Test preparation: Weigh not less than 20 tablets and determine the average tablet weight. Grind the tablets to a fine powder, mix to obtain a uniform mixture and transfer an accurately weighed quantity of it equivalent to the minimum labeled dosage to a 250 ml beaker. If wetting is desired, add not more than 5 ml of alcohol (neutralized to an apparent pH to 3.5), and mix to weight the specimen thoroughly. Add 70 ml of water and mix on the magnetic stirrer for 1 minute.
Procedure: Pipette 30 ml of 1 N Hydrochloric acid VS into the test preparation while continuing to stir with the magnetic stirrer.
[Note: Where the acid-neutralizing capacity of the specimen under test is greater than 25 mEq, use 60 ml of 1 N hydrochloric acid VS and make the appropriate modifications in the calculation.]
Stir for 15 minutes, accurately timed, after the addition of the acid, begin to titrate immediately and in a period not to exceed an additional 5 minutes, titrate the excess hydrochloric acid with 0.5 N Sodium Hydroxide VS to attain a stable (for 10 to 15 seconds) pH of 3.5.
Calculate the number of mEq of acid consumed by the formula:
Total mEq = (30 x NHCl) – (VNaOH x NNaOH)
In which NHCl and NNaOH are the normalities of the Hydrochloric acid VS and the Sodium Hydroxide VS, respectively and VNaOH is the volume of sodium hydroxide VS used for titration. Express the result in terms of mEq of acid consumed per g of the test sample.
Not less than 5 mEq of acid is consumed by the minimum single dose recommended in the labeling and not less than the number of mEq calculate as follows:
Result = (C x ANC) x F
C = Quantity of Calcium carbonate in the sample tested (mg).
ANC = Theoretical acid-neutralizing capacity of Calcium carbonate, 0.02 mEq/mg.
F = Acceptance factor for the lower limit of the required acid-neutralizing capacity, 0.9.