Aminobenzoic Acid

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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C₇H₇NO₂     137.14

Benzoic acid, 4-amino;

p-Aminobenzoic acid CAS RN^®: 150-13-0; UNII: TL2TJE8QTX.

1 DEFINITION

Aminobenzoic Acid contains NLT 98.0% and NMT 102.0% of aminobenzoic acid (C₇H₇NO₂), calculated on the dried basis. 

2 IDENTIFICATION

Change to read:

A. Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K _{(CN 1-May-2020)}

B. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

Procedure

Acetic acid solution: Glacial acetic acid and water (1:69)

Mobile phase: Methanol and Acetic acid solution (15:85)

Standard solution: 0.1 mg/mL of USP Aminobenzoic Acid RS in Mobile phase. Sonicate to aid dissolution. Sample solution: 0.1 mg/mL of Aminobenzoic Acid in Mobile phase. Sonicate to aid dissolution.

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3.0-mm × 15-cm; 3.5-µm packing L11

Flow rate: 0.4 mL/min

Injection volume: 5 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing: NMT 1.5

Relative standard deviation: NMT 1.0%

3.2 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of aminobenzoic acid (C₇H₇NO₂) in the portion of Aminobenzoic Acid taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

C_S = concentration of the Standard solution (mg/mL)

C_U = concentration of the Sample solution (mg/mL)

Acceptance criteria: 98.0%–102.0% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

4.1 Organic Impurities

Solution A: Acetonitrile and methanol (70:80)

Buffer: 1.5 g/L of monobasic potassium phosphate and 2.5 g/L of octanesulfonic acid sodium salt in water. Adjust with phosphoric acid to a pH of 2.2.

Mobile phase: Solution A and Buffer (20:80)

Standard stock solution: 0.25 mg/mL each of USP Benzocaine RS and 4-nitrobenzoic acid in methanol

Standard solution: 0.5 µg/mL each of USP Benzocaine RS and 4-nitrobenzoic acid in Mobile phase, from the Standard stock solution Sample solution: 0.25 mg/mL of Aminobenzoic Acid in Mobile phase

4.1.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 270 nm

Column: 4.0-mm × 15-cm; 5-µm packing L7

Flow rate: 1.0 mL/min

Injection volume: 20 µL

Run time: 11 times the retention time of the aminobenzoic acid peak

4.1.2 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of 4-nitrobenzoic acid or any unspecified impurity in the portion of Aminobenzoic Acid taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response of 4-nitrobenzoic acid or any unspecified impurity from the Sample solution

r_S = peak response of 4-nitrobenzoic acid from the Standard solution

C_S = concentration of 4-nitrobenzoic acid in the Standard solution (mg/mL)

C_U = concentration of Aminobenzoic Acid in the Sample solution (mg/mL)

Calculate the percentage of benzocaine in the portion of Aminobenzoic Acid taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 100

r_U = peak response of benzocaine from the Sample solution

r_S = peak response of benzocaine from the Standard solution

C_S = concentration of USP Benzocaine RS in the Standard solution (mg/mL)

C_U = concentration of Aminobenzoic Acid in the Sample solution (mg/mL)

Acceptance criteria: See Table 1. Disregard any impurity peaks less than 0.02%.

Table 1

4.2 Limit of Aniline and p-Toluidine

Diluent: 84 g/L of sodium hydroxide in water

Standard solution: 1.0 µg/mL each of aniline and p-toluidine in methylene chloride

Sample solution: Dissolve 1 g of Aminobenzoic Acid in 10.0 mL of Diluent, and extract with two quantities each of 10.0 mL of methylene chloride. Combine, and wash with 5 mL of water. Filter through anhydrous sodium sulfate, and wash the lter with methylene chloride.

Evaporate in a water bath at 50°–60° to obtain a volume of about 1–5 mL. Transfer to a 10-mL volumetric ask, and dilute with methylene chloride to volume.

4.2.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: GC

Detector: Flame ionization

Column: 0.32-mm × 30-m fused silica capillary, coated with a 0.5-µm lm of phase G27

Temperatures

Injection port: 280°

Detector: 300°

Column: See Table 2.

Table 2 

Carrier gas: Helium

Flow rate: 1.0 mL/min Injection volume: 2 µL Split ratio: 1:10

4.2.2 Analysis

Samples: Standard solution and Sample solution

[Note—The relative retention times for aniline and p-toluidine are about 0.8 and 1.0, respectively.]

Calculate, in ppm, the amount of aniline and p-toluidine in the portion of Aminobenzoic Acid taken:

Result = (r_U /r_S ) × (C_S /C_U ) × 10⁶

r_U= peak response of each impurity from the Sample solution

r_S = peak response of the corresponding impurity from the Standard solution

C_S = concentration of the corresponding impurity in the Standard solution (mg/mL)

C_U= concentration of Aminobenzoic Acid in the Sample solution (mg/mL)

4.2.3 Acceptance criteria

Aniline: NMT 10 ppm

p-Toluidine: NMT 10 ppm

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry a sample at 105° for 2 h.

Acceptance criteria: NMT 0.2%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers.

USP Reference Standards 〈11〉

USP Aminobenzoic Acid RS

USP Benzocaine RS

Benzoic acid, 4-amino-, ethyl ester.

C₉H₁₁NO₂      165.19