net electrical charge.

Conductivity measurements obtained for each sample remained fairly consistent from pH 4 to pH 11, which is an important property for zeta potential measurement. Below pH 4, conductivity was found to increase markedly, likely due to the substantial amounts of HCl needed in order to reach the low pH values. As a result, the concentration of TiO2 also decreased substantially in this pH range. In addition, the composition of each of the samples is not known. It is often found that TiO2 is coated with e.g. Al2O3 or ZrO2 which, especially in the case of Al2O3 exhibit increased solubility at pH values > pH 10. It is therefore strongly noted that data points below pH 4 and above pH 10 are unreliable in comparison to the rest of the data set.

Conclusions:
The test item G10-4 has an approximate isoelectric point of 6.0 in a dispersion (0.01% w/w) in 10-3 M KCl in deionised water.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2019
Report date:
2019

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Sample TiO2 dispersion at 0.01% w/w was prepared by adding 20 mg of sample TiO2 powder to a stirring solution of 200 ml 10-3 M KCl in deionised water. To ensure dispersion, the solution was then stirred under shear for 1 minute at 2500 rpm.
The pH was then adjusted to pH 11 by addition of 0.01 M NaOH in deionised water. The conductivity was recorded, and a sample was taken for zeta potential measurement. The pH was lowered by 1 pH value by addition of 0.01 M HCl in deionised water, and the conductivity and zeta potential were recorded. This process was repeated to obtain final conductivity and zeta potential measurements across the pH range from pH 11 to pH 1.
GLP compliance:
no
Type of method:
other: Dynamic light scattering (DLS), and pH meter and conductivity meter
Sampling:
please refer to `Principle of method of other than guideline´

Test material

Constituent 1
Chemical structure
Reference substance name:
Titanium dioxide
EC Number:
236-675-5
EC Name:
Titanium dioxide
Cas Number:
13463-67-7
Molecular formula:
O2Ti
IUPAC Name:
calcium carbonate
Test material form:
solid: particulate/powder
Details on test material:
Appearance: white odourless powder
Relative density: ~ 3.9
Specific details on test material used for the study:
Product name: Sample G1-1
Substance stability: Stable under normal conditions
Substance humidity: 0.9

Data gathering

Instruments:
- Magnetic stirrer plate
- Silverson L5 mixer
- Conductivity and pH were measured using a Mettler Toledo Five Easy pH Meter F20-Std-Kit.
- Zeta potential was measured using a Horiba SZ-100 particle sizer.
Calibration:
Both the pH meter and the conductivity meter were calibrated with standard buffers or conductivity standards, respectively, prior to use.

Results and discussion

Zeta potentialopen allclose all
Zeta potential:
-40.4 mV
St. dev.:
5.8 mV
pH:
11
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-40.2 mV
St. dev.:
2.3 mV
pH:
10
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-44.3 mV
St. dev.:
0.9 mV
pH:
9
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-32.5 mV
St. dev.:
1.5 mV
pH:
8
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-22.6 mV
St. dev.:
0.4 mV
pH:
7
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-27.1 mV
St. dev.:
10 mV
pH:
6
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-16.6 mV
St. dev.:
2.1 mV
pH:
5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
22.5 mV
St. dev.:
0.6 mV
pH:
4
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
23.6 mV
St. dev.:
1 mV
pH:
3
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
6.7 mV
St. dev.:
1 mV
pH:
2
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Zeta potential:
-8.3 mV
St. dev.:
5.3 mV
pH:
1
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Isoelectric point
Isoelectric Point:
4.5
Medium:
TiO2 dispersion (0.01% w/w) in 10-3 M KCl in deionised water
Remarks on result:
other: no St.dev. was stated

Any other information on results incl. tables

The point at which the curve crosses a zeta potential value of 0 mV is known as the isoelectric point, where the particles effectively carry no net electrical charge.

Conductivity measurements obtained for each sample remained fairly consistent from pH 4 to pH 11, which is an important property for zeta potential measurement. Below pH 4, conductivity was found to increase markedly, likely due to the substantial amounts of HCl needed in order to reach the low pH values. As a result, the concentration of TiO2 also decreased substantially in this pH range. In addition, the composition of each of the samples is not known. It is often found that TiO2 is coated with e.g. Al2O3 or ZrO2 which, especially in the case of Al2O3 exhibit increased solubility at pH values > pH 10. It is therefore strongly noted that data points below pH 4 and above pH 10 are unreliable in comparison to the rest of the data set.

Applicant's summary and conclusion

Conclusions:
The test item G1-1 has an approximate isoelectric point of 4.5 in a dispersion (0.01% w/w) in 10-3 M KCl in deionised water.