How can we know if the salt we are using has adequate amounts of iodine and iron?

For detecting the presence of iodine in salt, a salt testing kit (STK) can be used. When a drop or two of the starch solution in this kit is added to a teaspoon of salt, it will turn purple if the salt contains iodine. To determine the iodine and iron content in salt, the salt can be tested in an NABL accredited/FSSAI approved laboratory by titration.