A titanium dioxide supplier reports a pH of 6.8, while another lists 7.5. The higher value does not automatically mean the second pigment is more alkaline, less pure or unsuitable for a coating formulation. Before comparing the results, buyers need to know how each laboratory prepared and measured the sample.
Titanium dioxide pH testing measures an aqueous suspension of the pigment—not an intrinsic pH value of the dry powder.
The distinction matters when purchasing titanium dioxide (TiO₂, CAS 13463-67-7) for paints, coatings and other industrial formulations. Differences in suspension preparation, water quality, temperature and measurement procedures can make two apparently precise results difficult to compare.
There is also a timely standards issue. As of October 16, 2026, ISO 787-9:2019 remains the published international method for determining the pH of pigment and extender suspensions, while a replacement edition is under development.
For procurement and quality-control teams, that makes the exact testing method and edition essential parts of a reliable pigment specification.
Why Dry Titanium Dioxide Does Not Have a Directly Measurable pH
pH describes acidity or alkalinity in a solution or another appropriately defined measurement medium.
It is related to hydrogen ion activity, not simply the concentration or purity of a solid substance.
A dry titanium dioxide powder cannot be evaluated with a conventional glass pH electrode in the same way as an aqueous solution.
Instead, laboratories prepare a suspension by combining the pigment with a specified liquid under controlled conditions.
The electrode then measures the pH of that prepared system.
This introduces an important qualification: the result describes the suspension under the stated testing conditions.
It does not independently describe every chemical characteristic of the dry pigment.
Commercial titanium dioxide pigments may contain different surface-treatment materials or other constituents associated with their manufacturing and finishing processes.
These differences can influence how the pigment interacts with water.
However, the pH result alone cannot identify which constituents are present or establish their concentrations.
A supplier may report an acceptable suspension pH while other important characteristics, such as soluble impurities, particle-size distribution or dispersion behavior, still require evaluation.
For coating manufacturers, pH should therefore be treated as one quality-control measurement rather than a complete indicator of pigment performance.
ISO 787-9:2019 Is Still Current, but a Revision Is Coming
The international reference specifically addressing this measurement is ISO 787-9:2019, Determination of pH Value of an Aqueous Suspension.
The standard applies to determining the pH of an aqueous suspension of a pigment or extender.
It was published in March 2019 and confirmed during its 2024 review.
As of October 16, 2026, the International Organization for Standardization identifies it as the current published edition. ISO also identifies ISO/FDIS 787-9 as a replacement under development.
This creates a practical document-control issue.
A supplier may reference ISO 787-9:2019, while another laboratory may already be evaluating proposed changes associated with the forthcoming edition.
A draft standard is not automatically an effective replacement for the current published standard.
Purchasing teams should avoid treating proposed requirements as mandatory before the relevant standard is formally issued and adopted where applicable.
Likewise, an older laboratory procedure should not automatically be described as compliant with a future edition simply because the general subject is unchanged.
The detailed final requirements of the replacement edition may differ from the draft. Buyers should verify the published text when it becomes available.
For current supplier comparisons, the important questions are which edition was used, whether the procedure was followed and whether any deviations were documented.
A pH Meter Standard Does Not Define the Entire Pigment Test
Laboratories sometimes describe their procedure by referencing the measurement instrument rather than the complete sample-preparation method.
That can create confusion.
ASTM E70-24, Standard Test Method for pH of Aqueous Solutions With the Glass Electrode covers electrometric pH measurement using a glass electrode.
However, its published scope explicitly separates the electrode measurement procedure from the preparation of the solution being tested.
This distinction is critical for solid pigments.
A laboratory can use a properly calibrated glass electrode while preparing the titanium dioxide suspension differently from another laboratory.
The resulting measurements may therefore be different even when both instruments are functioning correctly.
ASTM E70-24 also identifies limitations when measuring solutions containing high concentrations of electrolytes or water-soluble organic compounds.
