Metrohm Oxidative Stability Index (OSI)

Oxidative Stability Index for Fats and Oils

If fats and oils are exposed to air and light for any length of time, they undergo oxidation and hydrolysis reactions. The fats and oils then develop an unpleasant taste and odor and are termed rancid. Oxidation stability is an estimate of how quickly a fat or oil will become rancid. Through the use of the 892 Professional Rancimat, it is also possible to characterize the efficacy of added antioxidants.

Oxidation Stability in Biodiesel

In contact with air, petroleum undergoes oxidizing reactions whose reaction products can cause problems in combustion engines. Polymeric, poorly soluble compounds in particular lead to deposits in and blockages of the fuel injector systems. The aging behavior, i.e., the oxidation stability, is therefore a very important property of vegetable oils and biofuels.

Determination according to national and international standards

Various standards describe the Rancimat method, including those listed below.

• AOCS Cd 12b-92 (AOCS – American Oil Chemists’ Society) Sampling and analysis of commercial fats and oils: Oil Stability Index
• ISO 6886 Animal and vegetable fats and oils – Determination of oxidative stability (accelerated oxidation test)
• 2.4.28.2-93 Fat stability test on Autoxidation. CDM, Japan

What is the Rancimat Method? 

Air is passed through the sample at an elevated temperature to bring about artificial aging. During this process, long-chain organic molecules are oxidized by oxygen, whereby highly volatile organic substances form in addition to insoluble polymer compounds. The former are driven out by the air flow, absorbed in water, and detected there by measuring conductivity. The time until these decomposition products occur is referred to as the induction time or the oil stability index (OSI) and characterizes the resistance of the sample towards oxidative aging processes, i.e., the oxidation stability.

Learn more about the Rancimat!