Estimation of Calcium (Titrimetric Method)

ESTIMATION OF CALCIUM (TITRIMETRIC METHOD)

Aim

To estimate the amount of calcium present in the given serum sample.

Principle

Calcium is precipated as calcium oxalate with ammonium oxalate. The precipate is washed with ammonia to remove the chloride ions. The washed precipate is then made to react with 1N sulphuric acid. The liberated oxalic acid is now estimated by titrating against standardised potassium permanganate.The amount of oxalic acid liberated is proportional to the amount of calcium.

Reagents Required

1. Ammonium oxalate solution (4 %)

4g of ammonium oxalate dissolved in 100ml of distilled water.

2. Ammonia solution (2%)

2ml of ammonia of specific gravity 0.88 is diluted to 100ml with distilled water.

3. Potassium permanganate (0.1N)

This is prepared by dissolving 3.16 g of potassium permanganate in 1 litre of distilled water.

4. Standard oxalic acid solution (0.1N)

It is prepared by dissolving 630mg of oxalic acid in 100ml of distilled water.

5. Sulphuric acid (1N)

Procedure

Standardisation of Potassium permanganate

10ml of oxalic acid is pipetted out into a clean conical flask and 10ml of dilute sulphuric acid is added and heated to 60 ° C. It is titrated against potassium permanganate in the burette. The end point is the appearance of pale permanent pink colour. Titrations are repeated for concordant values.

Precipitation of calcium oxalate

2ml of serum is taken in a centrifuge tube and 2ml of distilled water is added followed by 1ml of 4 % ammonium oxalate. The contents are mixed and allowed to stand overnight at 4 ° C for complete precipitation of calcium. The precipate is separated by centrifugation and the supernatant is discarded. To the precipitate 3ml of 2% ammonia is added and centrifuged. This procedure is repeated thrice and the supernatant is tested for the presence of chloride. 10 ml of 1N sulphuric acid is added and warmed for solubilisation. This solution is now titrated against potassium permanganate and the volume consumed is noted.

10 ml of 1N sulphuric acid is treated as blank and titrated against potassium permanganate. The end point is the appearance of pale permanent pink colour. Titrations are repeated for concordant values and the amount of calcium present is then calculated.

Tabular Column

Titration I

Standardisation of Potassium permanganate

Standard Oxalic acid Vs Potassium permanganate

Volume of oxalic acid V₁                                              = 10ml

Normality of oxalic acid.N₁                                 = 0.1N

Volume of potassium permanganate V₂         = x ml

Normality of potassium permanganate N₂ =?

Normality of potassium permanganate N₂ = V₁ N₁/ V₂

                                      =Y

                                      Titration II

Estimation of Calcium in serum

Calculation

The amount of calcium present in the given sample can be calculated by using the equation

1ml of 0.1N potassium permanganate is equivalent to 0.2 mg of calcium Therefore, X3 ml of' Y' N potassium permanganate is equivalent to

0.2 x X3 xY / 1 x 0.1 = Z mg of calcium.

2ml of serum contains Z mg of calcium

Therefore, 100 ml of serum contains 100 x Z / 2 mg of calcium

Result

The amount of calcium present in the given serum sample is_____mg/100ml