Potassium Carbonate

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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K₂CO₃ (anhydrous) 138.21

K₂CO₃ · 1½H₂O 165.23

Carbonic acid, dipotassium salt;

Dipotassium carbonate CAS RN®: 584-08-7.

1 DEFINITION

Potassium Carbonate contains NLT 99.5% and NMT 100.5% of potassium carbonate (K₂CO₃), calculated on the dried basis.

2 IDENTIFICATION

A. Identification Tests—General 〈191〉, Chemical Identification Tests, Potassium: Meets the requirements • B. Identification Tests—General 〈191〉, Chemical Identification Tests, Carbonate: Meets the requirements

3 ASSAY

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ProcedureUse carbon dioxide-free water to prepare the solutions.

Sample solution: Dissolve 0.5 g of Potassium Carbonate from the dried Potassium Carbonate obtained in the test for Loss on Drying in 100 mL of water, carbon dioxide-free. Use this solution promptly after preparation.

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 1 N hydrochloric acid VS

Endpoint detection: Potentiometric

Analysis: Titrate the Sample solution with Titrant. Determine the endpoint potentiometrically at the second injection point. Calculate the percentage of potassium carbonate (K₂CO₃) in the portion of Potassium Carbonate taken:

Result = V_S × N_A × F/W × 100

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

N_A = actual normality of the Titrant (mEq/mL)

F = equivalency factor, 69.11 mg/mEq

W = weight of the sample taken (mg) (USP 1-Dec-2020)

Acceptance criteria: 99.5%–100.5% on the dried basis

4 SPECIFIC TESTS

4.1 Loss on Drying 〈731〉

Analysis: Dry at 180° for 4 h.

Acceptance criteria: NMT 0.5%

4.2 Insoluble Substances

Sample solution: 1 g in 20 mL of water

Acceptance criteria: The solution is complete, clear, and colorless.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.