Clenbuterol Hydrochloride
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C12H18Cl2N2O·HCl 313.65
Ethanol, 1-(4-amino-3,5-dichlorophenyl)-2-(tert-butylamino), hydrochloride;    
4-Amino--[(tert-butylamino)methyl]-3,5-dichlorobenzyl alcohol, hydrochloride     [21898-19-1].
Clenbuterol Hydrochloride contains NLT 98.0% and NMT 102.0% of C12H18Cl2N2O·HCl, calculated on the anhydrous basis.
•  A. Infrared Absorption 197K
[Note—Alternatively, Infrared Absorption 197A may be used. ]
•  B. Identification Tests—General, Chloride 191: Meets the requirements
•  Procedure
Sample solution:  Dissolve 0.25 g in 50 mL of alcohol, and add 5.0 mL of 0.01 N hydrochloric acid.
Analysis:  Titrate with 0.1 N sodium hydroxide VS, determining the endpoint potentiometrically. Read the volume added between the two points of inflection. Perform a blank determination, and make any necessary correction (see Titrimetry 541). Each mL of 0.1 N sodium hydroxide is equivalent to 31.37 mg of C12H18Cl2N2O·HCl.
Acceptance criteria:  98.0%–102.0% on the anhydrous basis
Inorganic Impurities 
•  Residue on Ignition 281: NMT 0.1%, from 1–2 g
•  Heavy Metals, Method II 231: NMT 10 ppm
Organic Impurities 
•  Procedure
Buffer:  Dissolve 3.0 g of sodium 1-decanesulfonate and 5.0 g of monobasic potassium phosphate in 900 mL of water, adjust with dilute phosphoric acid (1 in 10) to a pH of 3.0, and dilute with water to 1000 mL.
Mobile phase:  Acetonitrile, methanol, and Buffer (2:2:6)
System suitability solution:  0.2 mg/mL each of USP Clenbuterol Related Compound B RS and Clenbuterol Hydrochloride in Mobile phase
Sample solution 1:  2.0 mg/mL of Clenbuterol Hydrochloride in Mobile phase
Sample solution 2:  2.0 µg/mL of Clenbuterol Hydrochloride in Mobile phase, from Sample solution 1
Chromatographic system 
Mode:  LC
Detector:  UV 215 nm
Column:  4.0-mm × 12.5-cm; 5-µm packing L1
Column temperature:  40
Flow rate:  0.5 mL/min
Injection size:  5 µL
System suitability 
Sample:  System suitability solution
Suitability requirements 
Resolution:  NLT 4.0 between clenbuterol related compound B and clenbuterol
Relative standard deviation:  NMT 2.0% for the clenbuterol peak
Samples:  Sample solution 1 and Sample solution 2
Calculate the percentage of impurities in the portion of C12H18Cl2N2O·HCl taken:
Result = (rU/rS) × (CS/CU) × 100
rU== peak response of each impurity from Sample solution 1
rS== peak response of clenbuterol from Sample solution 2
CS== concentration of Clenbuterol Hydrochloride in Sample solution 2 (mg/mL)
CU== concentration of Clenbuterol Hydrochloride in Sample solution 1 (mg/mL)
Acceptance criteria 
Individual impurities:  0.1%
Total impurities:  NMT 0.2%
[Note—The reporting level for impurities is 0.05%. ]
•  Optical Rotation, Specific Rotation 781S
Sample:  30 mg/mL in water, filter as necessary
Acceptance criteria:  10 to +10 at 20
•  pH 791: 5.0–7.0
Sample:  50 mg/mL in carbon dioxide-free water
•  Packaging and Storage: Preserve in well-closed containers, protected from light. Store at room temperature.
•  Labeling: Label it to indicate that it is for veterinary use only.
•  USP Reference Standards 11
USP Clenbuterol Hydrochloride RS Click to View Structure
USP Clenbuterol Related Compound B RS
1-(4-Amino-3,5-dichlorophenyl)-2-tert-butyl-aminoethanone hydrochloride.
    C12H16Cl2N2O·HCl        311.64
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Morgan Puderbaugh, B.S.
Associate Scientific Liaison
(SM32010) Monographs - Small Molecules 3
Reference Standards RS Technical Services
USP35–NF30 Page 2700
Pharmacopeial Forum: Volume No. 35(5) Page 1125