Percentage of iodine

[Tōtōchtin]

What percentage of iodine is used to check conversation?
Thank you for your time,
Tōtō

[still_stirrin]

I use the “tincture of Iodine” from the Walgreens or CVS store. I believe it is 2% iodine.

Just a drop on a sample is enough too.
ss

[Tōtōchtin]

Thank you for that. I ordered some which just arrived, I thought it was too weak of a solution when I saw the label.
Tōtō

[Yummyrum]

For the purposes of testing for the presence if starch , I don’t think it matters too much what the %of Iodine is .

We make up a bulk Iodine Solution at work . Unfortunately , I can’t say the proportions off hand but will let you know when I get to work tomorrow .

Iodine is very reactive , but it is pretty much insoluble in water , so it is always made up with Potassium Iodide which make the Iodine more soluble . When ever we are in the Chemical storeroom and remember , we get the Winchester of Iodine solution and give it a good shake to help the Iodine dissolve .

The stock Iodine solution is then diluted down 10:1 before use . It is always stored in Amber glass bottle's and preferably in the dark as light will break down the Iodine .

If we use a 1% starch solution ( thats 1 gram of starch in 100mls of water) one drop of Iodine solution will turn about 10mls Of that starch almost black .
Now the colour of that Iodine solution in an eye dropper is a straw brown colour .


Now , if we dilute that 1% starch solution down to 0.1% , we will get a dark blue test with the Iodine .

If we dilute that 1% starch solution down to 0.01% we still get a very noticeable Blue test with the Iodine .

Point being . Iodine is a very powerful indicator of presence of starch .

Also worth mentioning , Iodine solution will eventually loose its ability . It gets paler and paler . So long as it still had a brown appearance it will work . Once it is clear , it’s no longer useful . Keeping it cool and dark will help .

However , it will corrode out refrigerators ..

[Saltbush Bill]

This is what I've used and it works fine.

[stillanoob]

I just use the idophor that I have for sanitizing. I have no idea what the percentage is but it indicates starch clearly.

[Yummyrum]

In a Laboratory ,We use Lugol's Solution .
It is usually 1% Iodine ,although there are some recipes that use up to 2%.

1g Iodine
2g Potassium Iodide
100mls water.

Iodine solution used as an antiseptic is usually 2-5% Iodine with 7% and above being considered toxic to the skin.

So here is 1g of Iodine on the balance .You can see it is very quickly sublimating and the paper is staining

It took over half an hour on the Magnetic stirrer and even then , there was still a bit of undissolved Iodine .
So this is a lineup to show the relative colour of Iodine solution at 1% , 0.1% and 0.01% concentrations .

I have starch solutions of 1% ,0.1% and 0.01%.
Lets test them

First ten drops of Starch in each well .
Top row 1%
Middle row 0.1%
Bottom Row 0.01%

Then 1 drop of iodine
Left column 1%
Middle column 0.1%
Right Column 0.01%

This time , two more drops of Iodine in each well as per above .

notice that the 1% Iodine is so strong that it masks the weak starch test result . IE , if you have a very strong brown colour , you can"t see the subtle blue colour in a weak starch solution .


So in conclusion , Iodine solution is very good at detecting starch .
Any of the solutions that you buy from a Chemist will be more than strong enough .
Diluting the Iodine can detect lower starch levels by not masking it .

EDIT: just for shits and giggles I just tried 0.001% Iodine and it barely showed anything at all on the 1%starch and nothing on the others .

I’m of the opinion that Iodine in the range 0.01- 0.1% will give the best indication .
Stuff bought from chemist diluted 10:1 will be ideal . Undiluted , it may well be masking the facts and when you think you have full starch conversion , it isn’t

[Tōtōchtin]

I really appreciate for taking so much time to show us your trail. I guess that goes to show you a little bit can go a long ways,unless it's a good whiskey and a smoke.