Diethyltoluamide Topical Solution

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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1 DEFINITION

Diethyltoluamide Topical Solution is a solution of Diethyltoluamide in Alcohol or Isopropyl Alcohol. It contains NLT 92.0% and NMT 108.0% of the labeled amount of the meta-isomer of diethyltoluamide (C₁₂H₂,NO). If it contains Alcohol, NLT 95.0% and NMT 105.0% of the labeled amount of alcohol (C₁₂H₁₇OH) is present.

2 IDENTIFICATION

Change to read:

A. SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 1975 _{▲(CN 1-MAY-2020)}

Sample solution: Nominally 20 mg/mL of diethyltoluamide in carbon disulfide prepared as follows. Transfer a quantity of Topical Solution, equivalent to 200 mg of diethyltoluamide, into a beaker. Place the beaker into a vacuum oven containing silica gel and calcium chloride, and adjusted to a pressure of about 380 mm of mercury, and heat at 35° for 6 h. Transfer the residue with the aid of carbon disulfide to a 10-mL volumetric flask, and add carbon disulfide to volume.

Analysis: Spectral region between 8 and 15 µm

Acceptance criteria: Meets the requirements

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

3.1 PROCEDURE

Solution A: 1 mL of phosphoric acid in 1000 mL of water

Mobile phase: Methanol and Solution A (45:55)

Diluent: Methanol and water (45:55)

System suitability solution: 0.2 mg/mL of USP Diethyltoluamide RS (m-isomer) and 0.02 mg/mL of USP Diethyltoluamide Related Compound ARS in Diluent. [NOTE-USP Diethyltoluamide Related Compound A RS is the p-isomer of diethyltoluamide.]

Standard solution: 0.2 mg/mL of USP Diethyltoluamide RS in Diluent

Sample solution: Nominally 0.2 mg/mL of diethyltoluamide in Diluent

3.1.1 Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 235 nm

Column: 4.6-mm x 15-cm; 3.5-µm packing L1

Flow rate: 1 mL/min

Injection volume: 10 µL

3.1.2 System suitability

Samples: System suitability solution and Standard solution

3.1.3 Suitability requirements

Resolution: NLT 1.5 between diethyltoluamide (m-isomer) and diethyltoluamide (p-isomer), System suitability solution

Tailing factor: NMT 2.0, Standard solution

Relative standard deviation: NMT 1.0%, Standard solution

3.1.4 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of the m-isomer of diethyltoluamide (C₁₂H₁₇OH) in the portion of Topical Solution taken:

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

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution

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

C_U = nominal concentration in the Sample solution (mg/mL)

Acceptance criteria: 92.0%-108.0%

4 OTHER COMPONENTS

ALCOHOL DETERMINATION (611) (if present): 29.0%-89.0% of alcohol (C₂H₅OH) is found.

5 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in tight containers.

USP REFERENCE STANDARDS (11)

USP Diethyltoluamide RS

USP Diethyltoluamide Related Compound A RS

N,N-Diethyl-4-toluamide.

C₁₂H₁₇NO              191.27