A couple of years ago, I “bit off” packs of green onions from the store and ... slept for a week ... and when I woke up, I checked the rest of the product for nitrates. Was surprised by the fact that the topic is relevant to this day. I offer you a simple and reliable way to protect yourself and loved ones from such (dangerous!) Situations.indicator paper for determining the content of nitrates in fruits and vegetables. To date, there are two methods for the determination of nitrates and nitrites. The first is considered strictly specific. It is based on the diazo combination reaction, but it uses quite rare and, moreover, highly carcinogenic substances (the probability of oncological diseases is high). The second one is considered not specific, but in the case of food analysis - strict specificity is guaranteed! The method is well known to most from the school bench, only we were not taught to use knowledge ...It is called “jodkrahmalnaya reaction" For the manufacture of indicator paper will require: -strip white filter paper. -liter saucepan. -spoon -shallow bowl - necessary and sufficient number of clothespins. of reagents: -half a liter of water -starch (any, you can even "fruit and berry jelly") -potassium iodide (in the pharmacy - 200ml 3% solution - eye drops) Getting started.In a saucepan, bring to a boil 0.5 liters of water and in a thin stream while stirring, pour in a suspension of starch. Boil for another five minutes. When the liquid brightens, stop heating. In a hot liquid, dissolve 1-3 g of potassium iodide or simply pour in a bottle of eye drops with stirring. After the liquid cools it soak the paper. If the saucepan is not deep, you can do without the pan. From the impregnated strip, remove the excess solution using a subsequent strip. Dry with a clothes clip. The indicated amount of the reagent is quite enough to make hundreds of 250 * 100 mm strips. Paper in the absence of light has been stored for decades without changing its properties, but if it still darkens, you should not despair.It can spoil for a trivial reason: leaking pipes with cold water, and water is chlorinated. In this case, you must invite a dignity. equipment, troubleshoot and treat indicator paper with gaseous sulfur dioxide. In a few seconds, the display will be restored. In conclusion, and for completeness, I will provide some more information. Type "World" where you paint, find all shades of blue. So (with 10% error): BLACK - the concentration of nitrates is above 1000mg / kg of the 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") LAZURNO - 250 mg / kg - indisposition, weakness. BLUE - 100 mg / kg - acceptable SV.GOLUBOY - 50 mg / kg - safe. WHITE is absent - ideal. Perhaps this is all. The method is not perfect (there are spots on the Sun, too) colored juices will have to be compared with a control (simple) piece of paper. Good health and bon appetite to all!