The potato test

Discussion in 'Water Parameters and Additives' started by lappiesreef, 19 May 2008.

  1. lappiesreef

    lappiesreef

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    Hey Guys

    After chatting to 459b in the aberlite thread I decided to test one of my additives that is supposed to have iodine in it for Iodine.

    If you add iodine to a potato, the iodine and starch reacts to give a blue/purple colour.

    I tried with a red sea product called Ca plus 3. It is a calcuim additive plus iodine,strontium and molybnium.

    The test came up negative. There was no reactivity with the startch at all.

    It could be that the level of iodine in the porduct is so low that you can't test it this way, but is it effective then?

    Can a few guys please do the same test on one of the iodine additives so we can see if all the products have such low levels of iodine in?
     
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  3. lappiesreef

    lappiesreef Thread Starter

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    Hey 459b, do you have iodine in the lab? I don't use it this side...

    Can't you please perform a dilution series so we can see how far down the potato test goes?
     
  4. jacquesb

    jacquesb Retired Moderator

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    Hi LappiesReef - I use AlphaPharm (and some other) pure Iodine Tincture as additive to my tank. I don't use commercial iodine additives anymore..... Gone off it....
     
  5. lanzo

    lanzo Sponsor

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    how does it work for you jacques?
     
  6. 459b

    459b Moderator MASA Contributor

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    i have iodine somewhere around. Ill do a dilution series and test it.
    Odd that it didnt even go a faint blue.
     
  7. lappiesreef

    lappiesreef Thread Starter

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    Thansk 459 :) I hope the potato is just not sensitive enough. If that is the case, then buying the lab iodine will last a lifetime and then some...

    J please test your working solution on a potato...so we can see what it should like like if you have the right concentration to add to your tank ;)
     
  8. HenkHugo

    HenkHugo

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    i just tested Seachem reef Iodide - no reaction....
     
  9. lappiesreef

    lappiesreef Thread Starter

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    I wonder if we all getting dooped or if they have the iodine in a different form...Althoug most forms should react with startch...

    Henk do they give a concentration of the Iodide? I'kk do a search later on to check whether iodide reacts in the same way as iodine with startch...
     
  10. sunburst

    sunburst

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    I would like to suggest that someone overcook the potato slightly in a microwave. ie to partially dehydrate. 5 - 6 min Cooked rice or sago would also give a good reaction
     
  11. 459b

    459b Moderator MASA Contributor

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    So heres what i did....
    got hold of iodine, did a 10-fold series dilution down to 1 in 10000000
    at 1 in 1000 the solution was clear.
    Made a 20% starch solution (i think thats the approx starch concentration of potatoes)
    Added the starch to the iodine and only got a clear reaction down to 1 in 100. I think there might be some colour change at 1 in 1000 but that could be my imagination.
    By the intense colour of the 1 in 100 i think you will be able to see a definate reaction up to one in 500, possibly more.
     
  12. 459b

    459b Moderator MASA Contributor

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    sounds like stach additives are a rip off. Think we should follow Jacquesb and buy iodine tincture.
     
  13. sunburst

    sunburst

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    Weird; the reaction should be immediate. Will try as well tonight. What starch did you use 459b
     
  14. lappiesreef

    lappiesreef Thread Starter

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    Chemical Test for Starch or Iodine:
    Amylose in starch is responsible for the formation of a deep blue
    color in the presence of iodine. The iodine molecule slips inside of the amylose coil.
    Iodine - KI Reagent: Iodine is not very soluble in water, therefore the iodine reagent is made by dissolving iodine in water in the presence of potassium iodide. This makes a linear triiodide ion complex with is soluble. The triiodide ion ion slips into the coil of the starch causing an intense blue-black color.
    Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or other materials such as bread, crackers, or flour. A blue-black color results if starch is present. If starch amylose is not present, then the color will stay orange or yellow. Starch amylopectin does not give the color, nor does cellulose, nor do disaccharides such as sucrose in sugar.
    Iodine Test: When following the changes in some inorganic oxidation reduction reactions, iodine may be used as an indicator to follow the changes of iodide ion and iodine element. Soluble starch solution is added. Only iodine element in the presence of iodide ion will give the characteristic blue black color. Neither iodine element alone nor iodide ions alone will give the color result.
     
  15. Shaun

    Shaun Retired Moderator

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    On one forum they said you can add Lugol's Iodine, but can't remember how much to add p/l.
     
  16. 459b

    459b Moderator MASA Contributor

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    its analytical grade starch. Not sure what its derived from but its super pure.
     
  17. lappiesreef

    lappiesreef Thread Starter

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    Lugol's should react since it is a mixture of potasium iodide and iodine.

    Most prouct we buy should be a derivative of this anyway and hsould react.
    Looks like we paying allot for water with a mitnue amoutn of iodine in it...
     
  18. 459b

    459b Moderator MASA Contributor

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    pity there isnt such a simple test to check all the other additives.
     
  19. lappiesreef

    lappiesreef Thread Starter

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    Hear you there mate...

    I think the thing here is that companies add a bit of iodine to the product and thats it. To be soluble it needs to be mixed with iodide like Iodide potasuim. This is what reacts with the starch.

    Still I wonder if the products are use full at all if they only contain iodine without the iodide form...

    Bottom line. Iodine additives are way over priced!! How much was the pure stuff per L 459?
     
  20. 459b

    459b Moderator MASA Contributor

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    the pure stuff is about R1000 a litre for the really concentrate stuff. Might be cheaper and easier to buy iodine tincture. It comes in a small bottle, about 20ml, they sell it to treat wounds. think its even available at pick n pay.
     
  21. tinusb

    tinusb

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    Buy the tincture man! It's something like R6/bottle :) And should last about 3 months, or even more, depending on dosing the tank :) Thanx Jacques! :D
     
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