The Pharmaceutics and Compounding Laboratory
Powders and Granules

Granulations

Granules are particles ranging in size from about 4 to 10 mesh. Granules generally are made by first blending the powders together and then moistening the mixture to form a pasty mass. The mass is passed through a sieve and then dried in air or in an oven. They are prepared as a convenience for packaging, as a more stable product due to less surface exposure, and as a popular dosage form. Granulations are also used as intermediates in the preparation of capsules and tablets, since they flow more smoothly and predictably than do small powder particles.

The most popular compounded granulation is the effervescent powder (sometimes called effervescent salts). These granulations are popular due to their taste and psychological impression. When added to water, the granulation effervesces ("fizzes") as carbon dioxide is liberated.

Preparation of Effervescent Granulation

It has been found that citric acid monohydrate and tartaric acid used in the ratio of 1:2, respectively, produces a powder with good effervescent properties. Citric acid monohydrate is not used alone because it results in a sticky mixture that will not easily granulate. Tartaric acid is not used alone because the granules are too friable and crumble. The amount of sodium bicarbonate to be used may be calculated from the reaction which occur when the granules come in contact with water. The reaction equation between citric monohydrate and sodium bicarbonate is given below:

Reaction Equation

Setting up a proportion to determine the amount of sodium bicarbonate that will react with 1 gm of citric acid, one has:

equation

Similar calculations show that 2.24 gm of sodium bicarbonate react with 2 gm of tartaric acid.

Reaction equation 2 equation

Thus, with the acids in a ratio of 1:2, it has been calculated that 3.44 g (1.2 g + 2.24 g) of sodium bicarbonate is necessary to react stoichiometrically with the 3 g of combined acids. To enhance the flavor, the amount of sodium bicarbonate may be reduced to 3.4 gm to allow for a small amount of unreacted acid to provide a tart taste.