ANN 111: Principles of Animal Nutrition and Feed Technology (2+1)

THE SPECIAL ANALYTICAL METHODS FOR QUICK TESTS AND SPOT TEST FOR THE PRESENCE OF ADULTERANTS

Magnesium (Test for magnesium sulphate)

• Reagents
  • Solution A – Potassium hydroxide 1N.
  • Solution B – Dissolve 12.7g of iodine and 40g of potassium iodide in 25ml of distilled water. Stir and then dilute to 100ml.
• Procedure
  • Mix solution A with an excess amount of solution B to give a very dark brown colour mixture.
  • Take a small part of the dark brown colour mixture and add 2-3 drops of solution A until it turns a pale yellow.
  • Moisten the filter paper with this pale yellow solution and then sprinkle with the sample to be tested.
• Positive Results
  • Magnesium gives YELLOW BROWN SPOTS.
  • Note : The mixture of solution A and B deteriorates very quickly and should be freshly mixed for each test.

Salt (Sodium chloride)

• Reagents
  • Silver nitrate solution (5%)
  • Nitric acid Solution (1:2)
  • Ammonium hydroxide solution (1:1)
  • Standard sodium chloride solution (0,0.1, 0.2, 0.3 %)
• Procedure
  • Weigh 1g of sample and add 100ml of distilled water. Stir and filter with Whatman No.4
  • Pipette 1 ml of standard solution and 8 ml of nitric acid solution. Stir and add 1 ml of silver nitrate solution.
  • Stir and compare the test sample with the standard sample. This test should be read within 5 minutes.
• Positive Results
  • Salt gives a WHITE TURBIDITY

Urea

• Reagents
  • Urease solution – Dissolve 0.2g of urease powder in 50ml of distilled water.
  • Standard urea solution (0, 1, 2…….5%)
  • Cresol red indicator (0.1%)
• Procedure
  • Weigh 10g of test sample and add 100ml of distilled water. Stir and filter with Whatman No.4
  • Pippette 2ml of standard solution and test sample into white porcelain spot plates.
  • Add 2-3 drops of cresol red indicator and add 2-3 drops of urease solution.
  • Let it stand for 3-5 minutes, if urea is present, it will form a deep red-purple spreading like a spider’s web appearance, in contrast to the yellow colour of the indicator.
  • Compare the test sample with the standard urea sample. This test should be read within 10-12 minutes.