Vapor Pressure Testing for Chemical Registration: Methods, Standards, and Regulatory Compliance

Vapor pressure testing is a core physicochemical data requirement for chemical registration under regulations such as China's Measures for Environmental Management Registration of New Chemical Substances (MEE Order No. 12), EU REACH, and K-REACH. This article explains the accepted testing methods—including static, dynamic, isoteniscope, effusion, and gas saturation techniques—together with the relevant OECD, GB, ASTM, and ISO standards, sample requirements, and how vapor pressure data support hazard classification and risk assessment.

Technical Overview

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phase (liquid or solid) at a given temperature. It is one of the most important physicochemical endpoints in chemical registration because it directly indicates the volatility of a substance, which governs inhalation exposure potential, atmospheric release behavior, and evaporation losses during storage and use.

Under major chemical regulatory frameworks, vapor pressure is a standard data element of the physicochemical property package:

• China: MEE Order No. 12 requires vapor pressure data for new chemical substance registration, obtained in accordance with national or internationally recognized test guidelines.
• EU: REACH (Regulation (EC) No 1907/2006) Annex VII requires vapor pressure at 20 °C or 25 °C for substances manufactured or imported at 1 tonne per year or more, tested per EU Method A.4.
• South Korea, Japan, USA, and other jurisdictions similarly list vapor pressure among the minimum data set for inventory registration or notification.

Because vapor pressures of chemicals of regulatory interest span more than twelve orders of magnitude (from below 10⁻⁸ Pa to about 10⁵ Pa), no single measurement technique covers the full range. Test guidelines therefore define multiple methods, and results are typically plotted as log P versus 1/T and extrapolated to 20 °C or 25 °C using the Clausius–Clapeyron or Antoine equation.

Testing Samples

Liquid Substances

Liquid samples are the most common test items. Volatile liquids (vapor pressure above approximately 10 Pa at ambient temperature) can be measured directly, while low-volatility liquids require measurement at elevated temperatures followed by extrapolation. A typical sample requirement is 5 to 10 g of material with a stated purity, preferably ≥ 98 %.

Solid Substances

Solid samples with measurable sublimation behavior are tested using the static method, effusion techniques, or gas saturation. Solids of extremely low volatility are often reported as "less than a limit value" derived from the detection capability of the method. Thermal stability information (for example, from preliminary DSC screening) should be provided so that the test temperature does not cause decomposition.

Pure Substances and Mixtures

Registration data are normally generated on the pure active substance. For multi-constituent substances and UVCBs, testing is more complex because each component contributes a partial pressure; accredited third-party laboratories will assess the measurement strategy case by case, sometimes reporting the vapor pressure of the most volatile constituent. Petroleum-derived products may instead be characterized by Reid-type procedures such as ASTM D323 or ISO 3007.

Testing Items

The standard deliverables of a vapor pressure study for registration purposes include:

• Vapor pressure at specified reference temperatures (typically 20 °C and 25 °C).
• Vapor pressure curve over an experimentally accessible temperature range.
• Extrapolated or interpolated values calculated from the Clausius–Clapeyron or Antoine relationship.
• Derived enthalpy of vaporization (from the slope of the curve).
• Observations of thermal decomposition, if occurring within the tested range.
• Full test report with method description, raw data, calculation basis, and GLP or quality-system statement where required.

Testing Methods

Static Method

The sample is sealed in an evacuated apparatus held at constant temperature, and the equilibrium pressure is measured with a manometer or pressure sensor after outgassing. It is suitable for both liquids and solids over roughly 10⁻¹ Pa to 10⁵ Pa and is described in OECD Test Guideline 104, EU Method A.4, and GB/T 22228. It is the most widely used technique for registration studies of moderately volatile substances.

Dynamic Method (Ebulliometry)

The boiling temperature is recorded as a function of externally applied pressure. The method covers approximately 10³ Pa to 10⁵ Pa and simultaneously yields boiling point data. ASTM E1719 describes an ebulliometric procedure. It is best suited to thermally stable liquids.

Isoteniscope Method

The sample is held in a bulb connected to a manometer, with an auxiliary vacuum line removing dissolved gases. The method covers roughly 10² Pa to 10⁵ Pa and is standardized in ASTM D2879, which also provides an estimate of the initial decomposition temperature of liquids.

Effusion Methods (Vapor Pressure Balance and Knudsen Cell)

For very low vapor pressures (approximately 10⁻⁷ Pa to 1 Pa), effusion techniques measure the mass loss of vapor escaping through a small orifice into vacuum, either by direct weighing (Knudsen cell) or by molecular beam detection (vapor pressure balance). These methods are included in OECD Test Guideline 104 and are commonly selected for low-volatility solids and polymers.

Gas Saturation Method

An inert carrier gas is passed over or through the sample at constant temperature; the saturated vapor is trapped downstream and quantified analytically, typically by gas chromatography. The method reaches down to about 10⁻⁸ Pa and is the most sensitive validated approach, making it appropriate for substances of extremely low volatility such as high-molecular-weight solids.

Thermal Analysis Methods

Isothermal thermogravimetric analysis determines vapor pressure from the rate of mass loss using evaporation models, per ASTM E1782. It is a convenient screening and confirmation tool in the range of approximately 10⁻² Pa to 10⁵ Pa for pure, stable compounds.

Applications

Vapor pressure data generated for chemical registration serve multiple downstream purposes:

• Compliance dossiers for new chemical substance registration and existing chemical notification in China, the EU, South Korea, and other jurisdictions.
• GHS hazard communication: vapor pressure is a mandatory parameter in Section 9 of the Safety Data Sheet and supports classification decisions.
• Occupational exposure assessment and inhalation risk characterization for workers and consumers.
• Environmental fate evaluation, including volatilization from water and soil surfaces and atmospheric partitioning modeling.
• Transport and packaging safety, engineering design of ventilation and containment systems, and storage loss estimation.
• Screening of volatility for prioritization of testing under weight-of-evidence or (Q)SAR-based read-across strategies.

FAQ

How is the appropriate method selected?

Method selection depends on the expected vapor pressure range, the physical state of the sample, and its thermal stability. Laboratories usually begin with an estimated value from (Q)SAR tools or a boiling point measurement, then choose static, isoteniscope, effusion, or gas saturation testing accordingly.

Why must results be reported at 20 °C and 25 °C?

Registration regulations and SDS conventions require vapor pressure at standard reference temperatures (20 °C under EU REACH, 25 °C under other frameworks). Because direct measurement at ambient temperature is often impractical for low-volatility substances, values are extrapolated from measurements at several elevated temperatures.

Can vapor pressure testing be waived?

Yes. A waiver or adaptation may be justified where testing is technically not possible (for example, decomposition below measurable vapor pressure), or where reliable (Q)SAR estimates or read-across from structurally analogous registered substances adequately address the endpoint. The justification must be documented in the registration dossier.

How much sample is needed and how long does testing take?

Typical requirements are 5 to 10 g for static or isoteniscope methods and as little as 1 to 2 g for effusion or gas saturation studies. Project time is generally two to four weeks, depending on method, temperature program, and reporting requirements.

Is GLP compliance required?

For most registration schemes, physicochemical data must be generated in accordance with recognized test guidelines by accredited third-party laboratories; some jurisdictions explicitly require GLP compliance for hazard studies. Confirm the data quality provisions of the target regulation before commissioning the study.