Iodine Value Calculators
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What Is Iodine Value?
The iodine value (IV) quantifies the degree of unsaturation (number of C=C double bonds) in a fat or oil by measuring how much iodine it absorbs. Iodine adds across double bonds in the fatty acid chains:
−CH=CH− + I₂ → −CHI−CHI−
The more double bonds present, the more iodine absorbed, and the higher the iodine value.
IV = (g of I₂ absorbed / g of fat) × 100
Typical Iodine Values for Common Fats and Oils
- Coconut oil: 7–10 (highly saturated)
- Palm oil: 44–58
- Olive oil: 75–94 (primarily monounsaturated)
- Sunflower oil: 110–143 (polyunsaturated)
- Linseed (flaxseed) oil: 168–204 (highly polyunsaturated — drying oil)
- Butter: 25–40
- Lard: 45–70
Oils with IV > 130 are called drying oils — they polymerize and harden on exposure to air (used in paints and varnishes). Oils with IV < 100 are non-drying oils.
Standard Methods for Iodine Value
The two primary analytical methods are:
- Wijs method (ISO 3961): Uses iodine monochloride (ICl) in glacial acetic acid. Reacts with the sample for 30 minutes in the dark, then excess ICl is back-titrated with sodium thiosulfate using starch indicator. Most common for edible oils.
- Hubl method: Uses iodine solution; less reproducible than Wijs.
Iodine value formula from titration:
IV = ((V_blank − V_sample) × N × 12.69) / m
Where V = volume of thiosulfate (mL), N = normality of thiosulfate, m = sample mass (g), and 12.69 = equivalent weight factor for iodine (MW 253.8 / 2 / 10).
Iodine Value in Biodiesel Quality
Biodiesel derived from polyunsaturated oils has high iodine values, indicating more double bonds and greater susceptibility to oxidation. European biodiesel standard EN 14214 limits IV to ≤ 120 g I₂/100 g to ensure adequate oxidative stability.
Glossary
Frequently Asked Questions
Iodine value measures the degree of unsaturation in a fat or oil — specifically, the total number of carbon-carbon double bonds in the fatty acid chains. It is expressed as grams of iodine absorbed per 100 grams of fat. Higher iodine value = more double bonds = greater unsaturation. It is used to characterize edible oils, assess oxidative stability, and quality-control biodiesel and industrial lipids.
Highly polyunsaturated oils have the highest iodine values: linseed (flaxseed) oil (168–204), safflower oil (~145), sunflower oil (110–143), and corn oil (~120). These are rich in linoleic (C18:2) and linolenic (C18:3) acids. Highly saturated fats have very low iodine values: coconut oil (7–10), palm kernel oil (~17), and butter (25–40).
Oils with high iodine values (many double bonds) are more susceptible to oxidative rancidity — double bonds react with oxygen to form peroxides and aldehydes that produce off-flavors. They are also more prone to polymerization. Lower iodine value generally means better oxidative stability and longer shelf life. For cooking oils, stability is often preferred; for drying oils used in paints, high iodine values are desirable because polymerization creates a hard film.
The Wijs method (ISO 3961) uses iodine monochloride (ICl) in glacial acetic acid to react with double bonds in the fat sample. After a fixed reaction time, excess reagent is back-titrated with standardized sodium thiosulfate solution using starch as an indicator (turns from blue to colorless at the endpoint). Iodine value is calculated from the difference in thiosulfate volume between a blank and the sample.