1.2.1.5 Spot tests for minerals in finished feed

Preparation of sample

Usually the minerals in mixed feed are powder or fine particles. Sieve the sample through fine sieve and put the fine portion in chloroform or carbon tetrachloride in a 100 ml beaker. Shake thoroughly and keep it for 5 minutes. Pour off the floating feed material. Sprinkle the residue mineral portion over the paper with a small spatula for spot test.

Test for cobalt (Co), copper (Cu) and iron (Fe) Reagents

Solution A: Sodium potassium tartrate (Rochelle salt, KNaC .H O .H O). Dissolve 100 g of Rochelle salt and make volume 500 ml with distilled water.

Solution B: Dissolve 1 g of 1-nitroso-2-hydroxynaphthalene-3, 6 g disulfonic acid and make volume 500 ml with distilled water.

Procedure

Moisten the filter paper with 3 to 4 drops of solution A and B then sprinkle the feed sample on filter paper. Allow the filter paper to dry and check closely under low power stereoscopic microscope.

Positive results

Presence of cobalt will  produce a pink colour, copper will  produce light brown  coloured ring, and iron gives a deep green colour.

Test for manganese (Mn) Reagents

Solution A: 2 N Sodium hydroxide

Solution B: Dissolve 0.07 g of benzidine dihydro chloride in 10 ml of glacial acetic acid and dilute to 100 ml with distilled water.

Procedure

Moisten filter paper with solution A. Sprinkle the feed sample immediately, let it stand for 1 minute. Add 2-3 drops of solution B. If no reaction occurs immediately, add solution B again, without flooding.

Positive results

Presence of manganese will produce a dark blue colour with a black centre.

Test for iodine (Potassium iodide) Reagents

•         Starch paper.

•         Bromine solution: Dissolve 1 ml of saturated bromine in water and add distilled water to make the volume 20 ml.

Procedure

Moisten starch paper with bromine solution. Sprinkle the feed sample on the starch paper.

Positive results

Iodine will produce a blue purple colour.

Test for magnesium (Mg) Reagents

Solution A: 1 N potassium hydroxide

Solution B: Dissolve 12.7 g of iodine and 40 g of potassium iodide in 100 ml distilled water.

Procedure

Mix  solution A with  excess amount of solution B to produce a very dark brown  colour mixture and add 2 to 3 drops of solution A until it turns a pale yellow. Moisten the filter paper with pale yellow solution and sprinkle with feed sample.

Positive results

Magnesium gives yellow brown spots.

Note: The mixture of solution A and B should be freshly mixed for each test.

Test for zinc (Zn) Reagents

Solution A : 2N sodium hydroxide

Solution B: Dissolve 0.1 g dithiozone in 100 ml of carbon tetrachloride.

Procedure

Moisten filter paper with solution A, sprinkle the feed sample. Add 2 to 3 drops of solution B.

Positive results

Presence of zinc gives a strawberry red colour.

Test for phosphorus (P) Reagents

Solution A: Dissolve 5 g of ammonium molybdate in 100 ml of cold distilled water and add 36 ml concentrated nitric acid.

Solution B: Dissolve 0.05 g of benzidine (using base or its chloride) in 10 ml of conc. acetic acid and dilute with distilled water to 100 ml.

Solution C: Saturated sodium acetate solution.

Procedure

Moisten filter paper with solution A and dry it in an oven. Sprinkle the feed sample and add a drop of solution B and a drop of solution C.

Positive results

Presence of phosphorus will produce a blue ring.