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A couple of years ago, I “ate” packs of green onions from a store and ... lay down for a week ... and when I woke up, I checked the rest of the product for nitrate content. I was surprised by the fact that the topic is relevant to this day. I bring to your attention a simple and reliable way to protect yourself and loved ones from such (dangerous!) Situations.

indicator paper

indicator paper for determination of nitrate content in fruits and vegetables. To date, two methods are known for determining nitrates and nitrites. The first is considered strictly specific. It is based on the diazocomposition reaction, but it uses rather rare and, moreover, very carcinogenic substances (there is a high probability of cancer). The second - is considered not specific, but in the case of food analysis - strict specificity is guaranteed! The method is well known to most from school, only we were not taught to use knowledge ... It is called - "iodine starch reaction"

To make indicator paper you will need:
-strips of filtering white paper.
liter liter saucepan.
- shallow bowl
-necessary and sufficient number of clothespins.
from reagents:
half a liter of water
-starch (any, you can even "fruit and berry jelly")
potassium iodide (in a pharmacy - 200 ml of a 3% solution - eye drops)

Getting down. In a saucepan, bring to a boil 0.5 l of water and a thin stream with stirring, pour in a suspension of starch. Boil another five minutes. When the liquid brightens, we stop heating. Dissolve 1-3 g of potassium iodide in a hot liquid or just pour a bottle of eye drops with stirring. After the liquid cools with it, we impregnate the paper. If the saucepan is not deep, you can do without a bowl. Remove the excess solution from the impregnated strip with a subsequent strip. Dry using a clothespin. The indicated amount of reagent is quite enough for the manufacture of hundreds of strips of 250 * 100 mm.
Paper in the absence of light has been stored for decades without changing its properties, but if it is still darkened, you should not despair. It can go bad for a banal reason: pipes with cold water leak, and the water is chlorinated. In this case, you must invite the dignity. technique, eliminate the malfunction, and treat the indicator paper with gaseous sulfur dioxide. In a few seconds, the display will return.
In conclusion, and for the sake of completeness, I will give some more information. Type "World" where they draw, find all the shades of blue.

So (with a 10% margin of error):
BLACK - nitrate concentration is higher than 1000 mg / kg of product.
it is very dangerous (unfortunately I watched this) - severe poisoning is guaranteed
BLACK-BLUE - 1000 mg / kg - severe poisoning.
BLUE 750 mg / kg --........
LIGHT BLUE - 500 mg / kg - nausea, chills ... ("hangover")
COLOR - 250 mg / kg - malaise, weakness.
BLUE - 100 mg / kg - valid
SV. BLUE - 50 mg / kg - safe.
WHITE missing - ideal.

Perhaps this is all. The method is not ideal (there are also spots on the Sun) colored juices will have to be compared with a control (simple) piece of paper.
All good health and bon appetit!
come back
Comments (5)
  1. ALPom
    #1 ALPom Guests January 17, 2014 16:38
    The sample procedure is not fully described.
    Excerpt from the school workshop:
    Performing a test analysis

    1. Pour 25-50 ml of standard KNO3 solutions and water samples, squeezed plants, fruit and vegetable juices into chemical glasses, add strips of iodine starch paper prepared in advance.
    2. After 10 minutes remove the strips and air dry.
    3. Apply a drop of sulfanilic acid and? -Naphthylamine solutions to each strip of iodine starch paper. After about 5 minutes staining appears, the intensity of which depends on the concentration of nitrate ions.
    4. After the appearance of staining, make a conclusion about the approximate concentration of nitrate ions using the data in table 1

    I don’t know where to get sulfanilic acid and naphthylamine.
    In the form given by the author, the sample will not work: the color depends on the moisture of the paper strip and on the degree of impregnation of the paper with the solution, and not on the nitrate content.
  2. Iskander
    #2 Iskander Guests March 21, 2014 16:00
    And I tried and it turned out on cucumbers!
    Sulfamic acid can be replaced with vanillin or sulfanilamide (pharmacy
  3. Vitaliy
    #3 Vitaliy Guests April 18, 2014 10:28
    Nonsense. Nitrate ions practically do not show oxidizing properties in the solution, therefore, iodine will not be formed from potassium iodide, and your papers will not be stained.
  4. Chemist
    #4 Chemist Guests January 31, 2017 17:58
    The author, apparently, forgot about the simple and accessible ionometry method. The device costs money, of course, but not huge. And this is much more accurate than all this shamanism.
  5. Ilya
    #5 Ilya Guests August 11, 2017 17:54
    Well, add concentrated sulfuric acid and heat. Already nitric acid potassium iodide oxidizes.

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