Such measurements may provide useful process information without necessarily representing an accurate determination of hydrogen ion activity under all conditions.
For chemical buyers, specifying only the instrument type is not enough.
The purchasing specification should identify an appropriate complete pigment test method, including the sample-preparation requirements.
Five Factors That Can Change a Reported pH Result
A dependable comparison requires more than matching the word “pH” on two certificates of analysis.
The following measurement conditions deserve attention.
| Testing factor | Why it matters |
|---|---|
| Pigment-to-water ratio | Different suspension concentrations can change the chemical environment being measured |
| Water quality | Dissolved substances and absorbed carbon dioxide can influence the result |
| Sample conditioning | Moisture exposure, storage and sample history may affect reproducibility |
| Temperature | Temperature can influence both sample behavior and electrode response |
| Measurement procedure | Calibration, mixing, equilibration and electrode condition affect measurement consistency |
These factors do not necessarily influence every pigment in the same way.
Their importance depends on the material and the applicable analytical procedure.
Suspension Concentration Must Be Consistent
Consider two hypothetical laboratories testing the same titanium dioxide grade.
Laboratory A prepares a suspension containing 10% pigment by mass.
Laboratory B prepares a suspension containing 5% pigment by mass.
The laboratories subsequently report pH values of 6.8 and 7.3.
The difference is 0.5 pH units.
That result does not, by itself, establish a real difference in the supplied pigment.
Because the preparation conditions were different, the measurements may not be directly comparable.
The figures are illustrative, not experimental data or a recommended titanium dioxide testing procedure.
Qualified laboratories should use the concentration and preparation conditions required by the applicable standard or validated method.
Water Quality Can Affect the Measurement
Water is not automatically a chemically neutral background.
Its dissolved components, purity and exposure to the atmosphere can affect measured pH.
This is particularly relevant when laboratories use water with different characteristics.
For pigments whose aqueous suspensions have limited buffering capacity, differences in the measurement medium can become more significant.
A buyer investigating a disputed result should therefore establish whether both laboratories used the required water quality.
Simply requesting that each supplier retest the material may not resolve the discrepancy if the laboratories continue using different preparation conditions.
Temperature and Calibration Need Control
pH electrodes respond to electrochemical conditions, and those responses are temperature-dependent.
The laboratory must also account for the temperature characteristics of its calibration buffers.
Instrument compensation can help account for electrode response, but it does not automatically eliminate changes in the sample’s chemical behavior caused by temperature.
The measurement temperature should therefore be documented and controlled as required by the applicable method.
The instrument manufacturer’s guidance on pH meter calibration and maintenance emphasizes fresh calibration buffers, appropriate electrode maintenance and regular calibration.
It also identifies common causes of unstable readings, including electrode contamination and problems with the reference electrolyte.
For quality-control teams, a recorded pH value should be supported by evidence that the measurement equipment was suitable and functioning correctly.
Why a Higher pH Does Not Automatically Mean Better Titanium Dioxide
Titanium dioxide pigments are selected according to the requirements of their intended applications.
An architectural coating, an industrial protective coating and a plastics formulation may require different combinations of optical, physical and chemical properties.
pH can help characterize the pigment, but it cannot replace testing those properties.
The wider ISO 591-1:2000 standard for titanium dioxide pigments used in paints establishes a specification and testing framework for these materials.
Although the edition was originally published in 2000, ISO confirmed it again in September 2025, and it remains current.
Its continued use demonstrates why pigment qualification involves several characteristics rather than one laboratory number.
The existing article on titanium dioxide oil absorption test methods illustrates a related problem.
Two reported oil absorption values may differ partly because suppliers use different testing procedures.
Similarly, a pH comparison becomes meaningful only after establishing a consistent measurement basis.
A pigment with a favorable suspension pH may still require investigation of particle characteristics, surface treatment and performance in the intended formulation.
