Lugol’s contains iodine (I) and potassium iodide (KI). For a 1000ml amount: 48g of iodine and 96g of potassium iodide are added to distilled water and when dissolved this is topped up to
make 1000ml of solution.
What’s in our Lugol’s?
Per metric drop: 2.4mg of iodine and 3.6mg of iodide, yielding 6mg per drop of elemental iodine.
According to Wikipedia a
"5% solution consists of 5% (wt/v) iodine (I2) and 10% (wt/v) potassium iodide (KI)
mixed in distilled water." However, the convention for naming Lugol’s solution this way is misleading. Potassium iodide also contains iodine. In fact, 76% of the weight of each KI molecule is the
iodine atom. Therefore, in order to understand the full amount of iodine in a solution, add the amount of pure iodine (I2) PLUS 0.76 of the weight of potassium
iodide. For our solution the quantities are: 48g + (0.76 x 96g) = 120.96g. Rounding this down gives you our 12% solution (as calculated by a weight/volume measurement).
Other factors need to be considered that contribute to the strength of the solution. For example, how much is a “drop”? In providing the above information, we have decided to follow the standard
metric description that 1 drop = 1/20 of 1ml. Plus, whether the drop is a vertical or horizontal drop also factors in to the quantity. When comparing the strength that is claimed on a bottle of
Lugol’s Iodine, in addition to what has already been stated, other considerations include the quantity of distilled water used and the ambient temperature when the product is made.
Considering everything stated here, 12% can only be stated as an APPROXIMATE amount of iodine content.
The History of Iodine and Lugol’s
Jean Francois Coindet (1774-1834) was the first to use iodine for medicinal use. Lugol’s was first made by French physician J G A Lugol in 1829. Dr Lugol researched substances that could
help treat infections and found that iodine could be used and showed promise in this field. He used the 1:2 ratio of iodine to potassium iodide that is still used today.