EU A.5: Surface tension

The purpose of the study is to evaluate the surface tension of an aqueous solution by means of a ring tensiometer.

It is useful to have preliminary information on the water solubility  of the substance before performing these tests.

(If the water solubility is below 1 mg/l at 20°C the test does not need to be conducted).

Study Design

Course of the test

Apparatus - Tensiometer (model K8, KRÜSS)

Test Condition - 20 °C ± 0.5 °C

According to the guideline the concentration to use is depending on the water solubility of the test item.
The test concentration should be 90 % of the saturation solubility in case the solubility value is below 1 g/L. Otherwise 1g/L will be used as test concentration.

The cleaned measurement vessel will be filled with the test item solution and placed into the mobile sample table. The table will be raised until the ring is immersed below the surface of the solution. Subsequently, the table will be lowered until the ring is attached to the liquid surface. After additional lowering of the table, the ring exerts a torque on the force measuring system. Subsequently, the table top should be lowered gradually and evenly at a maximum rate of 0.5 cm/min to detach the ring from the surface. Lowering of the table and subsequent compensation of the resulting torque are continued in small increments until the maximum force is reached and the lamina breaks. This is when upward force completely overcomes the surface tension force and the ring is torn away from the surface. After completing the measurement, the ring will be immersed below the surface again and the measurement will be repeated at least 5 times until a constant value is reached. The time passed since the solution was transferred to the measurement vessel will be recorded for each determination.


The surface tension at 20 °C will be reported as mN/m (SI sub-unit) or dyn/cm (CGS system).

Guidelines and Literature

  • Commission Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) (originally published as Council Regulation (EC) No 440/2008, corrigendum according to Official Journal of the European Union (EN) dated June 3, 2008, L 143/55), Annex, Part A, A.5.: “Surface Tension”, Official Journal of the European Union, L 142, Volume 51, May, 31 2008
  • Organisation for Economic Co-operation and Development (OECD), Guidelines for Testing of Chemicals, Guideline No.: 115, “Surface Tension of Aqueous Solutions”, adopted October 02, 2012