A titanium dioxide supplier reports high electrical resistivity in a pigment’s water extract, while another reports a lower percentage of water-soluble matter. Which pigment is cleaner?
Neither result can answer that question alone.
Electrical conductivity and water-soluble matter are different measurements. Conductivity indicates how readily an aqueous extract carries electrical current. Water-soluble matter measures the material recovered from the pigment through a specified extraction and determination method.
The distinction matters when manufacturers purchase titanium dioxide (TiO₂, CAS 13463-67-7) for architectural paints, industrial coatings, printing inks and other applications where pigment consistency is important.
A low conductivity reading does not automatically prove a low sulfate concentration, and a low soluble-matter result does not establish that every potentially important ionic impurity is absent.
For procurement and quality-control teams, titanium dioxide conductivity testing should therefore be evaluated alongside the appropriate extraction method and, where needed, chemical-specific analysis.
What Conductivity Reveals About Titanium Dioxide Pigments
Titanium dioxide is a relatively insoluble inorganic compound. However, commercial pigments may contain soluble constituents associated with their manufacturing processes, surface treatments or subsequent handling.
When an appropriate pigment sample is contacted with water under controlled laboratory conditions, some soluble substances may enter the liquid.
If those substances produce dissolved ions, they can influence electrical conductivity.
The relevant international method is ISO 787-14:2019, Determination of Resistivity of Aqueous Extract.
The International Organization for Standardization published this third edition in March 2019 and confirmed it during its 2024 review. It remains the current published edition as of October 2026.
ISO 787-14 covers the determination of electrical resistivity or conductivity in aqueous extracts of pigments and extenders, except those that are soluble in water.
The standard makes an important distinction: electrical resistivity is treated as a separate property from the amount of water-soluble matter.
This is the central reason why supplier figures should not be compared as if they represented one measurement.
A pigment’s aqueous extract can have an electrical response influenced by the type and concentration of dissolved ions.
However, the result does not directly identify those ions.
It also does not establish how much total soluble material was extracted.
Why Conductivity Is Not a Sulfate Test
Sulfate ions, SO₄²⁻, can contribute to the conductivity of an aqueous solution.
Chloride, sodium and other dissolved ions may also contribute.
Different ions do not carry electrical current in exactly the same way, so the relationship between conductivity and mass concentration depends on the composition of the extract.
For example, two aqueous extracts could produce similar conductivity readings even though the proportions of sulfate and chloride differ.
This makes conductivity useful for monitoring a defined material and testing process, but it does not automatically make the measurement chemically specific.
If the purchasing requirement concerns sulfate concentration, the laboratory needs an analytical procedure capable of determining sulfate.
A conductivity meter alone cannot establish that result.
Conductivity and Resistivity Move in Opposite Directions
Suppliers may report the same general electrical property using different units.
Conductivity describes the ease with which current passes through the extract.
Resistivity describes its resistance to electrical conduction.
For a given sample at the same temperature, the two properties are mathematical reciprocals.
A laboratory may report conductivity in microsiemens per centimetre (µS/cm) and resistivity in ohm-metres (Ω·m).
For these units:
Resistivity (Ω·m) = 10,000 ÷ Conductivity (µS/cm)
Consider a hypothetical pigment extract with conductivity of 50 µS/cm.
Its corresponding resistivity would be:
10,000 ÷ 50 = 200 Ω·m
A second extract with conductivity of 200 µS/cm would have a resistivity of:
10,000 ÷ 200 = 50 Ω·m
The second sample has higher conductivity but lower resistivity.
These values illustrate the mathematical relationship; they are not actual titanium dioxide measurements, supplier acceptance limits or evidence of acceptable pigment quality.
A buyer comparing two certificates of analysis should therefore check whether the suppliers report conductivity or resistivity before concluding that one material has a more favorable result.
Temperature must also be considered because conductivity depends on the measurement conditions.
A value reported at one temperature should not automatically be compared with a value measured at another without a documented correction or common testing basis.
