Aluminum Dichlorohydrate

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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AI_y(OH)_3y-zCl_z · nH₂O

Aluminum chlorohydroxide;

Aluminum hydroxychloride.

1 DEFINITION

Aluminum Dichlorohydrate consists of complex basic aluminum chloride that is polymeric and loosely hydrated and encompasses a range of aluminum-to-chloride atomic ratios between 0.90:1 and 1.25:1. It contains the equivalent of NLT 90.0% and NMT 110.0% of the labeled amount of anhydrous aluminum dichlorohydrate [AI_y(OH)_3y-zCl_z].

2 IDENTIFICATION

A. Identification Tests—General, Aluminum〈191〉andChloride〈191〉

Sample solution: 100 mg/mL

Acceptance criteria: Meets the requirements

3 ASSAY

3.1 Procedure 1: Content of Chloride

Sample: 700 mg

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N silver nitrate VS

Electrode system: A glass silver–silver chloride electrode and a silver billet electrode system

Endpoint detection: Potentiometric

Analysis: Transfer the Sample to a 250-mL beaker, and add 100 mL of water and 10 mL of diluted nitric acid with stirring. Titrate with Titrant, and determine the endpoint potentiometrically. Each mL of 0.1 N silver nitrate is equivalent to 3.545 mg of chloride (Cl). Use the chloride content thus obtained to calculate the aluminum:chloride atomic ratio.

3.2 Procedure 2: Content of Aluminum

Edetate disodium titrant: Prepare and standardize as directed in Reagents, Volumetric Solutions, Edetate Disodium, Twentieth-Molar (0.05 M), except use 37.2 g of edetate disodium.

Sample solution: Transfer 200 mg of Aluminum Dichlorohydrate to a 250-mL beaker, add 20 mL of water and 5 mL of hydrochloric acid, boil on a hot plate for NLT 5 min, and allow to cool.

Titrimetric system

Mode: Back-titration

Titrant: 0.1 M zinc sulfate VS

Endpoint detection: Visual

Analysis: To the Sample solution add 25.0 mL of Edetate disodium titrant, and adjust with 2.5 N ammonium hydroxide or 1 N acetic acid to a pH of 4.7 ± 0.1. Add 20 mL of acetic acid–ammonium acetate buffer TS, 50 mL of alcohol, and 5 mL of dithizone TS. The pH of this solution should be 4.7 ± 0.1. Titrate the excess edetate disodium with Titrant until the color changes from green-violet to rose-pink. Perform a blank titration, and make any necessary correction. Each mL of 0.1 M Edetate disodium titrant consumed is equivalent to 2.698 mg of aluminum (Al). Use the aluminum content thus obtained to calculate the aluminum:chloride atomic ratio.

3.3 Procedure 3: Aluminum:Chloride Atomic Ratio

Analysis: Use the percentage of aluminum found in the test for Content of Aluminum and the percentage of chloride found in the test for Content of Chloride.

Calculate the aluminum:chloride atomic ratio (X) as follows:

Result = (p_Al /p_Cl ) × (A_Cl /A_Al) 

p_Al = percentage of aluminum found in Content of Aluminum

p_Cl = percentage of chloride found in Content of Chloride

A_Cl = atomic weight of chlorine (Cl), 35.453

A_Al = atomic weight of aluminum (Al), 26.98

Acceptance criteria: Between 0.90:1 and 1.25:1

3.4 Procedure 4

Analysis: Calculate the percentage of anhydrous aluminum dichlorohydrate [AI_y(OH)_3y-zCl_z] in the portion of Aluminum Dichlorohydrate taken:

Result = P_Al ({A_Al X + [M(3X− 1)] + A _Cl}/A _AlX)

P_Al = percentage of aluminum as obtained in the test for Content of Aluminum

A_Al = atomic weight of aluminum (Al), 26.98

X = aluminum:chloride atomic ratio, as determined in the test for Aluminum:Chloride Atomic Ratio

M = molecular weight of the hydroxide anion (OH), 17.01

A_Cl = atomic weight of chlorine (Cl), 35.453

Acceptance criteria: 90.0%–110.0% on the anhydrous basis

4 IMPURITIES

Change to read:

Arsenic 〈211〉, Procedures, Procedure 1 (CN 1-Jun-2023) : NMT 2 ppm

Change to read:

Limit of Iron

Standard solution: Transfer 2.0 mL of Standard Iron Solution, prepared as directed in Iron 〈241〉, Procedures, Procedure 1 (CN 1-Jun-2023) , to a 50-mL beaker.

Sample solution: Transfer 2.7 g of Aluminum Dichlorohydrate to a 100-mL volumetric ask, dilute with water to volume, and mix. Transfer 5.0 mL of this solution to a 50-mL beaker.

Analysis: To each of the beakers containing the Standard solution and the Sample solution, add 5 mL of 6 N nitric acid, cover with a watch glass, and boil on a hot plate for 3–5 min. Allow to cool. Add 5 mL of Ammonium Thiocyanate Solution (prepared as directed in Iron 〈241〉, Procedures, Procedure 1 (CN 1-Jun-2023) ), transfer to separate 50-mL color comparison tubes, and dilute with water to volume.

Acceptance criteria: 150 ppm; the color of the solution from the Sample solution is not darker than that of the solution from the Standard solution.

5 SPECIFIC TESTS

pH 〈791〉

Sample solution: 15 g of Aluminum Dichlorohydrate in 100 g of water

Acceptance criteria: 3.0–5.0

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

Labeling: The label states the content of anhydrous aluminum dichlorohydrate.