Phentermine Hydrochloride
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C10H15N·HCl 185.69

Benzeneethanamine, ,-dimethyl-, hydrochloride.
,-Dimethylphenethylamine hydrochloride [1197-21-3].
» Phentermine Hydrochloride contains not less than 98.0 percent and not more than 101.0 percent of C10H15N·HCl, calculated on the dried basis.
Packaging and storage— Preserve in tight containers.
USP Reference standards 11
USP Phentermine Hydrochloride RS
B: Ultraviolet Absorption 197U
Solution : 600 µg per mL.
Medium: 0.1 N hydrochloric acid.
Absorptivities at 256 nm, calculated on the dried basis, do not differ by more than 2.0%.
C: It responds to the tests for Chloride 191.
Melting range 741: between 202 and 205.
pH 791: between 5.0 and 6.0, in a solution (1 in 50).
Loss on drying 731 Dry it at 105 for 3 hours: it loses not more than 2.0% of its weight.
Residue on ignition 281: not more than 0.1%.
Chromatographic purity—
Standard preparations— Dissolve an accurately weighed quantity of USP Phentermine Hydrochloride RS in chloroform to obtain Standard preparation A having a known concentration of 2 mg per mL. Dilute this solution quantitatively with chloroform to obtain Standard preparations, designated below by letter, having the following compositions:
Dilution Concentration
(mg RS
per mL)
Percentage (%,
for comparison with
test specimen)
A (undiluted) 2.0 1.0
B (1 in 2) 1.0 0.5
C (1 in 5) 0.4 0.2
D (1 in 10) 0.2 0.1
Test preparation— Dissolve an accurately weighed quantity of Phentermine Hydrochloride in chloroform to obtain a solution containing 200 mg per mL.
Procedure— Apply separately 10 µL of the Test preparation and 10 µL of each Standard preparation to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Position the plate in a chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of chloroform, cyclohexane, and diethylamine (50:40:10) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate in air. Examine the plate under short-wavelength UV light. Compare the intensities of any secondary spots observed in the chromatogram of the Test preparation with those of the principal spots in the chromatograms of the Standard preparations: the sum of the intensities of secondary spots obtained from the Test preparation corresponds to not more than 1.0% of related compounds, with no single impurity corresponding to more than 0.5%.
Assay— Dissolve about 400 mg of Phentermine Hydrochloride, accurately weighed, in 40 mL of glacial acetic acid, and add 10 mL of mercuric acetate TS, warming slightly to effect solution. Cool to room temperature, and titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 18.57 mg of C10H15N·HCl.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Clydewyn M. Anthony, Ph.D.
(MDCCA05) Monograph Development-Cough Cold and Analgesics
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 3277
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.