Water-Soluble Matter Requires a Different Test
When the objective is to measure the amount of matter that can be extracted from a pigment using water, ISO provides separate methods.
One is ISO 787-3:2000, Determination of Matter Soluble in Water — Hot Extraction Method.
This standard addresses determination of water-soluble matter using hot extraction.
The other is ISO 787-8:2000, Determination of Matter Soluble in Water — Cold Extraction Method.
Both standards were confirmed during reviews in 2025 and remain current as of October 2026.
Their distinction matters because extraction conditions can influence which substances are recovered and in what quantities.
A hot extraction and a cold extraction should not automatically be expected to produce identical results.
The specific material and analytical procedure determine whether the difference is important.
For commercial titanium dioxide, a supplier reporting “water-soluble matter” without identifying the extraction method leaves an important part of the specification undefined.
Three Tests, Three Different Questions
| Measurement | Principal purpose | What it cannot establish alone |
|---|---|---|
| ISO 787-14:2019 | Electrical conductivity or resistivity of an aqueous pigment extract | Exact identities or total masses of dissolved substances |
| ISO 787-3:2000 | Matter soluble in water under hot-extraction conditions | Concentration of each individual soluble ion |
| ISO 787-8:2000 | Matter soluble in water under cold-extraction conditions | Whether the hot-extraction result would be identical |
A buyer needs to identify the property relevant to the manufacturing application before setting an acceptance requirement.
A low conductivity result does not automatically satisfy a soluble-matter specification.
Similarly, a water-soluble-matter percentage cannot be converted directly into conductivity using a universal formula.
The measurements are complementary, not interchangeable.
A Practical Supplier Comparison Shows the Problem
Consider two hypothetical titanium dioxide grades being evaluated for a waterborne industrial coating.
Supplier A provides an aqueous-extract conductivity result of 45 µS/cm.
Supplier B reports water-soluble matter of 0.08% by mass.
A purchasing team might initially regard Supplier A as offering a relatively low-ionic-content pigment and Supplier B as offering a reasonably low-soluble-content pigment.
But the two numbers cannot establish which product has fewer impurities.
Supplier A has supplied an electrical measurement.
Supplier B has supplied a mass-based measurement.
There is no valid direct comparison without additional information.
The buyer should first request equivalent measurements using agreed methods.
If the application is sensitive to specific ions, such as chloride or sulfate, the qualification process may also require targeted chemical analysis.
The original values remain useful as supplier data, but they do not provide sufficient evidence for ranking the materials against one common requirement.
This is not necessarily a supplier testing error.
It is a specification-design problem.
The purchasing agreement has not clearly defined which property is required.
Why Ion Chromatography May Be Needed
Electrical conductivity responds to the combined behavior of dissolved ions.
Ion chromatography provides a different analytical approach by separating and measuring specified ionic species.
The U.S. Environmental Protection Agency’s Method 300.0 for inorganic anions by ion chromatography covers substances including chloride, sulfate, nitrate, fluoride and other listed anions.
The cited Revision 2.1 was issued in August 1993 and identifies its applicable environmental sample types and quality-control requirements.
It includes procedures relevant to certain extracted solid samples.
However, EPA Method 300.0 is not automatically a validated titanium dioxide pigment test.
A laboratory intending to apply ion chromatography to a commercial pigment extract must establish that the extraction procedure, analytical method and sample matrix are suitable for the intended measurement.
The significance for chemical buyers is the difference between measuring an overall electrical property and identifying particular substances.
If a supplier claims that a pigment has low sulfate content, conductivity alone is insufficient to demonstrate that claim.
The laboratory should provide sulfate-specific analytical evidence obtained using an appropriate method.
The same applies to chloride or other individually specified impurities.
Why the Testing Basis Matters
When a laboratory reports sulfate concentration in an aqueous extract, the purchasing team must establish the reporting basis.
A result expressed as milligrams of sulfate per litre of extract is not automatically equivalent to milligrams of sulfate per kilogram of original pigment.
Converting between the two requires appropriate information about the extraction and sample quantities.
