Calcium Carbonate Tablets
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.
IDENTIFICATION
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.
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
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 = [(VS VB) × M × F × 100]/W
 VS = = volume of the Titrant consumed by the Sample solution (mL) VB = = 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
PERFORMANCE TESTS
[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
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, CS, in µg/mL of calcium, of the Sample solution.
Calculate the percentage of the labeled amount of calcium carbonate (CaCO3) dissolved:
Result = (Mr/Ar) × (C × D × V/L) × 100
 Mr = = molecular weight of calcium carbonate, 100.09 Ar = = 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.
Meet the requirements
SPECIFIC TESTS
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 × ANC) × F
 C = = quantity of CaCO3 in the sample tested (mg), based on the labeled amount ANC = = 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
•  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.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Natalia Davydova
Scientific Liaison
1-301-816-8328
(DS2010) Monographs - Dietary Supplements
711 Margareth R.C. Marques, Ph.D.
Senior Scientific Liaison
1-301-816-8106
(GCDF2010) General Chapters - Dosage Forms
USP35–NF30 Page 2445
Pharmacopeial Forum: Volume No. 28(5) Page 1392