Calcium Carbonate Tablets

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION 

Calcium Carbonate Tablets contain NLT 90.0% and NMT 110.0% of the labeled amount of calcium carbonate (CaCO₃). For Tablets labeled for any indication other than, or in addition to, antacid use, the Tablets contain NLT 90.0% and NMT 115.0% of the labeled amount of calcium carbonate. 

2 IDENTIFICATION 

A. Identification Tests—General, Calcium〈191〉: The addition of 6 N acetic acid to the Tablets produces effervescence, and the resulting solution, after being boiled to expel carbon dioxide and neutralized with 6 N ammonium hydroxide, meets the requirements. 

3 ASSAY 

Procedure 

Sample solution: Finely powder NLT 20 Tablets. Transfer a portion of the powder, equivalent to 200 mg of calcium carbonate, to a suitable crucible. Ignite to constant weight. Cool the crucible, add 10 mL of water, and dissolve the residue by adding sufficient 3 N hydrochloric acid, dropwise, to achieve complete solution. 

Blank: 150 mL of water and 15 mL of 1 N sodium hydroxide 

Titrimetric system 

(See Titrimetry 〈541〉.) 

Mode: Direct titration 

Titrant: 0.05 M edetate disodium VS 

Indicator: 300 mg of hydroxy naphthol blue 

Endpoint detection: Visual, change to distinct blue 

Analysis: Transfer the Sample solution completely to a suitable container, and dilute with water to 150 mL. Add 15 mL of 1 N sodium hydroxide and 300 mg of hydroxy naphthol blue. Titrate with the Titrant. 

Calculate the percentage of calcium carbonate (CaCO₃) in the sample taken: 

Result = [(V_S − V_B ) × M × F × 100]/W 

V_S = volume of the Titrant consumed by the Sample solution (mL) 

V_B = volume of the Titrant consumed by the Blank (mL) 

M = Titrant molarity (mmol/mL) 

F = equivalency factor, 100.09 mg/mmol 

W = weight of calcium carbonate taken (mg) 

Acceptance criteria: 90.0%–110.0% of the labeled amount of CaCO₃. For Tablets labeled for any indication other than, or in addition to, antacid use, 90.0%–115.0% of the labeled amount of CaCO₃

4 PERFORMANCE TESTS 

Dissolution 〈711〉 

[Note—For Tablets labeled for any indication other than, or in addition to, antacid use.] 

Medium: 0.1 N hydrochloric acid; 900 mL 

Apparatus 2: 75 rpm 

Time: 30 min 

Lanthanium chloride solution: 50 mg/mL of lanthanum chloride in 0.1 N hydrochloric acid 

Standard stock solution: 100 µg/mL of calcium in 0.1 N hydrochloric acid 

Standard solutions: Into separate 100-mL volumetric flasks containing 10.0 mL of Lanthanium chloride solution pipet 3-, 4-, 5-, and 6-mL portions of Standard stock solution and dilute each with 0.1 N hydrochloric acid to volume to obtain solutions with calcium concentrations of 3, 4, 5, and 6 µg/mL, respectively. 

Sample solution: Filter a portion of the solution under test. Pipet a volume of the filtrate, estimated to contain 1 mg of calcium, into a 250-mL volumetric flask. Add 25.0 mL of Lanthanium chloride solution, and dilute with 0.1 N hydrochloric acid to volume.

Instrumental conditions 

(See Atomic Absorption Spectroscopy 〈852〉.) 

Mode: Atomic absorption spectrophotometry 

Analytical wavelength: 422.8 nm 

Lamp: Calcium hollow-cathode 

Flame: Air–acetylene 

Blank: Lanthanium chloride solution and 0.1 N hydrochloric acid (1:9) 

Analysis 

Samples: Standard solutions and Sample solution 

Concomitantly determine the absorbances of the Standard solutions and the Sample solution against the Blank. Construct a standard curve by plotting absorbances versus calcium concentrations of the Standard solutions, then from it obtain the concentration, C, in µg/mL of calcium, of the Sample solution. 

Calculate the percentage of the labeled amount of calcium carbonate (CaCO₃3) dissolved: 

Result = (M_r/A_r) × (C × D × V/L) × 100 

M_r = molecular weight of calcium carbonate, 100.09 

A_r = atomic weight of calcium, 40.08 

C = measured concentration of calcium in the Sample solution (mg/mL) 

D = dilution factor for the Sample solution 

V = volume of Medium, 900 mL 

L = label claim (mg/Tablet) 

Tolerances: NLT 75% (Q) of the labeled amount of calcium carbonate (CaCO₃) is dissolved. 

Uniformity of Dosage Units 〈905〉: Meet the requirements 

5 SPECIFIC TESTS 

Acid-Neutralizing Capacity 〈301〉: For Tablets labeled for antacid use 

Analysis: Proceed as directed in the chapter. 

Acceptance criteria: NLT 5 mEq of acid is consumed by the minimum single dose recommended in the labeling, and NLT the number of mEq calculated as follows: 

Result = (C × A_NC) × F 

C = quantity of CaCO₃ in the sample tested (mg), based on the labeled amount 

A_NC = theoretical acid-neutralizing capacity of CaCO₃, 0.02 mEq/mg 

F = acceptance factor for the lower limit of the required acid-neutralizing capacity, 0.9 

6 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in well-closed containers. 

Labeling: Label it to indicate whether it is for use as an antacid, or as a dietary supplement, or both.