Conversely, a difference in suspension pH does not automatically prove that one supplier’s product is unsuitable.
The purchasing decision should be tied to the material’s actual application requirements.
Ferrous Sulfate pH Reports Need a Different Interpretation
The same general measurement principle applies to other industrial chemicals, but the analytical procedure must suit the actual substance.
Ferrous sulfate heptahydrate, FeSO₄·7H₂O (CAS 7782-63-0), is a water-soluble crystalline compound.
A pH measurement involving ferrous sulfate solution is not equivalent to measuring the aqueous suspension of a relatively insoluble titanium dioxide pigment.
For soluble chemicals, the concentration of the prepared solution can affect the reported pH.
The oxidation state of iron and changes occurring during sample preparation or storage may also become relevant to certain quality measurements.
A supplier should therefore identify the exact analytical conditions rather than report an unexplained pH value.
The existing guide to ferrous sulfate heptahydrate purchasing specifications explains why pH, free acidity, assay and oxidation-related properties must be interpreted separately.
An acceptable pH result does not independently establish the ferrous iron content or purity of a material.
Likewise, a pH measurement is not a substitute for a properly defined free-acidity test when that property is important to the manufacturing process.
These distinctions prevent buyers from comparing fundamentally different chemical measurements under one generic specification heading.
What Chemical Buyers Should Request From Suppliers
A reliable titanium dioxide pH specification should establish what is being measured and how the result will be evaluated.
For supplier approval and routine incoming inspection, the purchasing and quality teams should agree on the following information:
Chemical identity and grade: Identify the actual titanium dioxide product, crystal form where applicable and approved grade designation.
Test method and edition: Record the relevant recognized standard or validated internal procedure.
Sample preparation: Establish the prescribed suspension conditions and any preparation steps necessary to obtain comparable measurements.
Measurement conditions: Confirm the relevant water quality, temperature, equipment and procedural controls.
Acceptance criteria: Define a technically justified pH range appropriate to the intended application.
Result reporting: Require the actual measured result, associated method reference and appropriate reporting information.
The buyer should also establish whether the pH requirement is a routine lot-release criterion or a property used mainly during initial supplier qualification.
That distinction affects how frequently testing is necessary and what evidence should accompany shipments.
Keep Supplier Documentation in Its Proper Role
A certificate of analysis (CoA) reports selected results for an identified material lot. It should identify the relevant testing basis when pH is an acceptance requirement.
A product specification defines the agreed limits and applicable testing method.
A technical data sheet may report typical pH characteristics, but a typical value is not necessarily a guaranteed production-lot limit.
A safety data sheet (SDS) provides hazard and safe-use information. Its pH entry, when present, should not automatically be treated as an equivalent lot-release measurement.
An independent laboratory test can provide additional evidence, but only for the material, preparation and procedure actually evaluated.
If an independent result differs from the supplier’s CoA, quality teams should compare the testing methods before concluding that the material has changed.
Repeating an unsuitable procedure does not establish a more reliable answer.
Prepare for the ISO Revision Without Rewriting Specifications Prematurely
The forthcoming revision of ISO 787-9 creates a useful opportunity to improve supplier documentation.
Purchasers can begin by checking whether current agreements refer to ISO 787-9:2019, another recognized method or an internal laboratory procedure.
The next step is to establish whether different suppliers are reporting results using equivalent preparation and measurement conditions.
When the new ISO edition is officially published, its requirements can be reviewed against existing specifications and laboratory procedures.
Any necessary changes should be implemented through normal technical review and change control rather than assuming that every historical result becomes invalid.
Until then, ISO 787-9:2019 remains the published international reference.
For titanium dioxide procurement, the strongest decision is based on a traceable, reproducible measurement that matches the intended application.
A pH value without its testing method is incomplete technical information. A pH value supported by an appropriate standard, defined conditions and relevant acceptance criteria becomes useful evidence for material qualification.