Lugol’s Iodine Solution

Preservation and storage of water samples.

Colour of water sample correctly preserved with Lugol's Iodine
Colour of water sample correctly preserved with Lugol’s Iodine

• Samples for phytoplankton analysis should be preserved immediately after collection by adding Lugol’s Iodine Solution.

•  Lugol’s Iodine Solution should be added until the sample is the colour of weak tea/light beer (dark yellow/light brown) after preservation. The sample should be agitated during addition of the Lugol’s Solution to ensure thorough mixing.  The amount of Lugol’s solution required may vary from sample to sample, but for marine samples a final concentration of between 0.1% and 0.5% is normally adequate (eg; between 1.0mL and 5.0mL of Lugol’s Iodine Solution added to a  1000mL water sample).

• Lugol’s Iodine is light sensitive, so samples should be stored in the dark after they have been preserved.

Lugol’s Iodine stock solution

Recipes and recommended rates for Lugol’s Iodine solution vary between authors. We use the recipe of Hasle and Tomas in Tomas (1997). Lugols Iodine stock should be stored in glass, not plastic containers.


1. Measure1.0L distilled H20 into brown glass bottle
2. Dissolve 100g KI in 1.0L distilled H20
3. Add 50g I2 and mix thoroughly
4. Add 100mL glacial Acetic Acid
5. Store in dark in stoppered bottle.

Note: Lugol’s Iodine needs to be stored in the dark or it will degrade.

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