Boiling point is a fundamental physical property used to characterize liquids. While it may seem like a straightforward measurement, factors such as atmospheric pressure, sample composition and heating rate can influence the temperature observed in the laboratory.
At Dell Tech Laboratories, boiling point testing is performed using the Siwoloboff method in accordance with OECD Test Guideline 103: Boiling Point.
What Is Boiling Point?
The boiling point of a liquid is the temperature at which its vapour pressure equals the surrounding pressure. OECD 103 defines the normal boiling point as the temperature at which the vapour pressure of a liquid equals standard atmospheric pressure of 101.325 kPa.
Because boiling temperature is affected by atmospheric pressure, pressure is considered when reporting the result. Where measurements are made at pressures slightly different from standard atmospheric pressure, OECD 103 provides for correction of the measured boiling temperature to the normal boiling point.
What Is the Siwoloboff Method?
The Siwoloboff method is a capillary technique for experimentally determining the boiling temperature of a substance.
In this method, a small amount of the test substance is placed into a sample tube along with a specially prepared boiling capillary. The sample tube is positioned in a temperature-controlled liquid bath and gradually heated while the temperature and behaviour of the sample are observed.
As the sample approaches its boiling temperature, a rapid stream of bubbles begins to emerge from the open end of the capillary. The system is then allowed to momentarily cool. The boiling temperature is identified at the point where the continuous stream of bubbles stops and liquid suddenly rises into the capillary.
This observable transition provides a practical means of identifying the boiling temperature using a relatively small quantity of test material.
Why Is the Heating Rate Important?
Controlling the heating rate is an important part of the Siwoloboff procedure.
OECD 103 specifies an initial temperature increase of approximately 3 K/min. Once the bath reaches approximately 10 K below the expected boiling temperature, heating is reduced so that the temperature increases at less than 1 K/min. The bath is also stirred during the determination.
Slowing the heating rate as the boiling point approaches allows the characteristic change in bubbling behaviour to be observed under controlled conditions.
What Types of Materials Can Be Tested?
OECD 103 can be applied to liquid and low-melting substances, provided the material does not undergo a chemical change, such as degradation, rearrangement or auto-oxidation, below its boiling point.
Sample composition can also be important. OECD 103 notes that impurities may influence boiling point considerably, particularly when volatile impurities are present, and the substance may need to be purified before measurement.
These considerations make it important to evaluate the test material and the expected boiling range when determining whether the method is suitable.
What Does OECD 103 Testing Tell You?
The test provides an experimentally determined boiling temperature for the substance under the conditions of the measurement.
For the Siwoloboff method, OECD 103 lists an estimated accuracy of ±2.0 K up to 600 K. The final test report includes the method used, sample identity, estimated accuracy, boiling temperature and measurement pressure, along with relevant observations needed to interpret the results.
OECD 103 also specifies that the reported boiling temperature is the mean of at least two measurements that are within the estimated accuracy of the method.
Why Might Boiling Point Data Be Needed?
Boiling point is an important physicochemical property when characterizing chemical substances and products. Experimentally determined boiling-point data may be useful when reliable physical-property information is required for applications such as technical documentation, product characterization or regulatory assessment.
For clients preparing an SDS or other regulatory documentation, boiling point may also be one of the physical-property data points under consideration. The specific information required will depend on the substance, product and applicable regulatory framework.
OECD 103 Boiling Point Testing at Dell Tech Laboratories
Using the Siwoloboff capillary method, Dell Tech Laboratories can experimentally determine the boiling temperature of suitable liquid and low-melting test materials in accordance with OECD Test Guideline 103.
Understanding a product’s boiling point provides valuable information about its physical characteristics and can help support broader chemical characterization and regulatory needs.
Looking for OECD 103 boiling point testing? Contact Dell Tech Laboratories to discuss your sample and testing requirements.
Blog Author
Kate Hatherley
Katherine supports analytical testing in Dell Tech’s Lab Services. Prior to joining Dell Tech’s Lab Services Group in 2019, Katherine worked in project administration and geographic information systems in the Ontario forestry industry.
