The oxidative stability of the investigated oil samples can be checked byusing the Rancimat test (Läubli et al. 1988). The test is  performed on a 679 Rancimat apparatus (Methrom, Herisau, Switzerland). The oil samples (3 ml) are subjected to a temperature of 110°C at an air flow rate of 20 dm3 /hour. The determination is based on the conductometric detection of volatile acids. The results are  expressed

as the induction time (IT) in hours. The induction time represents the time needed for the  decomposition of hydroperoxides produced by oil oxidation (Läubli et al. 1988). T

Dear Marwan

The Rancimat method follows the oxidative breakdown of oils by measuring the conductivity of water impinged with the exhaust of the heated oil. As long as the oil is stable, oxygen is not oxidizing the oil but e.g. antioxidants. As soon as the antioxidative capacity is gone, oxygen starts to oxidizie the oil. As a result mainly formic acid is built which then is detetcted as a rise in conductivity. The meausrement of the formic acid is not quantitave. But to more or less linear periods of conductivity development can be recognized.

While the oil is stable, conductivity stays low. In the breakdown period conductivity rises more or less linear with time. The "induction time" or "induction period" is the extrapolated starting time of breakdown. Determination of that time can be done graphically by drawing the tangents to the two linear regions or mathematically at the point of highest curvature of the conductivity signal.

Volatile organics do not influence the results as long as they are not ionic. It has been recognized that some samples (e.g. butter) may show an initial rise in conductivity (like a step). but after this rise the conductivity gets stable again and the "induction period" can be detected easily.

Thanks Ravi Kant Upadhyay,

I know that (the operation condition of OSI), but I need to know the minimum and the maximum limits of low-molecular weight of volatile organic compounds? and How the device converts the conductivity of water to the indicators of oxidative damage?

We did check the evolution of organic acid in the process by IC. We almost exclusivel found formic acid.

Volatile compounds do not interfere with the measurement. Therefore there is no limit for them described.

Conductivity does not directly convert to oxidative damage. That means that there is no relation between conductivity and oxidative damage. Conductivity is just used to follow the evolution of the product of oxidative damage.

This is also the reason why no electrode calibration is required. The important areas re the slope before and after reaching the induction period.

Dear Markus,

Thank you very much, you've provided me with useful information.  I was reading one of your published scientific papers and found it with valuable information ((Determination of the Oxidative Stability of Fats and Oils: Comparison between the Active Oxygen Method (AOCS Cd 12-57) and the Rancimat Method )) JAOCS, Vol. 63, no. 6 (June 1986).

Kindly, I hope you to provide me with a detailed documentation about the scientific basis for Rancimat device if possible.

With all my regards.

The Rancimat method is an accelerated aging test. Air is passing through the sample in the reaction vessel at constant elevated temperature. In this process fatty acids are oxidized. At the end of the test volatile, secondary reaction products are formed, which are transported into the measuring vessel by the air stream and absorbed in the measuring solution (deionized water). The continuously recorded electrical conductivity of the measuring solution is increasing due to the absorption of the reaction products. Thus their appearance can be detected. The time until secondary reaction products are detected is called induction time. It characterizes the oxidation stability of oils and fats.

The measuring temperature depends on the oxidation stability of the sample. For the sample types described in this document, usually temperatures between 80 and 160 °C are appropriate. 50 to 220 °C are possible. Most tests are carried out at 120 °C (Iower stability – lower temperature). The rule of thumb is: a temperature increase of 10 °C lowers the induction time by a factor of two.

Also, you can check in this pdf, about correlation between molecular weight (MW, g/mol) of saturated fatty acid alkyl esters and oxidation time. A correlation was noticed in which the oxidation onset temperature (OT) of saturated fatty esters increased with decreasing molecular weight (R2 0.7328).

I think this machine able to measure all kinds of oils even Biodiesel, so you not need it to know the minim or maximum molecular weight of volatile compounds.  

Good luck my brother Dr. Marwan. :)

Hello Dr. Amr

There are adverse effects if it have taken in large doses, such as a bulging of stomach, vomiting or nausea and soft stool, also some of the collateral damage depends on the source of omega-3 (from sea food or plant food) like bitter taste and burping. But more serious is the side effects at high doses affect on blood clotting. Beware of take Omega-3 with aspirin only under medical supervision. And pregnant women should be avoided just under the supervision of physician because it may cause abnormalities of the fetus.

I hope the links below will help you.

Marwan Rashed

http://www.sciencedirect.com/science/article/pii/S096999611400103X

http://www.sciencedirect.com/science/article/pii/S1568163713000081

Also here are some important references

http://www.sciencedirect.com/science/article/pii/S0022346810008729

http://www.sciencedirect.com/science/article/pii/B9780081001370000080

http://www.sciencedirect.com/science/article/pii/S0939475308000185