Determination of Calcium In Milk

Milk is widely recognized as a significant source of calcium, an essential mineral that plays a crucial role in the development and maintenance of strong bones and teeth. This mineral is particularly important for infants and young children, whose rapidly growing bodies demand high levels of calcium to ensure proper bone formation and density.

Calcium’s presence in milk is not incidental; rather, it is a fundamental component that contributes to milk’s nutritional profile. The calcium content in milk is naturally balanced to meet the dietary needs of young mammals, including human infants. This makes milk an excellent dietary option for obtaining calcium, which is vital for various bodily functions beyond bone health, such as muscle function and nerve transmission.

Understanding the importance of calcium in the diet, especially for bone health, highlights why milk is often recommended as part of a balanced diet. The calcium found in milk is readily absorbed by the body, making it an efficient way to meet daily calcium requirements for individuals of all ages.

In summary, milk serves as a vital dietary source of calcium, essential for bone health and overall physical development. Its natural composition provides a convenient and effective means of ensuring adequate calcium intake, underscoring the importance of including milk and dairy products in a balanced and nutritious diet.

Requirements for Determination of Calcium In Milk

1. Ammonium Hydroxide Solution: A 1:1 volume-to-volume mixture of ammonium hydroxide is needed. This solution is used to adjust the pH of the milk sample, preparing it for further analysis by precipitating proteins and other components that might interfere with the calcium determination.
2. Ammonium Oxalate Solution: A saturated solution of ammonium oxalate is utilized to precipitate calcium ions from the solution. Calcium forms an insoluble compound with oxalate, which can be separated and measured, providing an indirect method of assessing the calcium content.
3. Hydrochloric Acid Solution: A dilute solution of hydrochloric acid, mixed in a 1:9 volume-to-volume ratio with water, is employed to dissolve the precipitate and adjust the acidity of the solution, optimizing conditions for the subsequent steps of the analysis.
4. Dilute Sulfuric Acid Solution: This solution, prepared at a 1:4 volume-to-volume ratio with water, is used to further adjust the acidity of the sample. The precise acidity is crucial for the accurate performance of the titration step that follows.
5. Standard Potassium Permanganate Solution: A 0.1 N solution of potassium permanganate is carefully prepared and standardized against a known concentration of sodium oxalate or oxalic acid. This solution acts as the titrant in the final step of the procedure. The end point of the titration is marked by a faint and persistent pink color, indicating the complete reaction of the permanganate with all available reducing agents in the sample, including the oxalate bound to calcium.

Procedure

1. Sample Preparation: Begin by accurately weighing 10 grams of the milk sample into a platinum or silica dish, which should be pre-ignited to remove any organic residues and then cooled in a desiccator filled with an effective desiccant.
2. Evaporation and Ashing: Evaporate the milk in the dish to dryness. Subsequently, place the dish in a muffle furnace set at 550°C to ash the sample thoroughly until all organic matter is decomposed, leaving behind a carbon-free ash. After ashing, cool the dish in a desiccator and weigh it to determine the ash content.
3. Dissolution of Ash: Dissolve the ash in a measured volume of dilute hydrochloric acid, ensuring complete dissolution of all soluble salts. Transfer this solution into a 100 ml graduated flask and dilute to the mark with distilled water to prepare a solution for analysis.
4. Initial Solution Preparation: Take a 20 ml aliquot of this ash solution and dilute it to 50 ml with distilled water in a beaker, preparing it for the precipitation process.
5. Precipitation of Calcium: Adjust the solution to a slightly alkaline pH by adding ammonium hydroxide (NH₄OH) solution until a precipitate forms. Add an excess of NH₄OH to ensure complete precipitation of calcium and magnesium as their respective oxalates.
6. Settling and Decantation: Bring the solution to a boil and allow it to stand for 3 minutes. Then, carefully decant the supernatant through a Whatman No. 42 filter paper, leaving the precipitate in the beaker.
7. Washing the Precipitate: Rinse the precipitate with 15-20 ml of hot water, decanting the clear solution through the same filter. This step helps remove soluble impurities.
8. Dissolution and Reprecipitation: Dissolve the remaining precipitate on the filter paper with hot hydrochloric acid, collecting the solution in the original beaker. Wash the filter paper several times with hot water to ensure all precipitate is transferred back into the beaker. Re-precipitate the calcium by adding ammonium hydroxide and a small amount of ammonium oxalate solution, then filter and wash as before.
9. Removal of Chlorides: Continue washing the precipitate with hot water until the washings are free from chloride ions, indicating that all soluble contaminants have been removed.
10. Preparation for Titration: Make a small hole in the filter paper and wash the calcium oxalate precipitate back into the beaker used for the initial precipitation.
11. Titration: Dissolve the precipitate in hot dilute sulfuric acid and titrate the solution at a temperature between 85-90°C with a standard potassium permanganate (KMnO₄) solution until a faint, permanent pink color appears, indicating the endpoint.

Results and Calculation for Determination of Calcium In Milk

In the analytical process of determining calcium content in milk, the endpoint of the procedure is marked by the titration of calcium oxalate precipitate with a standard potassium permanganate (KMnO₄) solution. The amount of calcium present in the milk sample is calculated based on the volume of potassium permanganate solution used in the titration process. The calculation employs a specific formula that correlates the volume of titrant to the percentage of calcium in the milk sample.

The formula used for calculating the calcium content is given by:

Calcium (%)=1.2×V/W

In this formula:

• V represents the volume in milliliters (ml) of the standard potassium permanganate solution that was required to reach the endpoint of the titration, where the solution maintains a faint, permanent pink color.
• W is the weight in grams (g) of the milk sample that was initially taken to prepare the ash, which is a common reference point in analytical chemistry for ensuring the consistency of the sample size.

To contextualize this calculation:

• The constant factor 1.21.2 in the formula is derived from the stoichiometry of the chemical reaction involved and the molar mass of calcium, adjusted for the specific conditions of the titration and the concentration of the potassium permanganate solution used.
• V, the volume of KMnO₄ solution, is a direct measurement obtained during the titration process. It reflects the amount of reactant required to completely react with the calcium oxalate, and thus, indirectly, the amount of calcium present in the sample.
• W ensures that the calculation is normalized to the amount of milk analyzed, allowing for the results to be expressed as a percentage. This normalization is crucial for comparing calcium content across different samples or for adhering to nutritional labeling standards.

Upon completion of the titration, the volume of potassium permanganate used provides a direct link to the amount of calcium in the sample, with the formula adjusting this relationship to yield the calcium content as a percentage of the milk sample’s weight. This result is vital for nutritional analysis, quality control in dairy production, and ensuring compliance with dietary recommendations and regulatory standards for calcium content in milk and milk products.