The laboratory should provide the final result in the units established by the purchasing specification, supported by the necessary analytical records.
It should also identify relevant method detection or quantitation limits when concentrations are near the required acceptance threshold.
A result described simply as “not detected” cannot establish that an impurity is absent.
It means the substance was not established at or above the applicable detection criterion under the conditions of the method.
Why the Extract Can Behave Differently From the Finished Coating
A pigment’s aqueous extract is a controlled laboratory system.
A finished coating is more complicated.
It may contain a binder, dispersants, extenders, surfactants, preservatives and other formulation components.
Those ingredients can influence the chemical environment and performance of the complete material.
A supplier’s conductivity result should therefore not be interpreted as a direct prediction of coating viscosity, opacity, gloss or long-term durability.
For example, a pigment can meet an agreed aqueous-extract conductivity specification while still behaving differently from an approved reference grade during dispersion.
Conversely, a pigment with a somewhat different conductivity result might perform acceptably in a particular formulation.
The relationship must be established through relevant material qualification and application testing.
Why pH Does Not Settle the Question Either
Electrical conductivity and pH can both be measured in aqueous systems, but they describe different properties.
pH concerns acidity or alkalinity under defined conditions.
Conductivity concerns the ability of the liquid to carry electrical current.
A solution can contain dissolved ions without having an extreme pH.
Likewise, two solutions with similar pH values can have substantially different conductivities.
The site’s guide to titanium dioxide pH testing explains why suspension preparation, water quality and measurement conditions affect supplier pH comparisons.
For procurement teams, this creates a broader principle: pH, conductivity and soluble-matter measurements should each have their own properly defined analytical basis.
One cannot automatically replace another.
What Purchasing Teams Should Require on a Titanium Dioxide CoA
A certificate of analysis becomes more useful when the result can be connected to a defined purchasing requirement.
For aqueous-extract conductivity or resistivity, the documentation should identify the applicable standard and edition, reporting unit and relevant measurement conditions.
For water-soluble matter, the report should identify whether hot or cold extraction was used and describe the result using the agreed reporting basis.
Where specific impurities are critical, additional analytical results may be required.
The purchasing specification should also establish whether the parameter is used for routine lot release, initial supplier approval or investigation of an unexpected manufacturing change.
Those decisions affect the evidence needed and how frequently the property must be measured.
Several documents can support the qualification process, but they serve different purposes.
A product specification defines the agreed quality requirements and acceptance limits.
A certificate of analysis (CoA) reports selected results for an identified material lot. It does not automatically establish all properties of the finished coating.
A safety data sheet (SDS) communicates chemical hazard and safe-use information. It is not a certificate of aqueous-extract conductivity, soluble-matter content or pigment suitability.
An independent laboratory report can strengthen the evidence for a tested sample and analytical procedure. However, the test must be relevant to the intended requirement and the sample must be representative.
When supplier results disagree, the first question should be whether they were obtained using comparable methods.
A difference caused by extraction conditions or reporting units should be resolved before concluding that one pigment grade is inferior.
The Best Specification Defines What Needs to Be Controlled
Titanium dioxide conductivity testing provides useful information about the electrical behavior of water extracts.
Water-soluble-matter testing provides a separate measurement of extracted material.
Targeted chemical analysis can answer more specific questions about individual impurities.
For industrial buyers, the most reliable approach is to select the measurement that matches the actual manufacturing concern.
If the objective is to monitor the overall ionic characteristics of an approved pigment grade, a consistently performed aqueous-extract conductivity test may be appropriate.
If the concern is total extractable matter, a defined hot- or cold-extraction procedure may be more relevant.
If a particular impurity has a specified limit, the purchasing agreement should require suitable substance-specific evidence.
The lowest conductivity number is not automatically the best pigment. The strongest material qualification decision combines a relevant analytical specification, consistent supplier documentation and demonstrated performance in the intended application.
That approach prevents misleading comparisons and gives quality teams a clearer basis for approving and monitoring titanium dioxide suppliers.