Sodium Borate

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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Na₂B₄O₇ · 10H₂O 381.37

Na₂B₄O₇    201.22

Borax CAS RN®: 1303-96-4.

Anhydrous CAS RN®: 1330-43-4.

1 DEFINITION

Sodium Borate contains an amount of Na₂B₄O₇ equivalent to NLT 99.0% and NMT 105.0% of Na₂B₄O₇ · 10H₂O.

2 IDENTIFICATION

A. Identification Tests—General, Sodium 〈191〉

Sample solution: 1 in 20

Acceptance criteria: Meets the requirements

B. Identification Tests—General, Borate 〈191〉

Sample solution: 1 in 20

Acceptance criteria: Meets the requirements

3 ASSAY

Procedure

Sample: 3 g of Sodium Borate

Titrimetric system

(See Titrimetry 〈541〉.)

Mode: Direct titration

Titrant: 0.5 N hydrochloric acid VS

Blank: 50 mL of water

Endpoint detection: Visual

Analysis: Dissolve the Sample in 50 mL of water, add methyl red TS, and titrate with 0.5 N hydrochloric acid VS. [Note—Heating on a steam bath may be required initially to effect solution.]

Calculate the percentage of sodium borate (Na₂B₄O₇ · 10H₂O) in the Sample taken:

Result = [(V − B) × N × F] × 100/W

V = volume of Titrant consumed by the Sample (mL)

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

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

F = equivalency factor, 190.7 mg/mEq

W = weight of the Sample (mg)

Acceptance criteria: 99.0%–105.0%

4 IMPURITIES

Carbonate and Bicarbonate

Sample solution: To 5 mL of a solution (1 in 20), contained in a test tube, add 1 mL of 3 N hydrochloric acid.

Acceptance criteria: No effervescence is observed.

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.