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:
Setting up a proportion to determine the amount of sodium bicarbonate that will react with 1 gm of citric acid, one has:
Similar calculations show that 2.24 gm of sodium bicarbonate react with 2 gm of tartaric acid.
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.