EU A.4: Vapour pressure

The vapour pressure gives an indication of the probability of the phase transitions liquid/gas and solid/gas. Vapour pressure data is required as a pre-requisite for animal as well as environmental studies.

The purpose of the study is to determine the vapour pressure of the test item using the isothermal thermogravimetrical effusion method. The evaporation rates of the test item at elevated temperatures and ambient pressure are determined by monitoring the weight loss. This method is suitable for substances with vapour pressures as low as 10-10 Pa (10-12mbar) and with purity as close as possible to 100% to avoid the misinterpretation of measured weight losses.

It is useful to have preliminary information on the melting point/melting range of the substance before performing these tests.

(The study does not need to be conducted if the melting point is above 300 °C. If the melting point is between 200 °C and 300 °C, a limit value based on measurement or a recognised calculation method is sufficient. Vapour pressure testing is also not required for chemicals with a standard boiling point of <30°C, as these substances will have vapour pressures above the limit of measurement (i.e. 105 Pa)).

Study Design

Course of the test

Apparatus – Q50 thermogravimetric analyzer (TGA)

Test Conditions - The experiments will be performed under a flow of nitrogen and at atmospheric pressure.

The evaporation rates VT of the test item at elevated temperatures and ambient pressure is determined by measuring the weight loss at defined temperatures over a period of time. The vapour pressure pT is calculated from the evaporation rates by using a linear relationship between the logarithm of the vapour pressure and the logarithm of the evaporation rate. The vapour pressure regression curve is established by measuring the evaporation rate of a set of reference compounds with known vapour pressure.

The test item will be applied to the surface of a roughened glass plate in a homogeneous layer. In the case the test item is solid; it will be suspended in appropriate solvent. The plate will be wetted uniformly by a solution of the test item. The temperature programs will be defined in the preliminary tests. The plate will be placed in the TGA instrument. The weight loss of the test item will be measured continuously as a function of time at at least four different temperatures (at least three replicates).

For the evaluation will be used only the values with the weight loss is ≥ 1µg/min and reproducible in all three replicates.


The vapour pressure [Pa] at 20 °C will be reported.

In case of vapour pressure cannot be determined, because of decomposition, the observation of the experiment - will be reported.

Guidelines and Literature

  • European Community (EC), EC No. 761/2009, Part A: Methods for the Determination of Physico-Chemical Properties, Guideline A.4: “Vapour Pressure", Official Journal of the European Union No. L220, August 24, 2009
  • Organisation for Economic Co-operation and Development (OECD), OECD Guidelines for the Testing of Chemicals No. 104: "Vapour Pressure", March 23, 2006