Detection Of Calcium And Phosphorus In Milk

Calcium and phosphorus are the important components of the milk. A growing baby derives Ca and P from the milk nourishing mothers/animals. Here, presence of these two in milk can be tested chemically. The first approach is to make milk free from protein and fat because unless these are separated, Ca and P cannot be tested.

Requirements

• Small amount of milk
• Boiling test tubes
• Test tubes
• Spirit lamp
• Filter paper
• Buchner funnel
• Acetic acid
• Nitric acid
• Ammonium oxalate
• Litmus paper
• Beakers

Procedure

 I. Removal of proteins and fats from the milk

1. Take small amount (10 ml) of milk in a boiling test tube and add 1% acetic acid until a white precipitate appears in the milk.
2. Measure the pH using a litmus paper. It shall be around 4.5.
3. Put a filter paper in a funnel, filter the acidified milk and collect the supernatant. The supernatant contains Ca and P.

II. Detection of Ca in milk supernatant

1. Take 5 ml of supernatant in a test tube.
2. Make the supernatant alkaline by adding a little amount of ammonia into it.
3. Now, add ammonium oxalate into the supernatant.

Results

A white precipitate appears on the top layer of the supernatant due to formation of calcium

oxalate. It shows the presence of Ca in milk.

III. Detection of P in milk supernatant

1. Follow the procedure from (i) to (iii) and take small amount of casein-free and fat- free
2. supernatant.
3. Add 1 ml of concentrated nitric acid and shake well.
4. Add 3 ml of ammonium molybdate.

Results

Yellow colour or yellow precipitate appears in the supernatant. This colour change is due to the presence of phosphorus in the milk.

Reference:

Dr. R. C. Dubey – Practical Microbiology